sPHENIX tracking discussion

[pinkenburg <pinkenburg AT bnl.gov>]

    that fell through the cracks. Here is our tpc gas in
https://github.com/sPHENIX-Collaboration/coresoftware/blob/master/simulation/g4simulation/g4main/PHG4Reco.cc:
    
     G4Material *CF4 = new G4Material("CF4", density = 3.72 * mg / cm3,
    ncomponents = 2, kStateGas, 288.15 * kelvin, 1 * atmosphere);
     
CF4->AddElement(G4NistManager::Instance()->FindOrBuildElement("C"),
    natoms = 1);
     
CF4->AddElement(G4NistManager::Instance()->FindOrBuildElement("F"),
    natoms = 4);
      // cross checked with original implementation made up of Ne,C,F
      // this here is very close but makes more sense since it uses Ne
    and CF4
      double G4_Ne_frac = 0.5;
      double CF4_frac = 0.5;
      const double den_G4_Ne =
G4NistManager::Instance()->FindOrBuildMaterial("G4_Ne")->GetDensity();
      const double den_CF4_2 = CF4->GetDensity();
      const double den_sphenix_tpc_gas = den_G4_Ne * G4_Ne_frac +
    den_CF4_2 * CF4_frac;
      G4Material *sPHENIX_tpc_gas = new G4Material("sPHENIX_TPC_Gas",
    den_sphenix_tpc_gas, ncomponents = 2, kStateGas);
      sPHENIX_tpc_gas->AddMaterial(CF4, den_CF4_2 * CF4_frac /
    den_sphenix_tpc_gas);
     
sPHENIX_tpc_gas->AddMaterial(G4NistManager::Instance()->FindOrBuildMaterial("G4_Ne"),
    den_G4_Ne * G4_Ne_frac / den_sphenix_tpc_gas);
    
    Ross, can you update this to the CF4/Ar mixture we will use?
    
    Thanks
    Chris

On 11/9/2022 4:38 PM, Michael Joseph Peters via sPHENIX-tracking-l wrote:

Ok, good to know. To maintain compatibility for efficiency studies, I'll change over to the new mixture only once the underlying Geant simulation does. 

As for the "junctions" I mentioned earlier, I found out that they're apparently x0 and x1 in the Sternheimer parametrization of the density correction in the Bethe-Bloch formula. In particular, x0 is the value of beta*gamma where the density correction "turns on"; the approximation is piecewise in two parts, with the switch between parts happening at x1. The values for these, for various materials, are tabulated in the full version of PDG.

Thanks,

Michael Peters

---

From: Ross Corliss <ross.corliss AT stonybrook.edu>
Sent: Wednesday, November 9, 2022 4:18 PM
To: Michael Joseph Peters
Cc: Michael Joseph Peters via sPHENIX-tracking-l
Subject: Re: [Sphenix-tracking-l] CA Seeder Bethe-Bloch Parameters

 

Probably hasn't been updated in geant ...yet.  We looked at the impact on the distortions and GEM performance mostly.  I expect the slight change in density won't do much directly, though some parameters (Z/A) will change, and some of those, about junction effects, are foreign to me.

-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 9, 2022, at 4:01 PM, Michael Joseph Peters <mjpeters AT mit.edu> wrote:

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

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Christopher H. Pinkenburg	;    pinkenburg AT bnl.gov
				;    http://www.phenix.bnl.gov/~pinkenbu

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