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Parton distributions incorporating QED contributions

A. D. Martin·R. G. Roberts·W. J. Stirling·R. S. Thorne
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Abstract

We perform a global parton analysis of deep inelastic and related hard-scattering data, including ${\cal O}(α_{\rm QED})$ 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 $\sin^2θ_W$ anomaly. A second consequence is the appearance of photon parton distributions $γ(x,Q^2)$ of the proton and the neutron. In principle these can be measured at HERA via the deep inelastic scattering processes $e N \to eγX$; our predictions are in agreement with the present data.

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A. D. Martin, R. G. Roberts, W. J. Stirling, R. S. Thorne. 2004-11-02. Parton distributions incorporating QED contributions. https://doi.org/10.1140/epjc%2Fs2004-02088-7

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