Backgroud subtraction

Introduction

The subtraction of thermal momentum components required when including recoil effects takes place in the analysis of the events. There are several options for doing this.

Constituent subtraction

For a detailed documentation of the procedure please refer to the paper (to be on the arxiv soon). For Rivet users, constituent subtraction (at event level) of JEWEL events is available as a Projection. The good news is that this is very convenient to use and saves a lot of run time when running several analyses in parallel, the bad news is that it has to be compiled into Rivet by hand.

(Examples and code for other ways of doing the subtraction will be made available here when they are ready.)

Installation of the Projection inside Rivet

If you want to go down that road, this is what you need to do:

• download the Projection code and unpack it
• copy the *.cc files into the .../Rivet-x.y.z/src/Projections/ directory of your local Rivet directory, the *.hh go into .../Rivet-x.y.z/include/Rivet/Projections/
• include the new .cc files in Makefile.am in .../Rivet-x.y.z/src/Projections/
• copile

Using the Projection in a Rivet analysis

The Projection can be used like any other Rivet Projection. Here is an example for how it could look like:

• include the header file: #include "Rivet/Projections/SubtractedJewelEvent.hh" #include "Rivet/Projections/SubtractedJewelFinalState.hh"
• declare the Projection, e.g. SubtractedJewelEvent sev(1.0); SubtractedJewelFinalState sfs(sev, Cuts::pt > 0.); declare(sfs, "SFS"); SubtractedJewelFinalState is derived from FinalState and so you can act on it with other FinalState classes, e.g. by projecting out the charged particles: ChargedFinalState csfs(sfs);
• apply the Projection, e.g. const Particles parts = apply(event, "SFS").particles();

Four-momentum and Grid subtraction

For a detailed documentation of the procedure please refer to the paper. An example Rivet analysis can be found here.

How to run the analysis

• Download and install Rivet (make sure you have a Rivet 2.x.y release). Set up the environment: source /path/to/your/rivet/local/rivetenv.sh
• First the analysis has to be compiled as a pugin to Rivet. rivet-buildplugin Rivet_JEWEL_BKGSUBTRACTION.so JEWEL_BKGSUBTRACTION.cc
• Run JEWEL and store the hepmc events in a file, say test.hepmc. Then run the Rivet analysis: rivet --pwd -a JEWEL_BKGSUBTRACTION -H out.yoda test.hepmc The .yoda file contains the histograms in YODA format.
• The analysis fills four histograms with the jet pT-spectrum, once un-subtracted and one for each subtraction method. To plot the histograms: rivet-mkhtml --mc-errs out.yoda This creates a directory plots containing a html page with the plots, which you can view by pointing your favourite browser at plots/index.html

For further information on writing Rivet analyses, formating your plots etc. please refer to the Rivet documentation. If you experience problems with this particular analysis, please contact Raghav Kunnawalkam Elayavalli (raghav.k.e@NOSPAMcern.ch).