[Rivet] Pileup in Rivet

[Christian Roehr]

Hi James,

Thanks for the advice. Indeed I didn't know of this pile-up option in 
Pythia. However, I guess there is no such option in Hw++. But anyway, 
heading for a generator-independent solution is more reasonable probably. 
I'll bear your suggestion in mind.

Cheers
Christian



On Tue, 12 Oct 2010, James Monk wrote:

> 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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