[Rivet] Sherpa+Rivet: m_io->fill_next_event fails

[Eike von Seggern]

On Wed, Dec 09, 2009 at 18:06 +0100, Eike von Seggern wrote:
> On Wed, Dec 09, 2009 at 15:42 +0000, Andy Buckley wrote:
> > Frank Siegert wrote:
> > > Frank Siegert, Thursday 26 November 2009:
> > >> Eike von Seggern, Thursday 26 November 2009:
> > >>> I'm trying to run Sherpa with the BaBar setup and analyse the events
> > >>> with Rivet. However, Rivet stops after processing a few events. I
> > >>> tracked it down to that the m_io->fill_next_event call in
> > >>> Run::processEvent fails. But no other error message is printed by
> > >>>  HepMC. Sherpa and Rivet are both built against HepMC 2.05 .
> > >>>
> > >>> I attach the Sherpa run card. The Rivet command is:
> > >>>
> > >>> rivet -l Rivet=DEBUG -a PDG_HADRON_MULTIPLICITIES babar.hepmc2g
> > >>>
> > >>> Has anyone an idea what's going wrong.
> > >> I don't have a solution, but it might be interesting to know whether it
> > >> works through Sherpa's internal Rivet interface (in 1.2.0). Our manual
> > >> describes how you can use that... could you give that a try?
> > > 
> > > Actually, I've just tested it, and it doesn't stall, but the analysis 
> > > isn't going to work for Babar events, since it looks at 2*"mean beam 
> > > momentum" instead of sqrt(s). This isn't the same for asymmetric beams.
> > 
> > Eike/Frank, does this now work with the updated analysis? If so, then I 
> > guess this *is* a problem with HepMC I/O. Why asymmetric beams would 
> > lead to a HepMC read fail I have no idea... but it's possible, and looks 
> > increasingly probable.
> 
> Yepp, I still get this with the current Rivet HEAD. So I think this is
> either Sherpa's fault or HepMC itself. But most likely HepMC, because
> writing out something without an error or anything strange and then not
> being able to read in the data afterwards looks to me that way.
> 
> I'll try this now with example code to check that it's not Rivet's
> fault.

Okay, it's not a Rivet problem and it's not a problem with asymmetric
beams either. I've attached a tool that just reads in HepMC and prints
out the event numbers.

(run){
  EVENTS = 100

  FILE_SIZE = 100000
  EVENT_MODE=HepMC
  HEPMC2_GENEVENT_OUTPUT = fails
}(run)

(beam){
  BEAM_1 = 11
  BEAM_ENERGY_1 = 9.0
  BEAM_2 = -11
  BEAM_ENERGY_2 = 9.0
}(beam)

(processes){
  Process 11 -11 -> 93 93
  CKKW pow(10,-2.25);
  Order_EW 2;
  End process;
}(processes)

(model){
  ORDER_ALPHAS = 0
  ALPHAS(MZ) = 0.127
}(model)

(me){
  ME_SIGNAL_GENERATOR = Internal Comix
}(me)


Adding another parton to the outgoing particles, i.e. appending "93{1}" to
the end of the Process line, fixes this and I can read in all events!

So it's either HepMC or Sherpa. Frank do you have an idea what could go wrong
here?

tschuess
    eike