sPHENIX tracking discussion

["Frawley, Anthony" <afrawley AT fsu.edu>]

Hi All,

We had two talks in the tracking meeting today, see the notes below.

Cheers

Tony

Developing a spec for fake track rates for each physics topic  - Mike McCumber and Tony Frawley

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Mike and I discussed the proposed process for developing a fake track specification for sPHENIX for each physics topic. This would then be used to decide how the tracker has to be configured.

We also asked for volunteers to work on the fast simulation for the physics topic(s) that they are most interested in. Please contact Mike and me.

Space Charge Calculations - Tom Hemmick

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Tom discussed the status of the space charge distortion simulations for the TPC.

Mike: What about the time dependence of the space charge?
Tom: Within an event the space charge is fixed, but from event to event we will have fluctuations in the space charge distribution.
We can assume a constant shape, scale with luminosity (STAR) - use power draw from power supplies to infer luminosity.
ALICE plans to use the TPC's time history of gain stage charge - ALICE thinks the STAR approach will not be adequate for them

The space charge formula contains 2 pieces - primary ionization and ion backflow
The primary ionization is more or less from instantaneous luminosity
The ion backflow cannot be scaled by instantaneous luminosity.

What does the primary ionization structure due to a finite number of tracks do?
At 50 kHz we will be stacking 5K events - Jamie Dunlop used a Poisson distribution with a mean of 5000 to study this, and found that fluctuations were very small.
Tom would like to do that calculation from 1st principles for sPHENIXx

General discussion

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John Haggerty: We need to augment the tracking effort through the tracking meetings.
e.g. RIKEN should participate.
e.g. Dan Cebra worked on homogeneity issues for STAR.
Tom: Suggest John send email to the collaboration pointing to the meeting agendas, describing what goes on, and asking interested parties to join.