DELPHI Event r064312e002237
from the 130-140 GeV Run
e+ e- ---> Tau+ Tau-
From 136.2 GeV run.
A positive track of 2.3 GeV/c is reconstructed from the VD/ID/TPC/OD.
It is MIP in HPC and deposits a small amount of energy in the HAB,
which identifies it as Pi+ or Mu+.
It is accompanied by a 66.5 GeV shower in HPC.
This faces a Phi crack of the TPC, but as no track is observed in the VD nor
ID, it corresponds to a neutral particle (a Pi0).
The Pi+ Pi0 system has 1.1 GeV mass.
On the oposite side, a very low energy particle is observed in the VD and the
ID jet chamber (but too slow to reconstruct a track).
This is a nice illustration of the importance of the granularity in the jet
chamber.
The event is interpreted as Tau+ Tau-,
where the Tau+ --> Pi+ Pi0 nu and the Tau- decays to
a rather unlikely configuration with a very slow charged particle and a
neutrino taking away most of the energy.
Shown by H.Dijkstra at the seminar on LEP 1.5 results 12/12/95.
Characteristics :
Evis = 69 GeV
Emiss = 67 GeV, Mmiss**2 = -(14 GeV)**2, P_(t,miss) = 65 GeV