Measurement of the Neutral Current Cross Section and Search for Contact Interactions with the H1 Experiment at HERA

Abstract

A measurement of the inclusive neutral current cross section for deep inelastic positron-proton scattering and a subsequent search for electron-quark contact interactions are presented. The analysis is based on data taken in 1999 and 2000 at a centre-of-mass energy of sqrt(s)=319 GeV with the H1 experiment at HERA. Substantial systematic improvements are achieved for the reconstruction of neutral current events at large four-momentum transfer Q^2. The precise measurement of the scattered electron using solely calorimetric information is established. The single and double differential cross sections dsigma/dQ^2 and d^2sigma/dxdQ^2 are measured in the range of 200<=Q^2<=30000 GeV^2 and 0.0032<=x_Bjorken<=0.65. The results are in good agreement with the Standard Model QCD prediction. The compatibility of the cross section measurement with the Standard Model and extensions beyond is quantified using a novel chi^2 fit, which strongly reduces the dependence on the shape of the proton parton densities. No significant indications of new physics are found. The analysis yields an upper bound on the quark radius of r_quark<1.1*10^(-18) m (CL=95%) and lower limits on electron-quark compositeness scales ranging from 1.5 to 4.8 TeV. The results are comparable to those of other analyses performed at HERA, LEP or TeVatron.