Medida de la sección eficaz de producción de fotones directos aislados en colisiones pp a $\sqrt{s}=7$ TeV en el experimento ATLAS

The production of prompt photons at hadron colliders provides means for testing perturbative QCD predictions, providing a colorless probe of the hard scattering process. The measurement of the inclusive production of prompt photons could be used to constrain the parton distribution functions; in particular it is sensitive to the gluon content of the proton through the $qg\to q\gamma$ subprocess, which at leading order dominates the inclusive prompt photon cross-section at the LHC. This thesis presents the measurement of the differential cross-section for the inclusive production of isolated prompt photons in $pp$ collisions at a center-of-mass energy $\sqrt{s} = 7~{\rm TeV}$. The measurement covers the pseudorapidity ranges $|\eta|<1.37$ and $1.52\leq|\eta|<2.37$ in the transverse energy range $45\leq E_T <400~{\rm GeV}$. The results are based on an integrated luminosity of 35 ${\rm pb}^{-1}$, collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.