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Real Time 2010 Monika Wielers (RAL) 1
ATLAS e///jet/ETmiss High Level
Trigger Algorithms Performance with first LHC collisions
Monika Wielers (RAL) on behalf of
the ATLAS Collaboration
Real Time 2010
Real Time 2010 Monika Wielers (RAL) 2
IntroductionOutline
Performance of the ATLAS High Level Trigger (HLT=L2 + EF)
Electrons and photonsTausJets
ETmiss
Next commissioning stepsConclusions
Will show plots from s = 900 GeV (~9 b-1 of stable beam data) and s= 7 TeV collisions (so far >10 nb-1 recorded)
Much more 7 TeV collisions data available compared to 900 GeV data. Access to much higher ET values in 7 TeV data
Commissioning done currently by running in pass-through mode at HLT starting from low-ET L1 triggers
We mainly see ‘fakes’ right now rather than the signals we are ultimately interested in
Real Time 2010 Monika Wielers (RAL) 3
Electrons and Photons: Overviewe/ selection key for many physics analyses
J/ψ, B physics low-pT e’s [ 5 – 20 GeV]
W, Z, top, Higgs, SUSY, prompt medium pT e’s and ’s [ 20 – 100 GeV]
G, Z’ high pT e’s and ’s [pT >100 GeV]
Processing stepsStarting point: L1 EM region of interests (RoI)clustering: a bit simplified compared to offlinetracking: 3 fast pattern recognition algorithms being evaluated online Use of calo shapes and cluster-track matching variables in selection Use of offline algorithmsRun clustering and tracking algorithms
Due to timing constraints: no conversion finding, no brem recovery
Use of calo shapes and cluster-track matching variables in selectionHLT and offline use same variables for signal identification
L2
EF
Real Time 2010 Monika Wielers (RAL) 4
We candidate as seen by the trigger
aa
Electron candidate
L1 tower ET in space
As seen by L2 As seen by offline
pT(e+)=34 GeV
(e+) = -0.42
ETmiss = 26 GeV
MT = 57 GeV
Real Time 2010 Monika Wielers (RAL) 5
Electrons and Photons: PerformanceGood trigger performance can be evaluated in terms of
Small resolution between trigger and offline selection variablesAgreement between data and MC for the selection variable distributions
Example:Shower shape in 2nd EM layer R=E(37)/E(77) (cell units, one unit is =0.025 0.025)Good agreement between trigger and offline found for resolutionData and MC agree reasonably well
As selection cuts were derived from MC for start-up a reasonable agreement gives confidence our selection will work online
R distributions for trigger objects matched to offline e candidates
Real Time 2010 Monika Wielers (RAL) 6
Tau HLT Performance: Overview
Tau’s are key signature forW, Z SM processesHhh, heavy HiggsSusy searches with a light tau slepton
~65% of ’s decay hadronically in 1- or 3-prongs (, +n0 or 3, 3+n0)Requires dedicated trigger looking for
“Narrow” jet in calorimeter1 or 3 associated tracks in tracking detector
Identification based on jet isolation, jet narrowness and track multiplicityHLT processing steps similar to electrons
Starting point: L1 tau RoI
Real Time 2010 Monika Wielers (RAL) 7
Tau HLT Performance in 900 GeV collisionsExamples:
L2 ET spectrum
EF EM and hadronic radius (measurement of shower size in -: EcellR2
cell/Ecell in =0.1 x 0.1)
Expect small values for tau’sReasonable agreement between data - MC
Gives us confidence that the selections optimised on MC will work!
Real Time 2010 Monika Wielers (RAL) 8
Jet Performance: Overview
Physics Motivation
Jet cross section
Susy
Black hole searches
HLT processing
Starts from a L1 jet RoI
Iterative cone algorithm with R<0.4 at L2
Cone jet algorithm with R<0.7 at EF (use of offline algorithm)
Note, other jet algorithms under evaluation
Real Time 2010 Monika Wielers (RAL) 9
Jets: HLT Performance in 900 GeV collisions
Relative energy resolution between L2 and offline jets at EM scale
Good agreement between data and MC Small shift in peak position arises from different jet finder used in HLT and offl.
