CalcHEP

CH error 53: regarding Regularization

Asked by Wei Shi

Dear CalcHEP experts,

An regularization error occurred when I was generating the elecroweak process pp->4mu with CalcHEP 3.7.1 using this batch script:
https://raw.githubusercontent.com/weishi10141993/DarkSector/master/pp4mu_13TeV_calchep_1k.txt

The output cs.out is here: https://raw.githubusercontent.com/weishi10141993/DarkSector/master/cs.out

And the cs.o here: https://raw.githubusercontent.com/weishi10141993/DarkSector/master/cs.o

These error didn't happen in previous CalcHEPversion. Is there any suggestion on how to resolve this?

Thanks,
Wei

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Alexander Belyaev (alexander.belyaev) said : 		#3

Dear Wei,

first of all, apologies for delay with our reply.

The problem happens because your cross section with your cuts is divergent:
the mass of the muon in SM is zero and there is an explicit singularity when invariant mass of m+,m- pair is zero.
The cut on muon PT does not solve the problem.
There are several easy solutions:
1. Introduce muon mass in the model
2. Set cut on the minimal mass of muon pair

Please try to use one of these and let us know.

P.S. In addition in the region of small invariant mass of two muons there could be the loss of precision(not necesserily your case),
in this case you can use longdouble or quadrouple -- by modifying include/nType.h
(just uncomment the respective line and recompile CalcHEP by typing 'make')

Can you help with this problem?

Provide an answer of your own, or ask Wei Shi for more information if necessary.

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