[Rivet] beams definiton

[Hannes Jung]

Dear Holger

ahh, thanks a lot, I will try this.
How are the beam particles extracted in rivet ?
Should this be included in the rivet part to define beam particles, or in the user code ?

Sorry for my ignorance
cheers
hannes

On 27.03.2011, at 22:25, Holger Schulz wrote:

> 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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Hannes Jung 
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http://www.desy.de/~jung                                           
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