cross section

This process has infrared divergence in case of massless electron. It appears when electron goes forward and when virtual gamma creates two electron with zero mass. If you assign to electron a non-zero mass, then these divergence
has to disappears but indeed at least quadruple precision is required to see in in practices.

 To solve this problem I propose to implement cuts for electron transverse momenta and e+,e- invariant mass. Say, 1GeV. You can do it via GUI or batch. It should looks like

 Cuts
!| Parameter |> Min bound <|> Max bound <|
 |T(E) | 1 |
 |T(e) | 1 |
 |M(e,E) |1 | |

After that you have to help to CalcHEP to detect singularities of matrix element caused by propagators. There are dangerous t-channel gamma and virtual W and Z.
You can done it via Regularization option

e,E->e,E,ne,Ne
 Regularization
 Momentum |> Mass <|> Width <| Power|
13 |0 |0 |1 |
24 |0 |0 |1 |
36 |MW |wW |2 |
45 |MW |wW |2 |
56 |MZ |wZ |2 |
134 |0 |0 |2 |
234 |0 |0 |2 |

These tricks should give you a reasonable precision.

Best
     Alexander Pukhov

.

Hi,
Dear Dr
How i can minimized the errors in the process :
W+ W-= W+W-
I've found a bad precesion.