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TAU/JET/E T MISS TRIGGERS IN ATLAS

TAU/JET/E T MISS TRIGGERS IN ATLAS. OUTLINE. Tau/Jet/E T MISS trigger description : what is in the TDR and what is new. An example of an analysis : optimization of tau and E T MISS triggers for W  at L=10 31-32. TAU/JET/E T MISS SOURCES AND INTEREST FOR PHYSICS.

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TAU/JET/E T MISS TRIGGERS IN ATLAS

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  1. TAU/JET/ETMISS TRIGGERS IN ATLAS

  2. OUTLINE • Tau/Jet/ETMISS trigger description : what is in the TDR and what is new. • An example of an analysis : optimization of tau and ETMISS triggers for W at L=1031-32

  3. TAU/JET/ETMISS SOURCES AND INTEREST FOR PHYSICS • Standard Model: • inclusive Wτν (Zττ) production • QCD. • SM and MSSM Higgs: • 100-150 GeV SM Higgs: qqH(ττ) • A/H ττ • H+τν (mH+ < mtop and mH+> mtop) • SUSY • Compositness

  4. The ATLAS trigger Level 1 (hardware): Defines Regions of Interest (RoI). Uses Calo cells and Muon chambers with reduced granularity. e/g, m, t, jet candidates. 2ms Execution time <75(100) kHz High Level Trigger 10ms Level 2 (software): Seeded by LVL1 RoI. Full granularity of the detector Performs calo-track matching ~2 kHz 1s ~200 Hz Event Filter (software): Offline-like algorithms. Refines LVL2 decision Full event building TIER 0 mass storage

  5. LVL1 Trigger Rates

  6. HIGH LEVEL TRIGGER RATES The rates for the HLT taken considering the EF performances equal to those one of the OFFLINE.

  7. LVL1 CALORIMETRIC SIGNAL PROCESSING TAU/JET/ETMISS triggers are calorimetric but they use two different processors

  8. TAU TRIGGER

  9. Hadronic Tau Trigger (I)(ATL-COM-DAQ-2003-030) as in the TDR For | |<2.5 LVL1 trigger: look at 4X4 matrix of calorimetrictowers(DhDf= 0.1 x 0.1 each trigger tower). ET threshold for the central core (EM+Had) and isolation thresholds between core and 12 external towers for e.m. and had. calorimeters. LVL2 trigger: look at the shower shape in the 2nd layer of e.m. calorimeter and at the track multiplicity inside the RoI defined at LVL1. Cut on the ratio between ET contained in a 3x7 cell cluster and ET in a 7x7 cell cluster and on track multiplicity second layer of EM calorimeter h + track multiplicity in the RoI f

  10. Hadronic Tau Trigger (II)(ATL-COM-DAQ-2003-030) as in the TDR • LVL3 (Event Filter) : • look at the complete event. • The variables of the offline algorithms are used as an approximation of the LVL3 trigger five variables: • number of reconstructed tracks, within DR = 0.3 of the candidate calorimeter cluster, between 1 and 3; • cut on isolation fraction, defined as the difference between the ET contained in a cone size of DR=0.2 and 0.1 normalized to the total jet ET; • cut on EM jet radius, an energy weighted radius calculated only in the e.m. calorimeter ; • cut on EM energy fraction, defined as the fraction of the total jet energy in the e.m. calorimeter; • threshold on the pT of the highest pT track.

  11. EFFECT OF TRIGGER SELECTIONS HAD iso ET core EM iso

  12. TAU TRIGGER EVOLUTION For the LVL1 different RoI sizes are under study (timing, resolution and efficiency,…) LVL2 : Calorimeter based approach LVL2 :Tracking based approach Perform tracking and obtain (h,f) (h,f) from EMSamp2 Calo variables (more variables used than in the TDR) New:studied for Very Low Lumi 1031 cm-2 s-1 Current approach Tracking (# of tracks, charge,…) Calorimeter variables Final decision : matching of cluster and tracks, energy estimate with energy flow Final decision : matching of cluster and tracks, energy estimate Under developing an EF tracking based algorithm.

