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ATLAS NOTEATLAS-CONF-2013-047

May 16, 2013Revision: June 30, 2013

Search for squarks and gluinos with the ATLAS detector in final stateswith jets and missing transverse momentum and 20.3 fb−1 of

√s = 8 TeV

proton-proton collision data

ATLAS Collaboration

Abstract

A search for squarks and gluinos in final states containing high-pT jets, missing trans-verse momentum and no electrons or muons is presented. The data were recorded in 2012by the ATLAS experiment in

√s = 8 TeV proton-proton collisions at the Large Hadron

Collider, with a total integrated luminosity of 20.3 fb−1. No significant excess above theStandard Model expectation is observed. In a simplified model with only gluinos and thelightest neutralino, gluino masses below 1350 GeV are excluded at the 95% confidence levelwhen the lightest neutralino is massless. For a simplified model involving the strong pro-duction of squarks of the first two generations, with decays to a massless lightest neutralino,squark masses below 780 GeV are excluded. In MSUGRA/CMSSM models with tan β = 30,A0 = −2m0 and µ > 0, squarks and gluinos of equal mass are excluded for masses below1700 GeV. These limits extend the region of supersymmetric parameter space excluded byprevious searches with the ATLAS detector.

The following have been revised with respect to the version dated May 16, 2013:squark mass contours in Figures 5 and 16 (left), mg̃ − mq̃ plane exclusion limits in Figures5 and 16 (right) and mass limit values for the MSUGRA/CMSSM scenario; cross-sections

and resulting exclusion limits for the simplified phenomenological MSSM scenario (Figures6 and 17).

c© Copyright 2013 CERN for the benefit of the ATLAS Collaboration.Reproduction of this article or parts of it is allowed as specified in the CC-BY-3.0 license.

1 Introduction

Many extensions of the Standard Model (SM) include heavy coloured particles, some of which could beaccessible at the Large Hadron Collider (LHC) [1]. The squarks and gluinos of supersymmetric (SUSY)theories [2–10] form one class of such particles. This note presents a new ATLAS search for squarksand gluinos in final states containing only jets and large missing transverse momentum. Interest in thisfinal state is motivated by the large number of R-parity conserving models [11–15] in which squarks, q̃,and gluinos, g̃, can be produced in pairs {g̃g̃, q̃q̃, q̃g̃} and can decay through q̃ → qχ̃0

1 and g̃ → qq̄χ̃01

to weakly interacting lightest neutralinos, χ̃01. The χ̃0

1 is the lightest SUSY particle (LSP) and escapesthe detector unseen. The analysis presented here updates previous ATLAS results obtained using similarselections [16–19]. Events with reconstructed electrons or muons are vetoed to avoid overlap with arelated ATLAS search [20, 21]. The search strategy was optimised in the (mg̃,mq̃)-plane (where mg̃,mq̃

are the gluino and squark masses respectively) for a range of models, including a simplified one in whichall other supersymmetric particles, except for the lightest neutralino, were given masses beyond the reachof the LHC. Although mostly interpreted in terms of SUSY models, the main results of this analysis (thedata and expected background event counts in the signal regions) are relevant for constraining any modelof new physics that predicts production of jets in association with missing transverse momentum.

2 The ATLAS Detector and Data Samples

The ATLAS detector [22] is a multipurpose particle physics detector with a forward-backward sym-metric cylindrical geometry and nearly 4π coverage in solid angle.1 The layout of the detector fea-tures four superconducting magnet systems, which comprise a thin solenoid surrounding inner track-ing detectors (covering |η| < 2.5) and three large toroids supporting a muon spectrometer (covering|η| < 2.5). The calorimeters are of particular importance to this analysis. In the pseudorapidity region|η| < 3.2, high-granularity liquid-argon (LAr) electromagnetic (EM) sampling calorimeters are used. Aniron/scintillator-tile calorimeter provides hadronic coverage over |η| < 1.7. The end-cap and forwardregions, spanning 1.5 < |η| < 4.9, are instrumented with LAr calorimeters for both EM and hadronicmeasurements.

The data sample used in this analysis was collected in 2012 with the LHC operating at a centre-of-mass energy of 8 TeV. Application of beam, detector and data-quality requirements resulted in atotal integrated luminosity of 20.3 fb−1. The uncertainty on the integrated luminosity is ±2.8%, derivedby following the same methodology as that detailed in Ref. [23] using a preliminary calibration of theluminosity scale derived from beam-separation scans performed in November 2012. The trigger requiredevents to contain a leading jet with an uncorrected transverse momentum (pT) above 80 GeV and anuncorrected missing transverse momentum above 100 GeV. The trigger reached its full efficiency forevents with a reconstructed jet with pT exceeding 130 GeV and more than 160 GeV of missing transversemomentum. For the data sample studied the trigger is fully efficient.

3 Object Reconstruction

Jet candidates are reconstructed using the anti-kt jet clustering algorithm [24,25] with a radius parameterof 0.4. The inputs to this algorithm are clusters [26,27] of calorimeter cells seeded by those with energysignificantly above the measured noise. Jet momenta are constructed by performing a four-vector sum

1 ATLAS uses a right-handed coordinate system with its origin at the nominal interaction point in the centre of the detectorand the z-axis along the beam pipe. Cylindrical coordinates (r, φ) are used in the transverse plane, φ being the azimuthal anglearound the beam pipe. The pseudorapidity η is defined in terms of the polar angle θ by η = − ln tan(θ/2).

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over these cell clusters, treating each as an (E, ~p) four-vector with zero mass. The jets are corrected forenergy from additional proton-proton collisions in the same or neighbouring bunch crossings (pile-up)using a method, suggested in Ref. [28], which estimates the pile-up activity in any given event, as well asthe sensitivity of any given jet to pile-up. The method subtracts a contribution from the jet energy equalto the product of the jet area and the event average energy density. The local cluster weighting (LCW)jet calibration method [26, 29] is used to classify topological cell clusters within the jets as either beingof electromagnetic or hadronic origin and based on this classification applies specific energy correctionsderived from a combination of Monte Carlo (MC) simulation and data. Further corrections, referred toas ‘jet energy scale’ or ‘JES’ corrections below, are derived from MC and data and used to calibrate theenergies of jets to the mean scale of their constituent particles [26]. Only jet candidates with pT > 20 GeVafter all corrections are retained. Jets are identified as originating from heavy-flavour decays using the‘MV1’ neural network based b-tagging algorithm with a 70% efficiency operating point [30]. Candidateb-tagged jets must possess pT > 40 GeV and |η| < 2.5.

Electron candidates are required to have pT > 10 GeV and |η| < 2.47, and to pass electron showershape and track selection criteria based upon those described in Ref. [31], but modified to reduce theimpact of pile-up and to match tightened trigger requirements. Muon candidates are formed by combin-ing information from the muon spectrometer and inner tracking detectors as described in Refs. [32, 33]and are required to have pT > 10 GeV and |η| < 2.4. Reconstructed photons are used to constrain Z+jetbackgrounds (see below), although they are not used in the main analysis. Photon candidates are requiredto possess pT > 130 GeV and |η| < 1.37 or 1.52 < |η| < 2.47, and to pass photon shower shape andelectron rejection criteria [34].

Following the steps above, overlaps between candidate jets with |η| < 2.8 and leptons (electrons ormuons) are resolved as follows. First, any such jet candidate lying within a distance ∆R ≡

√(∆η)2 + (∆φ)2 =

0.2 of an electron is discarded; then any lepton candidate remaining within a distance ∆R = 0.4 of anysurviving jet candidate is discarded.

The measurement of the missing transverse momentum two-dimensional vector EmissT (and its magni-

tude EmissT ) is based on the calibrated transverse momenta of all jet and lepton candidates and all calorime-

ter clusters not associated to such objects [35]. Following this step, all jet candidates with |η| > 2.8 arediscarded. Thereafter, the remaining lepton and jet candidates are considered “reconstructed”, and theterm “candidate” is dropped.

4 Signal and Control Region Definitions

Following the object reconstruction described above, events are discarded if any electrons or muonswith pT > 10 GeV remain, or if they have any jets failing quality selection criteria designed to suppressdetector noise and non-collision backgrounds (see e.g. Ref. [36]), or if they lack a reconstructed primaryvertex associated with five or more tracks. The criteria applied to jets include requirements on the fractionof the transverse momentum of the jet carried by charged tracks, and on the fraction of the jet energycontained in the electromagnetic layers of the calorimeter. A consequence of these requirements is thatevents containing hard photons have a high probability of failing the signal region selection criteria.

This analysis aims to search for the production of heavy SUSY particles decaying into jets and stablelightest neutralinos, with the latter creating missing transverse momentum. Because of the high massscale expected for the SUSY signal, the ‘effective mass’, meff , is a powerful discriminant between thesignal and most Standard Model backgrounds. When selecting events with at least N jets, meff is definedto be the scalar sum of the transverse momenta of the leading N jets and Emiss

T . The final signal selectionuses requirements on meff(incl.), which sums over all jets with pT > 40 GeV and Emiss

T . Requirementsplaced on meff and Emiss

T , which suppress the multi-jet background, formed the basis of the previousATLAS jets + Emiss

T + 0-lepton SUSY searches [17–19]. The same strategy is adopted in this analysis.

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Requirement

Channel

A (2-jets) B (3-jets) C (4-jets) D (5-jets) E (6-jets)

L M M T M T – L M T

EmissT [GeV] > 160

pT( j1) [GeV] > 130

pT( j2) [GeV] > 60

pT( j3) [GeV] > – 60 60 60 60

pT( j4) [GeV] > – – 60 60 60

pT( j5) [GeV] > – – – 60 60

pT( j6) [GeV] > – – – – 60

∆φ(jeti,EmissT )min > 0.4 (i = {1, 2, (3 if pT( j3) > 40 GeV)}) 0.4 (i = {1, 2, 3}), 0.2 (pT > 40 GeV jets)

EmissT /meff(N j) > 0.2 –a 0.3 0.4 0.25 0.25 0.2 0.15 0.2 0.25

meff(incl.) [GeV] > 1000 1600 1800 2200 1200 2200 1600 1000 1200 1500

(a) For SR A-medium the cut on EmissT /meff(N j) is replaced by a requirement Emiss

T /√

HT > 15 GeV1/2.

