DPF2015 Vector-Boson-Fusion Topology at CMS Andr es Fl ...people.physics.tamu.edu/kamon/research/talk/2015/...Andr es Fl orez (Uniandes - Colombia) DPF2015 August 4, 2015 13 / 25

DPF2015

Search for Chargino and Neutralino using Two Jets inVector-Boson-Fusion Topology at CMS

Andres Florez - Uniandes (COL)On behalf of the CMS Collaboration

August 4, 2015

Andres Florez (Uniandes - Colombia) DPF2015 August 4, 2015 1 / 25

Outline

1 Motivation

2 Electroweak SUSY SearchesProbing SUSY with VBF (CMS-SUS-14005)

3 Summary


http://cds.cern.ch/record/2002647

Motivation

Motivation

• The aim of the talk is to show the first results from CMS on SUSYsearches in the electroweak sector, using a VBF-like topology.

• The VBF topology includes forward jets with a large ∆η gap inopposite hemispheres of the detector.

• VBF SUSY provides a new handle to search for new physics incompressed mass-spectra scenarios where the τ and the LSP (χ0) arenearly mass degenerate, which is important to prove models thatinclude co-annihilation.

• Co-annihilation plays an important roll in several thermal dark matter(DM) scenarios in order to obtain the correct relic dark matter densitypredicted by cosmology.


Motivation

Classic SUSY Searches

• Initial SUSY searches focusedon the color sector.

• These type of signatures havefinal states with:EmissT + jets + leptons(photons)


Motivation

Dark Matter & Cosmology

It is important to directly probe the electroweak SUSY sector


Electroweak SUSY Searches


• Searches in the color sector have not yieldpositive signs of SUSY until now.

• SUSY searches in the electroweak (EWK)sector open a different avenue to find newphysics:

X Smaller predicted cross sections but lowerlevels of hadronic activity

X Complements the color searches

• The discovery of the Higgs opens up new SUSY searches:X Lightest neutral CP–even Higgs (h) expected to be SM–like, if others

are heavy.X χ±

1 and χ01 decay to h+LSP (RPC models) or V(W/Z) + χ0

1 (χ01 LSP)

X Would provide evidence for SUSY solution to hierarchy problem.



Third Generation EWK-SUSY Searches(CMS-SUS-13006)

• The experimental sensitivity infinal states containing thirdgeneration particles is limited,especially in compressed spectrascenarios.

Ωχ01h2 ∼

∫∞0

1<σanν>

dx

Lian Tao and Marcela Carenahttp://arxiv.org/pdf/1205.5842v1.pdf


http://link.springer.com/article/10.1140%2Fepjc%2Fs10052-014-3036-7

http://arxiv.org/pdf/1205.5842v1.pdf

Electroweak SUSY Searches Probing SUSY with VBF (CMS-SUS-14005)

Probing SUSY with VBF(CMS-SUS-14005)

• Eight final states: µµjj , eµjj , µτhjj , τhτhjj (OS & LS).• For the µµjj , eµjj , µτhjj channels we use an inclusive single muon trigger,

while for the τhτhjj channels we use a di-tau trigger.





Event Selection Criteria(CMS-SUS-14005)

Summary of the event selection criteria for the different final states considered in

the analysis. Note the selections for the µµjj and eµjj channels are presented in

one column (`(e/µ)µjj) as they are very similar.

Cut `(e/µ)µjj µτh jj τhτh jj

Central Selections

Trigger Iso µ pT > 24 GeV Iso µ pT > 24 GeV Double τ pT > 45 GeVpT (µ)[GeV ] ≥ 30 ≥ 30pT (e)[GeV ] ≥ 15 only eµjjpT (τh)[GeV ] ≥ 20 ≥ 45|η(`µ,e,τh )| < 2.1 < 2.1 < 2.1

Nb−tag jets (CSVL) 0 0 0

EmissT [GeV] > 75 > 75 > 30

pT (jets)[GeV ] ≥ 30/50 ≥ 50 ≥ 30|η(jets)| ≤ 5 ≤ 5 ≤ 5

∆R(`1e,µ,τh

, `2e,µ,τh

) ≥ 0.3 ≥ 0.3 ≥ 0.3

∆R(jet, `e,µ,τh ) ≥ 0.3 ≥ 0.3 ≥ 0.3

VBF Selections

∆η(jet1, jet2) > 4.2 > 4.2 > 4.2

ηjet1 · ηjet2 < 0 < 0 < 0mj, j[GeV ] ≥ 250 ≥ 250 ≥ 250

• We perform a shape-based analysis, using the mjj distribution as adiscrimination variable.