  13. JET AND ETMISS TRIGGER

  14. LVL1 JET TRIGGER as in the TDR • identify hadronic jets using calorimetric data; • classify them according to ET; • provide multiplicity of jets passing required threshold; • provide the coordinates of the candidates to the LVL2; • have an energy resolution as good as possible for high ET and low ET jets. For | |<3.2 JET ELEMENT : DhDf = 0.2 x 0.2 (now only one sample in depth) Algorithm : - 2x2 jet element cluster (0.4x0.4) to identify a jet RoI, it is a local ET maximum. - 4x4 jet element (or 3x3 or 2x2) trigger cluster to measure the jet ET. Trigger cluster size : -big enough to have a good energy resolution for high ET jets (containment) -not too big for low ET jets (noise and pileup) RoI size and step size : -spatial resolution and jet separation.

  15. ROI L2 LVL2 JET RECONSTRUCTION • LVL2 starts from LVL1 RoI information (, φ location) • Iterative cone algorithm (R=0.4) to calculate weighted , φenergy center. Possible granularities : cell-based, LVL1 trigger towers,…. Jet Jet Cone Size several iterations needed: timing is an important key. Jet calibration (energy scale and resolution) has an important effect on trigger efficiency.

  16. JETS AT THE EVENT FILTER Study of jet reconstruction at the EF : • Size of Region of Interest (RoI): • 16 (0.4x0.4), 32 (0.8x0.8), 64 (1.6x1.6) • Different types of clusters: • topological clusters or calorimeter towers • Algorithms: • Fast KT, Cone Dijets samples with 35 GeV < PT < 1120 GeV Results of the study: • Jet reconstruction is better with a higher size of RoI, • Higher size of RoI requires more time, • Topological clusters are faster than calorimeter towers but Towers reconstruct better pT of jets

  17. ETMISS TRIGGER ETMISS is a global variable. LVL1: Calorimeter energies summed into a map with a granularity DhDf = 0.2 x 0.2. Ex, Ey, ET, ETMISS are computed. ETMISS trigger is not a standalone trigger, but it will be used in association with jet or tau trigger. Rapidity coverage : critical for ETMISS trigger performances. as in the TDR For ||<5 For QCD events : trigger rate (KHz) ETMISS (GeV)

  18. Possible Strategies for ETMISS Trigger at LVL2 and EF LVL2 possible strategy: • Based on LVL1 Missing ET “ROI” (with scalar ET, ΣEx, ΣEy) • Based on LVL1 Jet ROIs - Use cell data for each RoI • Based on Trigger Towers: - Refine with better calibration and replace saturated towers • For all the above, add muons EF possible strategy: • Using FEB header ΣEX, ΣEY from RODs • Using full cell data. • For both of these, add muons.

  19. Algorithms for Tau/Jet/ETMISS triggers are still under development : not a final decision taken. ATLAS physics groups have started now to include trigger information in the simulations to perform analysis : a trigger part to perform a Trigger Aware Analysis has been added in the last releases of the ATLAS software. The Tau Trigger slice is going to be added now : no analysis available with the “true” simulation of the tau trigger. Trigger effects can be emulated : next slides will show an analysis.

  20. “Trigger aware analysis”from user perspective Trigger optimization and prospects for W nwith 100 pb-1(few weeks of data taking at very low luminosity 1031-1032 cm-2s-1 ) Data samples: 18 000 events W  n 124000 dijet events (J1-J2-J3) For topological studies ~10^8 events from fast simulation Daniel Froidevauxand Elzbieta Richter-Was

  21. Why W  ? • Extract signal for most abundant source of t-leptons as early as possible. This requires a performant t and ETmiss trigger from the very start! For L = 2 1033, baseline plan is to trigger on t25I + XE30 at LVL1 (for a rate of about 2 kHz) and to raise the thresholds to t35i + xE45 at the HLT (for an output rate of about 5 Hz) . • Measurment of W n/W ento confirm good understanding of trigger/reco/identification efficiencies • E/p measurement in single-prong  decay for calorimeter calibration. Assumed that trigger chain is fully operational and that the detector operates more or less as expected (especially in terms of ETmiss performance). Efficiencies of ~ 80% for the t trigger and of ~ 50% for the id/reco of t hadronic decays were assumed.

