DELPHI Z0 PEAK EVENT

DELPHI Event r0039265e0004287


e+ e- ---> e+ e- , forward , with converted gamma
Forward Bhabha event produced with a polar angle of 32 degree and where the electron and positron have associated showers in the EMF. The e+ (left in z,y projection) is reconstructed form the ID and TPC with a momentum of 16.9 GeV/c and has an associated EMF shower of 36.2 GeV. The e- (right in z,y projection) is reconstructed from the VD, ID and TPC and has 25.3 GeV/c momentum and an associated EMF shower of 34.9 GeV. Given their small polar angle, the tracks reconstructed without FCB (in which the electrons have showered) cannot have an accurately determined momentum. The e- is accompanied by a pair from the conversion of a photon at the exit of the ID or the entrance of the TPC, as is verified in the x,y projection. The pair has 1.65 GeV energy and a very small effective mass for electrons, compatible with the gamma hypothesis.