Table 1: Selection criteria used to define each of the channels in the analysis. Each channel is dividedinto between one and three signal regions on the basis of the requirements listed in the bottom two rows.The signal regions are indicated in the third row from the top and are denoted ‘loose’ (L), ‘medium’(M) and ‘tight’ (T). The Emiss

T /meff cut in any N jet channel uses a value of meff constructed from onlythe leading N jets (indicated in parentheses in the second row). However, the final meff(incl.) selection,which is used to define the signal regions, includes all jets with pT > 40 GeV.

The requirements used to select jets and leptons are chosen to give sensitivity to a broad range ofSUSY models. In order to achieve maximal reach over the (mg̃,mq̃)-plane, several analysis channels aredefined. Squarks typically generate at least one jet in their decays, for instance through q̃ → qχ̃0

1, whilegluinos typically generate at least two jets, for instance through g̃ → qq̄χ̃0

1. Processes contributing toq̃q̃, q̃g̃ and g̃g̃ final states therefore lead to events containing at least two, three or four jets, respectively.Decays of heavy SUSY and SM particles produced in q̃ and g̃ cascades tend to further increase the finalstate multiplicity.

Five inclusive analysis channels, labelled A to E and characterised by increasing jet multiplicity fromtwo to six, are defined in Table 1. Each channel is used to construct between one and three signal regions(SRs) with ‘loose’, ‘medium’, or ‘tight’ selections distinguished by requirements placed on Emiss

T /meff

and meff(incl.). The lower jet multiplicity channels focus on models characterised by squark pair pro-duction with short decay chains, while those requiring high jet multiplicity are optimised for gluino pairproduction and/or long cascade decay chains. In SR A-medium the cut on Emiss

T /meff is replaced bya requirement on Emiss

T /√

HT (where HT is defined as the scalar sum of the transverse momenta of allpT > 40 GeV jets), which has been found to lead to enhanced sensitivity to models characterised by q̃q̃production with a large q̃–χ̃0

1 mass splitting.In Table 1, ∆φ(jet,Emiss

T )min is the smallest of the azimuthal separations between EmissT and the re-

constructed jets. For channels A and B, the selection requires ∆φ(jet,EmissT )min > 0.4 using up to three

leading jets with pT > 40 GeV if present in the event. For the other channels an additional requirement∆φ(jet,Emiss

T )min > 0.2 is placed on all jets with pT > 40 GeV. Requirements on ∆φ(jet,EmissT )min and

EmissT /meff are designed to reduce the background from multi-jet processes.

Standard Model background processes contribute to the event counts in the signal regions. Thedominant sources are: W+jets, Z+jets, top quark pairs, single top quarks, and multiple jets. The produc-tion of semi-leptonically decaying dibosons is a small component (<13%) of the total background and

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CR SR background CR process CR selection

CRY Z(→ νν)+jets γ+jets Isolated photon

CRQ multi-jets multi-jets Reversed ∆φ(jet,EmissT )min and Emiss

T /meff(N j) requirementsa

CRW W(→ `ν)+jets W(→ `ν)+jets 30 GeV < mT (`, EmissT ) < 100 GeV, b-veto

CRT tt̄ and single-t tt̄ → bbqq′`ν 30 GeV < mT (`, EmissT ) < 100 GeV, b-tag

(a) For SR A-medium the selection requirement placed on EmissT /√

HT is reversed.

Table 2: Control regions used in the analysis: the main targeted background in the SR, the processused to model the background, and main CR cut(s) used to select this process are given. The transversemomenta of leptons(photons) used to select CR events must exceed 25(130) GeV.

is estimated with MC simulated data normalised to theoretical cross-section predictions. The majorityof the W+jets background is composed of W → τν events, with the τ-lepton decaying to hadrons, orW → eν, µν events in which no electron or muon candidate is reconstructed. The largest part of theZ+jets background comes from the irreducible component in which Z → νν̄ decays generate large Emiss

T .Top quark pair production followed by semi-leptonic decays, in particular tt̄ → bb̄τνqq′ with the τ-leptondecaying to hadrons, as well as single top quark events, can also generate large Emiss

T and pass the jet andlepton requirements at a non-negligible rate. The multi-jet background in the signal regions is caused bymisreconstruction of jet energies in the calorimeters leading to apparent missing transverse momentum,as well as by neutrino production in semileptonic decays of heavy quarks. Extensive validation of theMonte Carlo simulation against data has been performed for each of these background sources and for awide variety of control regions (CRs).

To estimate the backgrounds in a consistent and robust fashion, four control regions are defined foreach of the 10 signal regions, giving 40 CRs in total. The orthogonal CR event selections are designed toprovide independent data samples enriched in particular background sources. Each ensemble of one SRand four CRs constitutes a different ‘stream’ of the analysis. The CR selections are optimised to maintainadequate statistical weight and low SUSY signal contamination, while minimising as far as possible thesystematic uncertainties arising from the extrapolation to the SR.

The CRs are listed in Table 2. CRY is used to estimate the contribution of Z(→ νν)+jets backgroundevents to each SR by selecting a sample of γ+jets events with pT(γ) > 130 GeV. CRQ uses reversedselection requirements placed on ∆φ(jet,Emiss

T )min and on EmissT /meff(N j) (Emiss

T /√

HT in SR A-medium)to produce data samples enriched in multi-jet background events. CRW and CRT use respectively a b-jetveto or b-jet requirement together with a requirement on the transverse mass (mT) of a pT > 25 GeVlepton and Emiss

T to select samples of W(→ `ν)+jets and semi-leptonic tt̄ background events. These sam-ples are used to estimate respectively the W+jets and combined tt̄ and single-top background populations.With the exception of SR A-loose, the CRW and CRT selections do not use the SR selection requirementsapplied to ∆φ(jet,Emiss

T )min or EmissT /meff(N j) (Emiss

T /√

HT in SR A-medium) in order to increase CR dataevent statistics without significantly increasing theoretical uncertainties associated with the backgroundestimation procedure. For the same reason the final meff(incl.) requirements are loosened to 1300 GeVin CRW and CRT for signal regions D and E-tight. Cross-checks are performed using several ‘validationregion’ samples selected with requirements minimally correlated with those used in the CRs. For exam-ple, CRY estimates of the Z(→ νν̄)+jets background are validated with samples of Z(→ ``)+jets eventsselected by requiring lepton pairs of opposite sign and identical flavour for which the di-lepton invariantmass lies within 25 GeV of the mass of the Z boson. The results of these cross-checks are found to beconsistent with background expectations obtained from the CRs described above.

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5 Analysis procedure

The observed numbers of events in the CRs for each SR are used to generate internally consistent SMbackground estimates for the SR via a likelihood fit. This procedure enables CR correlations due tocommon systematic uncertainties and contamination by other SM processes and/or SUSY signal eventsto be taken into account. The same fit also allows the statistical significance of the observation in the SRto be determined. Key ingredients in the fit are the ratios of expected event counts (the transfer factorsTFs) from each background process between the SR and each CR, and between CRs. The TFs enableobservations in the CRs to be converted into background estimates in the SR using:

N(SR, scaled) = N(CR, obs) ×[

N(SR, unscaled)N(CR, unscaled)

], (1)

where N(SR, scaled) is the estimated background contribution to the SR by a given process, N(CR,obs) is the observed number of data events in the CR for the process, and N(SR, unscaled) and N(CR,unscaled) are a priori estimates of the contributions from the process to the SR and CR, respectively. Theratio appearing in the square brackets in Eqn. 1 is defined to be the transfer factor TF. Similar equationscontaining inter-CR TFs enable the background estimates to be normalised coherently across all the CRsin a given stream.

Background estimation requires determination of the central expected values of the TFs for each SMprocess, together with their associated correlated and uncorrelated uncertainties. The multi-jet TFs areestimated using a data-driven technique [17], which applies a resolution function to well-measured multi-jet events in order to estimate the impact of jet energy mismeasurement and heavy-flavour semileptonicdecays on Emiss

T and other variables. The other TF estimates use fully simulated Monte Carlo samplesvalidated with data. Some systematic uncertainties, for instance those arising from the jet energy scale(JES), or theoretical uncertainties in MC cross-sections, largely cancel when calculating the event countratios constituting the TFs.

The result of the likelihood fit for each SR-CR ensemble is a set of background estimates and un-certainties for the SR together with a p-value giving the probability for the hypothesis that the SR eventcount is compatible with background alone. However, an assumption has to be made about the migrationof signal events between regions. When searching for a signal in a particular SR, first it is assumed thatthe signal contributes only to the SR, i.e. the signal TFs are all set to zero, giving no contribution from thesignal in the CRs. If no excess is observed, then limits are set within specific SUSY model planes, takinginto account the contribution of signal in the CRs and the theoretical and experimental uncertainties onthe SUSY production cross-section and kinematic distributions. Exclusion limits are obtained using alikelihood test which compares the observed event rates in the signal regions with the fitted backgroundexpectation and expected signal contribution for a given model.

Monte Carlo samples are used to develop the analysis, optimise the selections, determine the transferfactors used to estimate the W+jets, Z+jets and top quark backgrounds, determine the diboson back-grounds, and to assess the sensitivity to specific SUSY signal models. The following MC generators areused:

• Samples of Z/γ∗ and γ events with accompanying jets are generated with SHERPA [37] with mas-sive b and c quarks. Theoretical uncertainties are evaluated by comparison with samples producedusing ALPGEN [38].

• Samples of W events with accompanying jets are generated with ALPGEN. Theoretical uncertaintiesare evaluated by comparison with samples produced using SHERPA.

• Samples of top quark pair events with accompanying jets, assuming mtop = 172.5 GeV, are gen-erated with MC@NLO [39, 40]. Theoretical uncertainties are evaluated by comparison with samples

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produced using SHERPA, POWHEG [41, 42] interfaced to PYTHIA6 [43], or POWHEG interfaced toHERWIG [44, 45] using JIMMY [46] for the underlying event.

• Samples of single top quark events with accompanying jets are generated with MC@NLO [47,48] forthe s-channel and Wt processes and AcerMC [49] interfaced to PYTHIA6 for the t-channel process.

• Samples of top quark pair events with accompanying jets and a W or Z boson are generated withMADGRAPH [50, 51] and PYTHIA6.

