e+e- beam energy distribution

Dear Chris,

Indeed we are now working on to include functionality for ISR and beamstralung for e+e- colliders,
and looking at available tools to provide beam profiles.

Could you tell us the documents/links about GuineaPig? Is there a common data format in the e+e- community? like LHAPDF?

Best regards,
Kentarou

I am also working on e+e- event generation and would like to know how best to implement ISR effects with MG 5.4.3 (I need to older version for the model used).

I am using the HEL_UFO model to generate "e+ e- > h e+ e- NP=1 QED=4" events. I've tried the pythia-pgs interface but I get an issue I understand is due to incompatibility with pythia 6. I've tried brute force "e+ e- > h e+ e- a" generation but this takes many hours to generate and is impractical. I am currently attempting to use pythia 8 on the files given from madevent. Is this the correct method or is there another, better way?

I can post this as a separate FAQ if you think that this is more appropriate. Thanks.

We let you know once the functionality of ISR and beamstralung for e+e- colliders is available.
The time scale should be a (few) month(s).

Kentarou

Hi Kenatarou,

You have probably already answered your own questions, but for the record here is what I know. I am not aware of any common format for e+e- beams like LHAPDF, but one seems desirable. GuineaPig exists in C and C++ versions, neither of which is consistently or persistently maintained, though a version for CLIC is currently maintained at CERN.

The reference for results obtained from GuineaPig used by the e+e- community is to D. Schulte's thesis since he is the code author, though this does not direct you to any code. For the ILC TDR a Whizard interface to the GuineaPig output text files (like pairs.dat and photons.dat) was written by Tim Barklow. The possibility to rapidly incorporate new accelerator parameters (bunch structure) is very nice, but on the other hand GuineaPig does not seem to be maintained in the optimal way for this to happen consistently.

Regarding beam energy spread, I'm concerned about how radiative return events are handled in MG5_aMC. The fraction of events in which the e+e- CME is reduced all the way back to the Z pole due to radiative losses by is large enough to make this a huge background, and I'm not even sure how to ask MG5_aMC to do it: e+e- > z a doesn't work, and neither does e+e- > z.

Thanks for taking this on. I will be releasing to the arXiv a study on e+e- backgrounds generated with MG5_aMC shortly, and include favorable comparison with results from Whizard. I look forward to MG5_aMC with beamstrahlung and ISR!

Best,

Chris

Hi Chris,

Thank you very much for your kind clarification.
We also look forward to seeing your paper.

keep in touch,
Kentarou

Hi Kentarou,

Thanks for the update.

Do you recommend waiting for the ISR implementation or will Pythia 8 ISR be appropriate for my needs now?

Thanks,
Morag

Hi Morag,

I would certainly recommend waiting for our implementation, i.e. the MG5aMC+Pythia8 interface for e+e- collisions.
But, of course, you can try it with your own responsibility.

cheers,
Kentarou