1 / 22

CMS High Level Trigger Selection

EPS-HEP 2003 Aachen, Germany. CMS High Level Trigger Selection. Giuseppe Bagliesi INFN-Pisa On behalf of the CMS collaboration. Outline. LHC Environment High Level Trigger strategy Object selection e/ g, m, Jet /n, t , b HLT rates and efficiencies Conclusions. p-p collisions at LHC.

mahola
Download Presentation

CMS High Level Trigger Selection

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. EPS-HEP 2003 Aachen, Germany CMS High Level Trigger Selection Giuseppe Bagliesi INFN-Pisa On behalf of the CMS collaboration

  2. Outline • LHC Environment • High Level Trigger strategy • Object selection • e/g, m, Jet/n,t, b • HLT rates and efficiencies • Conclusions G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  3. p-p collisions at LHC Event rate Crossing rate 40 MHz Event Rates: ~109 Hz Max LV1 Trigger 100 kHz Event size ~1 Mbyte Readout network 1 Terabit/s Filter Farm ~106 Si95 Trigger levels 2 Online rejection 99.9997% (100 Hz from 50 MHz) System dead time ~ % Event Selection: ~1/1013 Luminosity Low 2x1033 cm-2 s-1 High 1034 cm-2 s-1 “Discovery” rate G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  4. Operating conditions: one “good” event (e.g Higgs in 4 muons ) + ~20 minimum bias events) All charged tracks with pt > 2 GeV Reconstructed tracks with pt > 25 GeV Trigger environment 40 MHz Clock driven Custom processors 100 kHz Event driven PC network Totally software 100 Hz To mass storage two trigger levels Level-1 (~µs) 40 MHz High-Level ( ms-sec) 100 kHz Event Size ~ 106 Bytes G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  5. HLT: Reconstruction and selection of electrons, photons, muons, jets, missing ET, and b and t tagging. HLT has access to full event data (full granularity and resolution) maximum flexibility Main requirements: Satisfy CMS physics program with high efficiency Inclusive selection (we like to see also unexpected physics!) Must not require precise knowledge of calibration/run conditions Efficiency must be measurable from data alone The HLT code/algorithms must be as close as possible to the offline reconstruction Limitations: CPU time Output selection rate (~102 Hz) Precision of calibration constants High Level Trigger requirements and operation G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  6. Regional Reconstruction Global • process (e.g. DIGI to RHITs) each detector fully • then link detectors • then make physics objects Regional • process (e.g. DIGI to RHITs) each detector on a "need" basis • link detectors as one goes along • physics objects: same G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  7. e/g selection Level-1 ECAL reconstruction Threshold cut Level-2 Pixel matching Level-2.5 • In addition: • Isolation cuts (ECAL, pixel, track) • Had/EM isolation • p0 rejection Level-3 Photons Threshold cut Electrons Track reconstruction E/p, matching (Dh) cut G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  8. Level-2 electron: 1-tower margin around 4x4 area found by Lvl-1 trigger Apply “clustering” Accept clusters if EHCAL /EECAL <0.05 Select highest ET cluster HLT Electron selection (I) • Brem recovery: • Seed cluster with ET>ETmin • Road in f around seed • Collect all clusters in road •  “supercluster”and • add all energy in road Supercluster G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  9. Level-2.5 selection: add pixel information Very fast, high rejection high efficiency (e=95%), high background rejection (14) Pre-bremsstrahlung: Matching hits given by most electrons and by few photons Require at least 2 hits (3 pixel hits available almost always) HLT Electron selection (II) G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  10. HLT Electron selection (III) • Level-3electron: • Build tracks from pixel seeds found in pixel-matching step • Very loose track requirements • for high efficiency for radiating tracks: • 3-hit layers • Allow 2 consecutive missing layers • Track selection: • Barrel: E/p and Dh(track-cluster) • Endcap: E/p • Also (non-track): H/E • With tight cuts is always possible to select almost no-radiating electron with very high purity G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  11. Level-3 Algorithmic efficiency  Single muons 10<Pt<100 GeV/c HLT muon track reconstruction • Standalone Muon Reconstruction: “Level-2” • Seeded by Level-1 muons • Kalman filtering technique applied to DT/CSC/RPC track segments • GEANE used for propagation through iron • Trajectory building works from inside out • Track fitting works from outside in • Fit track with beam constraint • Inclusion of Tracker Hits: “Level-3” • Define a region of interest through tracker based on L2 track with parameters at vertex • Find pixel seeds, and propagate from innermost layers out, including muon G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  12. L2 & L3 muon pTresolution and efficiency PT resolution barrel Efficiency vs PT threshold L2 s=0.11 10 GeV threshold L3 L3 L1 s=0.013 30 GeV L2 10. 30. 50. (1/pTrec-1/pTgen) /(1/pTgen)

