| GEANT3 dEdx for low energy protons [message #6306] |
Tue, 08 April 2008 18:02  |
Sebastian Neubert
Messages: 282
Registered: March 2006
Location: Munich
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first-grade participant |
From: *e18.physik.tu-muenchen.de
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Hi!
We observe a remarkable behaviour with GEANT3 when we look at the energy loss distributions for 200MeV protons.
From BetheBloch we would expect something like dE/dx=22keV/cm in the TPC gas.
Please have a look to the following plots, where you see the dE/dx (in keV/cm) from MC-Points plotted against the dx (in cm) for different step limitations:
dx<2.5cm
dx<3cm
dx<4cm
One observes that as soon as a step is smaller than 3cm the dEdx calculation gives a wrong result, which is too low by a factor of 3 to 4 (6keV/cm instead of 22keV/cm).
It is remarkable, that this behaviour is observed for any short step, regardless of if it was triggered by the step limiter or by anything else. You see this in the third plot, where the points with too low dEdx still persist!
If we shut off the straggeling and just use the energy loss tables of GEANT (LOSS=4 option in SetCuts.C) we get the exepcted value for the dE/dx.
How should we deal with this?
Cheers!
Viola and Sebastian.
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Sebastian Neubert
Technische Universität München
Department Physik E18
sneubert@e18.physik.tu-muenchen.de
tel: +49-8928912592
[Updated on: Tue, 08 April 2008 18:03] Report message to a moderator |
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| Re: GEANT3 dEdx for low energy protons [message #6578 is a reply to message #6577] |
Wed, 23 April 2008 10:21  |
Sebastian Neubert
Messages: 282
Registered: March 2006
Location: Munich
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first-grade participant |
From: *e18.physik.tu-muenchen.de
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Hi Stefano!
We have played around with the cut variable a lot. It does not change the picture. The only thing that helps is to use the Urban model which according to the GEANT3 manual is also the recommended thing to do.
Sebastian.
Sebastian Neubert
Technische Universität München
Department Physik E18
sneubert@e18.physik.tu-muenchen.de
tel: +49-8928912592
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