• Samples of WZ, ZZ and Zγ events are generated with SHERPA, while samples of WW and Wγ

events are generated with ALPGEN. The samples are normalised to the Next-to-Leading Order(NLO) cross-sections obtained from MCFM [52], except for the νν̄qq, `+`−qq, Zγ and Wγ finalstates which are normalised to Leading Order (LO) cross-sections, with the resulting scale depen-dence (.25%) included in the theoretical uncertainties on these processes. Samples of WWW,WWZ and WWW events are generated with MADGRAPH and PYTHIA6, however their contributionis found to be null or negligible in all regions and hence they have not been used in the analysis.

Fragmentation and hadronisation for all ALPGEN and MC@NLO samples is performed with HERWIG, usingJIMMY for the underlying event. The NLO PDF set CT10 [53] is used with SHERPA, MC@NLO and POWHEG,while the LO PDF set CTEQ6L1 [54] is used with all other generators.

SUSY signal samples are generated with HERWIG++ [55] or MadGraph/PYTHIA6 using PDF setCTEQ6L1. Signal cross-sections are calculated to next-to-leading order in the strong coupling constant,including the resummation of soft gluon emission at next-to-leading-logarithmic accuracy (NLO+NLL)[56–60].

The MC samples are generated using the same parameter set as Refs. [61–63]. Most SM backgroundsamples are passed through the ATLAS detector simulation [64] based on GEANT4 [65], while SHERPAW/Z+jets and SUSY signal samples are passed through a fast simulation using a parameterisation of theperformance of the ATLAS electromagnetic and hadronic calorimeters. The fast simulation of SUSYsignal events has been validated against full GEANT4 simulation for several signal model points. Differ-ing pile-up (multiple proton-proton interactions in a given event) conditions as a function of the LHCinstantaneous luminosity are taken into account by overlaying simulated minimum-bias events generatedwith PYTHIA8 onto the hard-scattering process and reweighting them according to the mean number ofinteractions expected.

6 Systematic Uncertainties

Systematic uncertainties arise through the use of the transfer factors relating observations in the controlregions to background expectations in the signal regions, and from the MC modelling of minor back-grounds and the SUSY signal.

Systematic uncertainties in the background estimates are presented in Table 3. For the MC-derivedtransfer factors the primary common sources of systematic uncertainty are the jet energy scale (JES)calibration, jet energy resolution (JER), theoretical uncertainties, MC statistics and the reconstructionperformance in the presence of pile-up. In all cases correlations between uncertainties (for instancebetween scale uncertainties in CRs and SRs) are taken into account where appropriate.

The JES uncertainty has been measured using the techniques described in Refs. [26, 66], leading toa slight dependence upon pT and η. The JER uncertainty is estimated using the methods discussed inRef. [67]. Contributions are added to both the JES and the JER uncertainties to account for the effectof pile-up at the relatively high luminosity delivered by the LHC in the 2012 run. A further uncertaintyon the low-pT calorimeter activity included in the Emiss

T calculation is taken into account. The combined

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Signal Region A-loose A-medium B-medium B-tight C-medium C-tightTotal bkg 4700 122 33 2.4 210 1.6Total bkg unc. ±500 ±18 ±7 ±1.4 ±40 ±1.4∆µMulti−jets ±0.5 [0%] – ±0.1 [0%] – – –∆µTop ±120 [3%] ±1.6 [1%] ±0.7 [2%] ±0.6 [25%] ±4 [2%] ±0.9 [56%]∆µW+jets ±110 [2%] ±5 [4%] ±2.0 [6%] ±0.7 [29%] ±6 [3%] ±0.5 [31%]∆µZ+jets ±90 [2%] ±6 [5%] ±2.7 [8%] ±0.5 [21%] ±7 [3%] –MC statistics – ±9 [7%] ±3.1 [9%] ±0.5 [21%] – ±0.4 [25%]Jet/MET ±50 [1%] ±1.9 [2%] ±1.2 [4%] ±0.3 [13%] ±7 [3%] ±1.0 [63%]Theory Z+jets ±310 [7%] ±8 [7%] ±4 [12%] ±0.1 [5%] ±27 [13%] –Theory W+jets ±230 [5%] ±9 [7%] ±2.6 [8%] ±1.0 [42%] ±17 [8%] ±0.5 [31%]Theory Top ±130 [3%] ±1.9 [2%] ±1.3 [4%] ±0.3 [14%] ±10 [5%] ±0.4 [25%]Theory Diboson ±190 [4%] ±6 [5%] ±1.9 [6%] – ±11 [5%] –Theory scales unc. ±24 [1%] ±0.2 [0%] ±0.6 [2%] ±0.1 [6%] ±0.4 [0%] ±0.03 [2%]Other ±34 [1%] ±1.6 [1%] ±0.2 [1%] ±0.3 [10%] ±0.6 [0%] ±0.4 [25%]

Signal Region D E-loose E-medium E-tightTotal bkg 15 113 30 2.9Total bkg unc. ±5 ±21 ±8 ±1.8∆µMulti−jets ±0.1 [1%] ±0.1 [0%] – –∆µTop ±0.8 [5%] ±10 [9%] ±3.1 [10%] ±0.3 [11%]∆µW+jets ±0.6 [4%] ±5 [4%] ±1.4 [5%] ±0.2 [8%]∆µZ+jets ±1.3 [9%] ±2.2 [2%] ±0.8 [3%] ±0.4 [14%]MC statistics ±2.0 [13%] ±8 [7%] ±4 [13%] ±0.7 [24%]Jet/MET ±0.7 [5%] ±2.4 [2%] ±4 [13%] ±1.4 [48%]Theory Z+jets ±2.0 [13%] ±6 [5%] ±2.2 [7%] ±0.3 [10%]Theory W+jets ±2.3 [15%] ±4 [4%] ±2.0 [7%] ±0.4 [14%]Theory Top ±1.4 [9%] ±15 [13%] ±4 [13%] ±0.5 [17%]Theory Diboson ±1.9 [13%] ±2.1 [2%] ±0.8 [3%] –Theory scales unc. ±0.1 [1%] ±0.04 [0%] ±0.02 [0%] ±0.03 [1%]Other ±0.3 [2%] ±1.3 [1%] ±1.0 [3%] ±0.2 [7%]

Table 3: Breakdown of the dominant components of the systematic uncertainties on background esti-mates. Hyphens indicate negligible contributions. Note that components may be correlated and hencemay not sum quadratically to the total background uncertainty. ∆µ uncertainties arise from limited CRstatistics and systematic uncertainties related to the CR. Uncertainties relative to the expected total back-ground yields are listed in parenthesis.

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JES, JER and EmissT uncertainty ranges from 2% of the expected background in SR E-loose to 63% in SR

C-tight (where it dominates).Uncertainties arising from theoretical models of background processes are evaluated by comparing

TFs obtained from samples generated with a variety of different MC generators, as described in Section 5.In addition, the impact of uncertainties in renormalisation, factorisation and jet-parton matching scales isassessed with dedicated MC samples. The dominant such uncertainty is associated with the modelling ofW/Z+jets in the lower jet multiplicity signal regions (channels A–D), while in the higher jet multiplicitysignal regions (channel E) the uncertainty on top quark pair production dominates. The overall largesttheoretical modelling uncertainty arises from W+jet production in SR B-tight (42%).

Statistical uncertainties arising from the use of finite-size MC samples range up to 25% in SR C-tight.Uncertainties arising from finite data statistics and systematics in the control regions (listed as ‘∆µ’ inTable 3) are most important for the tighter signal regions, reaching 56% for CRT in SR C-tight. TheCR systematic uncertainties considered include photon and lepton reconstruction efficiency, energy scaleand resolution (CRY, CRW and CRT), b-tag/veto efficiency (CRW and CRT) and photon acceptance(CRY). Uncertainties on the multi-jet transfer factors are conservatively set to 100% in all signal regions,however the small magnitude of this background in all signal regions reduces the contribution made bythis uncertainty to the overall uncertainty budget. When combined with the uncertainty associated withthe modelling of pile-up in MC events the resulting uncertainty (labelled ‘other’ in Table 3) is found tobe less than 10% in all signal regions except SR C-tight, where its value (25%) is nevertheless smallerthan the JES, MC statistics and theoretical modelling uncertainties.

Initial state radiation (ISR) can significantly affect the signal acceptance for SUSY models with smallmass splittings. Systematic uncertainties arising from the treatment of ISR are studied with MC data byvarying the value of αS , renormalisation and factorisation scales, and the MadGraph/PYTHIA matchingparameters. For mass splittings ∆m < 100 GeV the uncertainty ranges from 25% to 45% depending onthe signal region. For fixed ∆m the uncertainty is found to be independent of the sparticle mass, while forfixed mass it falls approximately exponentially with increasing ∆m, with a characteristic decay constant∼ 200 – 300 GeV.

7 Results, Interpretation and Limits

The number of events observed in the data and the number of SM events expected to enter each of thesignal regions, determined using the likelihood fit, are shown in Table 4. Good agreement is observedbetween the data and the SM prediction, with no significant excess. The largest observed excess acrossthe ten SRs, with a p-value for the background-only hypothesis of 0.03, occurs in SR E-loose. Predictionsobtained from the likelihood fits for the numbers of events in the validation regions also agree wellwith the observations. Distributions of meff(incl.) before the final cut on this quantity for data and thedifferent MC samples normalised with the theoretical cross-sections are shown in Figs. 1–4 for eachof the channels. Examples of typical expected SUSY signals are shown for illustration. These signalscorrespond to the processes to which each SR is primarily sensitive – q̃q̃ production for the lower jetmultiplicity SRs (channel A), q̃g̃ associated production for intermediate jet multiplicity SRs (channel B),and g̃g̃ production for the higher jet multiplicity SRs (channels C, D and E).

