[Rivet] beams definiton

[Holger Schulz]

On 27/03/11 17:36, Hannes Jung wrote:
> Dear all
>
> I am rying to run PHOJET with rivet, I managed to write out the hepmc record and inserted the beam particles.
> It seems to be fine, but rivet cannot identify the beams. The following error appears:
> ----------
> ~/jung/cvs/rivet/myrivet>   ../../phojet/main1/main1<  ../../phojet/main1/mb.inp>  test.out&
> [3] 12393
> ~/jung/cvs/rivet/myrivet>  ../build/Rivet-1.5.0/bin/rivet-nopy /tmp/example_out.dat CMS_FWD_11_001
> Rivet.Analysis.Handler: WARN  Analysis 'CMS_FWD_11_001' is unvalidated: be careful, it may be broken!
>   CMS_FWD_11_001 init phase
>   new event
> Assertion failed: (beams.first&&  beams.second), function project, file Beam.cc, line 53.
> zsh: abort      ../build/Rivet-1.5.0/bin/rivet-nopy /tmp/example_out.dat CMS_FWD_11_001
> ----------
>
> The first few lines of the hepmc file look like:
>
> HepMC::Version 2.03.11
> HepMC::IO_GenEvent-START_EVENT_LISTING
> E 0 -1 -1.0000000000000000e+00 -1.0000000000000000e+00 -1.0000000000000000e+00 0 0 167 1 2 0 0
> H 0 0 0 0 0 0 0 0 0 0 0 0 0
> F 0 0 0 0 0 0 0
> V -1 0 0 0 0 0 1 1 0
> P 1 2212 0 0 3.5000000000000000e+03 3.5000000000000000e+03 9.3827000000000005e-01 3 0 0 -1 0
> P 3 1 -1.9197591135156278e+00 -3.9088666188920991e-02 1.8743428161779718e+01 1.8841528606871407e+01 9.9000002932664519e-03 2 0 0 -3 0
> V -2 0 0 0 0 0 1 27 0
> P 2 2212 0 0 -3.5000000000000000e+03 3.5000000000000000e+03 9.3827000000000005e-01 3 0 0 -2 0
> P 4 -2 4.9018658469058018e-01 5.6550380835818814e-01 -2.0026574606985077e+03 2.0026576005398924e+03 5.5999254606944934e-03 2 0 0 -4 0
> P 5 -1 -2.1560772467809458e-01 -1.8019388783202768e+00 2.5303300407030580e+00 3.1138623182516181e+00 9.8999999999710413e-03 2 0 0 -5 0
> .....
>
> Any idea what I am doing wrong here ?
>
> Thanks a lot
> Cheers
> Hannes
>
>
>    
Hi Hannes,

I am not 100 percent sure but it could be that the beams have not 
properly been
set in the HepMC event record. Something similar showed up when recently we
solved a problem with the Whizard event generator. There is a solution 
by Frank
Siegert that may apply here as well. When filling the HepMC stuff, you could
iterate over all particles and look for those without a mother and 
explicitly
set those as beam particles.

Here is a code snippet that solved the Whizard problem,
the lines in blue do the beam particle finding:

// Function copied from Frank siegert
bool cmpGenParticleByEDesc(const HepMC::GenParticle* a, const 
HepMC::GenParticle* b) {
   return a->momentum().e() > b->momentum().e();
}

extern "C" void io_gen_event_write_event
( IO_GenEvent* iostream, GenEvent* evt) {
   // Add beam particles by trying to find those particles without a mother
if (!evt->valid_beam_particles()) {
     std::vector<HepMC::GenParticle*> beams;
     for ( HepMC::GenEvent::particle_const_iterator p = 
evt->particles_begin();
           p != evt->particles_end(); ++p ) {
       if (!(*p)->production_vertex() && (*p)->pdg_id()!=0) {
         beams.push_back(*p);
       }
     }
    // Set the beam particles
    evt->set_beam_particles(beams[0], beams[1]);
   }
   // Write the event
   iostream->write_event( evt);
}


Hope that helps,
Holger





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