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Muon ID work @ UCSB Claudio Jan 25, 07

Muon ID work @ UCSB Claudio Jan 25, 07. At the 1 st meeting we gave a brief summary of what we have been working on Time on the agenda today  give a few more details This is talk that we gave at 11-28-06  -PRS http://indico.cern.ch/conferenceDisplay.py?confId=9118

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Muon ID work @ UCSB Claudio Jan 25, 07

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  1. Muon ID work @ UCSBClaudio Jan 25, 07 • At the 1st meeting we gave a brief summary of what we have been working on • Time on the agenda today  give a few more details • This is talk that we gave at 11-28-06 -PRS • http://indico.cern.ch/conferenceDisplay.py?confId=9118 • With additions for background (in purple)

  2. Muons at CMS • (Up to) 4 muon stations @ CMS • Barrel: Drift Tubes (DT), Europe • EndCaps; Cathode Strip Chambers (CSC), USA • In return B-field • Each station measures a segment (X, Y, X', Y') • X & Y : local coordinates • Outermost station only X view

  3. Traditional  reco @ CMS • Reconstruct track in muon detector only • StandAlone muon • Put together with silicon track into single fit • Global muon • PT improvement for global muon vs Si-track only above ~250 GeV • if dE/dX & multiple scattering treated correctly (remember that ~ TeV muon starts to shower!) • if B field is OK • if muon system aligned to ~ O(100 )

  4. High PT • Slide from Valuev, Z' PTDR analysis • Three different methods for Pt reco: • Global Muon Reconstructor (GMR); standard ORCA. Fit to all tracker and muon hits on track. Vulnerable to muon bremsstrahlung. • “Truncated” Muon Reconstructor (TMR), UCLA (J. Mumford’s talk at PRS/μ meeting on Sept. 16th, 2003). Optimized combination of tracker-plus-first-muon-station and tracker-only fits. • “Picky” Muon Reconstructor (PMR), Warsaw (P. Traczyk’s talk at PRS/μ meeting on March 15th, 2005). Fit to tracker plus all muon chambers not appearing to contain electromagnetic showers. • Best possible job at high PT is not simple

  5. How we got involved • Obviously need code to propagate track (and covariance) into muon detectors • knowing about MS, dE/dX, geometry, B-field • ORCA code based on GEANT3  not for CMSSW • Were asked to step in and do quick-and-dirty job for CMSSW while waiting for more better code • Long story short: only code that works and is being used for now and foreseeable future is SteppingHelixPropagator (Slava) • Slava committed to maintaining and improving it

  6. Alternative approach to muons (1) • Take Si-track, swim it to muon chambers, see if there are matching segments • also calorimeter energy deposition • No loss of PT resolution up to ~ 250 GeV • and above things are not so simple.... • Less requirements on  system • alignment, material, geometry, B-field, fitting... • Get more information on  quality • Useful for BG rejection • Global  object only contains 2 of global fit !!!!

  7. Alternative approach to muons (2) • Complementarity with global  approach • Play one against the other to find problems • Good monitoring tool • eg, quick plots of track-segment matches, etc • Possibility for alternative HLT approach • comments at the end

  8. Alternative approach to muons (3) • Not a new idea • was in ORCA, PTDR • CMS-speak: Muon-ID as opposed to Muon-Reconstruction (?) • low PT muons for b-tagging • I think that, potentially, can be more than a niche-algorithm for b-tagging • particularly at startup • Opportunity to do it "our way"

  9. Update on Sitrack--segment match algorithm Claudio Campagnari, Dmytro Kovalskyi, Slava Krutelyov, Jake Ribnik UC Santa Barbara

  10. Reminder •  ID starting from Si-track propagated to calorimeter and  detector • Calculate energy deposition in calorimeter • Calculate distance between extrapolated track and reconstructed segments • Based on • SteppingHelixPropagator (Slava) • TrackAssociator (Dmytro) • Last PRS presentation: Jake, August 22 2006 • Demonstrated that basic code works • Track-segment pulls ~ 1 • Calorimeter energies make sense

  11. Some Plots from Jake's talk (1) Single  gun Monte Carlo events PT = 5 40 GeV Plot of energy in crossed ECAL and HCAL cells

