Pythia mCP Simulation

This is a Pythia simulation of the hadronic contribution to mCP estimated by modifying the muon mass in Pythia to stand in for mCP and adjusting the hadron branching ratios to muons. The new branching ratio is estimated by fitting a quadratic to the branching ratios of e, mu, and a zero branching ratio when the mCP mass reaches half the decaying hadron mass. Further, the pi0 branching ratio to e+e- is modified with a linear approximation and the e from pi0 are also chosen to stand in for mCP. The simulation is of pp collisions at 13 TeV. The main program, py_sim, outputs a root file containing a TTree of mCP pairs from hadron decay along with their pT, pseudorapidity, and other misc vars. The TTree weight is scaled by the cross section (in mb) and total event weight. Each event has a weight stored in the weight variable.

Configuration

To configure the simulation pass commandline arguments as follows or edit the py_sim.cc file defaults before compilation. User-configurable options are at the start of main.

The following commandline flags are available at runtime.
-n NUM_EVENTS: Number of events to generate. (default: 100)
-m MASS: mCP mass in GeV. (default: 0.05)
-p PT_CUT: Jet pT cut (pTHat) in GeV. (default: 0)
-f FILENAME: Output ROOT file name. (default: "out.root")
-v: Be verbose and output found mCP information

For example, to manually configure with the default options run the program after compilation with ./py_sim -n 100 -m 0.05 -p 0 -f out.root.

Compilation and Running

1. If running on CernVM or lxplus skip to step 2. Otherwise, download and compile Pythia 8. If you have appropriate dependencies, this should be as simple as running make in the extracted directory.
2. Clone the git repository to a local working directory and modify the Makefile so that PREFIX_LIB and PREFIX_INCLUDE point to the /lib and /include directories of your compiled Pythia 8 installation. Modify environ.sh so that PYTHIA8DATA points to the /share/Pythia8/xmldoc folder in your compiled Pythia 8 installation. Note there is included commented out code to point these variables to compiled cvmfs versions that work for CernVM and lxplus. To compile on lxplus or an slc6 based version of CernVM you will also need to set an appropriate gcc version by running source /cvmfs/sft.cern.ch/lcg/external/gcc/4.8.4/x86_64-slc6-gcc48-opt/setup.sh
3. Ensure that ROOT is installed and the root-config utility is available in the commandline. If not, this can be ensured by sourcing thisroot.sh in your ROOT installation's bin directory.
4. Compile py_sim by running make all in the project directory.
5. Run source environ.sh to set up the xmldoc directory so you can run the compiled binary. The compiled binary should now run as expected with ./py_sim.

Analysis of Data

A ROOT macro, ptcut.cc, is included to help calculate the number of mCP that pass a pT cut and would be seen by milliQan. To use the macro, run root -b -q -l 'ptcut.cc(0.0,{"out.root"})' with the first argument being the desired mCP pT cut in GeV and the second argument being a comma separated list of the py_sim root output files you want to run on. The macro will combine all the listed files for calculation. The calculation for mCP seen is done assuming mCP charge of 1e-3 and 300 fb^-1 of data. This can be easily changed by modifying the macro.