Measurement of the Production Cross Section of the Photon + Charm Final State in 8-TeV Proton-Proton Collisions using the ATLAS Detector at the LHC

This thesis presents the measurement of the production cross section of high energy isolated prompt photons in association with charm flavour jets in 20.1 fb$^{-1}$ of proton-proton collisions at a center of mass energy of 8 TeV using the ATLAS detector. Isolated prompt photons are well described theoretically and well measured experimentally, providing unique advantages when probing parton level dynamics and the content of the proton. As such, measurements of this type can be used in global parton distribution fits to better constrain the charm quark content of the proton in the Large Hadron Collider (LHC) environment. The differential cross sections are measured with respect to the photon transverse energy, $E^{\gamma}_T$, in two photon pseudorapidity regions: $\lvert \eta^{\gamma} \rvert < 1.37$ and $1.56 < \lvert \eta^{\gamma} \rvert < 2.37$. The measurement spans $25 < E^{\gamma}_T < 300$ GeV and $25 < E^{\gamma}_T < 250$ GeV for the two regions, respectively. The ratio of the measured cross sections in the two regions is also reported. This ratio provides enhanced sensitivity through the cancellation of correlated systematic and theoretical uncertainties. The measurement is compared to next-to-leading order theory predictions using a variety of parton distribution functions. The measurement is consistent with each of the predictions within uncertainties.