Divergent Cross Section in e+e- -> e+e-

9/1/22 20:50, Mauricio Oviedo пишет:
> New question #703013 on CalcHEP:
> https://answers.launchpad.net/calchep/+question/703013
>
> Hello,
>
> I am beginner in CalcHEP, and here appear a problem with the calculation of the cross section in the process
>
> e+,e- -> e+,e-
>
> I am study the search of a new Z' boson considering only SM photon and Z boson as background, and my problem appear in the calculation of the cross section of that background. The cross section calculate with bad precision and is divergent.

Yes,  cross section for changed particles always is divergent because of
photon t-channel exchange. Physically it means that even in  collision
with large impact parameter a  small deviation of direction of motion
takes place. To avoid this divergence you have to apply a cut for angle
of  scattering (A label in CalCHEP),  or for  cosine of  angle ( C), or
for transverse momentum:

  T("e") |1 |

It is example of realization of cut  Pt>  1GeV.

>
> I use a regularization
>
> 34 | MZ | wZ | 2
>
> and I put cuts only in the invariant mass
>
> 1000 GeV < M(e+,e-) < 2000 GeV

Such  cut does not restrict angle of scattering.

Best

      Alexander Pukhov

>
> How I can solve my problem?
>