8

Signal Region A-loose A-medium B-medium B-tight C-medium C-tightMC expected events

Diboson 428.6 15.0 4.3 0.0 25.5 0.0Z/γ∗+jets 2044.4 83.1 20.6 2.3 119.4 2.6W+jets 2109.0 58.8 16.4 2.1 88.7 1.0tt̄(+EW) + single top 785.9 8.2 2.0 0.3 45.9 0.3

Fitted background eventsDiboson 430 ± 190 15 ± 7 4.3 ± 2.0 – 26 ± 11 –Z/γ∗+jets 1870 ± 320 57 ± 11 16 ± 5 0.2 ± 0.5 80 ± 29 0.0+0.6

−0.0W+jets 1540 ± 260 42 ± 11 10 ± 4 1.6 ± 1.2 55 ± 18 0.7 ± 0.9tt̄(+EW) + single top 870 ± 180 7.8 ± 2.8 2.2 ± 2.0 0.6 ± 0.7 50 ± 11 0.9 ± 0.9Multi-jets 33 ± 33 – 0.1 ± 0.1 – – –Total bkg 4700 ± 500 122 ± 18 33 ± 7 2.4 ± 1.4 210 ± 40 1.6 ± 1.4Observed 5333 135 29 4 228 0〈εσ〉95

obs[fb] 66.07 2.52 0.73 0.33 4.00 0.12S 95

obs 1341.2 51.3 14.9 6.7 81.2 2.4S 95

exp 1135.0+332.7−291.5 42.7+15.5

−11.4 17.0+6.6−4.6 5.8+2.9

−1.8 72.9+23.6−18.0 3.3+2.1

−1.2p0 (Zn) 0.45 (0.1) 0.27 (0.6) 0.50 (0.0) 0.34 (0.4) 0.34 (0.4) 0.50 (0.0)

Signal Region D E-loose E-medium E-tightMC expected events

Diboson 2.0 5.5 1.7 0.0Z/γ∗+jets 8.5 19.6 6.3 1.9W+jets 4.8 23.1 5.2 0.8tt̄(+EW) + single top 5.0 67.3 16.8 1.5

Fitted background eventsDiboson 2.0 ± 2.0 5.5 ± 2.1 1.7 ± 0.8 –Z/γ∗+jets 3.8 ± 2.5 12 ± 7 2.9 ± 2.6 0.4 ± 0.6W+jets 3.3 ± 2.5 18 ± 7 4.9 ± 2.7 0.7 ± 0.5tt̄(+EW) + single top 5.8 ± 2.1 76 ± 19 20 ± 6 1.7 ± 1.4Multi-jets – 1.0 ± 1.0 – –Total bkg 15 ± 5 113 ± 21 30 ± 8 2.9 ± 1.8Observed 18 166 41 5〈εσ〉95

obs[fb] 0.77 4.55 1.41 0.41S 95

obs 15.5 92.4 28.6 8.3S 95

exp 13.6+5.1−3.5 57.3+20.0

−14.4 21.4+7.6−5.8 6.5+3.0

−1.9p0 (Zn) 0.32 (0.5) 0.03 (1.9) 0.14 (1.1) 0.22 (0.8)

Table 4: Numbers of events observed in the signal regions used in the analysis (L = 20.3 fb−1) comparedwith background expectations obtained from the fits described in the text. Background uncertaintiesinclude both TF systematics (see Section 6) and CR data statistical uncertainties. No signal contributionis considered in the CRs for the fit. Empty cells correspond to estimates lower than 0.1 events. Alsoshown are 95% CL upper limits on the visible cross-section (〈εσ〉95

obs), the visible number of signalevents (S 95

obs ) and the number of signal events (S 95exp) given the expected number of background events,

as well as ±1σ excursions on the expectation. The p0-values give the probabilities of the observationsbeing consistent with the estimated backgrounds and are constrained to ≤ 0.5. Also presented are theequivalent Gaussian significances Zn.

9

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Figure 1: Observed meff(incl.) distributions for channel A for ‘loose’ (left) and ‘medium’ (right) selec-tion criteria. With the exception of the multi-jet background (which is estimated using the data-driventechnique described in the text), the histograms denote the MC background expectations, normalised tocross-section times integrated luminosity. In the lower panels the yellow error bands denote the experi-mental and MC statistical uncertainties, while the green bands show the total uncertainty. The red arrowsindicate the values at which the requirements on meff(incl.) are applied. Expected distributions for twobenchmark model points characterised by q̃q̃ production are also shown for comparison (masses in GeV).

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Figure 2: Observed meff(incl.) distributions for channel B for ‘medium’ (left) and ‘tight’ (right) selec-tion criteria. With the exception of the multi-jet background (which is estimated using the data-driventechnique described in the text), the histograms denote the MC background expectations, normalised tocross-section times integrated luminosity. In the lower panels the yellow error bands denote the experi-mental and MC statistical uncertainties, while the green bands show the total uncertainty. The red arrowsindicate the values at which the requirements on meff(incl.) are applied. Expected distributions for twobenchmark model points characterised by q̃g̃ production are also shown for comparison (masses in GeV).

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Figure 3: Observed meff(incl.) distributions for channels C (left) and D (right). With the exceptionof the multi-jet background (which is estimated using the data-driven technique described in the text),the histograms denote the MC background expectations, normalised to cross-section times integratedluminosity. In the lower panels the yellow error bands denote the experimental and MC statistical uncer-tainties, while the green bands show the total uncertainty. The red arrows indicate the values at whichthe requirements on meff(incl.) are applied. Expected distributions for two benchmark model points arealso shown for comparison (masses in GeV).

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Figure 4: Observed meff(incl.) distributions for channel E for ‘loose’ (top left), ‘medium’ (top right) and‘tight’ (bottom) selection criteria. With the exception of the multi-jet background (which is estimatedusing the data-driven technique described in the text), the histograms denote the MC background ex-pectations, normalised to cross-section times integrated luminosity. In the lower panels the yellow errorbands denote the experimental and MC statistical uncertainties, while the green bands show the totaluncertainty. The red arrows indicate the values at which the requirements on meff(incl.) are applied. Ex-pected distributions for two benchmark model points characterised by g̃g̃ production are also shown forcomparison (masses in GeV).

12

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ATLAS Preliminary

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SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

Stau LSP

Figure 5: Exclusion limits for MSUGRA/CMSSM models with tan β = 30, A0 = −2m0 and µ > 0 pre-sented (left) in the m0–m1/2 plane and (right) in the mg̃–mq̃ plane. Exclusion limits are obtained by usingthe signal region with the best expected sensitivity at each point. The blue dashed lines show the expectedlimits at 95% CL, with the light (yellow) bands indicating the 1σ excursions due to experimental andbackground-theory uncertainties. Observed limits are indicated by medium (maroon) curves, where thesolid contour represents the nominal limit, and the dotted lines are obtained by varying the signal cross-section by the theoretical scale and PDF uncertainties. The black star indicates the MSUGRA/CMSSMbenchmark model used in Fig. 3(left).

In the absence of a statistically significant excess limits are set on contributions to the SRs from newphysics. Model independent limits are listed in Table 4 for the number of new physics events and thevisible cross-section σvis (defined as the product of the production cross-section times reconstructionefficiency times acceptance), computed assuming an absence of signal in the control regions.

Data from all the channels are used to set limits on SUSY models, taking the SR with the bestexpected sensitivity at each point in several parameter spaces. A profile log-likelihood ratio test incombination with the CLs prescription [68] is used to derive 95% CL exclusion regions. The nominalsignal cross-section and the uncertainty are taken from an ensemble of cross-section predictions usingdifferent PDF sets and factorisation and renormalisation scales, as described in Ref. [69]. Observed limitsare calculated for both the nominal cross-section, and ±1σ uncertainties. Numbers quoted in the text areevaluated from the observed exclusion limit based on the nominal cross-section less one sigma on thetheoretical uncertainty.

In Fig. 5 the results are interpreted in the tan β = 30, A0 = −2m0, µ > 0 slice of MSUGRA/CMSSMmodels 2. The best performing signal regions are E-tight for m0 & 1500 GeV and C-tight for m0 .1500 GeV. Results are presented in both the m0–m1/2 and mg̃–mq̃ planes. The sparticle mass spectra anddecay tables are calculated with SUSY-HIT [70] interfaced to the SOFTSUSY spectrum generator [71] andSDECAY [72].

An interpretation of the results is also presented in Fig. 6 as a 95% CL exclusion region in the(mg̃,mq̃)-plane for a simplified set of phenomenological MSSM (Minimal Supersymmetric extension ofthe SM) models with mχ̃0

1equal to 0, 395 GeV or 695 GeV. In these models the gluino mass and the

masses of the ‘light’-flavour squarks (of the first two generations, including both q̃R and q̃L, and assum-ing mass degeneracy) are set to the values shown on the axes of the figure. All other supersymmetricparticles, including the squarks of the third generation, are decoupled.

2Five parameters are needed to specify a particular MSUGRA/CMSSM model: the universal scalar mass, m0, the universalgaugino mass m1/2, the universal trilinear scalar coupling, A0, the ratio of the vacuum expectation values of the two Higgs fields,tan β, and the sign of the higgsino mass parameter, µ = ±.

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) = 0 GeV Observed1

0χ∼) m(­17TeV (4.7fb

Figure 6: Exclusion limits for a simplified phenomenological MSSM scenario with only strong produc-tion of gluinos and first- and second-generation squarks (of common mass), with direct decays to jetsand lightest neutralinos. Three values of the lightest neutralino mass are considered: mχ̃0

1= 0, 395 and

695 GeV. Exclusion limits are obtained by using the signal region with the best expected sensitivity ateach point. The dashed lines show the expected limits at 95% CL, with the light (yellow) band indicatingthe 1σ experimental and background-theory uncertainties on the mχ̃0

1= 0 limit. Observed limits are

indicated by solid curves. The dotted lines represent the mχ̃01

= 0 observed limits obtained by varying thesignal cross-section by the theoretical scale and PDF uncertainties. Previous results for mχ̃0

1= 0 from

ATLAS at 7 TeV [17] are represented by the shaded (light blue) area. Results at 7 TeV are valid forsquark or gluino masses below 2000 GeV, the mass range studied for that analysis.

In Fig. 7 limits are shown for three classes of simplified model in which only direct production of(a) gluino pairs, (b) light-flavour squarks and gluinos or (c) light-flavour squark pairs is kinematicallypossible, with all other superpartners, except for the neutralino LSP, decoupled. This forces each light-flavour squark or gluino to decay directly to jets and an LSP. Cross-sections are evaluated assumingdecoupled light-flavour squarks or gluinos in cases (a) and (c), respectively. In all cases squarks of thethird generation are decoupled. In case (b) the masses of the light-flavour squarks are set to 0.96 timesthe mass of the gluino. The expected limits for case (c) do not extend substantially beyond those obtainedfrom the previous published ATLAS analysis [17] because the events closely resemble the predominantW/Z + 2-jet background, leading the background uncertainties to be dominated by systematics.