Background Estimation Strategy(CMS-SUS-14005)

• We use a common BG estimation methodology across channels:1 We obtain SFs in high purity CRs to correct for any mismodeling in

simulation, after applying central selections (No VBF selections).2 When possible, we measure the VBF efficiency from data.3 The contribution of a given BG in the SR, estimated with the method

described above, is performed using the following formula:

NDataBG = NMC

BG (central) · SFCR1central · εCR2

VBF(mjj)

4 A closure test is performed in MC. The difference between the nominaland predicted yields in the closure test, is taken as a systematic error.

5 When possible we also perform closure tests with data.6 We check that the signal contamination in the CRs is negligible.

• If the BGs are small, when possible we first show that the VBF shapesare well modelled in simulation and then simply correct the MCprediction with a SF:

NDataBG = NMC

BG (SR) · SFCR1central





tt Background Estimation For OS/LS µµ(CMS-SUS-14005)

• tt is the largest BG source for both µµ channels (OS & LS)• The estimation of this BG is done in a semi-data-driven way.• Three CRs are used:

1 CR1: SFCR1central for central selections for OS events.

2 CR2: SFCR2central for central selections for LS events.

3 CR3: measure VBF efficiency and dijet mass shape from data.

250

1

w/ iso

Isolation

N(b)

w/o iso

1

w/ iso

N(b)

w/o iso

OS SIGNAL

0

OS

21 *qq

),( jjm

1

w/ iso

Isolation

N(b)

w/o iso

1

w/ iso

Isolation

N(b)

w/o iso

CR1 CR3

CR2 CR3

Top Pair Background Estimation & Validation/Closure Strategy

Isolation

LS

CR3

CR3

LS SIGNAL





mjj Distributions(CMS-SUS-14005)

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• The band includes the total systematic and statistical uncertainties.Correlations across BGs and across channels have been considered.

• The largest source of systematic uncertainty comes from closure tests insimulation for the BG estimates.





Final yields: OS Channels(CMS-SUS-14005)

Number of observed events in data and estimated background rates for the OS

search channels. The uncertainties are based on the number of observed events in

the CRs as well as the statistics in simulation.

Process µ±µ∓jj e±µ∓jj µ±τ∓h jj τ±h τ∓h jj

DY + jets 4.3 ± 1.7 3.7±2.11.9 19.9 ± 2.9 12.3 ± 4.4

W + jets < 0.01 4.2±3.32.5 17.3 ± 3.0 2.0 ± 1.7

VV 2.8 ± 0.5 3.1 ± 0.7 2.9 ± 0.5 0.5 ± 0.2tt 24.0 ± 1.7 19.0±2.3

2.4 11.7 ± 2.8 –QCD – – – 6.3 ± 1.8Higgs 1.0 ± 0.1 1.1 ± 0.5 – 1.1 ± 0.1VBF Z – – – 0.7 ± 0.2Total 32.2 ± 2.4 31.1±4.6

4.1 51.8 ± 5.1 22.9 ± 5.1

Observed 31 22 41 31





Final yields: LS Channels(CMS-SUS-14005)

Number of observed events in data and estimated background rates for the LS

channels. The uncertainties are based on the number of observed events in the

CRs as well as the statistics in simulation.

Process µ±µ±jj e±µ±jj µ±τ±h jj τ±h τ±h jj

DY + jets < 0.01 0±1.70 0.5 ± 0.2 < 0.01

W + jets 0.1 ± 8.2 × 10−4 0±3.00 9.3 ± 2.3 0.5 ± 0.1

VV 2.1 ± 0.3 1.9±0.40.2 1.1 ± 0.2 0.1 ± 6.5 × 10−2

tt 3.1 ± 0.1 3.5±0.70.9 6.7 ± 2.8 0.1 ± 1.2 × 10−2

Single top – – – < 0.1QCD – – – 7.6 ± 0.9Higgs – – – < 0.01Total 5.4 ± 0.3 5.4±3.5

0.9 17.6 ± 3.8 8.4 ± 0.9

Observed 4 5 14 9





SUSY Scenario 1 – Compressed Mass Spectra& Large Mass Gaps




SUSY Scenario 2 – Compressed Mass Spectra& Large Mass Gaps

(CMS-SUS-14005)





Results - Combined Limits: Scenario 1(CMS-SUS-14005)

• No excess above the SM backgroundis observed.

