[Rivet] Problems when simulating an analysis

[Andy Buckley]

On 19/04/13 11:25, Chiara Zampolli wrote:
> Hi James,
> 
> One more question. On the web
> page http://rivet.hepforge.org/code/dev/a00140.html I see the
> documentation for the ChargedFinalState. I have a doubt about the
> minimum eta value: here you find:
> 
> ChargedFinalState <http://rivet.hepforge.org/code/dev/a00140.html> 	(
> double  	/mineta/ = |-MAXRAPIDITY
> <http://rivet.hepforge.org/code/dev/a00611.html#a2b7b3b854d8a789b4f8479ad849f29a7>|,
> 
> 		double  	/maxeta/ = |MAXRAPIDITY
> <http://rivet.hepforge.org/code/dev/a00611.html#a2b7b3b854d8a789b4f8479ad849f29a7>|,
> 
> 		double  	/minpt/ = |0.0*GeV
> <http://rivet.hepforge.org/code/dev/a00611.html#aec0e126d9991db8ad0b26139f5860568>| 
> 
> 	) 		
> 
> 
> In my analysis I defined:
> 
> ChargedFinalState cfs15(-0.8, 0.8, 0.15);
> 
> Shuold the first number be also positive? I need particles in [-0.8, 0.8].

No, it should be negative. You can use e.g. cfs15(-0.1, 0.8, 0.15) to
select only particles in a non-central region on one side of the
detector if you really want! (We're hoping to make this a bit more
powerful in future, but the implementation requires using some C++
features that aren't yet in widespread HEP production use.)

> Moreover, from here I think that the "*GeV" is not strictly needed, but
> I will add to be on the safe side.

It should definitely be added. I forget the exact units behaviour at the
moment -- I think we convert the incoming HepMC event to have GeV as the
base unit, but this isn't guaranteed to work forever. Plus, the code is
more humanly readable when the "*GeV" is there! The same thing applies
to using "/GeV" (or "/MeV", or whatever) when filling histograms with
dimensionful quantities.

Andy


> On Apr 19, 2013, at 10:47 AM, James Monk wrote:
> 
>> Hi Chiara,
>>
>> I don't know exactly what your problem is, but I can suggest a few
>> things that spring to mind:
>>
>> when you construct the ChargedFinalState with a pT cut, be explicit
>> about the pT units because the momentum scale provided by the event
>> depends on which HepMC library was used, i.e. do
>>
>> ChargedFinalState cfs15(-0.8, 0.8, 0.15*GeV);
>>
>> When you generate the Pythia events, make sure the particle lifetime
>> cut is consistent in the ALICE analysis and your standalone Pythia
>> run.  Experiments typically generate events with a ctau (lifetime) cut
>> of 10mm, meaning that any particle whose species has an average
>> lifetime of more than 10mm will not be decayed, but this setting may
>> well not be present in a standalone run of Pythia unless you set it
>> yourself.
>>
>> The weight does not have to be one, although it quite often is with
>> soft-QCD runs.  Therefore you should include it in the histogram
>> filling.  Do you know why your events in this case have a weight - is
>> it something added by ALICE (by an event filter, for example).  Pythia
>> standalone min bias events would not usually have a weight, and as far
>> as I know Pythia cannot generate such events with a weight.  This may
>> be an indication that you have a problem (e.g. not generating the same
>> process in the two samples).
>>
>> cheers,
>>
>> James
>>
>>
>>
>> On 19 Apr 2013, at 10:07, Chiara Zampolli wrote:
>>
>>> Dear all,
>>>
>>>        I am attaching here the files for an analysis that I am trying
>>> to perform with Rivet. When I compared the results with Rivet
>>> with those that I obtain runnin
>>> g with the ALICE analysis tools (at MonteCarlo level), with the same
>>> Pythia tune, I obtain different
>>> results (see attachment). The analysis is meant to produce the
>>> multiplicity distributions of charged particles with eta in [-0.8,
>>> 0.8], pt > ptcut,
>>> for ONLY the events with at least one such particle. The ptcut value
>>> can be 0.15, 0.5 or 1 GeV/c, and they correspond to the three
>>> histograms of the analysis.
>>>
>>>        Could someone please take a look at the analysis I wrote
>>> (which is very short) and see if I made any mistake there? I tried to
>>> check the standard analysis (the one not with Rivet),
>>> and there I cannot find anything weird… Even though I might be wrong,
>>> of course. But if i could exclude that the problem is in the Rivet
>>> code, it would be helpful.
>>>
>>> I have also noticed that if I remove the weight in the filling of the
>>> histograms, I obtain different results (see further attachment for
>>> two out of the three histograms created in my analysis).
>>> What is this "weight"? How is it calculated? I thought it was equal to 1.
>>>
>>> Thanks in advance for your help, and Regards,
>>>
>>>                Chiara
>>>
>>>
>>> <ComparisonWithRivet.png>
>>>        I am attaching here
>>> <PastedGraphic-5.png>
>>> the files for an analysis that I am trying to perform with Rivet.
>>> When I compared the results with Rivet
>>> with those that I obtain running with the ALICE analysis tools (at
>>> MonteCarlo level), with the same Pythia tune, I obtain different
>>> results. The analysis is meant to produce the multiplicity
>>> distributions of charged particles with eta in [-0.8, 0.8], pt > ptcut,
>>> for ONLY the events with at least one such particle. The ptcut value
>>> can be 0.15, 0.5 or 1 GeV/c.
>>>        Could you please take a look at the analysis I wrote (which is
>>> very short) and see if I made any mistake there? Or if there
>>> is someone else to whom I
>>> should better write, could you please let me know?
>>>
>>>        Thanks in advance, and sorry to bother you again.
>>>
>>>                Chiar
>>> <ALICE_2013_DRAFT_Mult_7.cc><ALICE_2013_DRAFT_Mult_7.info><ALICE_2013_DRAFT_Mult_7.plot>_______________________________________________
>>> Rivet mailing list
>>> Rivet at projects.hepforge.org <mailto:Rivet at projects.hepforge.org>
>>> http://www.hepforge.org/lists/listinfo/rivet
>>
> 
> 
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-- 
Dr Andy Buckley, Royal Society University Research Fellow
Particle Physics Expt Group, University of Edinburgh

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