muon tag efficiency puzzle

LHCb Trigger Meeting – December 15, 2003, CERN Massimiliano Ferro-Luzzi 1

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Muon Tag Efficiency PuzzleMuon Tag Efficiency Puzzle

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Before trigger, tag() is much smaller for offsel B than for offsel BJ/()K* (and also the wrong-tag fraction ).Possible explanation: misID prob increases with increasing number of true muons in the Muon System (MS).

Remember the problem pointed out by Niels:


PiMu and MuMu efficienciesPiMu 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 samplesTDR: 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 ?


DLLmupi without Muon System Info

DLLmupi without Muon System Info

RICH provides some PID for pi-museparation, however:

Not very powerful as it is nowNote 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 onDLL for those events, than in the case the MS info isavailable.)

(looks the same for Bs->KK)

Bs->J/()


Various definitions of efficiency

Various definitions of efficiency

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)

Bs->KKBs->J/()

Use this one!


Muon p and pT spectraMuon p and pT spectra

Bs->KK

Bs->J/()

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!


PiMu and MuMu efficienciesPiMu and MuMu efficiencies

Part

icle

s (p

>3G

eV/c

and

Lon

g tr

ack)

mat

ched

to M

C

MC= MC=

effi

cien

cy

(

%) efficiency

(%

)

DLL DLL (note: if MS Info, DLL set to –inf.)

Bs->KK

efficiency

(%)ef

fici

ency

(

%)

Bs->J/()


PiMu and MuMu efficienciesPiMu and MuMu efficienciesef

fici

ency

(

%)

DLL(note: if MS Info, DLL set to –inf.)

Bs->KK

efficiency

(%)

efficiency (%)

Bs->J/()

Summary: DLLcut OTDR (Bs->JPsiKs) 93 % 1 % -8Here (Bs->JPsiPhi) 95.7% 1.0% -8Here (Bs->KK) 70.3 % 0.5% -8


What ’s are id’ed as ’s ?What ’s are id’ed as ’s ?

Mostly decays.

The rest is probably punch-through or random combinations (“overflows”)

Zend / mm of MC asso’ed to a p>3GeV/c Long track id’ed as

Bs->J/()

Bs->KK


Sources of MuonsSources of Muons

Bs->J/() Bs->KK

# MC in event with MuonCoords>1 # MC in event with MuonCoords>1

Each color should add up to ~20k Each color should add up to ~26k

MC Origin:z<400mmx,y<5mm


Number of Muons per EventNumber of Muons per Event

# MC with MuonCoords>1 excluding from -decay


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

Bs->J/() Bs->KK

Mean 0.438Mean 2.467


… the result… the result# Particles associated to a MC and id’ed as

# Particles associated to a MC =

(Particle = Long track and p>3GeV/c.Sum numerator and denominator over all events)

ef

fici

ency


# MC with MuonCoords>1 originating from near IP

Bs->KK Bs->J/()

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.

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.

ef

fici

ency

DLL>-8.0 and MS info available


MCParticle <-> MuonIDMCParticle <-> MuonIDTo 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.

e

K

Probable HEP ID of MCParticle associated to the MuonID object of a isidentified non-decaying MC pion (when it is a different MCParticle)

Bs->KK(looks the same for Bs->JPsiPhi)

There are 12 more events where it is the same MC pion !


Can this explain the Muon Tag Efficiency Puzzle ?

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 tag puzzle ?

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)

= 5.9%

= 7.9%

Bs->KK

Bs->J/()

To be continued…

Signal daughter clone problem ?


ID of MCParticle associated to the selected TagMuon

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


Mu-pi opening angle in Lab

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

muo

n an

gle

(de

g)

Lab Epion / GeV

muon tag efficiency puzzle

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