, Volume 39, Issue 2, pp 155-161

Parton distributions incorporating QED contributions

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We perform a global parton analysis of deep inelastic and related hard-scattering data, including \({{\mathcal{O}}}(\alpha_{\rm QED})\) 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.

Received: 3 November 2004, Published online: 11 January 2005
R.S. Thorne: Royal Society University Research Fellow.