[Rivet] Use proton-lead MC generators with Rivet

[Andy Buckley]

Hi Hans,

The rivet command-line tool has an --ignore-beams option for this sort 
of reason. But you haven't said what analysis you are trying to run: if 
it's one that you're writing yourself, just use ANY rather than PROTON 
in the Beams specification in the analysis' .info file.

We've been upgrading tools for HI and cosmic-ray analysis over the last 
year, so are hoping to start building up the collection. Very happy to 
help with anything that's currently a blocker!

Andy


On 28/02/17 11:10, Hans Jozef H Van Haevermaet wrote:
> Dear Rivet authors,
>
> I am a member of CMS (forward and small-x community in fact), and I’m
> trying to get Rivet running with proton-lead events coming from the EPOS
> MC generator.
> It turns out however, that this is not possible (?).
> When executing Rivet, it stops because it detected that the incoming
> beams are different for each event:
> Event beams mismatch: [PROTON, PROTON] @ 1.87656 GeV vs. first beams
> [NEUTRON @ 2511.57 GeV, NEUTRON @ 2511.57 GeV] @ 1.87914 GeV
>
> This in turn, is caused by the fact that the EPOS generator writes out
> the interacting nucleon (p or n) in the HEPMC file, and not the particle
> id code of lead itself.
>
> Could you let us know if it is possible for Rivet to get compatible with
> these kind of situations?
> One direct option (for me) is to comment out this function:
> https://rivet.hepforge.org/code/dev/AnalysisHandler_8cc_source.html
> At line 95.
>
> But that can lead to unwanted behaviour in other cases, I guess. Maybe
> one can include a parameter to turn this check on/off? So that it is the
> user’s responsibility? i.e. by default the check is done, but the user
> can turn it off manually if needed.
>
> It would be very good to solve this incompatibility, since in CMS we try
> to get Rivet routines from all our analyses, and it would be nice to be
> able to extend this to proton-lead, or even lead-lead measurements. As
> far as I can see on the web, I did not find any Heavy Ion analysis
> implemented in Rivet?
>
> Thanks!
> Best Regards,
> Hans
>
>
>
>
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-- 
Dr Andy Buckley, Lecturer / Royal Society University Research Fellow
Particle Physics Expt Group, University of Glasgow