Integration issue?

Asked by Igal


I used WO to calculate the following SM processes: gamma e- > gamma e-, gamma e- > gamma gamma e-, gamma e- > e- e+ e-, and gamma e- > gamma e- e+ e-, see typical Sindarin script used. For some of the channels mentioned earlier, the cross-section value deviates a lot from one simulation to another. My understanding is when there is a large deviation in the cross-section calculation, it means the integration is diverging, the remedy is usually to apply pseudo-rapidity cuts to remove the extreme backward and forward angles where usually the integration is diverging. However, the extreme angles are the region where my detectors are placed and where the bulk of the signal is. Is there an alternative solution to pseudo-rapidity cuts to make converging the integration?

Thanks, cheers,

Typical Sindarin script used:
# WHIZARD SINDARIN script for LEPS (II) & GlueX setups

# This is the generic WHIZARD SM

model = SM

seed = 2176003

process ae_to_aeee_unpol_eg11000MeVT0 = "gamma", "e-" => "gamma","e+","e-","e-"

iterations = 8:20000,3:40000


!!! Tests can be run multi-threaded
! openmp_num_threads = 4

beams = "gamma", "e-"
beams_momentum = 11000 MeV, 0 MeV

integrate (ae_to_aeee_unpol_eg11000MeVT0)

n_events = 1000

sample_format = lhef

simulate (ae_to_aeee_unpol_eg11000MeVT0)

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Juergen Reuter (j.r.reuter) said :

Dear Igal,
this should be very similar to Bhabha scattering as e.g. a means to make a luminosity measurement at an e+e- machine. There you are also going to extreme angles, e.g. theta of the order 10-20 mrad. But such a cut is needed for processes containing photons and (massless) electrons. You have a collinear singularity that is regulated only by the electron mass, which could be numerically ok for you as you are considering only Belle beam energies of 11 GeV. But you also have a soft singularity from your photon in the final state for which you need an energy cut.

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Juergen Reuter (j.r.reuter) said :

Seems to be ok.