Re: how to select charged particles?

From: Alfredo Ferrari (alfredo.ferrari@cern.ch)
Date: Tue Jan 09 2007 - 21:49:35 CET

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    Hi all

    Sebastien is almost right:

       Zfftrk = <Z_eff^2>^1/2 (that is Zfftrk^2 is the average Z_eff^2)

       Zfrttk = current (random) (Z_eff^2)^1/2 (that is Zfrttk^2 is the current
                                                Z_eff^2)
       Ichrge(Jtrack) = "bare" particle charge

    Please note that Zfftrk and Zfrttk make sense only for dE/dx calculations.
    Zfftrk is computed on the basis of recent <Z_eff^2> parametrizations and
    should be reasonable until the energy of the ion is not very low (below
    100 keV/n). Zfrttk is computed on the basis of a rough model which is
    tuned to reproduce reasonably the dE/dx straggling due to charge changing
    events. Since there is at least another semi-empirical parameter which
    enters, Zfrttk could well be non-physical but still be perfectly
    meaningful in the framework of the dE/dx fluctuation calculations.

    Never forget that for a random variate r, the distribution of r is not
    the one of r^2 and viceversa, and that <r^(2n)> != <r^n>^2 and similar.
    In short, don't try to compute an actual particle charge out of those
    variable. They make sense only for dE/dx calculations.

                      Ciao
                     Alfredo

    On Thu, 21 Dec 2006, Sebastien WURTH wrote:

    > Hello Konstantin,
    >
    > This might be confirmed but I think that :
    > Zfftrk = <Z_eff> is the "average" Z_eff
    > Zfrttk = actual Z_eff = real Z_eff
    >
    > Regards.
    > Sebastien.
    >
    > Konstantin Batkov a ecrit :
    >
    >> Hello,
    >>
    >> I have two more questions.
    >> 1. I would like to analyze only charged particles in mgdraw.f. Is it
    >> correct to use the following expression?
    >>
    >> IF (ZFRTTK .GT. ZERZER)
    >> * ....
    >> END IF
    >>
    >> 2. What is the difference between these variables :
    >> Zfftrk = <Z_eff> of the particle
    >> Zfrttk = actual Z_eff of the particle
    >> from TRACKR? (I do not understand what does word "actual" mean here.)
    >> I have already asked this question but nobody answered to me.
    >>
    >> Konstantin
    >
    > 

    -- 
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