Second run: switching things on and off

Updated 1,756 Days AgoPublic

Actions

Simulation of a dijet production event at the LHC for 7 TeV center-of-mass energy, using the ATLAS_2012_I1082936 Rivet plugin for data analysis.

Please download the following input file and move it to your work directory:

Input file:

Alternatively, you can use the following command-line codes:

mkdir LHC-dijet

cd LHC-dijet

wget https://phab-files.hepforge.org/file/data/t3xfju3okq5wi673rn4x/PHID-FILE-ezqalzvdwzekwjnetzgq/LHC-dijet.in

You can run the dijey event, using

Herwig read LHC-dijet.in

You should see an error message appearing on your console

Error: MatchboxFactory: No matrix elements have been found.
      Please check if your order of Alpha_s and Alpha_ew have the right value.

This indicated that the Matchbox does not contain this specific process and you must use either an external matrix element (ME) provider of a Les Houches input file. Let us consider the former option at the moment. We will return to the Les Houches case later on.

There is a section in the input files for choosing the possible external ME providers:

##################################################
## Matrix element library selection
##################################################

## Select a generic tree/loop combination or a
## specialized NLO package

# read Matchbox/MadGraph-GoSam.in
# read Matchbox/MadGraph-MadGraph.in
# read Matchbox/MadGraph-NJet.in
# read Matchbox/MadGraph-OpenLoops.in

Please uncomment the "read Matchbox/MadGraph-OpenLoops.in" option. This would tell the event handler to use MadGraph and OpenLoops for the tree-level and one-loop MEs, respectively. You can see that there are a number of different options to choose from, based on the event that you want to simulate.

Now, you can try running the event again:

Herwig read LHC-dijet.in

You will see a message, informing you that the external ME provider is engaged and will create a parton level amplitude for you:

Initializing external amplitudes.

>>> Compiling MadGraph amplitudes. This may take some time -- please be patient.
>>> In case of problems see ./Herwig-scratch/Build/MadGraphAmplitudes/MG.log for details.

This process may take several minutes to complete, based on the number of channels involved in the event. You can reduce the time by changing the shower selection options:

##################################################
## Matching and shower selection
##################################################

read Matchbox/MCatNLO-DefaultShower.in
# read Matchbox/Powheg-DefaultShower.in
## use for strict LO/NLO comparisons
# read Matchbox/MCatLO-DefaultShower.in
## use for improved LO showering
# read Matchbox/LO-DefaultShower.in

# read Matchbox/MCatNLO-DipoleShower.in
# read Matchbox/Powheg-DipoleShower.in
## use for strict LO/NLO comparisons
# read Matchbox/MCatLO-DipoleShower.in
## use for improved LO showering
# read Matchbox/LO-DipoleShower.in

# read Matchbox/NLO-NoShower.in
# read Matchbox/LO-NoShower.in

The "read Matchbox/MCatNLO-DefaultShower.in" option is chosen by default, activating an MC@NLO matched angular ordered parton shower. By choosing the "read Matchbox/MCatLO-DefaultShower.in" option, you can speed up the process with the price of lowering the accuracy.

After the "read" command is completed, you can run the event by:

Herwig run LHC-dijet.run -N 10000

and plot the results by

rivet-mkhtml LHC-dijet.yoda