[12gevmoller_sim] [JeffersonLab/remoll] c270f9: MG5 doesn't seem to understand fixed target mode, ...

[GitHub]

  Branch: refs/heads/develop
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  Commit: c270f91d6cb030844e9b397b203a714ce9dd09af
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  Author: Wouter Deconinck <wdconinc at gmail.com>
  Date:   2019-01-23 (Wed, 23 Jan 2019)

  Changed paths:
    M generators/MG5/e-e-/template/run_card.dat

  Log Message:
  -----------
  MG5 doesn't seem to understand fixed target mode, so use half target mass

For massless particles 1 and 2, the Mandelstam s is defined as 2 p1 p2.
- For colliders this turns into 4 E1 E2.
- For fixed targets this turns into 2 m E.

Unfortunately MG5 requires that one specifies E1 and E2 and this is always
used to calculate s = 4 E1 E2 using the collider formula.

So, this commit gets MG5 to use the right value of s by telling it that we
are colliding a massless beam of 11 GeV electrons with a massless beam of
255.5 keV electrons. No, it doesn't make sense. It does, however, produce
the correct cross sections and, presumably, pT distributions. Stay tuned.



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