DELPHI Z0 PEAK EVENT

DELPHI Event r0049139e0001931


e+ e- ---> q qbar , 2 Lambda decays
In this Z0 --> qqbar event there is a high momentum Lambda-Lambdabar pair with a small rapidity difference. The Lambdas are shown as dashed lines, the outgoing pions as red solid lines and the protons as blue ones. Although there were no TEs (track elements) reconstructed in the ID for the Lambda that decayed in the ID (at R = 17.9 cm), the vertex is reconstructed right in front of the first measured ID TD (TDs are single point measurements that are not directly included in the track reconstruction but only via TEs). The tracks belonging to the other Lambda decaying at R = 4.4 cm have both 3 associated VD RPhi hits. Three other tracks which are very close to the two Lambdas have been erased, because otherwise one could not see the vertices.
Events with baryon pairs are used to study fragmentation issues.
The two Lambdas have the following properties:
                    Lambda1       Lambda2
--------------------------------------------
Phi                    67.7        71.9   
Rapi.                   3.01        2.59  
|p|       [GeV]        14.90       11.73  
R_xy_vtx   [cm]         4.39       17.86