Inclusive Jet Production in DIS at High Q2and Extraction of the Strong Coupling

Abstract

Jet production in neutral current (NC) deep-inelastic scattering (DIS) at HERA provides an important testing ground for Quantum Chromodynamics (QCD). The Born contribution in DIS gives only indirect information on the strong coupling αs via scaling violations of the proton structure functions. At leading order (LO) in αs additional processes contribute: QCD-Compton and boson-gluon fusion. In the Breit frame of reference [2], where the virtual boson and the proton collide head on, the Born contribution generates no transverse momenta. Partons with transverse momenta are produced in lowest order by the QCD-Compton and boson-gluon fusion processes. Jet production in the Breit frame therefore provides direct sensitivity to αs and allows for a precision test of QCD. In this workshop contribution new measurements of the inclusive jet cross section are presented, based on data corresponding to twice the integrated luminosity and a higher centre-of-mass energy than in the previous H1 analysis [3]. The larger data set together with improved understanding of the hadronic energy measurement significantly reduces the total uncertainty of the results. The data were collected with the H1 detector at HERA in the years 1999 and 2000. During this period HERA collided positrons of energy Ee = 27.5 GeV with protons of energy Ep = 920 GeV giving a centre-of-mass energy √ s = 319 GeV. The data sample used in this analysis corresponds to an integrated luminosity of 65.4 pb−1. The DIS phase space covered by this analysis is defined by 150 < Q < 15000 GeV , 0.2 < y < 0.7 , where y quantifies the inelasticity of the interaction. These two variables are reconstructed from the four momenta of the scattered positron and the hadronic final state particles using the electron-sigma method [4]. The jet analysis is performed in the Breit frame. The boost from the laboratory system to the Breit frame is determined by Q, y and the azimuthal angle of the scattered positron. Particles of the hadronic final state are clustered into jets using the inclusive kT algorithm [5] with the pT recombination scheme and with distance parameter R = 1 in the η-φ plane. The inclusive kT algorithm is infrared safe and results in small hadronisation corrections [3]. Every jet with 7 < ET < 50 GeV contributes to the inclusive jet cross section, regardless of the jet multiplicity in the event. In addition, the normalised inclusive jet cross section is investigated, calculated as the ratio of the number of jets to the number of selected NC