1 BaBar Collaboration Randall Sobie Institute for Particle Physics University of Victoria

Randall Sobie Tau2004 Workshop 2 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

Randall Sobie Tau2004 Workshop 3 Data Samples BABAR has collected 244 /fb These analyses use /fb Approximately 100 million tau- pair events Results quoted are preliminary

Randall Sobie Tau2004 Workshop 4 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

Randall Sobie Tau2004 Workshop 5 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

Randall Sobie Tau2004 Workshop 6 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

Randall Sobie Tau2004 Workshop 7 Signal hemisphere selection Tracks required to be pions 2 pi0 candidates  2 clusters : M= 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 candidates selected Background 21%  tau decays with pi0s or K0’s Efficiency 3-4.5%

Randall Sobie Tau2004 Workshop 8 5 pion mass distribution I

Randall Sobie Tau2004 Workshop 9 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

Randall Sobie Tau2004 Workshop 10 Comparison with other measurements

Randall Sobie Tau2004 Workshop 11

Randall Sobie Tau2004 Workshop 12 BABAR has searched for the production of phi(1020) mesons

Randall Sobie Tau2004 Workshop 13 Systematic uncertainties Largest Sources Background9.3%0.9%1.8% Efficiency for pi0 finding6.5% Efficiency for pi+- identification3.0% Tracking efficiency2.4% Luminosity and cross section2.3% Total12.3%8.9%8.6% Largest Sources Tracking Efficiency3.1% Luminosity and cross section2.3% pi0 contamination2.0% Background1.5% Lepton tag1.0% Total4.7%

Randall Sobie Tau2004 Workshop 14 Decay mechanism. Background subtracted mass distribution

Randall Sobie Tau2004 Workshop 15 CLEO has observed this decay mode in 1- and 3-prong tau decays 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 CLEO result

Randall Sobie Tau2004 Workshop 16 Summary I ChannelPreliminary branching fraction BaBar has studied the tau decays :

Randall Sobie Tau2004 Workshop 17 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