In Fig. 8 limits are shown for pair produced gluinos each decaying via an intermediate χ̃±1 to twoquarks, a W boson and a χ̃0

1, and pair produced light squarks each decaying via an intermediate χ̃±1 toa quark, a W boson and a χ̃0

1. Results are presented for models in which either the χ̃01 mass is fixed to

60 GeV, or the mass splitting between the χ̃±1 and the χ̃01, relative to that between the squark or gluino

and the χ̃01, is fixed to 0.5.

In Fig. 9 the results are interpreted in the context of a Non-Universal Higgs Mass model with gauginomediation (NUHMG) [73] with parameters tan β = 10, µ > 0, m2

H2= 0, and A0 chosen to maximize the

mass of the lightest Higgs boson. The two remaining free parameters of the model m1/2 and m2H1

arechosen such that the next-to-lightest SUSY particle (NLSP) is a tau-sneutrino with properties satisfyingBig Bang Nucleosynthesis constraints.

In Fig. 10(left) limits are presented for a simplified phenomenological SUSY model in which pairsof gluinos are produced, each of which then decays to a top squark and a top quark, with the top squarkdecaying to a charm quark and χ̃0

1.In addition to these interpretations in terms of SUSY models, an alternative interpretation in the

context of the minimal universal extra dimension (mUED) model [75] with similar phenomenological

14

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SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

, 7 TeV)­1Observed limit (4.7 fb

, 7 TeV)­1Expected limit (4.7 fb

Figure 7: Exclusion limits for direct production of (case a – top left) gluino pairs with decoupled squarks,(case b – top right) light-flavour squarks and gluinos and (case c – bottom) light-flavour squark pairs withdecoupled gluinos. Gluinos (light-flavour squarks) are required to decay to two jets (one jet) and a neu-tralino LSP. Exclusion limits are obtained by using the signal region with the best expected sensitivityat each point. The blue dashed lines show the expected limits at 95% CL, with the light (yellow) bandsindicating the 1σ excursions due to experimental and background-theory uncertainties. Observed limitsare indicated by medium (maroon) curves, where the solid contour represents the nominal limit, and thedotted lines are obtained by varying the signal cross-section by the theoretical scale and PDF uncertain-ties. Previous results from ATLAS [17] are represented by the shaded (light blue) areas and light bluedotted lines. The black stars indicate the benchmark models used in Figs. 1–4.

properties to R-parity conserving SUSY is also presented in Fig. 10(right). This scenario is the minimalextension of the SM with one additional spatial dimension. The properties of the model are fully deter-mined by three parameters: the compactification radius of the extra dimension R, the cut-off scale Λ andthe Higgs boson mass mh. In this analysis the Higgs boson mass is fixed to 125 GeV while R and Λ aretreated as free parameters. 1/R sets the mass scale of the new Kaluza-Klein (KK) particles predicted bythe model while Λ · R is related to the degree of compression of the KK-particle mass spectrum: mod-els with small values of Λ · R possess small mass splittings between KK-particle states and vice versa.Exclusion limits are set in the 1/R versus Λ · R plane.

In the CMSSM/MSUGRA case, the limit on m1/2 is greater than 340 GeV for m0 < 6 TeV andreaches 800 GeV for low values of m0. Equal mass light-flavour squarks and gluinos are excluded below1700 GeV in this scenario. A limit of 1700 GeV for equal mass light-flavour squarks and gluinos is foundfor the simplified MSSM scenario with a massless lightest neutralino shown in Fig. 6. In the simplifiedmodel cases of Fig. 7 (a) and (c), when the lightest neutralino is massless the limit on the gluino mass(case (a)) is 1350 GeV, and that on the light-flavour squark mass (case (c)) is 780 GeV.

15

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, 7 TeV)­1Observed limit (4.7 fb

)theory

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)exp

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χ∼m(

, 7 TeV)­1Observed limit (4.7 fb

)theory

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)exp

σ1 ±Expected limit (

LSP

g~

squark mass [GeV]

200 400 600 800 1000 1200

,LS

P)

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(∆

,LS

P)/

± χm

(∆

x=

0

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1

1.2

1.4

1

0χ∼

1

0χ∼

­W

+ Wq q→

1

­χ∼

1

+χ∼ q q→* q~q~Simplified model,

ATLAS

=8 TeVs, ­1

L dt = 20.3 fb∫Preliminary

0­lepton combinedm(LSP)=60[GeV]

, 7 TeV)­1Observed limit (4.7 fb

)theory

SUSYσ1 ±Observed limit (

)exp

σ1 ±Expected limit (

squark mass [GeV]

0 200 400 600 800 1000 1200

LS

P m

ass [

Ge

V]

0

200

400

600

800

1000

1200

1

0χ∼

1

0χ∼

­W

+ Wq q→

1

­χ∼

1

+χ∼ q q→* q~q~Simplified model,

ATLAS

=8 TeVs, ­1

L dt = 20.3 fb∫Preliminary

0­lepton combined) + m(LSP))/2q~)= (m(±

χ∼m(

, 7 TeV)­1Observed limit (4.7 fb

)theory

SUSYσ1 ±Observed limit (

)exp

σ1 ±Expected limit (

LSP

q~

Figure 8: Exclusion limits for pair produced gluinos each decaying via an intermediate χ̃±1 to two quarks,a W boson and a χ̃0

1 (top) or pair produced light squarks each decaying via an intermediate χ̃±1 to a quark,a W boson and a χ̃0

1 (bottom). The left-hand figures show results for models with fixed m(χ̃01) = 60

GeV and varying values of x = (mχ̃±1− mχ̃0

1)/(my − mχ̃0

1), where y = g̃(y = q̃) for the top(bottom) figure.

The right-hand plots show results for models with a fixed value of x = 1/2 and varying values of mχ̃01.

Exclusion limits are obtained by using the signal region with the best expected sensitivity at each point.The blue dashed lines show the expected limits at 95% CL, with the light (yellow) bands indicating the1σ excursions due to experimental and background-theory uncertainties. Observed limits are indicatedby medium (maroon) curves, where the solid contour represents the nominal limit, and the dotted linesare obtained by varying the signal cross-section by the theoretical scale and PDF uncertainties. Previousresults from ATLAS [17] are represented by the shaded (light blue) areas.

16

]2

[GeV2

1Hm

2000 3000 4000 5000 6000 7000

310×

[G

eV

]1

/2m

450

500

550

600

650

700

750

800

850

900

NLSPτν∼NUHM model with gaugino mediation and

=8 TeVs, ­1

L dt = 20.3 fb∫0­lepton combined

ATLAS Preliminary

Observed limit 95% CLth

obsσ1 ±

)expσ1 ±Expected limit 95% CL (

LSP0

1χ∼

tachion1

τ∼

Figure 9: Exclusion limits in the m1/2 versus m2H1

plane for the NUHMG model described in the text.Exclusion limits are obtained by using the signal region with the best expected sensitivity at each point.The blue dashed lines show the expected limits at 95% CL, with the light (yellow) bands indicating the1σ excursions due to experimental and background-theory uncertainties. Observed limits are indicatedby medium (maroon) curves, where the solid contour represents the nominal limit, and the dotted linesare obtained by varying the signal cross-section by the theoretical scale and PDF uncertainties.

[GeV]g~m

400 600 800 1000 1200 1400

[G

eV

]t~

m

200

300

400

500

600

700

800

900

1000

t for

bidd

en

t~

→g~

1

0χ∼ ct→t t

~ →g

~ production, g

~­g

~

=8 TeVs, ­1

L dt = 20.3 fb∫0­lepton combined

)theory

SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

SAll limits at 95% CL

ATLAS Preliminary

)theory

SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

1/R [GeV]

700 800 900 1000 1100 1200

.RΛ

10

20

30

40

50

60minimal Universal Extra Dimensions model

ATLAS

=8 TeVs, ­1

L dt = 20.3 fb∫Preliminary

0­lepton combined

Observed limit

)exp

σ1 ±Expected limit (

Figure 10: Exclusion limits for pair produced gluinos each decaying into a t̃ and a χ̃01, with the subse-

quent decay t̃ → c χ̃01 and ∆M(t̃, χ̃0

1) = 20 GeV (left), and in the 1/R versus Λ · R plane for the mUEDmodel described in the text (right). Exclusion limits are obtained by using the signal region with the bestexpected sensitivity at each point. The blue dashed lines show the expected limits at 95% CL, with thelight (yellow) bands indicating the 1σ excursions due to experimental and background-theory uncertain-ties. Observed limits are indicated by medium (maroon) curves, where the solid contour represents thenominal limit. In the left-hand figure the dotted lines are obtained by varying the signal cross-sectionby the theoretical scale and PDF uncertainties. In the right-hand figure theoretical uncertainties are notavailable. Models with 1/R . 650 GeV are excluded by previous analyses as described in Ref. [74].

17

8 Summary

This note reported a search for new physics in final states containing high-pT jets, large missing trans-verse momentum and no electrons or muons, based on a 20.3 fb−1dataset recorded by the ATLAS ex-periment at the LHC in 2012. Good agreement was seen between the numbers of events observed in thedata and the numbers of events expected from SM processes.

Results were presented for a variety of SUSY models and for a specific model of extra dimensions.In particular the results were interpreted in terms of MSUGRA/CMSSM models with tan β = 30, A0 =

−2m0 and µ > 0, and in terms of simplified models with only light-flavour squarks, or gluinos, or both,together with a neutralino LSP, with the other SUSY particles decoupled. In the MSUGRA/CMSSMmodels, values of m1/2 < 340 GeV are excluded at the 95% confidence level for m0 < 6 TeV andm1/2 < 800 GeV for low m0. Equal mass squarks and gluinos are excluded below 1700 GeV in thisscenario. A limit of 1700 GeV for equal mass light-flavour squarks and gluinos was found for simplifiedMSSM models with a massless lightest neutralino. For a massless lightest neutralino, gluino massesbelow 1350 GeV are excluded at the 95% confidence level in a simplified model with only gluinos andthe lightest neutralino. For a simplified model involving the strong production of squarks of the first twogenerations, with decays to a massless lightest neutralino, squark masses below 780 GeV are excluded.

