WHIZARD

ISR simulations in WHIZARD

Asked by Suchita

Dear WHIZARD authors,

I am interested in simulating four fermion operator induced processes at e+e- machine at several centre of mass energies. My final state contains visible particles, thus I do not need to generate a hard photon. However I do wish to generate the correct ISR effects, which could be relevant specially for simulating correct kinematics of the final states.

Perhaps the easiest way to do that is to set 'beams=e1,E1 =>isr'. However this always generates two ISR photons, one per beam. I think I should however get events with 0,1,2 photons if the simulation is done correctly. I understand I can't get 1 photon due to WHIZARD ISR setup, thus I should get events with 0 and 2 photons.

I would therefore think that one needs a weighted sum of events with no isr and with isr to get desired events. Is there a way to simulate this with one .sin script? I could always generate two event sets separately and add them later on, but perhaps there is a more intelligent way of doing this. Hence I ask.

I thank you very much for your help in advance,
Suchita.

Question information

Language:
English Edit question
Status:
Solved
For:
WHIZARD Edit question
Assignee:
Juergen Reuter Edit question
Solved by:
Suchita
Solved:
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Last reply:
Revision history for this message
Juergen Reuter (j.r.reuter) said : 		#1

Dear Suchita,
this all depends a little bit of what you want to cover with your event samples. If you are just interested in the best possible estimate for the cross section value, then a simulation with ISR on, but with purely collinear approximation (unobservable photons) would be the best option. If you are interested in the kinematics of the photon, you need to simulate them with the exact matrix elements. If you are interested in a best prediction of the cross section with a potential study of systematics from photon contamination, then the two photons as proxies in the sample are a good approximation.
From your first paragraph, I read that you are interested in the correct kinematics of your final state: I believe then an explicit simulation with ME photons is the best way, with a matching to the ISR spectrum with the help of pT veto/cut.
Cheers,
    JRR (Juergen)

Revision history for this message
Suchita (suchita-kulkarni) said : 		#2

Thank you very much for the quick answer Juergen. This answers my question.