Performance of the missing E T trigger with 7 TeV data

Performance of the missing ET trigger with 7 TeV data Alex Pinder University of Oxford L1Calo/trigger joint meeting CERN, May 7 2010

Introduction Purpose of Missing ET (MET) trigger: Discovery in no-lepton channels (SUSY etc) Validation of other trigger slices (unbiased preselection): Egamma Tau Also triggers based on SumET for black holes and detector performance L2 takes L1 MET/SumET and (optional) adds muon correction MET and SumET calculated from L1Calo towers Muon correction not used initially  L2 = L1 EF takes all cells over a given threshold (currently 3σ) Similar to offline MET_Base No calibration constants applied initially; at EM scale L1Calo/trigger joint meeting

Preliminaries: datasets used Datasets used – data: data10_7TeV.00152409.physics_MinBias.recon.ESD.f238  long run before L1Calo timing change data10_7TeV.00152845.physics_MinBias.recon.ESD.f243 data10_7TeV.00152878.physics_MinBias.recon.ESD.f243 data10_7TeV.00152933.physics_MinBias.recon.ESD.f244 good runs > 20 μb-1 after timing change data10_7TeV.00153030.physics_MinBias.recon.ESD.f247 data10_7TeV.00153134.physics_MinBias.recon.ESD.f249 Dataset used – MC: mc09_7TeV.105001.pythia_minbias.recon.ESD.e517_s804_s808_r1233 L1Calo/trigger joint meeting

Preliminaries: timing and cleaning cuts All plots are made with collision candidate events, defined thus: L1_MBTS_1_1 passed |ΔtMBTS| < 10 ns |ΔtLAr| < 5 ns Some plots use jet cleaning cuts (now ~1 week old) – bad jets have: Timing > 50 ns OR (n90 ≤ 5 AND emfrac < 0.2) OR (quality > 0.8 AND emfrac > 0.95) L1Calo/trigger joint meeting

Effect of changes to L1Calo timing (1) Change to L1Calo timing has positive effect on EF MET and SumET EF Sum ET distribution after L1 threshold preselection now closer to ‘ideal’ (EF-only) distribution Plots show EF Sum ET distributions: ideal (black), passing L1 TE30 (red) Clear improvement Before timing change After timing change L1Calo/trigger joint meeting

Effect of changes to L1Calo timing (2) Another way to see effect: look at turn-on curves with EF MET/SumET as the reference variable Get sharper turn-on after L1Calo timing change  indicates better correlation between L1 and EF Samuel has demonstrated better correlation between L1 and offline L1 XE10 L1 TE30 L1Calo/trigger joint meeting

Effect of change to L1 noise threshold EM threshold test: 4σ 3σ Nothing to show here! HLT was not switched on for these runs Samuel has shown benefits in terms of offline MET/SumET Benefits are likely to apply at EF as well L1Calo/trigger joint meeting

Stability of MET trigger: L1 Want to show we get the same distributions from run to run Demonstrate the trigger performs consistently For L1 = L2 this certainly seems to be the case Note: no jet cleaning done in these plots: want to be able to spot anomalous contributions to the tale L1Calo/trigger joint meeting

Stability of MET trigger: EF Want to show we get the same distributions from run to run A strange tail is apparent in EF MET for run 153030 Also visible in SumET The source is understood: noisy strip in tile barrel (see next) Note: no jet cleaning done in these plots L1Calo/trigger joint meeting

Discovering detector problems with the MET trigger (1) Run 153030 had a noisy strip in tile barrel eta ≈ [0.0,1.0], phi ≈ –1.7 Due to data corruption problem with two modules Effect is most noticeable in offline SumET Heavier noise suppression at EF so feature is more subtle No feature apparent at L1; towers rather than cells Offline L1 EF L1Calo/trigger joint meeting

Discovering detector problems with the MET trigger (2) Small feature in plots of trigger MET and SumET becomes obvious when looking at turn-on curves Effect on turn-on curves is large because the noisy area has different effects at L1, EF and offline Impact on L1 TE efficiency is huge in this case Clearly potential here to see much more subtle detector problems by careful monitoring of MET trigger performance L1 TE30 EF TE100 L1Calo/trigger joint meeting