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Appendix A: Control Region meff(incl.) plots

(incl.) [GeV]eff

m

0 500 1000 1500 2000 2500 3000 3500 4000

eve

nts

/ 1

00

Ge

V

1

10

210

310

410

510

­1L dt = 20.3 fb∫

= 8 TeV)sData 2012 (

SM Total

+jetsγ

Multijet

W+jets

& single toptt

Diboson

PreliminaryATLAS

CRYA ­ 2 jets

) > 0.20 jets

(Neff

/mmiss

Tafter cut: E

Al

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

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510­1

L dt = 20.3 fb∫ = 8 TeV)sData 2012 (

SM Total

+jetsγ

Multijet

W+jets

& single toptt

Diboson

PreliminaryATLAS

CRYA ­ 2 jets

> 15 TH/miss

Tafter cut: E

Am

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

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­1L dt = 20.3 fb∫

= 8 TeV)sData 2012 (

SM Total

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& single toptt

Z+jets

Diboson

PreliminaryATLAS

CRWA ­ 2 jets

Al Am

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

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(incl.) [GeV]eff

m

0 500 1000 1500 2000 2500 3000 3500 4000

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/ 1

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V

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410­1

L dt = 20.3 fb∫ = 8 TeV)sData 2012 (

SM Total

W+jets

& single toptt

Z+jets

Diboson

PreliminaryATLAS

CRTA ­ 2 jets

Al Am

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

00.5

11.5

22.5

Figure 11: Observed meff(incl.) distributions in control regions CRY (top left for ‘loose’ selection criteria,top right for ‘medium’ selection criteria), CRW (bottom left) and CRT (bottom right) corresponding tochannel A. The histograms denote the MC background expectations, normalised to cross-section timesintegrated luminosity. The error bands shown in the lower panels denote the experimental and MCstatistical uncertainties in yellow and the total uncertainty including theory uncertainties in green. Thered arrows indicate the values at which the requirements on meff(incl.) are applied.

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(incl.) [GeV]eff

m

0 500 1000 1500 2000 2500 3000 3500 4000

eve

nts

/ 1

00

Ge

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= 8 TeV)sData 2012 (

SM Total

+jetsγ

Multijet

W+jets

& single toptt

Diboson

PreliminaryATLAS

CRYB ­ 3 jets

) > 0.30 jets

(Neff

/mmiss

Tafter cut: E

Bm

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

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ve

nts

/ 1

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L dt = 20.3 fb∫ = 8 TeV)sData 2012 (

SM Total

+jetsγ

Multijet

W+jets

& single toptt

Diboson

PreliminaryATLAS

CRYB ­ 3 jets

) > 0.40 jets

(Neff

/mmiss

Tafter cut: E

Bt

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

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/ 1

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= 8 TeV)sData 2012 (

SM Total

W+jets

& single toptt

Z+jets

Diboson

PreliminaryATLAS

CRWB ­ 3 jets

Bm Bt

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

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(incl.) [GeV]eff

m

0 500 1000 1500 2000 2500 3000 3500 4000

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­1L dt = 20.3 fb∫

= 8 TeV)sData 2012 (

SM Total

W+jets

& single toptt

Z+jets

Diboson

PreliminaryATLAS

CRTB ­ 3 jets

Bm Bt

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

00.5

11.5

22.5

Figure 12: Observed meff(incl.) distributions in control regions CRY (top left for ‘medium’ selectioncriteria, top right for ‘tight’ selection criteria), CRW (bottom left) and CRT (bottom right) correspondingto channel B. The histograms denote the MC background expectations, normalised to cross-section timesintegrated luminosity. The error bands shown in the lower panels denote the experimental and MCstatistical uncertainties in yellow and the total uncertainty including theory uncertainties in green. Thered arrows indicate the values at which the requirements on meff(incl.) are applied.

24

(incl.) [GeV]eff

m

0 500 1000 1500 2000 2500 3000 3500 4000

eve

nts

/ 1

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Ge

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410­1

L dt = 20.3 fb∫ = 8 TeV)sData 2012 (

SM Total

+jetsγ

Multijet

W+jets

& single toptt

Diboson

PreliminaryATLAS

CRYC ­ 4 jets

) > 0.25 jets

(Neff

/mmiss

Tafter cut: E

Ct Ct

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

00.5

11.5

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(incl.) [GeV]eff

m

0 500 1000 1500 2000 2500 3000 3500 4000

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/ 1

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Ge

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­1L dt = 20.3 fb∫

= 8 TeV)sData 2012 (

SM Total

W+jets

& single toptt

Z+jets

Diboson

PreliminaryATLAS

CRWC ­ 4 jets

Cm Ct

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

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11.5

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(incl.) [GeV]eff

m

0 500 1000 1500 2000 2500 3000 3500 4000

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/ 1

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Ge

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10

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­1L dt = 20.3 fb∫

= 8 TeV)sData 2012 (

SM Total

W+jets

& single toptt

Z+jets

Diboson

PreliminaryATLAS

CRTC ­ 4 jets

Cm Ct

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

00.5

11.5

22.5

Figure 13: Observed meff(incl.) distributions in control regions CRY (top left), CRW (top right) andCRT (bottom) corresponding to channel C. The histograms denote the MC background expectations,normalised to cross-section times integrated luminosity. The error bands shown in the lower panelsdenote the experimental and MC statistical uncertainties in yellow and the total uncertainty includingtheory uncertainties in green. The red arrows indicate the values at which the requirements on meff(incl.)are applied.

25

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m

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nts

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= 8 TeV)sData 2012 (

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+jetsγ

Multijet

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& single toptt

Diboson

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) > 0.20 jets

(Neff

/mmiss

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Dt

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TA

/ M

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= 8 TeV)sData 2012 (

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& single toptt

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CRWD ­ 5 jets

Dt

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

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/ M

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nts

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310­1

L dt = 20.3 fb∫ = 8 TeV)sData 2012 (

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& single toptt

Z+jets

Diboson

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CRTD ­ 5 jets

Dt

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

00.5

11.5

22.5

Figure 14: Observed meff(incl.) distributions in control regions CRY (top left), CRW (top right) andCRT (bottom) corresponding to channel D. The histograms denote the MC background expectations,normalised to cross-section times integrated luminosity. The error bands shown in the lower panelsdenote the experimental and MC statistical uncertainties in yellow and the total uncertainty includingtheory uncertainties in green. The red arrows indicate the values at which the requirements on meff(incl.)are applied.

26

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m

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eve

nts

/ 1

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= 8 TeV)sData 2012 (

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+jetsγ

Multijet

W+jets

& single toptt

Diboson

PreliminaryATLAS

CRYE ­ 6 jets

) > 0.15 jets

(Neff

/mmiss

Tafter cut: E

El

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

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m

0 500 1000 1500 2000 2500 3000 3500 4000

eve

nts

/ 1

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= 8 TeV)sData 2012 (

SM Total

+jetsγ

Multijet

W+jets

& single toptt

Diboson

PreliminaryATLAS

CRYE ­ 6 jets

) > 0.20 jets

(Neff

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Tafter cut: E

Em

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DA

TA

/ M

C

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nts

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SM Total

+jetsγ

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& single toptt

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) > 0.25 jets

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Et

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DA

TA

/ M

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L dt = 20.3 fb∫ = 8 TeV)sData 2012 (

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& single toptt

Z+jets

Diboson

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El Em Et

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

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m

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eve

nts

/ 1

00

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V

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10

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­1L dt = 20.3 fb∫

= 8 TeV)sData 2012 (

SM Total

W+jets

& single toptt

Z+jets

Diboson

PreliminaryATLAS

CRTE ­ 6 jets

El Em Et

(incl.) [GeV]effm0 500 1000 1500 2000 2500 3000 3500 4000

DA

TA

/ M

C

00.5

11.5

22.5

Figure 15: Observed meff(incl.) distributions in control regions CRY (top left for ‘loose’, top right for‘medium’ selection criteria, middle left for ‘tight’ selection criteria), CRW (middle right) and CRT (bot-tom) corresponding to channel E. The histograms denote the MC background expectations, normalisedto cross-section times integrated luminosity. The error bands shown in the lower panels denote the exper-imental and MC statistical uncertainties in yellow and the total uncertainty including theory uncertaintiesin green. The red arrows indicate the values at which the requirements on meff(incl.) are applied.

27

Appendix B: Alternative versions of limit plots

[GeV]0

m

1000 2000 3000 4000 5000 6000

[G

eV

]1

/2m

300

400

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(1400 G

eV

)

q ~

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eV

)

q ~

(2200 G

eV

)

q ~

(1000 GeV)g~

(1200 GeV)g~

(1400 GeV)g~

(1600 GeV)g~

(1800 GeV)g~

H (1

24 G

eV

)

H (1

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eV

)

H (1

26 G

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)

Et

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Et

Ct

Et

Ct

Et

>0µ, 0= ­2m0

= 30, AβMSUGRA/CMSSM: tan

=8 TeVs, ­1

L dt = 20.3 fb∫0­lepton combined

ATLAS Preliminary

)theory

SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

Stau LSP

gluino mass [GeV]

800 1000 1200 1400 1600 1800 2000 2200

sq

ua

rk m

ass [

Ge

V]

1000

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Em

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Et

Ct Ct

>0µ, 0= ­2m0

= 30, AβMSUGRA/CMSSM: tan

=8 TeVs, ­1

L dt = 20.3 fb∫0­lepton combined

ATLAS Preliminary

)theory

SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

Stau LSP

Figure 16: Exclusion limits for MSUGRA/CMSSM models with tan β = 30, A0 = −2m0 and µ > 0 pre-sented (left) in the m0–m1/2 plane and (right) in the mg̃–mq̃ plane. Exclusion limits are obtained by usingthe signal region with the best expected sensitivity at each point. The blue dashed lines show the expectedlimits at 95% CL, with the light (yellow) bands indicating the 1σ excursions due to experimental andbackground-theory uncertainties. Observed limits are indicated by medium (maroon) curves, where thesolid contour represents the nominal limit, and the dotted lines are obtained by varying the signal cross-section by the theoretical scale and PDF uncertainties. The black star indicates the MSUGRA/CMSSMbenchmark model used in Fig. 3(left). The signal regions providing the best expected sensitivity at aselection of model points are indicated.

