In case of the two-photon Bethe-Heitler process,  we can factorize the process: u(x)*|A(u)|^2 + d(x)*|A(d)|^2 = [u(x)+d(x)/4]*|A(u)|^2 (A : Feynman amplitude) neglecting the mass difference. But in case of the electroweak (EW) process where Z0 couples to a quark line,  coupling structures are different between u and d quarks, i.e. the ratios of vector and pseudo-vector coupling constants are different.  Therefore we cannot do such a factorization. Also in case of the QED process where two types of diagrams exist: (1) one photon connected to a quark line and (2) two photons connected to a quark line,  again we cannot do such a factorization.

Anyway using the MERGE card as seen in Table1 of the GRAPE paper is the best we can do for saving time.

Comments  to  Tetsuo ABE (
Last  updated  on  July 11,  2001