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Muon Tag Efficiency Puzzle

?. ?. ?. ?. Muon Tag Efficiency Puzzle. Remember the problem pointed out by Niels:. Before trigger,  tag (  ) is much smaller for offsel B  than for offsel B  J/  (  )K* (and also the wrong-tag fraction  ).

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Muon Tag Efficiency Puzzle

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  1. ? ? ? ? Muon Tag Efficiency Puzzle Remember the problem pointed out by Niels: • Before trigger, tag() is much smaller for offsel B than for offsel BJ/()K* (and also the wrong-tag fraction ). • Possible explanation:  misID prob increases with increasing number of true muons in the Muon System (MS).

  2. PiMu and MuMu efficiencies • Try to reproduce  and  efficiency numbers of reop-TDR • In ntuples: 26k offline-selected Bs->KK and 20k Bs->J/() • Store in ntuple all Particles (Long and VTT) • Store a subset of MCParticles: All , , e (not from ) and K , if they have Ekin>1 GeV, <0.5 rad + all those associated to a stored Particle or MuonID (+signal B and other-side B) • Note: somewhat different definition of reference event samples • TDR: require extrapolation of the track to be in M1-5 and p>3GeV/c • Here: require Long track and p>3GeV/c, use offline-selected events • In addition, modify the DaVinci DLL: if no MS Info, then set DLL to –inf. (DV: if (!proto->muonBit()) … i.e. do not attempt muon identification without MS info) Was this also the case for the TDR ?

  3. DLLmupi without Muon System Info RICH provides some PID for pi-mu separation, however: • Not very powerful as it is now • Note the zooming factor 300 for muons! Note in passing: • Was it optimized for low-momentum particles ? • BTeV claims using this for pi-mu separation (tagging) This study: will set all these DLLs to -infinity. (If “RICH-only” PID is allowed, then one should at least put a more stringent cut on DLL for those events, than in the case the MS info isavailable.) Bs->J/() (looks the same for Bs->KK)

  4. Bs->J/() Various definitions of efficiency Bs->KK Say efficiency = N/D. The 3 pairs of plots show the result for  and  with 3 different definitions of the numerator N and denominator D: • Do not require MS info for either N and D (“RICH-only” identification allowed) • Require MS info for positive identification (i.e. for N only) NOTE THE DIFFERENT SCALES! • Require MS info in the reference sample (i.e. for both N & D) Use this one!

  5. Muon p and pT spectra • Difference in muon p and pT spectra due to the fact that most muon come from the B in one case and not in the other. This explains difference in muon PID efficiency. • Do not get confused ! This should not be the reason for the difference in muon tag efficiency (tag ) for B-> and for Bs-> J/()K*, because the tag muon is supposed to be from a B in both cases! Bs->KK Bs->J/()

  6. PiMu and MuMu efficiencies MC=MC= efficiency  (%) Bs->J/() efficiency  (%) Particles (p>3GeV/c and Long track) matched to MC Bs->KK efficiency  (%) efficiency  (%) DLL DLL (note: if  MS Info, DLL set to –inf.)

  7. PiMu and MuMu efficiencies Bs->KK Bs->J/() Summary:  DLLcut O • TDR (Bs->JPsiKs) 93 % 1 % -8 • Here (Bs->JPsiPhi) 95.7% 1.0% -8 • Here (Bs->KK) 70.3 % 0.5% -8 efficiency  (%) efficiency  (%) DLL (note: if  MS Info, DLL set to –inf.) efficiency  (%)

  8. What ’s are id’ed as ’s ? Mostly  decays. The rest is probably punch-through or random combinations (“overflows”) Bs->KK Bs->J/() Zend / mm of MC  asso’ed to a p>3GeV/c Long track id’ed as 

  9. Sources of Muons Bs->J/() Bs->KK Each color should add up to ~20k Each color should add up to ~26k MC Origin: z<400mm x,y<5mm # MC  in event with MuonCoords>1 # MC  in event with MuonCoords>1

  10. Number of Muons per Event Try to unravel effect of random combinations on misId: • Bin the number of MC muons per event which hit M2-5 but which are not from a decaying pion (see plots below) • For each such bin sum up isidentified pions over all events Mean 2.467 Mean 0.438 Bs->J/() Bs->KK # MC  with MuonCoords>1 excluding  from -decay # MC  with MuonCoords>1 excluding  from -decay

  11. … the result DLL>-8.0 and MS info available (Particle = Long track and p>3GeV/c. Sum numerator and denominator over all events) # Particles associated to a MC  and id’ed as  # Particles associated to a MC   = Clear dependence of misId efficiency on number of muons! Note: All these isidentified MC pions have 0 or 1 MuonCoords. • Misidentification most probably due to random combinations. efficiency  efficiency  Bs->KK Bs->J/() # MC  with MuonCoords>1 excluding  from -decay # MC  with MuonCoords>1 originating from near IP

  12. MCParticle <-> MuonID • To support the rnd combination hypothesis: tried to associate MS info of isidentified pions to MCParticles… • Done in a shaky way: retrieve MuonId object, from which I retrieve a (number of) MuonCoord, each being then associated to a MCParticle. • Problem: several MCParticles in the basket … • Take the one that comes most often (the 1st one in case of a draw) • How good is this ? I have no clue. • If correct, it confirms that misId is not due to punch-thru, but rather to rnd associations. Bs->KK  (looks the same for Bs->JPsiPhi)  K e Probable HEP ID of MCParticle associated to the MuonID object of a isidentified non-decaying MC pion (when it is a different MCParticle) There are 12 more events where it is the same MC pion !

  13. Can this explain the Muon Tag Efficiency Puzzle ? Fully explains the jump in the average  presented a few slides up: Bs->KK  = 0.5% Bs->J/()  = 1.0% But can it explain the tagpuzzle ? B->tag = 6.5% Bs-> J/()K* tag = 10% Did a rapid small exercise: pseudo tagging muons: use DLL>-9 and add pT>1.2 GeV/c and p>5 GeV/c and remove muons which are associated to an MC muon from signal B. Get for 26k offline-selected events: 0.43 % x 49911 = 215  215+1323 88.7 % x 1491 = 1323  26157 1.14 % x 40146 x R = 586  586+1467 88.8 % x 1290 x R = 1467  26157 R = 26157/20427 (ratio of offline selected events) Signal daughter clone problem ? • Bs->KK • Bs->J/() = 5.9% = 7.9% To be continued…

  14. ID of MCParticle associated to the selected TagMuon Bs->KK Bs->J/() (26k off-sel) (20k off-sel) K- 46 68 - 91 145 + 422 319 E+ 0 4 none 63 52 e- 1 10 - 862 664 + 83 177 K+ 69 97

  15. Mu-pi opening angle in Lab   • Pion => muon + neutrino • Muon momentum = 30 MeV/c in pion rest frame • Maximum muon opening angle versus boost (pion energy in lab frame)     Max muon angle  (deg) Lab Epion / GeV

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