sPHENIX tracking discussion

[Michael Joseph Peters <mjpeters AT mit.edu>]

​Hi,

Thanks for the update! Is this reflected in the Geant simulations yet?

Thanks,

Michael Peters

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From: Ross Corliss <ross.corliss AT stonybrook.edu>
Sent: Wednesday, November 9, 2022 3:59 PM
To: Michael Joseph Peters; Michael Joseph Peters via sPHENIX-tracking-l
Subject: Re: [Sphenix-tracking-l] CA Seeder Bethe-Bloch Parameters

 

Hi Michael,

The war in Ukraine has had a major impact on the cost and availability of neon.  Because of that, our current expectation is to use 60:40 Ar:CF4 rather than the original neon mixture.  

-Ross

==========
Dr. Ross Corliss
Research Assistant Professor
Center for Frontiers in Nuclear Science
Stony Brook University
virtual office:  https://stonybrook.zoom.us/my/rossoffice?pwd=ZmZ2SlRIMVFvUUJwbUkyOVNVTmE5QT09

On Nov 8, 2022, at 10:22 AM, Michael Joseph Peters via sPHENIX-tracking-l <sphenix-tracking-l AT lists.bnl.gov> wrote:

Hi,

The material corrections used in the Kalman filter and propagator depend on several parameters that are likely material specific (​see https://github.com/sPHENIX-Collaboration/coresoftware/blob/master/offline/packages/trackreco/GPUTPCTrackParam.cxx#L340). Namely:

- Density of TPC gas (current value: 2.27925e-3 g/cm^3)

- "Density effect first junction point" (current value: 2)

- "Density effect second junction point" (current value: 4)

- Mean excitation energy of TPC gas (current value: 14e-9 GeV)

- Mean Z/A of TPC gas (current value: 0.47999)

- Radiation length of TPC gas (current value: 14.403 g/cm^2)

The value for density is calculated from the CF4 density given at https://github.com/sPHENIX-Collaboration/coresoftware/blob/master/simulation/g4simulation/g4main/PHG4Reco.cc and the Geant4 Materials Database for G4_Ne. I'm confident this one is correct.

The two "density effect junction points" are copied from ALICE code; I don't know how to find the correct values for these.

The mean excitation energy comes from an unknown source, and is likely incorrect; the ALICE value is 140e-9 GeV, which is similar to the excitation energy of pure neon (listed as 137 eV in the Geant4 Materials Database).

The current value for the mean Z/A is actually slightly incorrect; calculation just now gives a value of 0.48640, and I'm not sure where the current value comes from. 

Likewise, I'm not sure where the current value of radiation length comes from.

Does anyone have any idea where to find the correct values for these parameters?

Thanks,

Michael Peters

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