[Rivet] Pileup in Rivet

[James Monk]

Hi Christian,

A HepMC pile-up compositor sounds like a useful tool.  Can I suggest the same pipe idiom used by rivet, but with two input pipes  - one providing the signal events and another providing the pile-up (which could come from a different generator entirely).

Another possibility is that some generators have an option to produce pile-up on top of the signal I think.  I'm pretty sure Pythia has this feature (MSTP(131)), but I guess you're more interested in Herwig :)

cheers,

James

On 8 Oct 2010, at 11:57, Christian Roehr wrote:

> 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!
> 
> Christian
> 
> 
> 
> 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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