Re: BXDRAW - tag for beam particles?

From: Olaf Hartmann <>
Date: Mon, 28 Sep 2009 12:09:27 +0200

Ciao Giuseppe,

> Please send your input and routines. LTRACK should not be zeo.
> In any case let me add some additional comment about LTRACK, the
> generation number.

It was a problem of formats ... I tried to transport float(Ltrack) onto
a variable declared as Double_t in ROOT. I changed to Int_t, and now it

> For primary particles LTRACK = 1. After each interaction, all exiting
> particles
> have the generation number increased by 1. Here we might enter into a
> subtle discussion
> Generation number is increased by 1 at all interactions, including
> elastic ones.
> Therefore asking for LTRACK = 1 is equivalent to ask for particles that
> had no interaction at all.
> In reality (experiment) you would call "beam particle" a particle having
> almost the same
> energy and direction of the beam. The risk (depending on your needs) is
> that
> you migh fall into a selection which results academic when compared to
> real life. For instance
> think of a primary muon which undergoes a "small" bremmstrahlung event,
> in which its direction
> and energy are negligibly changed. In an experiment you will probably
> call it a "primary muon",
> but in the code it will have LTRACK > 1.
> Therefore it is up to you to decide if this selection is what you need
> or not.

Thanks, I'll keep this in mind. In the present case, with a 3 GeV proton
beam on a liquid hydrogen target, I think asking for Ltrack>1 for
particles leaving the target should be fine since Ltrack=1 particles are
not measured.

Received on Mon Sep 28 2009 - 12:49:21 CEST

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