This is the simulation of a `P + P -> Z + jet` production event at the LHC for 7 TeV center-of-mass energy, using the [[ https://rivet.hepforge.org/analyses/ATLAS_2011_I945498.html | ATLAS_2011_I945498 ]] and [[ https://rivet.hepforge.org/analyses/MC_ZINC.html | MC_ZINC ]] Rivet plugins for data analysis. Please download the following input file and move it to your work directory: Input file: {F543471} Alternatively, you can use the following command-line codes: ``` mkdir LHC-Z+jet cd LHC-Z+jet wget https://phab-files.hepforge.org/file/data/n36vm5xhxosaddw7xe4x/PHID-FILE-etk5vfa3ii64fngxon2w/LHC-Z_jet.in ``` Before running this event, let us take a look at the input file ``` less LHC-Z+jet.in ``` As you can see, the process selection section has been completely deactivated. This is because for a process like `P + P -> Z + jet`, Herwig needs to use the external matrix element (ME) providers. However, the use of these tools in the docker/VM would be problematic. In an installed version of the Herwig, one can easily use these external ME providers by selecting the hard-process in the `Process selection` and choosing the ME providers from `Matrix element library selection`. ``` ################################################## ## Process selection ################################################## ## Model assumptions # read Matchbox/StandardModelLike.in # read Matchbox/DiagonalCKM.in ## Set the order of the couplings # cd /Herwig/MatrixElements/Matchbox # set Factory:OrderInAlphaS 1 # set Factory:OrderInAlphaEW 1 ## Select the process # do Factory:Process p p -> Z0 j ################################################## ## 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 ``` Fortunately, Herwig comes equipped with a set of Pre-calculated ME (you can see the complete list of these at Herwig_directory/share/Herwig/LHC.in): ``` ################################################## # Pre-calculated ME for hadron-hadron collisions ################################################## cd /Herwig/MatrixElements/ # Z+jet insert SubProcess:MatrixElements[0] MEZJet ``` Now, we can run the Z+jet event using ``` Herwig read LHC-Z+jet.in Herwig run LHC-Z+jet.run -N 10000 ``` and plot the results by ``` rivet-mkhtml LHC-Z+jet.yoda ``` Please change the name of the produced yoda files ``` mv LHC-Z+jet.yoda Z+jet_MCNLO.yoda ``` and take a look at the parton shower selection section ``` ################################################## ## 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. Please choose the "read Matchbox/MCatLO-DefaultShower.in" option, to choose the MC@LO and try running the event again: ``` Herwig read LHC-Z+jet.in Herwig run LHC-Z+jet.run -N 10000 mv LHC-Z+jet.yoda Z+jet_MCLO.yoda ``` Repete this process again, this time with "read Matchbox/LO-NoShower.in" option and rename the yoda file as ``` mv LHC-Z+jet.yoda Z+jet_NOPS.yoda ``` At this point, you are in the position of 3 separate Z+jet production events, each with different parton shower settings. You can compare your findings by plotting these yoda files altogether: ``` rivet-mkhtml Z+jet_MCNLO.yoda:MC_NLO Z+jet_MCLO.yoda:MC_LO Z+jet_NOPS.yoda:NO_PS ``` and check out your result by ``` firefox rivet-plots/index.html ``` Switching things on and off ------------------------------- At this point, we are going to modify our copy of the LHC-dijet.in input file and make a few more runs. 1. [[ https://herwig.hepforge.org/tutorials/gettingstarted/onoffthings.html | Shower handlers ]] These commands control the major modules of the event generator. You can switch them on and off, rerun the event and observe the produced effects of the results. ``` ################################################## ## ShowerHandler(s) ################################################## cd /Herwig/EventHandlers # set EventHandler:CascadeHandler:MPIHandler NULL # set EventHandler:DecayHandler NULL # set EventHandler:HadronizationHandler NULL # set EventHandler:CascadeHandler NULL ``` 2. [[ https://herwig.hepforge.org/tutorials/hardprocess/matchbox.html#scale-choices | Scale choices ]] Your choice for the scale of the hard-process is made in this section. The primary option for a dijet production event, "set Factory:ScaleChoice Scales/HTScale", is pre-selected here. You can choose other options and see the effect. ``` cd /Herwig/MatrixElements/Matchbox/ # set Factory:ScaleChoice Scales/FixedScale # set Scales/FixedScale:FixedScale 91.1876*GeV set Factory:ScaleChoice Scales/HTScale # set Factory:ScaleChoice Scales/HTPrimeScale # set Factory:ScaleChoice Scales/LeptonPairMassScale # set Factory:ScaleChoice Scales/LeptonPairPtScale # set Factory:ScaleChoice Scales/MaxJetPtScale # set Factory:ScaleChoice Scales/SHatScale # set Factory:ScaleChoice Scales/TopPairMassScale # set Factory:ScaleChoice Scales/TopMTScale ``` 3. [[ https://herwig.hepforge.org/tutorials/hardprocess/matchbox.html#cuts | Cuts ]] You can impose any constraint that you want on your event. To find out the compete list of cuts and how to use them, see Herwig documentaion on [[ https://herwig.hepforge.org/tutorials/hardprocess/matchbox.html#cuts | cuts ]]. ``` ################################################## ## Cut selection ## See the documentation for more options ################################################## cd /Herwig/Cuts/ ## cuts on jets read Matchbox/DefaultPPJets.in insert JetCuts:JetRegions 0 FirstJet insert JetCuts:JetRegions 1 SecondJet # set /Herwig/Cuts/JetFinder:Variant Kt # set /Herwig/Cuts/JetFinder:ConeRadius 0.4 # set /Herwig/Cuts/FirstJet:PtMin 20.*GeV # do /Herwig/Cuts/FirstJet:YRange -5.0 5.0 ```