Single photon inclusive in mg5amc@nlo

Asked by Richard Ruiz on 2020-08-20

Hi Folks,

I am interested in computing single photon inclusive at NLO in QCD and would appreciate guidance on the setup.

I have in mind the syntax,
generate p p > a j QED=1 QCD =1 [QCD]

At Born- and loop-level, the process is finite and well-defined independent of jet criterion so long as sensible photon cuts are applied, e.g.,
ptgmin = 100
etagamma = 2.4
R0gamma = 0.4

The tree-level process p p > a j j, is what stumps me. Arguable, if one j becomes soft/collinear to j, then the (jj) system is clustered together and everything is hunky dory since IR poles are canceled by counter / loop terms and the Born-like configuration is recovered.

What happens though if one j becomes soft/collinear to a? Technically this is a QED correction to dijet production, but then do I really need to worry about this if I have a sufficiently large set of jet and photon radius parameters? At the moment I am only worried about total normalizations, so I do not mind working with the EW@NLO branch if needed.

Thanks for looking into this!

best,
richard

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
Rikkert Frederix Edit question
Solved by:
Richard Ruiz
Solved:
2020-08-20
Last query:
2020-08-20
Last reply:
2020-08-20
Rikkert Frederix (frederix) said : #1

dear Richard,

The default photon cuts at NLO are the smooth isolation cuts, as described in hep-ph/9801442 (see also the run_card, with the additional parameters that determine the smooth isolation). They should take care of your worries.

Best,
Rikkert

Richard Ruiz (rruiz) said : #2

Hi Rikkert,

Thanks for the fast answer and confirmation that the default run_card settings will do the job. Just to clarify, I can remove the jet pT and eta cuts and still get a sensible answer, correct?

best,
richard

Rikkert Frederix (frederix) said : #3

Correct.

Richard Ruiz (rruiz) said : #4

excellent!