[Rivet] Problems when simulating an analysis

[Chiara Zampolli]

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].

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

Thanks again, and cheers,

Chiara



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
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