Theory seminar: Samuel Favrod




"QCD Anatomy of Photon Isolation"

In order to differentiate photons produced from different origins at hadron colliders, it is necessary to impose some isolation requirements. For cones with small radius $R$ , photon isolation effects can be captured by a fragmentation function describing the fragmentation of a parton into a photon accompanied by soft radiation. We computed these fragmentation functions for fixed energy cones and Frixione cones to gain a better understanding of the effects of the isolation parameters on the cross section of $pp \to \gamma+X$. The fragmentation function prediction is compared to the NLO predictions. Finally, we resum the leading logarithms of $R$ and of $\epsilon_{\gamma}$, the ratio of energy inside the cone to the photon energy, and compared it to the measurement performed at ATLAS.