1

BaBar Collaboration

Randall SobieInstitute for Particle PhysicsUniversity of Victoria

0Study of the 2 2 and

3 2 Decays h h

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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