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Forum: Event and Track Management
Re: Question Does the postpone stack induce cross section bias? (Evan Rand)
Date: 11 May, 2016
From: Marc Verderi <Marc Verderi>

Hi Evan,

Postponing a track to the next event will just do this and will not 
cause bias. The track is taken as it is (time, position, energy, etc.) 
and put in the stack. In the next event, it will be taken back as it is 
and be tracked. Doing so does not introduce any bias. The track "does 
not know" (and does not need to know) in what event it is tracked, and 
from the point of view of the track (and of the physics applied to it), 
the event "partitioning" is somewhat arbitrary.

It would be true that the postponing would introduce a bias if the track 
characteristics would be changed : for example assume that the event 
would give "the time" T0  of all primary tracks, then keeping 
artificially alive a track by postponing it would bias its lifetime. But 
this is not the way it is. (And for the case of the time, for example, 
it is carried by the primary vertices the primary tracks originate from, 
and an event may have several of them, each having its own time.)


On 11/05/2016 15:29, Evan Rand wrote:
> *** Discussion title: Event and Track Management
> Hi G4Experts,
> Does the postpone stack induce cross section bias? In my case I'm using
> the postpone stack with hadronic physics (ParticleHP).
> For example, if I stop a particle in the stepping action at some time
> (t0), and then send the track to postpone stack. When the track starts
> during the next event, will the track have a complete knowledge of its
> history? For example, does it know how many steps it made in the
> previous event, and therefore correctly calculate the probably of a
> hadronic event for the next step? Or does the postpone stack create a
> NEW track at every event, and therefore the tracks lose their history
> and induce some form of a cross section bias.
> Thanks in advance for any help, Cheers, Evan
> -------------------------------------------------------------
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