[Rivet] Pileup in Rivet

Christian Roehr roehr at particle.uni-karlsruhe.de
Fri Oct 8 11:57:50 BST 2010

Hi Andy, hi all,

Thanks for your mail, that's quite helpful anyway, even if Rivet does
not do pileup. My guess is also that there shouldn't be much difficulty
in realising that at HepMC level, in principle. However, maybe some
tricks are necessary since HepMC stores any step of the event
generation, as far as I am aware of. Thus it will be somewhat restricted
to one event only.

Thank you especially for offering your help on that. I'll be happy to
come back to that at some point! For now I'm still dealing with the
actual analysis first, preparing for studying pile-up based on that.

Okay, I see, there are even further sources of contamination. In theory,
everything is so easy... :) Thanks for the hint, I will have a chat on
that with Jon Butterworth, who is my supervisor in this project.

I will get in touch with you. Cheers!


On Wed, 6 Oct 2010, Andy Buckley wrote:

> 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!
> Cheers,
> Andy
> -- 
> Dr Andy Buckley
> SUPA Advanced Research Fellow
> Particle Physics Experiment Group, University of Edinburgh

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