# comparing EPA with full matrix element calculation

Hello,

I'm simulating a photon-fusion process in an electron nucleus collision (e N > e N ax, ax is an axion, N is modelled as a charged fermion with a form factor) and decided to compare

the results from the electron equivalent-photon approximation (EPA) implementation (a N > ax N with lpp1 = 3 in the run_card) and direct calculation using the full 2->3 matrix element (e N > e N ax).

My expectation is that the EPA should be relatively close to the full calculation when one removes cuts (here the final state electron pT which regulates the collinear divergence), similar to the general results in https:/

My question is -- are there any hidden cuts in the EPA calculation that are not apparent in the run_card or banner.py that might lead to this discrepancy?

Thank you!

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