**From:** Alfredo Ferrari (*alfredo.ferrari@cern.ch*)

**Date:** Tue Jan 09 2007 - 21:49:35 CET

**Previous message:**Alberto Fasso': "Re: particles in beam interacting with each other"**In reply to:**Sebastien WURTH: "Re: how to select charged particles?"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]

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
*

*>
*

*>
*

-- +----------------------------------------------------------------------------+ | Alfredo Ferrari || Tel.: +41.22.767.6119 | | CERN-AB || Fax.: +41.22.767.7555 | | 1211 Geneva 23 || e-mail: Alfredo.Ferrari@cern.ch | | Switzerland || Alfredo.Ferrari@mi.infn.it | +----------------------------------------------------------------------------+

**Previous message:**Alberto Fasso': "Re: particles in beam interacting with each other"**In reply to:**Sebastien WURTH: "Re: how to select charged particles?"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]

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