[Rivet] Pileup in Rivet

Andy Buckley andy.buckley at ed.ac.uk
Wed Oct 6 22:01:11 BST 2010

On 04/10/10 19:34, Christian Roehr wrote:
> Hallo Andy,
> I am wondering if a certain feature is present in Rivet and if not, how
> to deal with it.
> Currently I'm studying pileup effects, i.e. the presence of particles
> from additional minimum bias scatters within one bunch crossing (some 20
> or so). Effectively, this should be quite easy, since the additional
> scatterings are not colour-connected whatsoever to the tagged event.
> So, the straightforward way of analyzing that should be to simply add
> the fs particles of these minbias events to the final state of the
> original event. And analyze the resulting final state afterwards.
> Is there a possibility to do that in Rivet? I could not find anything
> like that (looked in the documentation and in the 1.2.1 code).
> Any help is very welcome, Andy. :)

Hi Christian,

Sorry, pile-up isn't something that Rivet simulates intrinsically and
isn't planned either. However, it should not be *too* hard to write a
little HepMC filter which aggregates min bias events and superimposes a
number of them on top of a signal event -- with semi-proper beam spot
and N_pileup sampling. We could help with putting that together if you
are interested.

You should also make sure that the same-event pile-up is sufficient: I'm
involved in the detector simulation for ATLAS, and there is actually
quite a bit of complexity to handling the effect of bunch structure on
pile-up, as well as the more homogeneous backgrounds from thermalised
neutrons in the cavern (which will still be bouncing around 10 turns
after a min bias event) and beam halo. We actually do the
superimposition of these at the post-Geant4 stage, so I'm not actually
sure how good HepMC is at dealing with event structures like this...
shouldn't be a problem, I think, but I've said that before ;)

Sorry to disappoint, but as I said if you'd be interested in trying to
make a pile-up builder at HepMC level then I'm sure we'll help with
building it and I would see no reason not to bundle it with Rivet to
help the next person to turn up with the same question!


Dr Andy Buckley
SUPA Advanced Research Fellow
Particle Physics Experiment Group, University of Edinburgh

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