Here we reconstructed the momentum spectra produced by monoenergetic pions and kaons
at momenta 0.2 GeV/c and 0.5 Gev/c, by using Physics off (LOSS, MULS and DCAY) in Normal
Geometry case, and Physics none3 (LOSS and DCAY) in Special Geometry case. The analysis
was done by using a StEvent analyser that we have written .
In particular, the analyser finds a pathlength s for all primary (parent)
tracks. To find the parents that decay inside the TPC, we look for daughters
within a certain dca_min to the parent. This dca is the distance between the
parent helix to the origin of the daughter-candidate track. If there is a
daughter, s for the parent is found from the helix pathlength from the
primary vertex to the origin of the daughter track.
Below shows the reconstructed momenta spectra for the TPC at
0.2GeV/c, 0.5GeV/c, for two ways of geometry: Normal (run a simplified geometry with the
entire STAR detector), and Special (run a simplified geometry with only the pipe, TPC,
FTPC and SVT) for two cases (89 deg and 70 deg) by applying StEvent analyser.
In the decay spectra figures, P is the momentum of the daughter in the rest frame of
a parent particle, and it is unique for a given two body decay.
See
table
In these figures, we plot pathlength (from primary vertex to origin of daughter) for the
parent versus P
The colored points represent the Fraction of pions of mass m=0.140 (GeV)
or kaons of mass m=0.497 (GeV) surviving after a distance d which is given by : N/No = exp(-d*m/(p*ctau)) , ctau(pions) =7.8 m , ctau(kaons) =3.7 m.
For more information about the standard settings of the events click
here
For more information about the kinematics of the events click here
StEvent Analyser
Normal Geometry 
89 degree
