DELPHI Event r0039265e0004451

e+ e- ---> Tau+ Tau- , 1 vs 3 prongs
The Tau pair is cleanly identified by a 1 vs 3 topology.

The Tau+ gives rise to a very low energy track, 1.1 GeV/c momentum, but accompanied by a shower of 18.0 GeV in the HPC and pointing to the beginning of the track. This is probably an e+ which radiated a photon at the exit of the ID or entry of the TPC.

The Tau- decays into 3 very collimated particles, Pi+ (14.9 GeV), Pi- (19.5 GeV), Pi- (10.0 GeV), all three being minimum ionizing in the HPC. They deposit 33 GeV energy in the HAB. The 3-particle system has 44.4 GeV energy and 1.16 GeV mass, hence compatible with a Tau. No additional showers are observed in the HPC. A likely interpretation is that the Tau- decayed into an a_1.