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Adding a Level 1 Trigger to Calibrate the CMS ECAL with π 0 s

Adding a Level 1 Trigger to Calibrate the CMS ECAL with π 0 s. Sean Simon, Elizabeth Dusinberre, Jim Branson. Outline. The Parasitic π 0 Calibration It works Some problems π 0 Calibration with a L1 Trigger Less systematic problems Calibrate at high  faster Use less of the HLT Farm

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Adding a Level 1 Trigger to Calibrate the CMS ECAL with π 0 s

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  1. Adding a Level 1 Trigger to Calibrate the CMS ECAL with π0s Sean Simon, Elizabeth Dusinberre, Jim Branson

  2. Outline • The Parasitic π0 Calibration • It works • Some problems • π0 Calibration with a L1 Trigger • Less systematic problems • Calibrate at high  faster • Use less of the HLT Farm • CMS can attempt both parasitic and triggered calibration • The basic L1 trigger and π0 selection • Triggering for High  • Outlook

  3. Parasitic Calibration • Use all the 50 kHz of L1 triggers • Called parasitic because it does not have its own trigger. All the π0s are “volunteers”. • Search for π0s around all L1 isolated electron triggers • About 2-5% of the L1 triggered events have a usable π0 • Reconstruct like HLT (High rate) • Write minimal amount of info per event to a calibration stream. ~ 1-2 days to calibrate

  4. π0 Calibration Status • It has been shown that the CMS ECAL can be calibrated with a statistical error of less than 0.5% using the decay π0 • Method is surprisingly insensitive to s/b ratio. 2-3000π0s needed for a “typical” crystal in the barrel; several times more for high  crystals. Need ~108 π0s total

  5. Systematics of Parasitic Calibration In QCD events there is a systematic shift in the calibration due to extra energy from signal π0s in jets Mean = 0.993 Mean = 0.969 Calibration on out-of-jet π0s show no shift Even without background, in-jet π0s show systematic shift

  6. High  in Parasitic Calibration • About 0.5-1% of L1 triggers have a π0 at ||>1 ~ 3 days to calibrate ||>1 • We want to improve on that to calibrate the whole barrel rather quickly.

  7. π0 Calibration with L1 Trigger(s) • Develop L1 triggers that have a high probability to yield usable π0s. • Trigger will likely be pre-scaled to some fixed L1 rate. • It is possible to drop all but ECAL regional data in the RU. • Bandwidth limit is at ECAL FED output. • Could take 10 kHz or more of this trigger.

  8. Study Use of a L1 Trigger • Analysis using CMSSW_1_3_1_HLT6 • Need π0s (ECAL SR) and L1 trigger emulator to work • Probably still not true in any CMSSW version released • 2M MinBias events using CRAB: /MinBias/CMSSW_1_3_4-Spring07-1679/GEN-SIM-DIGI-RECO • Goal: Formulate a L1 trigger decision optimizing the ratio of signal π0s reconstructed to number of triggered events (π0s/event) and signal to background (S/B)

  9. ECAL Selective Readout • We use the default SRO in CMSSW131 • Caltech noticed differences between ORCA and CMSSW131 due to SRO • A new SRO is implemented in CMSSW 160 ORCA CMSSW V. Litvin, “Pi0 Calibration and Selective Readout”, ECAL DPG, 29 May 2007 Implementation of SRO may not be fully understood

  10. L1Trigger Information Note  asymmetry! • L1 “Extra” Particles (ET, , , …) • Isolated and Non-isolated EM • Forward, Central, and “Tau” Jets • L1 ET Sums • Total ET • Hadronic ET • Missing ET

  11. Also found  Problem • The  of the L1 objects is shifted up by half the width of a supermodule (10 or 0.175 radian) L1 emulator people found this error a week prior. Fixed in CMSSW_1_6_0 onward a) b) Signal Background Signal Background  between π0 and the nearest L1isoEm a) original b) fixed

  12. π0 Selection • Mass between 0.095 and 0.14 GeV • wider window for background analysis • Isolation: No energy within the blue shaded region (∆R = 0.2 and ∆  = 0.05) • Reconstructed π0 within ∆R < 0.3 of nearest L1 isolated trigger We have removed many cuts because larger number of π0s is more important than good S/B.

  13. π0 Selection Note Ks00 indication Signal Background 0.095 < mπ0 < 0.14 Signal Background Signal Background < 0.05 ∆R < 0.3

  14. L1 Trigger Cuts ********************** L1isoEm_Et > 2.5 Gev ********************* 1 L1isoEms: EVTS: 29800 SGNL: 6891 BKGD: 3373 S/B: 2.04 SGNL/EVT: 0.231 2 L1isoEms: EVTS: 5506 SGNL: 1853 BKGD: 983 S/B: 1.89 SGNL/EVT: 0.337 3 L1isoEms: EVTS 948 SGNL: 371 BKGD: 200 S/B: 1.85 SGNL/EVT: 0.391 4 L1isoEms: EVTS 140 SGNL: 55 BKGD: 32 S/B: 1.72 SGNL/EVT: 0.393 ***** CUMMULATIVE TABLE ***** 1+L1isoEms EVTS: 36394 SGNL: 9170 BKGD: 4588 S/B: 2 SGNL/EVT: 0.252 2+L1isoEms EVTS: 6594 SGNL 2279 BKGD: 1215 S/B: 1.88 SGNL/EVT: 0.346 3+L1isoEms EVTS: 1088 SGNL: 426 BKGD: 232 S/B: 1.84 SGNL/EVT: 0.392 4+L1isoEms EVTS: 140 SGNL: 55 BKGD: 32 S/B:1.72 SGNL/EVT: 0.393 ************************************************************************* > 2.5 GeV >1 • Cuts studied include: • L1isoEm ET threshold • nL1isoEm passing ET • L1TotalEt 40 - 140 GeV

