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Exclusive production (via proton or pomeron)

Madgraph

Madgraph is able to simulate both exclusive and inclusive γγ→XX processes (where either proton remain intact or dissociate). Here is an recommended settings for simulating MG exclusive events:

#common settings
set automatic_html_opening False

#set scale (new from 2.7.1)
set fixed_fac_scale True
set dsqrt_q2fact1 2
set dsqrt_q2fact2 2

# use elastic photons (will use EPA instead of PDF)
set lpp1 2  # proton 
set lpp2 2  # proton 

#if using inelastic photons, set up the PDF to LUXqed17_plus_PDF4LHC15_nnlo_100
#set lhaid 82200

Calculation of processes that include box diagrams at QED are available loop_qcd_qed_sm-full model, for example CEP of H₅₀₀→tt can be calculated using:

import model loop_qcd_qed_sm-full
generate a a > h > t t~ [noborn=QED]
output cep_ttbar
launch cep_ttbar
set param_card mass 25 500.0
set param_card decay 25 68.0

Producing gridpack

Here is the short list of instructions on how to generate gridpacks with CMSSW. See QuickGuideMadGraph5aMCatNLO for more details about production with Madgraph.

Setup the code:

git clone https://github.com/cms-sw/genproductions.git
cd genproductions/bin/MadGraph5_aMCatNLO/
./gridpack_generation.sh  
# e.g. ./gridpack_generation.sh wplustest_4f_LO cards/examples/wplustest_4f_LO 

Madgraph generates collinear photons, and the protons are not stored in the LHE event info. The workaround is to add proton manually (using FixLHE.py code) which will be later used by proton direct simulation, which is done .

The following steps are used to generate GEN event files:

Read LHE content

The LHE files can be explored via the LHEEventProduct objects:

Events->SetAlias("LHE","LHEEventProduct_source__LHEFile.obj")
Events->Scan("LHE.hepeup().IDUP : LHE.hepeup().ISTUP");

-- MichaelPitt - 2020-04-09