---
author:
- ZEUS Collaboration
date: March 2016
title: |
     Combined QCD and electroweak analysis\
    of HERA data\
---

Introduction {#sec-int}
============

Data on deep inelastic scattering (DIS) of leptons from nucleons have been used for many years in many ways to test the Standard Model (SM) of the electroweak and strong interactions [@MANDY] and have been fundamental in unravelling the structure of nucleons. The electron–proton, $ep$, collider HERA extended the reach in the four-momentum-transfer squared, $Q^2$, and in Bjorken $x$ by several orders of magnitude with respect to previous fixed-target experiments [@rmp:71:1275]. At HERA, the values of $Q^2$ extend up to $50\,000\,{{\,\text{Ge}{\kern-0.06667em}\text{V\/}}}^2$, where the $Z$-exchange contribution is comparable to that of the photon exchange. This, together with the longitudinal polarisation of the electrons[^1] in the beam, have made a significant test of the couplings of the $Z$ to the quarks possible. The on-shell value of the electroweak mixing angle, $\sin^2\theta_W$, and of the mass of the $W$ boson, $M_W$, were also determined via a combined QCD and electroweak analysis.

The HERA collider was operated in two phases, HERAI: 1992–2000 and HERAII: 2003–2007. During the HERAII phase, the electron beams were longitudinally polarised to a level between 25% and 35%. 