Gluon Gluon Fusion cross-section for Higgs Production with 'heft' model

Hi,

I am also trying these things with 'loop_sm' model in MG5.

There it is showing the following error for g g > h [QCD] process:

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MG5_aMC>import model loop_sm --modelname
INFO: Restrict model loop_sm with file models/loop_sm/restrict_default.dat .
INFO: Run "set stdout_level DEBUG" before import for more information.
Kept definitions of multiparticles p / j / l+ / l- / vl / vl~ unchanged
Defined multiparticle all = g gh gh~ d u s c d~ u~ s~ c~ a ve vm vt e- m- ve~ vm~ vt~ e+ m+ b t b~ t~ z w+ h w- tt- tt+
MG5_aMC>generate g g > h [QCD]
INFO: Checking for minimal orders which gives processes.
INFO: Please specify coupling orders to bypass this step.
INFO: Trying coupling order WEIGHTED<=2: WEIGTHED IS QCD+2*QED
INFO: Trying coupling order WEIGHTED<=3: WEIGTHED IS QCD+2*QED
Error detected in "generate g g > h [QCD]"
write debug file MG5_debug
If you need help with this issue please contact us at https://answers.launchpad.net/mg5amcnlo
str :
 Automatic process-order determination lead to negative constraints:
 QED: 3, QCD: -2
 Please specify the coupling orders from the command line.

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Consulted the slides found here : https://indico.cern.ch/event/555228/sessions/203428/attachments/1315471/1970459/tutorial-CMSandATLAS-2016.pdf

It says that the process g g > h [QCD] should work and also giving the cross-section at the ballpark of 15-17 pb.

Hi,

Since 3.0.0 for loop-induced you need to specify a coupling order to have it working
generate g g > h qed<=1 [QCD]
works

Now in the loop-sm model, you have massive b and therefore you will include the (negative b-t) interference
and your cross-section will be slightly smaller than if you do not include that contribution (like using loop_sm-no_b_mass)
The prediction for loop_sm-no_b_mass should match the one of the heft model

This process has been used to validate the implementation of the loop-induced processes within mG5aMC, so you will have all the details in the loop-induced paper: 1507.00020

Cheers,

Olivier

PS: The Higgs production is know to have very (very) large K-factor (even larger than naive scale variation) both from LO to NLO and also from NLO to NNLO. Therefore since all the computation done at loop-induced level (or at tree level within heft) under-estimate the total cross-section by large number. Consequently, such type of simulation should not be used for the normalization but rather for the shape of the distribution where error / impact of higher order are milder.

Thanks for the detailed explanation and for the reference 1507.00020.

But when I am trying to use:

g g > h qed<=1 [QCD]

it gives the following error:

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MG5_aMC>generate g g > h QED<=1 [QCD]
Command "generate g g > h QED<=1 [QCD]" interrupted with error:
Exception : Potentially ambigious syntax detected. Note that the syntax of paper 1804.10017 (used in 3.0.x) is not used anymore (since version 3.1.0).
 If you want to follow the syntax of that paper, you can just replace "QED" by "aEW" and "QCD" by "aS".
 More information here: http://amcatnlo.cern.ch/co.htm
 If you know the current meaning of the syntax you can bypass this crash by running (once per machine) this command:
  set acknowledged_v3.1_syntax True --global
Please report this bug on https://bugs.launchpad.net/mg5amcnlo
More information is found in 'MG5_debug'.
Please attach this file to your report.
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tried with 'QED', 'aEW', 'aS', but didn't work.

Can you please suggest which model to import to do such!

Sincerely,
Samadrita

you can either run
set acknowledged_v3.1_syntax True --global
(you need to run that command only once)
and then reuse the above command

or move to
generate g g > h QED<=1 [noborn=QCD]

Cheers,

Olivier

Thanks a lot. It worked.