DELPHI Z0 PEAK EVENT

DELPHI Event r0015563e0005372


e+ e- ---> Mu+ Mu- Mu+ Mu-
One pair of Mu+ (60.7 GeV) Mu- (41.0 GeV) is produced back to back, the other pair is made of Mu+ (8.3 GeV) and Mu- (3.0 GeV) with small opening angle (less than 15 degree) and thus forms a "V".

Both Muons of the "V" are identified as minimum ionizing in the HPC and HAB and associate to hits in both planes of the MUB. They are clear Muons.

The fast Mu+ is emitted at about 45 degree and hits the corner of the HPC. It is minimum ionizing in the HPC and HAF. It misses the Muon chambers in the barrel and forward.

The fast Mu- is more forward (30 degree) and is seen as minimum ionizing in the FEMC. The HAF gives a 28 GeV deposit in the first layer and minimum in the subsequent ones. The signal in layer one is probably noise. The track is also assciated to a hit of the MUF outer plane.

The event can be interpreted as a radiative Mu+ Mu- with the photon converting to Mu+ Mu-. The probability to produce such an event is of approximately 1 in 10**5 hadronic Z0 events.