Correlation of L1 and offline MET Use only good runs with new L1Calo timing from now on (4/4 noise cuts) Many bad jets give large offline MET but small MET at L1 Question: is there one particular cleaning cut that removes this population of events? Second population of bad jet events with large MET at L1 and offline A L1 threshold of XE10 kills many bad jet events, so these should have only a small effect on our rate at EF Events with bad jets killed All collision candidates L1Calo/trigger joint meeting

Correlation of L1 and offline SumET Effect of bad jets here is generally to increase the dispersion L1 SumET is much smaller than offline in most cases, as we expect Events with bad jets killed All collision candidates L1Calo/trigger joint meeting

Correlation of EF and offline MET Bad jet events contribute significantly to the tail of EF MET But L1 preselection (a normal MET chain!) kills many of these Note 2nd plot is zoomed in (no events outside this window) Events with bad jets killed All collision candidates L1Calo/trigger joint meeting

Correlation of EF and offline SumET Bias of +10 GeV in EF SumET because of noise suppression Only cells with energy > 3σnoise are counted Correlation with offline is very good Would be good to understand the single outlier – properties of jets etc All collision candidates Events with bad jets killed L1Calo/trigger joint meeting

Comparison with Monte Carlo (L1) All coll cand Big discrepancy After cleanup cuts L1Calo/trigger joint meeting

Comparison with Monte Carlo (EF) Tail from bad jets All coll cand After cleanup cuts L1Calo/trigger joint meeting

Comparison with Monte Carlo (observations) EF displays excellent agreement for MET Discrepancy for SumET is present offline too Known issue: MC does not model SumET well L1 MET data does not agree with MC Something bad in the MC sample used? (r1233) It was hypothesised that activity in barrel+endcap region was the cause: barrel energy not included in tower sum (not modelled by MC) But killing events with a jet in the crack region does improve things w/o crack jets With crack jets L1Calo/trigger joint meeting

Effect of L1 cut on EF MET tail All XE chains start with L1 XE10 or higher This preselection cuts out many bad jets and reduces tail at EF Plots shows reduced tail following L1 XE10 preselection (green squares) The tail is reduced but does not disappear: clearly there are ≥ 2 types of bad jet, only some of which have small L1 MET Currently investigating this L1Calo/trigger joint meeting

Efficiency of the triggers (L1 XE) Offline reference for MET trigger efficiency is MET_Topo Missing ET Difference in L1 MET shape means data and MC do not agree Would be good to understand why Turn-on is slow, but improved slightly by changes to L1Calo noise cuts (EM = 3σ) and internal timing L1 XE5 L1 XE20 L1Calo/trigger joint meeting

Efficiency of the triggers (L1 TE) Again, large disagreement between data and MC We do not seem to understand L1 MET or SumET Much sharper turn-on following L1Calo timing change: that’s good! Changing noise cut to 3σ also has positive effect (Samuel’s talk) L1 TE10 L1 TE30 L1Calo/trigger joint meeting

Efficiency of the triggers (EF XE) Excellent agreement between data and MC It looks like EF is well-understood! Very sharp turn-on, indicating good correlation between EF and offline EF XE20 EF XE5 L1Calo/trigger joint meeting

Efficiency of the triggers (EF TE) Excellent agreement between data and MC It looks like EF is well-understood! Very sharp turn-on, indicating good correlation between EF and offline TE30 reaches plateau before 30 GeV offline because of 10 GeV bias in EF Effect of bias has gone by TE100 EF TE100 EF TE30 L1Calo/trigger joint meeting

Conclusions Event filter appears to be well-understood, insofar as it agrees with the Monte Carlo prediction L1 has a puzzling discrepancies both for MET and SumET Barrel+endcap towers appear not to be the cause Effect of bad jets is to increase scatter between trigger and offline and to create long tails in MET/SumET Many bad jets (probably those with a few noisy cells) have small missing ET at L1 and so do not affect rate at EF MET trigger is a sensitive tool for finding calorimeter problems Future: Validate trigger by comparing different signatures: MBTS events (nearly no bias to MET trigger) Electrons (Weν) Muons (Wμν) Dealing with effects of early pile-up Look at calibration schemes for EF trigger (currently EM scale) Evaluate use of muon corretion: is it worth the effort? L1Calo/trigger joint meeting

Performance of the missing E T trigger with 7 TeV data