  22. Algorithm to “emulate” LVL1 trigger • seed “RoI” with topo-clusters, accept if ET > 5 GeV • calculate energy in 2x2 and 4x4 towers of 0.1x0.1 (hxf) • noise subtraction not applied, cells with negative energy suppressed from enegy counting • energy in HAD (originaly at EM scale) multiplied by 1.25 • remove overlapping “RoI” with iterative procedure, imposing separation by DR > 0.3 • missing energy taken from ”uncalibrated calo off-line”.

  23. L1 tower multiplicity More on LVL1-like RoI’s signal ET spectrum multiplicity DR between RoI’s <> = 1.5 < Total QCD DR between RoI’s ET spectrum multiplicity <> = 0.78

  24. Energy resolution for signal RoI and threshold efficiency 2x2 RoI 4x4 RoI Threshold: 0.75 * 20 GeV 90% efficient at ETvisible = 20 GeV

  25. Energy resolution for background RoI and threshold efficiency 2x2 RoI 2x2 RoI 4x4 RoI Threshold: 0.75 * 20 GeV Factor 10 rejection at ETvisible = 20 GeV

  26. Isolation for EMTau RoI ETL1otherEM/ETL1core < 1.0 ETL1otherHAD/ETL1core < 0.25 ETL1core/ETL1tower > 0.5 ETL1otherEM/ETL1coreEM < 1.0 ETL1otherHad/ETL1coreHad < 1.0 L1core = 2x2 L1tower = 4x4 Full cirles: with threshold ETL1tower > 0.75 * 20 GeV signal QCD Isolation very loose .... Factor 5 rejection at 80% efficiency but almost no improvement if ET threshold added.

  27. More on ETmiss : we have only off-line available ETmiss, ETMissFinal,ETTruthNonInt,ETMissAtlfast truth off-line Atlfast ETmiss is calculated at EM scale, from calo only.

  28. Concluding on LVL1-like selection L=10^31 LVL1 trigger: “ ETL1tower 20 GeV Isol + ETmiss 20 GeV ” ( this means ETL1tower 0.75 * 20 GeV and isol_1+ isol_2 ) Isolation criteria rather weak. We use ETmiss from uncalibrated calo at EM scale... Rates: 0.02 Hz signal  2* 105 events for 100pb-1 60 Hz QCD bgd S/B ~ 0.0003

  29. The LVL2 like selection:explore track-seeded reconstruction Algorithm for tauL2 : • start from track with pT > 9 GeV accept if no more than 2 associated tracks in DR < 0.2 and pT > 2 GeV • store info on “track quality” of leading track for futher discrimination • build energy from simplified Eflow (energy overestimated by 10%-20%mostly because noise not suppressed) • calo identification variables from EM2 or all EM calo • Same definition for ETMISS as at LVL1 Signal response < > = 1.16 s = 0.17 Bgd response < > = 0.86 s = 0.18

  30. Concluding on LVL2-like selection L=10^31 LVL2 trigger: “ETL2tower 20 GeV + track quality + id EM2 + id all Cal + ETmissFinal 20 GeV” Loose triger selection, now we have to supress bgd in off-line analysis Rates: 0.01 Hz signal  105 signal events “on tape”for 100pb-1 5 Hz QCD bgd S/B ~ 0.002

  31. Off-line analysis We start offline analysis with S/B ~ 0.002 and predicted~10^5 signal events “on tape” Need rejection ~ 10^3 for effic ~ 50%or increase ETmissthreshold How fast bgd is supressed with the off-line ETmiss threshold. ~ LVL2 thresh. ~ LVL2 thresh. ETmiss > 60 GeV gives bgd: rejection 10^3, signal: accept 10% -> still 10^4 evt for 100pb-1, S/B ~ 0.2 without refined tau indentification Results with only fast-sim offline, ETmiss has no instrumental tails ! ~ 10^8 QCD events in fine pTbins

