1 BaBar Collaboration Randall Sobie Institute for Particle Physics University of Victoria.
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Transcript of 1 BaBar Collaboration Randall Sobie Institute for Particle Physics University of Victoria.
1
BaBar Collaboration
Randall SobieInstitute for Particle PhysicsUniversity of Victoria
0Study of the 2 2 and
3 2 Decays h h
Randall Sobie Tau2004 Workshop
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Introduction
Tau semi-leptonic decays are an ideal place to study strong interaction effects
The large sample of tau data from BABAR allows us to re-examine many of the well-known hadronic decays but to look in detail at the decays that were previously limited by statistics
This work focuses on 2 of the 5-hadron final state decays of the tau lepton
0 02 2 ( , , )
3 2h h
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Data Samples
BABAR has collected 244 /fb
These analyses use 110-124 /fb
Approximately 100 million tau-pair events
Results quoted are preliminary
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DIRC (PID)
1.5 T solenoid
Drift Chamber
Silicon Vertex Tracker
e+ (3.1 GeV)e- (9.0 GeV)
Instrumented Flux Return
BABAR Detector at SLAC
EMC
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Simulation
KK2F generates the tau pair events
Tauola decays the tau leptons 3-prong signal events arise from two separate classes:
The final states are generated using a phase space distribution
events are generated using a phase space distribution
0 0 and are generated separately
3 2h h
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Selection of signal candidates
Event selection Reduce non-tau background (Bhabhas, dimuons, 2-photon and
multihadrons) using thrust, transverse momentum and missing energy
Event split into 2 hemispheres in CM frame using thrust Each hemisphere is associated with a tau
The decay products are collimated due to the relativistic momentum of the tau Look for 1-3 and 1-5 topology
Tag hemisphere selection Require single track with track being either an electron or muon
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Signal hemisphere selection
Tracks required to be pions 2 pi0 candidates
2 clusters : M=100-160 MeV and E>215 MeV
M(5pion) < 1.8 GeV
9900 candidates selected Background 15%
Mainly tau decay background Efficiency 0.65%
Pion or kaon tracks allowed Veto electrons, photon
conversions and pi0’s M(5hadron) < 1.8 GeV
15869 candidates selected Background 21%
tau decays with pi0s or K0’s Efficiency 3-4.5%
3 2h h 02 2
1
2bkgdselfN
BN
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5 pion mass distribution I
4
( 3 2 )
(8.52 0.09 0.40) 10
B h h
0
3
( 2 2 )
(4.51 0.07 0.56) 10
B
(5 )M
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5 pion mass distribution II
Background subtracted mass distribution.
Note that the background is scaled to reproduce the mass distribution above 1.8 GeV.
The disagreement between data and MC is similar for
02 2
3 2h h
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Comparison with other measurements
4( 3 2 ) (10 )B h h
0 3
BABAR 4.51 0.07 0.56
CLEO 5.2 0.5
ALEPH 5.0 0.
( 2 2 ) (1
.7
0
7
)
0
B
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02 2 0
3
( )
(1.71 0.12 0.16) 10
B
3(1.74 0.24) 10 PDG
0
3
( )
(3.66 0.10 0.31) 10
B
3(4.3 0.5) 10 PDG
- 0Mass
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0Limit on the decay mode
BABAR has searched for the production of phi(1020) mesons
0B( ) 15%
0 4( ) 4.5 10
90% Confidence limit
B
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Systematic uncertaintiesLargest Sources
Background 9.3% 0.9% 1.8%
Efficiency for pi0 finding 6.5% 6.5% 6.5%
Efficiency for pi+- identification 3.0% 3.0% 3.0%
Tracking efficiency 2.4% 2.4% 2.4%
Luminosity and cross section 2.3% 2.3% 2.3%
Total 12.3% 8.9% 8.6%
02 2 0 0
02 2
Largest Sources
Tracking Efficiency 3.1%
Luminosity and cross section 2.3%
pi0 contamination 2.0%
Background 1.5%
Lepton tag 1.0%
Total 4.7%
3 2h h
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Decay mechanism
. - 0Mass of the recoiling
0
Background subtracted mass distribution
3 2h h
-Mass of the combinations
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1Study of the (1285) decayf
CLEO has observed this decay mode in 1- and 3-prong tau decays 1f
The f1 can also decay to a 4-pion final state
BABAR observes a peak in the 4-pion mass distribution that is consistent with the CLEO result
lepton-tag 41( ) (4.6 1.2 0.7) 10B f
41( ) (5.8 2.3) 10B f CLEO result
1( (1285) 2 2 ) 11%B f
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Summary I
Channel Preliminary branching fraction
BaBar has studied the tau decays :
02 2
3 2h h
0 4
41
3 2 (excl. K ) (8.52 0.09 0.40) 10
(1285) (4.6 1.2 0.7) 10
h h
f
0 3
0 3
0 3
0 4
2 2 (4.51 0.07 0.56) 10
(1.71 0.12 0.16) 10
(3.66 0.10 0.31) 10
4.5 10 (90%CL)
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Summary II
The large data sets have been used to investigate the structure of the decays The data shows that a phase space distribution does not
adequately describe the data in 3 and 5 prong tau decays New limit on the decay mode : Peak in the 4-pion mass distribution is consistent with the CLEO
observation of
0
1(1285)f