Good agreement between data and MC simulations also seen in -resolution at L2 and EF
Real Time 2010 Monika Wielers (RAL) 10
Missing ET: Overview
Physics motivation
Susy searches and searches for extra-dimensions
ETmiss triggers often combined with jet triggers
HLT processing
Correct L1 ETmiss for muon contribution (can’t read out all
calorimeter cell information due to time constraints)
Apply ETmiss cut in hypothesis step
Compute ETmiss based on full calorimeter cell information
Apply 2 noise cut at cell level
Apply simple layer based calibration
Apply ETmiss cut in hypothesis step
L2
EF
Real Time 2010 Monika Wielers (RAL) 11
Missing ET: HLT Performance in 7 TeV collisions
Strong linear correlation between EF and offline Missing ET measurements
Some of the high ETmiss values arise from “bad” jets (due to noise
fluctuations and will be removed in offline)
Most of the events with fake ETmiss don’t pass the L1 XE10
selectionET
miss after XE10 (no offline clean-up)
Real Time 2010 Monika Wielers (RAL) 12
Missing ET: HLT Performance in 7 TeV collisions
Excellent agreement between data and MC bin-by-bin turn-on curves
Sharp turn-on curves minimal distortion of the offline ETmiss
measurement by trigger
Higher threshold is statistically limitedThe EF Missing ET trigger performs as expected on physics events
EF Missing ET > 5 GeV EF Missing ET > 20 GeV
Real Time 2010 Monika Wielers (RAL) 13
Next commissioning steps for e///jet/ETmiss
1st commissioning stepDeploy the HLT online without active rejection Verify HLT results w.r.t. offline, MC
2nd commissioning stepStart active rejection re-do studies using physics signals
Physics running Measure performance on signal enriched sample
Tag&Probe for Z and J/, ETmiss trigger for Wl
Start optimising triggers for higher luminosities (includes pile-up)
HLT rejectionAlready active for minimum bias triggers since a whileHLT rejection for lowest L1 EM thresholds enabled in night from 24th to the 25th of May for run with peak luminosity of 2.1 1029 cm-2s-1 Lowest muon triggers will be the next ones to go in HLT rejectionJets will use mixture of pre-scale and HLT
Ultimate goal
In progess
Just started!
Real Time 2010 Monika Wielers (RAL) 14
Summary
Data from s = 900 GeV and 7 TeV LHC collisions have moved the commissioning of the ATLAS HLT one step ahead
L1 calorimeter and muon trigger system working reliably
HLT algorithms are running routinely online in pass-through mode (no active rejection, but results are created and available for analysis)
Lowest threshold e/ triggers just went into rejection!Comparison of trigger quantities with reference offline objects show in general reasonable agreement and performance is reasonably well reproduced by MC simulations
We increased our confidence that the selections we set-up will work as expected
Trigger system in very good shape and we can face the challenge to select good quality physics data… interesting times lie ahead of us
Real Time 2010 Monika Wielers (RAL) 17
A 3 level trigger system:
Region of Interest ( RoI ) concept: only detector information contained in an angular region x = 0.2x0.2 around L1 cluster position are processed by next Δη Δφ
level (increase speed and reduce network load)
~40 MHz
even
t rat
e
~75 KHz
~2 KHz
~200 Hz
2 sμ
40 ms
~4 s
leve
l lat
ency
L1
L1Trigger (LVL1):hardware basedonly muon and calo informationreduced granularity
EF (HLT): software based full event information available ‘quasi’ offline algorithms
Level2 (HLT):software basedall detectors available (RoI approach) dedicated algorithms and calibration
L2
EF
on detector
The ATLAS Trigger System
Real Time 2010 Monika Wielers (RAL) 18
Towards the Physics menu at 1031 cm-2s-1
Example: Jet plans
Keep running HLT in pass-through (including multijets)
Then enable multi jet signature only
Then enable HLT
Example: Tau plans
From HLT pass-through chains (starts from L1 tau RoI > 5 GeV) to…
Real Time 2010 Monika Wielers (RAL) 19
Electrons and Photons: Performance in 7 TeV collisions
Example: Electron identification variable Δη: difference in between cluster and extrapolated track
L2 distribution well described by MC simulations (also observed at EF)Good EF resolution w.r.t. offlineL2 resolution is ~ factor 3 worse: due to the completely different tracking algorithm (IdScan) used
To be approved
To be approved