  32. Now we can go back to plot from page 25: Off-line 60 GeV Atlfast

  33. Now we can go back to full-sim samples Verify what off-line tauid rejection is possible.... since some discriminantion power already explored when accepting LVL2 (calo+tracks) candidates. We take tauL2 candidate “on tape” (after LVL2 tauiD) and check efficiency for matchingtau1P, tau3P identified with PDE-RS optimisation(one MVA technique among many) tau1P tau3P tau1p (tau3p) ; track-based offline algorithm to identify 1-prong (3-prong) tau decay. signal bgd signal bgd pT = 20 – 40 GeV discriPDERS > 0.85 68% 6.5% 46% 3.0% 0.90 50% 3.5% 23% 1.0% 0.95 40% 1.0% 4% 0.2% After L2 track-based trigger, discrimination fairly flat as function of pT

  34. Summary:  LVL1 and LVL2 selection (calo+tracks) emulated for W tnanalysis  With rather soft selection ETmiss > 20 GeV + EMTauRoI > 20 GeV estimated for 10^31: 60 Hz after LVL1 5 Hz after LVL2  For off-line analysis start with S/B ~ 0.002~ 10^5 signal events accepted for 100pb-1 Increasing ETMISS threshold helps in the background rejection: at 60 GeV threshold, supression 10^2-10^3 at 10% efficiency. • Offline tau selection has to do the final work to extract the signal. Low luminosity provides unique opportunity to study low energy  hadronic signatures in ATLAS (in view of SUSY) : important possibility to verify the understanding of tauID and ETMISSreco before attacking “New Physcics”.

  35. BACKUP SLIDES

  36. Electromagnetic Liquid Argon Calorimeters Tile Calorimeters η=1.475 η=1.8 η=3.2 Forward Liquid Argon Calorimeters Hadronic Liquid Argon EndCap Calorimeters Sistema calorimetrico di ATLAS EM LAr || < 3 : Pb/LAr 24-26 X0 3 sezioni longitudinali 1.2   = 0.025  0.025 – 1% equal. Central Hadronic || < 1.7 : Fe(82%)/scintillatore(18%) 3 sezioni longitudinali 7.2   = 0.1  0.1 End Cap Hadronic1.7 <  < 3.2 : Cu/LAr – 4 sezioni longitudinali  < 0.2  0.2 Forward calorimeter3 <  < 4.9 : EM Cu/LAr – HAD W/LAr 3 sezioni longitudinali

  37. Tau Trigger Rate

  38. More on ETmiss : we have only off-line available

  39. S.Levy, HCP session, July 2005

  40. Signal and background at 14 TeV cross-section(PYTHIA) signal ~ 10 x higher QCD bgd ~ 102-103 x higher than in CDF. ( ERW, ATL-PHYS-2000-023) signal <> = 22.6 GeV spectrum rather soft for ETmiss, pTvis signal signal <> = 16.6 GeV <> = 18.4 GeV (ATL-PHYS-2000-023)

  41. Results from past studies (ATLAS) E/p measurements for calibration of hadronic calorimeters C. Biscarat COM-CAL-99-0003 280Hz rates predicted after HTL at 10^33 Rejection 70 340 2 total id rejection: 10^5 total id effic: ~ 25% .trigger-like: ETmiss > 35 GeV + pTjet > 20 GeV preselection: veto iso lepton, veto iso photon tau-jet selection: track with pT> 30 GeV single-track: veto if extra tracks pT>1 GeV in tau cone narrow-jet: calo isolation Events for 100 pb-1: | 5270 Wtnpn | 3630 Wtnrn| 320 QCD jets (bb)

  42. Off-line analysis ~ 10^8 QCD events in fine pTbins We don’t have enough events to continue with full-sim samples. We have move to fast-sim samples to study topological selection only and to estimate how much bgd suppression is possible:

  43. Off-line analysis ~ 10^8 QCD events in fine pTbins Vetoying any other jet ‘a la CDF’ gives 30% accept for signal 25% acept for bgd We have looked at few more distribributions.... nothing obvious to optimise on... We started offline analysis with S/B ~ 0.002 and predicted ~10^5 signal events “on tape” Need rejection ~ 10^3 for effic ~ 50% or increase ETmiss threshold

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