README.md

Equivalent photon approximation in one- and two-photon exchange processes

This repository contains the relevant code and data files for my Master's thesis on the equivalent photon approximation.

Code files

The main code files are FullME.cc and EPA.cc. These calculate the (approximately) differential cross sections $\mathrm{d}\sigma_{\mu^+\mu^-}/\mathrm{d}W_{\mu^+\mu^-}$ for muon pair production in proton-proton collisions using the full matrix element (Eq. (6.31)) and the equivalent photon approximation (Eq. (6.40)), respectively.

Alongside these main files are a few utility files, which contain code common to both calculations.

The code computes the differential cross section in units $\mathrm{pb}/\mathrm{GeV}$ without dividing by bin width. Division by bin width must be done afterwards.

Dependencies

The integrals are calculated using GSL's VEGAS algorithm, so GSL must be installed. The code has been tested on GSL 2.7.1.

In addition, OpenMP is used for parallelization.

Building

The files FullME.cc and EPA.cc must be built separately, but the same build command should work for both.

On a UNIX system, the following command can be used for building either FullME.cc or EPA.cc:

g++ -std=c++17 -Wall -lgsl -lgslcblas -I/path/to/gsl/include -L/path/to/gsl/lib -fopenmp -lgomp -O3 -ffast-math -DNDEBUG <file>.cc -o <output>

where /path/to/gsl leads to the GSL installation direction. <file>.cc and <output> should be replaced by appropriate names.

On macOS, the flag -Xpreprocessor might be necessary, and the flag -lgomp should be replaced by -lomp.

Removing the flag -DNDEBUG enables assertions.