28

gluino mass [GeV]

800 1000 1200 1400 1600 1800 2000 2200 2400

squark

mass [G

eV

]

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

Am

Am

Bm

Bt

Bt

Ct

CtCt

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Ct

Bm

Am

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Bm

Am

Ct

Am

D

Ct

Ct

Am

Bm

Ct

Bt Bt

Bt

Al

Ct

Am

Ct

Ct

Bm

) = 0 GeV0

1χ∼Squark­gluino­neutralino model, m(

=8 TeVs, ­1

L dt = 20.3 fb∫ATLAS Preliminary

0­lepton combined

Observed limit

)expσ1 ±Expected limit (

) Observed­17TeV (4.7fb

Figure 17: Exclusion limit for a simplified phenomenological MSSM scenario with only strong produc-tion of gluinos and first- and second-generation squarks (of common mass), with direct decays to jetsand lightest neutralinos. The mass of the lightest neutralino is set to zero. Exclusion limits are obtainedby using the signal region with the best expected sensitivity at each point. The dashed line shows theexpected limit at 95% CL, with the light (yellow) band indicating the 1σ experimental and background-theory uncertainties. The observed limit is indicated by the solid curve. The dotted lines represent theobserved limits obtained by varying the signal cross-section by the theoretical scale and PDF uncertain-ties. Previous results for mχ̃0

1= 0 from ATLAS at 7 TeV [17] are represented by the shaded (light blue)

area. Results at 7 TeV are valid for squark or gluino masses below 2000 GeV, the mass range studied forthat analysis. The signal regions providing the best expected sensitivity at a selection of model points areindicated.

29

[GeV]g~

m

200 400 600 800 1000 1200 1400

[G

eV

]0

1χ∼

m

200

400

600

800

1000

1200

1400

0

1χ∼ q q →g

~ production; g

~g~

=8 TeVs, ­1

L dt = 20.3 fb∫0­lepton combined

PreliminaryATLAS

Ct

D

Cm

Am

El

Am

Et

Cm

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CmEl

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CmCm El

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)theory

SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

, 7 TeV)­1Observed limit (4.7 fb

, 7 TeV)­1Expected limit (4.7 fb

[GeV]g~

m

200 400 600 800 1000 1200 1400 1600 1800 [

Ge

V]

0

1χ∼

m

200

400

600

800

1000

1200

1400

1600

1800

0

1χ∼ q q →g

~,

0

1χ∼ q →q

~ production; g

~q~

g~=0.96m

q~m

=8 TeVs, ­1

L dt = 20.3 fb∫0­lepton combined

PreliminaryATLAS

Ct

Bm

Am

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)theory

SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

[GeV]q~

m

200 300 400 500 600 700 800 900 1000 1100

[G

eV

]0

1χ∼

m

100

200

300

400

500

600

700

0

1χ∼ q →q

~ production; q

~q~

=8 TeVs, ­1

L dt = 20.3 fb∫0­lepton combined

PreliminaryATLAS

Cm

Ct

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El

)theory

SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

, 7 TeV)­1Observed limit (4.7 fb

, 7 TeV)­1Expected limit (4.7 fb

Figure 18: Exclusion limits for direct production of (case a – top left) gluino pairs with decoupledsquarks, (case b – top right) light-flavour squarks and gluinos and (case c – bottom) light-flavour squarkpairs with decoupled gluinos. Gluinos (light-flavour squarks) are required to decay to two jets (one jet)and a neutralino LSP. Exclusion limits are obtained by using the signal region with the best expected sen-sitivity at each point. The blue dashed lines show the expected limits at 95% CL, with the light (yellow)bands indicating the 1σ excursions due to experimental and background-theory uncertainties. Observedlimits are indicated by medium (maroon) curves, where the solid contour represents the nominal limit,and the dotted lines are obtained by varying the signal cross-section by the theoretical scale and PDFuncertainties. Previous results from ATLAS [17] are represented by the shaded (light blue) areas andlight blue dotted lines. The black stars indicate the benchmark models used in Figs. 1–4. The signalregions providing the best expected sensitivity at a selection of model points are indicated.

30

[GeV]g~

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~ production; g

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PreliminaryATLAS

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167

1188

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540

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281

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449747

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exclu

de

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ross s

ectio

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]s

Nu

mb

ers

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e 9

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CL

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SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

, 7 TeV)­1Observed limit (4.7 fb

, 7 TeV)­1Expected limit (4.7 fb

[GeV]g~

m

200 400 600 800 1000 1200 1400 1600 1800 [

Ge

V]

0

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m

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~,

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~ production; g

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g~=0.96m

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=8 TeVs, ­1

L dt = 20.3 fb∫0­lepton combined

PreliminaryATLAS

2.8

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141 13.4

27494

300

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3642

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)expσ1 ±Expected limit (

, 7 TeV)­1Observed limit (4.7 fb

, 7 TeV)­1Expected limit (4.7 fb

Figure 19: Exclusion limits for direct production of (case a – top left) gluino pairs with decoupledsquarks, (case b – top right) light-flavour squarks and gluinos and (case c – bottom) light-flavour squarkpairs with decoupled gluinos. Gluinos (light-flavour squarks) are required to decay to two jets (one jet)and a neutralino LSP. Exclusion limits are obtained by using the signal region with the best expected sen-sitivity at each point. The blue dashed lines show the expected limits at 95% CL, with the light (yellow)bands indicating the 1σ excursions due to experimental and background-theory uncertainties. Observedlimits are indicated by medium (maroon) curves, where the solid contour represents the nominal limit,and the dotted lines are obtained by varying the signal cross-section by the theoretical scale and PDFuncertainties. Previous results from ATLAS [17] are represented by the shaded (light blue) areas andlight blue dotted lines. The black stars indicate the benchmark models used in Figs. 1–4. The upper limiton the cross-section times branching ratio (in fb) is indicated for each model point.

31

gluino mass [GeV]

200 400 600 800 1000 1200 1400 1600

,LS

P)

g~m

(∆

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P)/

± χm

(∆

x=

0

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±χ∼1

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ATLAS

=8 TeVs, ­1

L dt = 20.3 fb∫ Preliminary

0­lepton combinedm(LSP)=60[GeV]

, 7 TeV)­1Observed limit (4.7 fb

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ATLAS

=8 TeVs, ­1

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Figure 20: Exclusion limits for pair produced gluinos each decaying via an intermediate χ̃±1 to two quarks,a W boson and a χ̃0

1 (top) or pair produced light squarks each decaying via an intermediate χ̃±1 to a quark,a W boson and a χ̃0

1 (bottom). The left-hand figures show results for models with fixed m(χ̃01) = 60

GeV and varying values of x = (mχ̃±1− mχ̃0

1)/(my − mχ̃0

1), where y = g̃(y = q̃) for the top(bottom) figure.

The right-hand plots show results for models with a fixed value of x = 1/2 and varying values of mχ̃01.

Exclusion limits are obtained by using the signal region with the best expected sensitivity at each point.The blue dashed lines show the expected limits at 95% CL, with the light (yellow) bands indicating the1σ excursions due to experimental and background-theory uncertainties. Observed limits are indicatedby medium (maroon) curves, where the solid contour represents the nominal limit, and the dotted linesare obtained by varying the signal cross-section by the theoretical scale and PDF uncertainties. Previousresults from ATLAS [17] are represented by the shaded (light blue) areas. The signal regions providingthe best expected sensitivity at a selection of model points are indicated.

32

gluino mass [GeV]

200 400 600 800 1000 1200 1400 1600

,LS

P)

g~m

(∆

,LS

P)/

± χm

(∆

x=

0

0.2

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ATLAS

=8 TeVs, ­1

L dt = 20.3 fb∫ Preliminary

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gluino mass [GeV]

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1

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ATLAS

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ATLAS

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χ∼m(

, 7 TeV)­1Observed limit (4.7 fb

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Figure 21: Exclusion limits for pair produced gluinos each decaying via an intermediate χ̃±1 to two quarks,a W boson and a χ̃0

1 (top) or pair produced light squarks each decaying via an intermediate χ̃±1 to a quark,a W boson and a χ̃0

1 (bottom). The left-hand figures show results for models with fixed m(χ̃01) = 60

GeV and varying values of x = (mχ̃±1− mχ̃0

1)/(my − mχ̃0

1), where y = g̃(y = q̃) for the top(bottom) figure.

The right-hand plots show results for models with a fixed value of x = 1/2 and varying values of mχ̃01.

Exclusion limits are obtained by using the signal region with the best expected sensitivity at each point.The blue dashed lines show the expected limits at 95% CL, with the light (yellow) bands indicating the1σ excursions due to experimental and background-theory uncertainties. Observed limits are indicatedby medium (maroon) curves, where the solid contour represents the nominal limit, and the dotted linesare obtained by varying the signal cross-section by the theoretical scale and PDF uncertainties. Previousresults from ATLAS [17] are represented by the shaded (light blue) areas. The upper limit on the cross-section times branching ratio (in fb) is indicated for each model point.

33

]2

[GeV2

1Hm

2000 3000 4000 5000 6000 7000

310×

[G

eV

]1

/2m

450

500

550

600

650

700

750

800

850

900

Ct

Et

Ct

AmAm

D

Ct

D

Ct

Ct

Ct

Ct

Ct

Ct

Ct

Ct Ct

Ct

Ct

Ct

Ct

D

D

Ct

Ct

D

D

D

D

Ct

DD

Ct

Ct

D

Ct

Ct

D

Ct

Ct

Ct

Ct

Ct

Ct

Ct

Ct

D

Ct

Ct

Ct

NLSPτν∼NUHM model with gaugino mediation and

=8 TeVs, ­1

L dt = 20.3 fb∫0­lepton combined

ATLAS Preliminary

Observed limit 95% CLth

obsσ1 ±

)expσ1 ±Expected limit 95% CL (

LSP0

1χ∼

tachion1

τ∼

Figure 22: Exclusion limits in the m1/2 versus m2H1

plane for the NUHMG model described in the text.Exclusion limits are obtained by using the signal region with the best expected sensitivity at each point.The blue dashed lines show the expected limits at 95% CL, with the light (yellow) bands indicating the1σ excursions due to experimental and background-theory uncertainties. Observed limits are indicatedby medium (maroon) curves, where the solid contour represents the nominal limit, and the dotted linesare obtained by varying the signal cross-section by the theoretical scale and PDF uncertainties. Thesignal regions providing the best expected sensitivity at a selection of model points are indicated.

