# EPA dependence on epa_mass

I am trying to use the equivalent photon calculation for a cross-section photon photon > b bbar

What is the minimal sindarin to compute the total cross-section of this process?

process proc = "A", "A" => "b","bbar"

beams = "e-", "e+" => epa, epa

epa_x_min = 1e-10 !mandatory

epa_mass = 0.105 GeV ! 511 keV !mandatory

!epa_q_min = 0.105 GeV ! suggested in "minimal viable scenario" of the Manual

Changing epa_mass in this setting gives very little variation compared to the expectation. e.g. at 3 TeV e+e- I get 9 pb for epa_mass 511 keV and 3 pb for epa_mass 0.105 GeV. As ln(200)~5 the two cross-section cannot be just a factor 3 different, unless I am badly misunderstanding the dependence of this cross-section on the emitter mass.

Thanks for the clarification.

Roberto

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- Wolfgang Kilian Edit question

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