MadGraph5_aMC@NLO

Photon isolation in e+e- collisions at LO

Asked by Richard Ruiz

Hi Photon Experts,

I am trying to understand how photon isolation works at LO in e+e- collisions. Suppose I have the process:
e+ e- > mu+ mu- a

at sqrt(s) = 240 GeV, and I impose Ea > 10 GeV with |eta^a|<3, along with obligatory cuts on the muons. If I set
isoem=true

will photon isolation kick in, resulting in a finite cross section, or do I need to explicitly include dR(mu,a) cuts?

cheers,
richard

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

This parameters behave like @NLO where the default run_card contains more information about it:

#***********************************************************************
# Photon-isolation cuts, according to hep-ph/9801442. When ptgmin=0, *
# all the other parameters are ignored. * *
#***********************************************************************
 %(ptgmin)s = ptgmin ! Min photon transverse momentum
 %(etagamma)s = etagamma ! Max photon abs(pseudo-rap)
  %(r0gamma)s = R0gamma ! Radius of isolation code
  %(xn)s = xn ! n parameter of eq.(3.4) in hep-ph/9801442
  %(epsgamma)s = epsgamma ! epsilon_gamma parameter of eq.(3.4) in hep-ph/9801442
 %(isoem)s = isoEM ! isolate photons from EM energy (photons and leptons)

Note that in particular, if ptgmin is set to zero this parameter is actually never used in the code.

 Cheers,

Olivier

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