  12. Some Plots from Jake's talk (2) typical pulls CSC, X station 2 DT, X station 3 DT, Y station 1 CSC, Y station 1

  13. What is new Started to work on algorithm (producer) to make information persistent for a subset of Si-tracks

  14. Loop over all Si tracks P or Pt > min Propagate to calorimeter &  detector Assign segment to track if matching is good enough Discard track unless segments from enough stations are there If tracks share segment perform arbitration (or perhaps not) Make information from surviving tracks persistent Stuff in red to be determined. Much of it configurable at run time

  15. What is arbitration? • Can have > 1 Si-track reasonably well matched to a segment • Can happen esp. in jets • Arbitration: • decide which track the segment really belongs to • essentially pattern recognition problem • Leave it to the user or do it in producer? • our sense is that we should do it in producer • but code should be written such that this feature can be easily turned off

  16. Producer • Built around TrackAssociator • which works! • Simple matter to wrap some code around it to do what we want • but still needs to be written! • Goals of this study • give a 1st conservative guess for the requirements (in red) on page 4 • Take a look at arbitration, with conservative requirements • is it a serious issue or a 2nd order effect?

  17. Data Sets •  gun events • CMSSW 0_9_2 • 5 < Pt < 50 GeV/c • CSA06 tt events • Simulated with CMSSW 0_8_2 • Reconstructed with CMSSW 0_9_2

  18. 1st conservative guess at requirements Loop over all Si tracks P or Pt > min PT > 2 GeV/c quite low.. maximizes confusion Propagate to calo &  detector Assign segment to track if matching is good enough |Xlocal| < 5 OR |Xlocal| < 5 cm No requirement on Ylocal Discard track unless segments from enough stations are there If tracks share segment perform arbitration (or perhaps not) Nstations¸ 2 Make information from surviving tracks persistent

  19. Nstations¸ 2 3 4 2 0 1 Number of stations on single  gun events

  20. Arbitration Issues • tt MC has isolated  from W decays and non-isolated  from b and c decays • A good testing ground for these issues • Before arbitration we find (PT>2 GeV/c) • ~15% of  from W share segments with other tracks • ~33% of  from other sources share segments with other tracks • For PT > 5 GeV/c, fractions are ~ 5% and 20%

  21. Two simple arbitration algorithms • Pick segments with best Dx • Pick segments with best Results: (PT > 2 GeV/c and PT> 5 GeV/c)

  22. Conclusions about arbitration • It does not seem to be a major issue • We'll implement these two algorithms in the producer • Can be re-visited at a later stage

  23. What is missing • For ultimate  ID, a candidate  that goes through the middle of a (working) station and leaves no segment, should be "penalized" • Current code cannot distinguish between cracks in coverage and true misses • Fuzzy distinction because of multiple scattering • TrackAssociator is built around concept of "calculate distance between track and segment" • At the moment provides no information for stations where there are no segments Need to add functionality

  24. Future Plans • Implement producer as outlined in this talk • Paying some attention to execution time • Add (fuzzy) information on whether segment in station was expected or not • Necessitates some rework of TrackAssociator • in progress (Dmytro) • Anticipate release of producer in January

  25. What is new since then • Dmytro reworked TrackAssociator to be able to answer the question of missing segments • Does track extrapolate into or out of chamber acceptance? • What is the distance from the edge, in cm as well as number-of-MS-sigmas • Now: debugging phase • Have plan on how to store info in "muonID" object • This kind of info will be useful for global muon too! • Currently, global muon is fit to 2 or more stations • If station 3 and 4 are missing, is it OK, or is it because the "muon" is really a pion that stopped?

  26. Plan • Hope to put producer in 1_3_0 • Interest from people to start using it • eg, to define b tagging algorithm

  27. A word about HLT (1) • Default plan: • Level 2: Standalone muon reconstruction • HLT: Global muon reconstruction • either: by "standard" Si-tracking pattern recognition done in "region of interest" • or: by "custom" pattern recognition seeded by L2 muon (Richman, Vlimant, UCSB) • Can imagine alternative: • Skip L2, go directly to HLT, with "custom" pattern recognition seeded by L1, only reconstruct Si-track, then use "-ID" for final decision • Or some combination

  28. A word about HLT (2) • Optimal strategy depends on details of timing and what standalone (L2) reconstruction really rejects • Hard to tell from MC • Not pursuing these ideas at the moment • Richman & Vlimant will try reconstruction from L1 seed

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