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Monika Wielers (RAL) on behalf of the ATLAS Collaboration

ATLAS e/  /  /jet/E T miss High Level Trigger Algorithms Performance with first LHC collisions. Monika Wielers (RAL) on behalf of the ATLAS Collaboration. Real Time 2010. Introduction. Outline

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Monika Wielers (RAL) on behalf of the ATLAS Collaboration

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  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 Monika Wielers (RAL)

  2. Introduction • Outline • Performance of the ATLAS High Level Trigger (HLT=L2 + EF) • Electrons and photons • Taus • Jets • ETmiss • Next commissioning steps • Conclusions • 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 Monika Wielers (RAL)

  3. Electrons and Photons: Overview • e/ 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 steps • Starting point: L1 EM region of interests (RoI) • clustering: a bit simplified compared to offline • tracking: 3 fast pattern recognition algorithms being evaluated online • Use of calo shapes and cluster-track matching variables in selection • Use of offline algorithms • Run clustering and tracking algorithms • Due to timing constraints: no conversion finding, no brem recovery • Use of calo shapes and cluster-track matching variables in selection • HLT and offline use same variables for signal identification L2 EF Monika Wielers (RAL)

  4. We candidate as seen by the trigger As seen by L2 As seen by offline Electron candidate • aa L1 tower ET in  space pT(e+)=34 GeV (e+) = -0.42 ETmiss = 26 GeV MT = 57 GeV Monika Wielers (RAL)

  5. Electrons and Photons: Performance R distributions for trigger objects matched to offline e candidates • Good trigger performance can be evaluated in terms of • Small resolution between trigger and offline selection variables • Agreement between data and MC for the selection variable distributions • Example: • Shower shape in 2nd EM layer R=E(37)/E(77) (cell units, one unit is =0.025  0.025) • Good agreement between trigger and offline found for resolution • Data 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 Monika Wielers (RAL)

  6. Tau HLT Performance: Overview • Tau’s are key signature for • W, Z SM processes • Hhh, heavy Higgs • Susy searches with a light tau slepton • ~65% of ’s decay hadronically in 1- or 3-prongs (, +n0 or 3, 3+n0) • Requires dedicated trigger looking for • “Narrow” jet in calorimeter • 1 or 3 associated tracks in tracking detector • Identification based on jet isolation, jet narrowness and track multiplicity • HLT processing steps similar to electrons • Starting point: L1 tau RoI Monika Wielers (RAL)

  7. Tau HLT Performance in 900 GeV collisions • Examples: • L2 ET spectrum • EF EM and hadronic radius (measurement of shower size in -: EcellR2cell/Ecell in =0.1 x 0.1) • Expect small values for tau’s • Reasonable agreement between data - MC • Gives us confidence that the selections optimised on MC will work! 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 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 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 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 selection ETmiss after XE10 (no offline clean-up) Monika Wielers (RAL)

  12. Missing ET: HLT Performance in 7 TeV collisions EF Missing ET > 5 GeV EF Missing ET > 20 GeV • 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 limited • The EF Missing ET trigger performs as expected on physics events Monika Wielers (RAL)

  13. Next commissioning steps for e///jet/ETmiss • 1st commissioning step • Deploy the HLT online without active rejection • Verify HLT results w.r.t. offline, MC • 2nd commissioning step • Start 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 Wl • Start optimising triggers for higher luminosities (includes pile-up) • HLT rejection • Already active for minimum bias triggers since a while • HLT 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 rejection • Jets will use mixture of pre-scale and HLT  In progess Just started! Ultimate goal 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 Monika Wielers (RAL)

  15. Backup Monika Wielers (RAL)

  16. The ATLAS Detector Monika Wielers (RAL)

  17. The ATLAS Trigger System ~40 MHz L1 2 μs on detector ~75 KHz 40 ms L2 ~2 KHz ~4 s EF ~200 Hz A 3 level trigger system: • L1Trigger (LVL1): • hardware based • only muon and calo information • reduced granularity event rate level latency • Level2 (HLT): • software based • all detectors available (RoI approach) • dedicated algorithms and calibration • EF (HLT): • software based • full event information available • ‘quasi’ offline algorithms • Region of Interest ( RoI ) concept: only detector information contained in an angular region ΔηxΔφ= 0.2x0.2 around L1 cluster position are processed by next level (increase speed and reduce network load) 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… 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. offline • L2 resolution is ~ factor 3 worse: due to the completely different tracking algorithm (IdScan) used To be approved To be approved Monika Wielers (RAL)

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