  15. L1 Trigger Cuts 40 < L1TotalEt < 140 GeV Signal Background

  16. Increased π0 Yield with L1 Trigger • L1 Trigger Decision: • At least 2 L1isoEm objects with ET > 2.5 GeV • Require L1TotalEt to be in the range of 40 to 140 GeV • We see that a π0/event of ~35% can be achieved while maintaining a S/B ~ 1.9 Can calibrate in about 6 days / kHz L1 trigger less than a day using 10 kHz of L1 trigger

  17. L1 Trigger and High  Calibration Signal Background   • The π0s found are not uniformly distributed in  • We observe a reduced rate of π0s and worse S/B at high  • Propose a L1 trigger specifically aimed at optimizing π0s/event and S/B at high  

  18. L1 Trigger and High  Calibration • Cuts: Consider only  > 1 • L1isoEm ET threshold • nL1isoEm passing ET • L1TotalEt ********************** L1isoEm_Et > 3.5 Gev ********************* 1 L1isoEms: EVTS: 9409 SGNL: 756 BKGD: 452 S/B: 1.67 SGNL/EVT: 0.0803 2 L1isoEms: EVTS: 318 SGNL: 39 BKGD: 36 S/B: 1.08 SGNL/EVT: 0.123 3 L1isoEms: EVTS: 11 SGNL: 1 BKGD: 4 S/B: 0.25 SGNL/EVT: 0.0909 4 L1isoEms: EVTS: 0 SGNL: 0 BKGD: 0 S/B: 0 SGNL/EVT: 0 ***** CUMMULATIVE TABLE ***** 1+L1isoEms EVTS: 9738 SGNL: 796 BKGD: 492 S/B: 1.62 SGNL/EVT: 0.0817 2+L1isoEms EVTS: 329 SGNL: 40 BKGD: 40 S/B: 1 SGNL/EVT: 0.122 3+L1isoEms EVTS: 11 SGNL: 1 BKGD: 4 S/B: 0.25 SGNL/EVT: 0.0909 4+L1isoEms EVTS: 0 SGNL: 0 BKGD: 0 S/B: 0 SGNL/EVT: 0 ************************************************************************* > 0 > 3.5 GeV < 130 GeV 

  19. L1 Trigger and High  Calibration L1TotalEt < 130 GeV Signal Background

  20. Increased π0 Yield with High  L1 Trigger • L1 Trigger Decision: • At least 1 L1isoEm object at >1 with ET > 3.5 GeV • Require L1TotalEt to be less than 130 GeV • We can acheive a π0/event ~ 8% with a S/B ~ 1.6 also calibrate in about 6 days / kHz L1 trigger if used in conjunction with the basic L1 trigger discussed above

  21. Outlook • Need fix for asymmetry in L1  (expect improvement) • Bump in mass peak (KS?) • Effects of Pile-up • Check mass shift for trigger/no trigger • Write proposal to implement L1 trigger

  22. References • CMS TDR Vol 1- Detector Performance and Software • Gataullin, Marat, et al. “Calibration of the CMS Barrel Electromagnetic Calorimeter Using π0 Decays”, CMS Internal Note, 29 Dec, 2006 • Vladimir Litvin, Marat Gataullin“Pi0 Calibration and Selective Readout”, Talk given at ECAL DPG meeting, 29 May, 2007

  23. Backup

  24. L1 Total-ET Cut(π0s matched to any L1isoEm) No Cut 40 < L1 Total-ET < 140 GeV

  25. L1 Total-ET Cut(π0s matched only to triggered L1isoEm) No Cut 40 < L1 Total-ET < 140 GeV

  26. High L1 Total-ET Cut(π0s matched to any L1isoEm) No Cut L1 Total-ET< 130 GeV

  27. L1TotalEt in Various Triggers 1 2 1 2 3 4 3 4 No L1isoEm ET Cut L1isoEm ET > 2.5 GeV Can see dependence of L1 Total ET on the L1 ET threshold and the number of L1isoEms passing this threshold

  28. How long does it take to calibrate? Calibration Time 1 day 2 days 3 days 6 days Yield of our L1 trigger

  29. Delta R between L1 isolated triggers Signal Background No useful cut here

  30. Planned Calibrations • Crystals will be pre-calibrated to about 4% using photons from a 60Co source, some calibrated more precisely with the test beam and cosmic rays • Use  independence to inter-calibrate to about 1.5% precision for each phi ring in ~10 hrs on 1 kHz of jet triggers • Use high energy electrons from Zs and Ws to calibrate in situ, but this will take months at start up • Need tracker operational and well - aligned • Electrons radiate in tracker • Need 5fb-1 and that only calibrates the inner barrel to 0.5% 5 fb-1 W  e

  31. Planned Calibrations Continued • Laser monitoring system to track the fastest changes due to radiation damage • Use some of ~3s beam gap to inject pulse • Takes about 30 minutes to do whole ECAL • Possibility of π0 calibration suggested in 2004 and, at first, dismissed due to low rate • Later retried with improved selection and idea of using all L1 Triggers as source for calibration events

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