BaBar Collaboration Randall Sobie Institute for Particle Physics University of Victoria

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

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 110-124 /fb • Approximately 100 million tau-pair events Results quoted are preliminary Randall Sobie Tau2004 Workshop

4. BABAR Detector at SLAC 1.5 T solenoid EMC DIRC (PID) e+ (3.1 GeV) e- (9.0 GeV) Drift Chamber Silicon Vertex Tracker Instrumented Flux Return 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. 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% Signal hemisphere selection 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 Randall Sobie Tau2004 Workshop

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

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

16. Summary I 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 Randall Sobie Tau2004 Workshop