rjones30
commented
3 years ago Sean,
Yes, this comparison looks typical to me. The low-energy carbons are from elastic Rutherford scattering on the carbons in the scintillator. These are not generated in geant3 because they are below the 1MeV energy cut for hadrons, so the energy loss from these interactions gets lumped in with ionization energy loss. If you look closely at the g4 type spectrum, you can also see the aluminum recoils from the support structure (type=74) and lead recoils (type=111) although most of the lead recoils are below that cut-in-range cutoff for g4.
You are right about the high-energy tail for neutrons in HADR=1 being potentially spurious. It looks too hard for what is commonly seen in hadron calorimetry.
-Richard Jones
On Thu, Dec 3, 2020 at 7:05 PM Sean Dobbs notifications@github.com wrote:
I'm starting this issue as a follow-up from discussions about issue #111 https://github.com/JeffersonLab/HDGeant4/issues/111 and some of the proton timing issues that Lubomir has reported in J/psi production. He recently showed a comparison of the thrown and reconstructed-based-on-BCAL-showers times for protons in J/psi MC using hdgeant4 (g4) and hdgeant with HADR 1 (g3)
Nov20_g3_vs_g4_dtlog.pdf https://github.com/JeffersonLab/HDGeant4/files/5639678/Nov20_g3_vs_g4_dtlog.pdf
Hao agreed to do a comparison of proton timing in a sample of his gp -> ppbar p events which have similar kinematics, but as a precursor to this, I wanted to look at the secondary particles generated by proton interactions in the BCAL, since secondary hadrons are the likely cause of the tails in the timing distributions.
I used a particle gun to throw 10k protons with momentum = 0.8 - 2.0 GeV/c and theta = 10 - 30 degrees. using v2.18.0 of hdgeant4 and the master of halld_sim as of Nov 2, 2020 with TRAJECTORIES 2 enabled in the control.in. I looked at MCTrajectoryPoints that were generated within the BCAL volume ( r = 65 - 90 cm ). A couple interesting things pop up right away.
First we can look at the yields of secondary particles that are being created.
GEANT4
[image: ptype_g4] https://user-images.githubusercontent.com/1182058/101104415-0c720700-3599-11eb-99d8-46040baf2f74.png
GEANT3 (HADR 1)
[image: ptype_g3_h1] https://user-images.githubusercontent.com/1182058/101104412-0bd97080-3599-11eb-948a-c2485349cc14.png
GEANT3 (HADR4)
[image: ptype_g3_h4] https://user-images.githubusercontent.com/1182058/101104414-0c720700-3599-11eb-9531-09997a5a97b5.png
A few things show up already. First, geant4 seems to generate a bunch of C12 nuclei (ID=67) which geant3 does not. Between the different simulations, there are different rates of proton (ID=14) and neutron (ID=13) production, with geant3 with HADR=1 apparently generating the most neutrons.
We can get more insight by looking at the energy spectra of these generated particles. In the following, the blue histogram is Geant4, green is Geant3 w/ HADR 1, red is Geant3 w/ HADR 4.
Neutrons
[image: n_en] https://user-images.githubusercontent.com/1182058/101104813-ffa1e300-3599-11eb-9472-accd040cdd51.png
Even though Geant3 w/ HADR 1 generates the most neutrons, it seems like a lot of them are generated with only a tiny amount of energy, and there is a strong tail to high energies. Maybe this is part of the cause of the timing tails?
Protons
[image: p_en] https://user-images.githubusercontent.com/1182058/101104816-003a7980-359a-11eb-8d8e-8eb3142600d5.png
This is neat - at high energies all the models agree, but diverge at lower energies. It seems like geant4 has some process that the others don't.
C12
[image: c12_en_g4] https://user-images.githubusercontent.com/1182058/101104409-0b40da00-3599-11eb-824b-decbbe6914df.png
Just for comparison - the carbon nuclei are unsurprisingly slow.
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sdobbs
gleasonc
beattite
I'm starting this issue as a follow-up from discussions about issue #111 and some of the proton timing issues that Lubomir has reported in J/psi production. He recently showed a comparison of the thrown and reconstructed-based-on-BCAL-showers times for protons in J/psi MC using hdgeant4 (g4) and hdgeant with HADR 1 (g3)
Nov20_g3_vs_g4_dtlog.pdf
Hao agreed to do a comparison of proton timing in a sample of his gp -> ppbar p events which have similar kinematics, but as a precursor to this, I wanted to look at the secondary particles generated by proton interactions in the BCAL, since secondary hadrons are the likely cause of the tails in the timing distributions.
I used a particle gun to throw 10k protons with momentum = 0.8 - 2.0 GeV/c and theta = 10 - 30 degrees. using v2.18.0 of hdgeant4 and the master of halld_sim as of Nov 2, 2020 with TRAJECTORIES 2 enabled in the control.in. I looked at MCTrajectoryPoints that were generated within the BCAL volume ( r = 65 - 90 cm ). A couple interesting things pop up right away.
First we can look at the yields of secondary particles that are being created.
GEANT4
GEANT3 (HADR 1)
GEANT3 (HADR4)
A few things show up already. First, geant4 seems to generate a bunch of C12 nuclei (ID=67) which geant3 does not. Between the different simulations, there are different rates of proton (ID=14) and neutron (ID=13) production, with geant3 with HADR=1 apparently generating the most neutrons.
We can get more insight by looking at the energy spectra of these generated particles. In the following, the blue histogram is Geant4, green is Geant3 w/ HADR 1, red is Geant3 w/ HADR 4.
Neutrons
Even though Geant3 w/ HADR 1 generates the most neutrons, it seems like a lot of them are generated with only a tiny amount of energy, and there is a strong tail to high energies. Maybe this is part of the cause of the timing tails?
Protons
This is neat - at high energies all the models agree, but diverge at lower energies. It seems like geant4 has some process that the others don't.
C12
Just for comparison - the carbon nuclei are unsurprisingly slow.