07/16/2002 p. 1 muon fake ratespetra merkel muon fake rates concept: determine rate of fake muons...
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07/16/2002 p. 1Muon Fake RatesPetra Merkel
Muon Fake Rates
Concept: determine rate of
• fake muons due to pion/kaon punch-through (PT)
• muons out of pion/kaon decay-in-flight (DIF)
Need source of identified high-pt pions/kaons:
• reconstruct D K
• reconstruct Ks
Method in Run1:
• use inclusive photon sample, look for isolated high-pt tracks therein
• compute probability for PT per track from hadronic interaction lengths
• compute probability for DIF per track from c / cK
• sum over all high-pt tracks in sample
• see: Thesis by J.Berryhill, PRD of note 5569; no dedicated note found
07/16/2002 p. 2Muon Fake RatesPetra Merkel
Ks Selection
• Use B_CHARM dataset:
• L1: (2 XFT tracks, opp. charge, < 135 , Pt > 5.5) or (7 tracks w/ Pt > 2)
• L2: 2 SVT tracks, < 25, Pt > 2, 100 m < |d0| < 1 mm
• L3: 2 SVX-COT hybrid tracks, Pt > 2, || < 1.2, 120 m < |d0| < 1 mm,
opp. charge, |Z0| < 5 cm, 2 < || < 90, Lxy > 200 m, Pt > 5.5
• Offline selection:
• Track cuts: Nax > 24, Nst > 24, |Z0| < 60 cm, || < 1.2, Pt > 2
• Track pairs: opp. charge, |Z| < 5 cm, 2 < || < 90, 1 leg Pt > 5
• Secondary vertex fit: CTVMFT algorithm, x2 < 8, Lxy > 1 cm,
d0(Ks) < 0.3 mm (SVX) / d0(Ks) < 0.3 cm (COT)
07/16/2002 p. 3Muon Fake RatesPetra Merkel
Ks Peak – BCHARM sample
M [GeV]
Peak: 0.46 < M < 0.53
SB: 0.425 < M < 0.46
0.53 < M < 0.565
07/16/2002 p. 4Muon Fake RatesPetra Merkel
Pions – Kinematics
eta
Pt [GeV]
D0 (SVX) D0 (COT)
D0 (SVX) : both legs have silicon hits
D0 (COT) : only one leg or none have silicon hits
peak
sideband
07/16/2002 p. 5Muon Fake RatesPetra Merkel
Muon Cuts
Use same cuts as in (W ) analysis:
• Tracking: Nax > 24, Nst > 24
• Calorimeter, isolation: E(R<0.4)corrected for track < 2
• Calorimeter, MIP: Eem < max(2, 2+0.0115 (Pt – 100))
Ehad < max(6, 6+0.028 (Pt – 100))
• Matching: |x|CMU < 3 cm, |x|CMP < 6 cm, (no cut for CMX)
07/16/2002 p. 6Muon Fake RatesPetra Merkel
Fake Rate – BCHARM sample
Ks in peak: 16,316 (Pt>5): 17,724 [%] is : 117 = 0.66 +- 0.06 Muon fake rate from is CMU : 90 = 0.51 +- 0.05 PT and DIF [%]: is CMP : 31 = 0.17 +- 0.03 is CMUP : 20 = 0.11 +- 0.03 peak – SB: is CMX : 17 = 0.10 +- 0.02 all : 0.65 +- 0.06
CMU : 0.52 +- 0.06
Events in SB: 1,032 CMP : 0.16 +- 0.03
(Pt>5): 1,179 [%] CMUP : 0.11 +- 0.03
is : 9 = 0.76 +- 0.25 CMX : 0.09 +- 0.02
is CMU : 4 = 0.34 +- 0.17
is CMP : 5 = 0.42 +- 0.19
is CMUP : 2 = 0.17 +- 0.12
is CMX : 2 = 0.17 +- 0.12
07/16/2002 p. 7Muon Fake RatesPetra Merkel
Fake Rate
BC
HA
RM ALL
PH
OTO
N
DIP
HO
TO
N
ELE8
x2
0
ELEN
OV
peak
sideband
07/16/2002 p. 8Muon Fake RatesPetra Merkel
Fake Rate – diff. distr.
CMU
CMP
CMUP
eta Pt [GeV]
Only Ks peak fake rates shown, not SB subtracted yet…
07/16/2002 p. 10Muon Fake RatesPetra Merkel
Physics Bias?
Observe systematic difference between different datasets:
•BCHARM, DIPHOTON: high fake rates
•PHOTON, ELECTRON: low fake rates
BCHARM, DIPHOTON are muon enriched
Hypothesis: in muon enriched samples the pion track gets accidentally matched to the stub from a real muon nearby
Check: loosen / tighten |x| cut on CMU, CMP : fake rate /
(check it both for the BCHARM and the electron sample)
07/16/2002 p. 11Muon Fake RatesPetra Merkel
Physics Bias!
Difference between datasets is good handle on systematic uncertainty of this measurement
Tendency also seen in electron dataset…but within statistical error…
BCHARM ELECTRONS
|x|<15 cm
|x| < 3 / 6 cm
|x| < 1 cm
07/16/2002 p. 12Muon Fake RatesPetra Merkel
Comparison to Run1 Numbers
In Run1 (photon-lepton analysis, J.Berryhill):
1.87 +- 0.99 PT background events
1.08 +- 1.20 DIF background events
2.95 +- 2.19 background events DIF+PT
398 high-Pt tracks in inclusive photon sample
Using (0.65 +- 0.06)% fake rate for Run2
Combine with 398 tracks:
2.6 +- 0.2 background events
Main systematic uncertainty in Run1 was pion/kaon fraction, probably much too pessimistic…