sPHENIX tracking discussion

[Anthony Frawley <afrawley AT fsu.edu>]

Hello All,

Following a discussion in the TPC electronics meeting this morning, I have been trying to understand the origin of the clusters in the TPC that do not come from primary tracks, by looking at clusters and G4 hits from evaluator ntuples made from 100 central Hijing simulations.

The answer is that they come from a variety of secondary particles. Please see the attached three plots.

The first plot shows the particle flavor (gflavor) of clusters associated with (left) primary tracks and (right) secondary tracks. The plot on the left shows pions and kaons. The plot on the right shows entries from:

a) secondary pions (+/- 211)

b) secondary muons (+/- 13)

c) secondary electrons (+/- 11)

d) delta electrons (-11 only, the excess of -11 over +11)

The second plot shows (left) the truth energy deposit for each reconstructed cluster and (right) the truth pT distribution for the reconstructed clusters. These are shown separately for the primary pi+and p-, and for secondary mu+ and mu-, secondary pi+ and pi-, and secondary e+ and e-.  The delta electrons appear in the left plot as the excess of e- over e+, and in the right plot they can be seen to sit at essentially zero pT.

The third plot is the same as the second plot except that it is made from the G4 hits ntuple. It just shows that there are a large number of delta electrons recorded as G4 hits, but most of them are not reconstructed as clusters.

I should point out that these plots should not be read as showing the relative yields of the secondary particles. They show the number of clusters due to different types of particles. The secondary particles are at low pT and If a low pT muon (for example) loops in the magnetic field it will make many more clusters than a higher momentum track.

The conclusion is, I think, that Tom is correct in his belief that delta electrons could not double the occupancy in the TPC. They do not. The occupancy in the simulation is doubled by a combination of decay and conversion particles, combined with delta electrons. 

Unfortunately, the evaluator does not contain truth track information for secondary particles. Therefore I can't extract from my ntuples the relative yields of the secondary particles. I need to figure out how to get that info into the ntuples in future.

All comments welcome.

Tony

Attachment: cluster_flavor_primary_secondary.pdf
Description: cluster_flavor_primary_secondary.pdf

Attachment: cluster_energy_pT.pdf
Description: cluster_energy_pT.pdf

Attachment: g4hit_energy_pT.pdf
Description: g4hit_energy_pT.pdf