Structure Functions at Very High Q From HERA

Measurements of Deep-Inelastic Neutral and Charged current interactions are presented in lepton proton scattering at HERA. The measurements are obtained from taken during 1996 to 1999 and consists of 30 pb of ep and 16 pb of ep data. The addition of the new high statistics electron data with the positron data allows the first extraction of the parity violating structure function xF3 and tests of high-Q electroweak effects of the heavy bosons Z and W are observed and found to be consistent with the Standard Model expectation. INTRODUCTION Deep–Inelastic scattering (DIS) of leptons off nucleons has played a fundamental role in understanding the structure of matter. HERA the first electron-proton (ep) collider ever built is capable of investigating the two main contributions to DIS, Neutral Current (NC) interactions, ep → eX and Charged Current (CC) interactions, ep → νX. In the Standard Model a photon (γ) or a Z boson is exchanged in a NC interaction, and a W boson is exchanged in a CC interaction. DIS can be described by the four-momentum transfer squared Q, Bjorken-x and inelasticity y defined as: Q = −q ≡ (k − k) (1) x = Q 2p · q (2) y = p · q p · k (3) with k(k) and p being the four-momentum of the incident (scattered) lepton and proton respectively. The centre-of-mass energy √ s of the ep interaction is given by s ≡ (p+ k) = Q/xy. In this paper measurements are presented of the NC and CC cross-sections at high Q > 200GeV for both electron and positron scattering from both the H1 and ZEUS experiments. The integrated luminosity in the ep data sample is 35.6 pb (30 pb) and in the ep data sample is 16 pb (16 pb) for the H1 (ZEUS) collaborations. I EXPERIMENTAL SETUP The H1 and ZEUS detectors are described elsewhere [1], [2]. Both detectors are nearly hermetic multi-purpose apparatus built to investigate ep interactions. The measurements in both experiments rely primarily on the calorimetry, tracking and the luminosity detectors. In both experiments the Charged Current event selection is based on the observation of large P T , which is assumed to be the transverse momentum carried by the outgoing neutrino. For NC events it is based on the identification of a scattered electron (positron), further fiducial (NC) and kinematic cuts (CC and NC) are then applied. Details of the selection procedure can be found in [2,3]. II CROSS SECTIONS The electroweak Born-level NC DIS cross section dσ/dxdQ for the reaction ep → eX can be written as: dσ ±p Born dxdQ = 2πα xQ [ Y+F2(x,Q )∓ Y−xF3(x,Q2)− y2FL(x,Q2) ]