Event Details

Dr. Kubik will present the differential cross sections for the photons emitted in Z → μ+μ−γ decays as a function of the transverse energy of the photon and its angular separation from the nearest muon. Although the QED processes responsible for the photon emission in these events are well understood, the quark-antiquark initial state gives rise to mixed QCDxQED corrections which are challenging to calculate. We therefore also extend the analysis to isolate regions of phase space where these corrections are most important. Results are compared to the predictions of the (NLO in QCD) POWHEG program using PYTHIA to simulate parton showers and final state photons. These measurements also support current and future precision Electroweak and Higgs measurements at CMS, such as the W mass measurement and H → Zγ search. Dr. Kubik will also present an ongoing analysis to probe the photon contribution to the proton parton distribution functions (PDFs) using high invariant mass dilepton pairs. The photon contribution to the proton PDFs is in most cases absent in PDF sets commonly used for LHC physics, and at this time is unmeasured and largely unconstrained at LHC beam energies. Constraining this PDF will be crucial for future precision measurements at the LHC.