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. 9Muon Fake RatesPetra Merkel

ELECTRON sample

M [GeV]

d0 [cm]

SVX COT

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…

07/16/2002 p. 13Muon Fake RatesPetra Merkel

ToDo

• Still to do for Ks: go to lower Pt (2 instead of 5 GeV) to see Pt dependence better

plot peak-SB fake rate vs. eta and Pt

• Do the same for D in order to get to higher Pt and to get kaons:

the signal is there, needs clean-up: