8-13 August 2011
Rhode Island Convention Center
US/Eastern timezone

Three-Pion Decays of the tau Lepton, the a_1(1260) Properties, and the a_1-rho-pi Lagrangian

11 Aug 2011, 11:58
554 (Rhode Island Convention Center)


Rhode Island Convention Center

Parallel contribution Heavy Flavor Physics (bottom, charm, tau) Heavy Flavor Physics


Prof. Peter Lichard (Silesian University in Opava)


We show that the a_1-rho-pi Lagrangian is a decisive element for obtaining a good phenomenological description of the three-pion decays of the tau lepton. We choose it in a two-component form with a flexible mixing parameter sin(theta). In addition to the dominant a_1-> rho+pi intermediate states, the a_1-> sigma+pi ones are included. When fitting the three-pion mass spectra, three data sets are explored: (1) ALEPH 2005 pi-pi-pi+ data, (2) ALEPH 2005 pi-pi0pi0 data, and (3) previous two sets combined together and supplemented with the ARGUS 1993, OPAL 1997, and CLEO 2000 data. The corresponding confidence levels are (1) 28.3%, (2) 100%, and (3)7.7%. After the inclusion of the a_1(1640) resonance, the agreement of the model with data greatly improves and the confidence level reaches 100% for each of the three data sets. From the fit to all five experiments [data set (3)] the following parameters of the a_1(1260) are obtained m_{a_1}=(1233+/-18) MeV, Gamma_{a_1}=(431+/-20) MeV. The optimal value of the Lagrangian mixing parameter sin(theta)=0.459+/-0.004 agrees with the value obtained recently from the e+e- annihilation into four pions.

Primary author

Prof. Peter Lichard (Silesian University in Opava)


Dr Martin Vojik (Silesian University in Opava)

Presentation Materials