34

[GeV]g~m

400 600 800 1000 1200 1400

[G

eV

]t~

m

200

300

400

500

600

700

800

900

1000

t for

bidd

en

t~

→g~

1

0χ∼ ct→t t

~ →g

~ production, g

~­g

~

=8 TeVs, ­1

L dt = 20.3 fb∫0­lepton combined

)theory

SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

SAll limits at 95% CL

ATLAS Preliminary

)theory

SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

El EtEm

Em

Ct

Em

Et

Et

Et

Et

Cm

Et

Cm

CtEt

Et

Et

Em

EtEt

Et

Et

Cm

Et

Et

Et

Em Et

Et

Em

Ct

Em

El

El

Em

Et

Et

El

El

Cm

El

Cm EtEl

Et

Em

Et

Et

1/R [GeV]

700 800 900 1000 1100 1200

.RΛ

10

20

30

40

50

60minimal Universal Extra Dimensions model

ATLAS

=8 TeVs, ­1

L dt = 20.3 fb∫Preliminary

0­lepton combined

Observed limit

)exp

σ1 ±Expected limit (

Ct

Ct

Ct

Ct

Am

Bm

Ct

Am

Am

Am

Cm

Am

Am

Am

Bm

Figure 23: Exclusion limits for pair produced gluinos each decaying into a t̃ and a χ̃01, with the subse-

quent decay t̃ → c χ̃01 and ∆M(t̃, χ̃0

1) = 20 GeV (left), and in the 1/R versus Λ · R plane for the mUEDmodel described in the text (right). Exclusion limits are obtained by using the signal region with the bestexpected sensitivity at each point. The blue dashed lines show the expected limits at 95% CL, with thelight (yellow) bands indicating the 1σ excursions due to experimental and background-theory uncertain-ties. Observed limits are indicated by medium (maroon) curves, where the solid contour represents thenominal limit. In the left-hand figure the dotted lines are obtained by varying the signal cross-sectionby the theoretical scale and PDF uncertainties. In the right-hand figure theoretical uncertainties are notavailable. Models with 1/R . 650 GeV are excluded by previous analyses as described in Ref. [74]. Thesignal regions providing the best expected sensitivity at a selection of model points are indicated.

35

[GeV]g~m

400 600 800 1000 1200 1400

[G

eV

]t~

m

200

300

400

500

600

700

800

900

1000t f

orbi

dden

t~

→g~1

0χ∼ ct→t t

~ →g

~ production, g

~­g

~

=8 TeVs, ­1

L dt = 20.3 fb∫0­lepton combined

)theory

SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

SAll limits at 95% CL

ATLAS Preliminary

)theory

SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

258 13.144.5

374

3.3

84.9

24.9

705

3931

868

364

19.4

277

4.420.1

153

53.9

149

113352

16.0

31.1

109

10.6

422

25.6

31.4 7.9

46.3

2449

4.0

387

614

881

64.9

122

9.1

34792

4619

1436

1127

124 13.696.0

7.4

2161

117

9.4 e

xclu

ded c

ross s

ection x

BR

[fb

]s

Num

bers

giv

e 9

5%

CL

Figure 24: Exclusion limits for pair produced gluinos each decaying into a t̃ and a χ̃01, with the subsequent

decay t̃ → c χ̃01 and ∆M(t̃, χ̃0

1) = 20 GeV. Exclusion limits are obtained by using the signal region withthe best expected sensitivity at each point. The blue dashed lines show the expected limits at 95%CL, with the light (yellow) bands indicating the 1σ excursions due to experimental and background-theory uncertainties. Observed limits are indicated by medium (maroon) curves, where the solid contourrepresents the nominal limit. The dotted lines are obtained by varying the signal cross-section by thetheoretical scale and PDF uncertainties. The upper limit on the cross-section times branching ratio (infb) is indicated for each model point.

36

App

endi

xC

:Cut

-flow

tabl

efo

rse

lect

edsi

gnal

mod

els

Proc

ess

q̃q̃di

rect

q̃g̃di

rect

g̃g̃

dire

ctg̃g̃

one-

step

Poin

tm

(q̃)=

450

GeV

m(q̃

)=85

0G

eVm

(q̃)=

662

GeV

m(g̃

)=14

25G

eVm

(g̃)=

1612

GeV

m(g̃

)=11

62G

eVm

(g̃)=

1065

GeV

m(g̃

)=12

65G

eVm

(χ̃0 1)

=40

0G

eVm

(χ̃0 1)

=10

0G

eVm

(χ̃0 1)

=28

7G

eVm

(χ̃0 1)

=52

5G

eVm

(χ̃0 1)

=37

GeV

m(χ̃

0 1)=

337

GeV

m(χ̃± 1)=

785

GeV

m(χ̃± 1)=

865

GeV

m(χ̃

0 1)=

505

GeV

m(χ̃

0 1)=

465

GeV

Num

bero

fgen

erat

edev

ents

2000

050

0010

000

5000

5000

5000

2000

020

000

Sign

alR

egio

nA

-med

ium

A-m

ediu

mC

-med

ium

B-m

ediu

mB

-tig

htD

DE

-tig

htIn

2728

8.6

(100

.0)

280.

4(1

00.0

)19

44.9

(100

.0)

78.0

(100

.0)

19.8

(100

.0)

122.

4(1

00.0

)27

8.8

(100

.0)

52.3

(100

.0)

Jetc

lean

ing

2720

2.0

(99.

7)

279.

3(9

9.6

)19

37.1

(99.

6)

77.7

(99.

7)

19.7

(99.

6)

122.

1(9

9.8

)27

8.3

(99.

8)

52.2

(99.

8)

0L

epto

n24

528.

0(8

9.9

)27

6.2

(98.

5)

1910

.0(9

8.2

)76

.4(9

8.0

)19

.6(9

8.8

)12

0.5

(98.

5)

177.

6(6

3.7

)33

.2(6

3.5

)E

mis

sT

>16

0G

eV40

82.9

(15.

0)

252.

0(8

9.9

)15

69.2

(80.

7)

72.7

(93.

3)

19.0

(95.

9)

108.

7(8

8.9

)13

9.5

(50.

0)

29.1

(55.

6)

p T(j

1)>

130

GeV

3527

.9(1

2.9

)25

1.6

(89.

7)

1555

.0(8

0.0

)72

.7(9

3.3

)19

.0(9

5.8

)10

8.7

(88.

8)

137.

4(4

9.3

)29

.1(5

5.6

)p T

(j2)>

60G

eV24

63.8

(9.0

)24

5.1

(87.

4)

1471

.1(7

5.6

)72

.0(9

2.4

)18

.8(9

5.2

)10

8.6

(88.

8)

137.

3(4

9.2

)29

.1(5

5.6

)p T

(j3)>

0-6

0G

eV24

63.8

(9.0

)24

5.1

(87.

4)

686.

7(3

5.3

)53

.4(6

8.5

)15

.0(7

5.7

)10

6.6

(87.

1)

135.

5(4

8.6

)29

.0(5

5.4

)p T

(j4)>

0-6

0G

eV24

63.8

(9.0

)24

5.1

(87.

4)

223.

7(1

1.5

)53

.4(6

8.5

)15

.0(7

5.7

)90

.7(7

4.1

)12

4.2

(44.

5)

28.0

(53.

4)

p T(j

5)>

0-6

0G

eV24

63.8

(9.0

)24

5.1

(87.

4)

223.

7(1

1.5

)53

.4(6

8.5

)15

.0(7

5.7

)50

.1(4

0.9

)95

.9(3

4.4

)24

.2(4

6.3

)p T

(j6)>

0-6

0G

eV24

63.8

(9.0

)24

5.1

(87.

4)

223.

7(1

1.5

)53

.4(6

8.5

)15

.0(7

5.7

)50

.1(4

0.9

)95

.9(3

4.4

)16

.6(3

1.7

)∆φ

(ji,

Em

iss

T)>

0.4

1919

.9(7

.0)

221.

9(7

9.2

)19

6.8

(10.

1)

47.0

(60.

4)

13.1

(66.

2)

41.9

(34.

2)

81.5

(29.

2)

13.8

(26.

5)

∆φ

(ji>

40G

eV,E

mis

sT

)>

0-0

.219

19.9

(7.0

)22

1.9

(79.

2)

180.

4(9

.3)

47.0

(60.

4)

13.1

(66.

2)

34.9

(28.

6)

68.7

(24.

6)

11.2

(21.

3)

Em

iss

T/√

HT>

0-1

572

3.0

(2.6

)13

9.8

(49.

9)

180.

4(9

.3)

47.0

(60.

4)

13.1

(66.

2)

34.9

(28.

6)

68.7

(24.

6)

11.2

(21.

3)

Em

iss

T/m

eff(N

j)>

0.15

-0.4

723.

0(2

.6)

139.

8(4

9.9

)13

9.2

(7.2

)34

.9(4

4.8

)6.

3(3

1.8

)27

.0(2

2.1

)60

.2(2

1.6

)6.

3(1

2.0

)m

eff(i

ncl.)>

1-2

.2Te

V36

.2(0

.1)

46.2

(16.

5)

57.6

(3.0

)21

.4(2

7.5

)4.

5(2

2.8

)16

.4(1

3.4

)5.

5(2

.0)

4.1

(7.9

)

Tabl

e5:

Cut

-flow

sfo

rexp

ecte

dnu

mbe

rsof

even

tsfo

rsom

em

odel

poin

tsus

ing

the

sign

alre

gion

expe

cted

tope

rfor

mbe

stfo

rthe

mod

el,n

orm

alis

edto

L=

20.3

fb−

1 .The

abso

lute

effici

ency

in%

ispr

ovid

edin

pare

nthe

sis.

37