  13. Before isolation After isolation Isolation and physics content after muon Level-3 Isolation is based on transverse energy (ET ) or momentum (PT ) measurements in cones around the muon Calorimeter isolation - ET from calorimeter towers in a cone around the muon Pixel isolation - PT of 3-hit tracks in the pixel detector in cone around the muon - Requires that contributing tracks come from same primary vertex as the Level-3 muon (to reduce pile-up contamination) Tracker isolation - PT of tracks in the Tracker (regional reconstruction around L3 muon) Muons from b,c,K,p decays are greatly suppressed by isolation G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  14. HLT efficiencies on H WW  2m2n L3 muon thresholds at low luminosity: Single m: 19 GeV Doublem: 7 GeV L3 threshold Efficiency @ low lumi: MH=120 GeV: single mu 74% , di-mu exclusive 14% , combined: 87 % MH=160 GeV: single mu 87% , di-mu exclusive 5% , combined: 92 % G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  15. Jet rates and thresholds • Low luminosity: • 1 kHz at Level-1: 177 GeV (1 jet), 85 GeV (3 jet), 70 GeV (4 jet) • 1 Hz at HLT: 657 GeV (1 jet), 247 GeV (3 jet), 149 GeV (4 jet) • High luminosity: • 1 kHz at Level-1: 248 GeV (1 jet), 112 GeV (3 jet), 95 GeV (4 jet) • 1 Hz at HLT: 860 GeV (1 jet), 326 GeV (3 jet), 199 GeV (4 jet) • Very high rates and thresholds! • HLT triggers need some other condition • to have acceptably low threshold • MET, leptons, isolation, vertices… G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  16. MET Rates • Calorimeter coverage: |h|<5 • Generator level: • real neutrinos -> ETmiss>60 GeV • ETmiss<60 GeV mostly due to limited coverage • Much higher ETmiss at HLT than • at generator level • “ETmiss” objects selection is done in association with other requirements, like a energetic jet G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  17. Momentum resolution Full tracker Impact parameter resolution Full tracker Partial track reconstruction strategy at HLT Reconstruct only a ROI (Region Of Interest) from LVL1 candidate objects (regional tracking) Use a reduced number of hits (conditional tracking) • At HLT ultimate resolution is not needed • Good track parameter resolution is obtained already with 4 or more hits • The time for track reconstruction increases linearly with the number of hits

  18. Tracker @ HLT: tau tagging • TEST CHANNELS • A0/H0 (200, 500 GeV) -> t-jet t-jet, t-jet lepton • H+(200, 400 GeV) -> t-jet n • Efficiencies ~ 40-50%, • Background rej. after LVL1 ~103 • Regional Tracking: • Look only in Jet-track matching cone • Loose Primary Vertex association Conditional Tracking: Stop track as soon as Pixel seed found (PXL) / 6 hits found (Trk) If Pt<1 GeV with high C.L. Reject event if no “leading track” found Regional seeding: look for seeds in a specific region • Regional Tracking: • Look only inside isolation cone • Loose Primary Vertex association Conditional Tracking: Stop track as soon as Pixel seed found (PXL) / 6 hits found (Trk) If Pt<1 GeV with high C.L. Essential at High Luminosity activity well advanced Reject event as soon as additional track found

  19. Inclusive b tagging at HLT Regional Tracking: Look only in Jet-track matching cone Loose Primary Vertex association Conditional Tracking: Stop track as soon as Pixel seed found (PXL) / 6 hits found (Trk) If Pt<1 GeV with high C.L. ~300 ms low lumi ~1 s high lumi Performance of simple signed IP “track counting” tags ~ same as after full track reconstruction Use tracks to define Jet axis (if rely on L1 Calo Jet ~ randomize signed IP) Inclusive b tag at HLT possible, provided alignment under control G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  20. Level-1 rate “DAQ staging”: 50 KHz Total Rate: 105 Hz Average HLT CPU: 300ms*1GHz Improvements are possible HLT table: LHC start… • HLT performances: • Priority to discovery channels G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  21. All numbers for a 1 GHz, Intel Pentium-III CPU HLT: CPU usage Total: 4092 s for 15.1 kHz  271 ms/event Time completely dominated byslow GEANE extrapolationin muons– will improve! Consider ~50% uncertainty! • Today: ~300 ms/event • on a 1GHz Pentium-III CPU • Physics start-up (50 kHz LVL1 output): • need 15,000 CPUs • Moore’s Law: 2x2x2 faster CPUs in 2007 • ~ 40 ms in 2007, ~2,000 CPUs • ~1,000 dual-CPU boxes in Filter Farm G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

  22. The regional/conditional reconstruction is very useful to reduce CPU time and very effective in the HLT selection Tracker at HLT: Essential for muons, electron and tau selection inclusive/esclusive b-trigger is possible Standard Model physics: “just do it” at lower initial luminosity (“dedicated” triggers could be implemented) Pre-scale or lower thresholds when luminosity drops through fill Conclusions Start-up system 50kHz (Level-1) and 105 Hz (HLT) satisfy basic “discovery menu” The HLT design based on a purely software selection will work: Maximum flexibility and scalability Possibility to use “off-line” reconstruction/algorithms Summary G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003

More Related