Photon-initiated processes at high mass

We present phenomenological results for vector boson pair production at the LHC, obtained using the parton-level next-to-leading order program MCFM. We include the implementation of a new process in the code, pp -> \gamma\gamma, and important updates to existing processes. We incorporate fragmentation contributions in order to allow for the experimental isolation of photons in \gamma\gamma, W\gamma, and Z\gamma production and also account for gluon-gluon initial state contributions for all relevant processes. We present results for a variety of phenomenological scenarios, at the current operating energy of \sqrt{s} = 7 TeV and for the ultimate machine goal, \sqrt{s} = 14 TeV. We investigate the impact of our predictions on several important distributions that enter into searches for new physics at the LHC.

We perform a global parton analysis of deep inelastic and related hard-scattering data, including \({\cal O}(\alpha_{\rm QED})\) corrections to the parton evolution. Although the quality of the fit is essentially unchanged, there are two important physical consequences. First, the different DGLAP evolution of u and d type quarks introduces isospin violation, i.e. \(u^p \neq d^n\), which is found to be unambiguously in the direction to reduce the NuTeV \(\sin^2\theta_W\) anomaly. A second consequence is the appearance of photon parton distributions \(\gamma(x,Q^2)\) of the proton and the neutron. In principle these can be measured at HERA via the deep inelastic scattering processes \(e N \to e\gamma X\); our predictions are in agreement with the present data.