[Rivet] Use proton-lead MC generators with Rivet

[Hans Jozef H Van Haevermaet]

Dear all,

Great! Thank you very much for your help!

Cheers,
Hans


On 28 Feb 2017, at 18:06, Sercan Sen <Sercan.Sen at cern.ch<mailto:Sercan.Sen at cern.ch>> wrote:


Hi Andy, Leif,

Let me know if this solves your problem, and if so I/we will apply it to the development version that'll become Rivet 2.5.4.

I use this patch with Rivet 2.5.3 and it solves the problem. Thanks for implementing the patch in the next release.

Cheers,
Sercan



On Feb 28, 2017, at 6:36 PM, Andy Buckley <a.g.buckley at gmail.com<mailto:a.g.buckley at gmail.com>> wrote:

Hi Hans & Sercan,

Actually, Leif understood this faster than I did, and has posted a patch below. Unfortunately his email only went to the Rivet list, so you didn't see it!

Let me know if this solves your problem, and if so I/we will apply it to the development version that'll become Rivet 2.5.4.

Andy


-------- Forwarded Message --------
Subject: Re: [Rivet] Use proton-lead MC generators with Rivet
Date: Tue, 28 Feb 2017 12:43:36 +0100
From: Leif Lönnblad <leif.lonnblad at thep.lu.se<mailto:leif.lonnblad at thep.lu.se>>
Reply-To: leif.lonnblad at thep.lu.se<mailto:leif.lonnblad at thep.lu.se>
Organisation: Theoretical Physics, Lund University
To: rivet at projects.hepforge.org<mailto:rivet at projects.hepforge.org>

Hi Hans,

There is actually a flag for rivet to --ignore-beams, but it only prevents checks that the different analyses included requires the same beams. It doesn't seem unreasonable to me if the checking of beams in the code you pointed to was switched off if --ignore-beams is given, ie.

   if ( !_ignoreBeams ) {
   // Ensure that beam details match those from the first event
     const PdgIdPair beams = Rivet::beamIds(ge);
     const double sqrts = Rivet::sqrtS(ge);
     if (!compatible(beams, _beams) || !fuzzyEquals(sqrts, sqrtS())) {
       cerr << "Event beams mismatch: "
            << PID::toBeamsString(beams) << " @ " << sqrts/GeV
            << " GeV" << " vs. first beams "
            << this->beams() << " @ " << this->sqrtS()/GeV
            << " GeV" << endl;
       exit(1);
     }
   }

Of course, individual analyses may still fail if they require specific beams.


/Leif

On 2017-02-28 12:10, 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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