• A combined observed upper boundlimit of 280 GeV and an expectedlimit on 295 GeV is set, for the largemass gap scenario where the massdifference between the chargino andthe slepton is 5 GeV and the LSPmass is 0 GeV.

• For the compressed mass spectrascenario, where the mass differencebetween the chargino and the LSP is50 GeV, we set a combined observedupper bound limit of 170 GeV and anexpected limit of 180 GeV.

[GeV]2

0χ∼ = m1

±χ∼m100 150 200 250 300 350 400

[fb

]σ

1

10

210

310Observed

= 50 GeV1

0χ∼ - m1

±χ∼, mσ 1±Expected

= 0 GeV1

0χ∼, mσ 1±Expected

jj) (LO)χ∼χ∼ →(pp σ


= 5 GeVτ∼ - m1

±χ∼m

hτhτ, h

τµ, µ, eµµ, τ τ∼ →

2

0χ∼ , τν τ∼ → 1

±χ∼





Results - Combined Limits: Scenario 2(CMS-SUS-14005)

• No excess above the SM backgroundis observed.

• A combined observed upper boundlimit of ≈ 300 GeV and an expectedlimit on ≈ 310 GeV is set, for thecompressed mass spectra scenario.

• We do not have sensitivity to excludeany masses in the large mass gapscenario, for this slepton massdefinition.

[GeV]2

0χ∼ = m1

±χ∼m100 150 200 250 300 350 400

[fb

]σ

1

10

210

310Observed

= 50 GeV1

0χ∼ - m1

±χ∼, mσ 1±Expected

= 0 GeV1

0χ∼, mσ 1±Expected

jj) (LO)χ∼χ∼ →(pp σ


±1

χ∼m21 + 0

1χ∼m2

1 = 1τ∼m

hτhτ, h

τµ, µ, eµµ, τ τ∼ →

2

0χ∼ , τν τ∼ → 1

±χ∼





Latest Limits in the Electroweak SUSY Sector

neutralino mass = chargino mass [GeV]

100 200 300 400 500 600 700 800

LSP

mas

s [G

eV]

0

100

200

300

400

500

600

700

800

900

10χ∼

= m1

±χ∼m

Z+m1

0χ∼

= m1

±χ∼m

H+m1

0χ∼

= m1

±χ∼m

ICHEP 2014 = 8 TeVs

CMS Preliminary

production1

±χ∼-2

0χ∼

) 1

0χ∼)(W 1

0χ∼ (H → 1

±χ∼ 2

0χ∼

)1

0χ∼)(W 1

0χ∼ (Z → 1

±χ∼ 2

0χ∼

) )=0.5-l+l, BF(Ll~ (

1

±χ∼ 2

0χ∼

) )=1-l+l, BF(Ll~ (

1

-χ∼ 1

+χ∼

)τν∼τ∼ (1

±χ∼ 2

0χ∼

) )=1-l+l, BF(Rl~ (

1

±χ∼ 2

0χ∼

-1SUS-13-006 19.5 fb-1SUS-14-002 19.5 fb

Observed

Expected

10χ∼

= m1

±χ∼m



Summary

Summary

• The first VBF SUSY search from CMS is been presented.

• The search is a promising avenue to target compressed-mass-spectrascenarios with taus.

• Stay tuned for the next run of the LHC!


Summary

BACKUP


Summary

µµjj - mjj Distributions(CMS-SUS-14005)

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Summary

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Documents

DPF2015 Vector-Boson-Fusion Topology at CMS Andr es Fl ...people.physics.tamu.edu/kamon/research/talk/2015/...Andr es Fl orez (Uniandes - Colombia) DPF2015 August 4, 2015 13 / 25