Determination of electroweak parameters at HERA with the H1 experiment

Abstract. Using deep inelastic e ± p charged and neutral current scattering cross sections previously published, a combined electroweak and QCD analysis is performed to determine electroweak parameters accounting for their correlation with parton distributions. The data used have been collected by the H1 experiment in 1994-2000 and correspond to an integrated luminosity of 117.2 pb −1. The W boson mass is determined via the propagator and in the on-mass-shell scheme. A first measurement at HERA is made of the light quark weak couplings to the Z 0 boson. THE HERA INCLUSIVE DIS DATA The H1 experiment has collected 117.2 pb −1 of data during the first phase of HERA operation (HERA I) with unpolarised e ± beams. The inclusive deep inelastic scattering (DIS) cross section [1, 2, 3, 4] have been measured in neutral current (NC) and charged current (CC). The precise low x,Q 2 data became the cornerstone of any QCD analysis (the so called QCD fits) aiming at extracting the parton distribution functions (PDFs). The addition of CC data allowed the flavor separation of PDFs and thus a QCD analysis based solely on H1 data has been performed [4], with the advantage of a consistent treatment of correlated systematic errors. A COMBINED ELECTROWEAK-QCD ANALYSIS The combined EW-QCD analysis aims at determining EW and PDFs parameters in the same fit to NC and CC data. This removes a bias due to the fact that PDFs parameters are obtained with assumptions on EW parameters, so the use of fixed PDFs parameters to fit the EW ones is not a consistent procedure. The combined fitting allows to consistently take into account the uncertainty coming from the proton’s structure. THE H1PDF2000 QCD ANALYSIS The basis for the combined EW-QCD analysis is the H1 QCD analysis of HERA I data, the so-called H1PDF2000 [4, 5]. In this analysis five combinations are parameter-ized and fitted, the gluon g, the up-type quarks U = u+c, the down-type quarks D = d+s and the anti-quarks distribution U,D. The parameterization space is explored with a systematic procedure until a χ 2 saturation is reached. The resulting paramterization has a total of 10 free parameters.