Measurement of inclusive jet production in deep-inelastic scattering at high and determination of the strong coupling☆
Introduction
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 (Fig. 1a) gives only indirect information on the strong coupling via scaling violations of the proton structure functions. At leading order (LO) in additional processes contribute: QCD-Compton (Fig. 1b) and boson–gluon fusion (Fig. 1c). In the Breit frame of Refs. [1], [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 and allows for a precision test of QCD.
Analyses of inclusive jet production in DIS at high four momentum transfer squared were previously performed by the H1 [2] and ZEUS [3], [4] Collaborations at HERA. Perturbative QCD (pQCD) calculations supplemented with hadronisation corrections were found to describe the data. The strong coupling and the gluon density in the proton were both extracted.
In this Letter 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 [2]. The larger data set together with improved understanding of the hadronic energy measurement significantly reduces the total uncertainty of the results. Differential inclusive jet cross sections are measured as functions of the hard scales and the transverse jet energy in the Breit frame in the ranges and . In addition, the ratio of the jet cross section to the inclusive NC DIS cross section, in the following referred to as the normalised inclusive jet cross section, is determined. This observable benefits from a partial cancellation of experimental and theoretical uncertainties. The measurements are compared with pQCD predictions at next-to-leading order (NLO), and the strong coupling is determined from a fit of the predictions to the data.
Section snippets
Experimental method
The data were collected with the H1 detector at HERA in the years 1999 and 2000. During this period HERA collided positrons of energy with protons of energy giving a centre-of-mass energy . The data sample used in this analysis corresponds to an integrated luminosity of .
NLO QCD calculation
Reliable quantitative predictions of jet cross sections in DIS require the perturbative calculations to be performed to at least next-to-leading order of the strong coupling. In order to compare with data, hadronisation corrections have to be applied to the perturbative calculations. By using the inclusive jet algorithm [11] the observables in the present analysis are infrared and collinear safe and the hadronisation corrections are small. In addition, by applying this algorithm in the Breit
Results
In the following, the differential cross sections are presented for inclusive jet production and for normalised inclusive jet production. Table 1, Table 2 list the measured cross sections together with their experimental uncertainties, separated into bin-to-bin correlated and uncorrelated parts. These measurements are subsequently used to extract the strong coupling .
Conclusion
Measurements of inclusive jet cross sections in the Breit frame in deep-inelastic positron–proton scattering in the range are presented, together with the normalised inclusive jet cross sections, defined as the ratio of the inclusive jet cross section to the NC DIS cross section within the given phase space. Calculations at NLO QCD, corrected for hadronisation effects, provide a good description of the single and double differential cross sections as functions of the jet
Acknowledgements
We are grateful to the HERA machine group whose outstanding efforts have made this experiment possible. We thank the engineers and technicians for their work in constructing and maintaining the H1 detector, our funding agencies for financial support, the DESY technical staff for continual assistance and the DESY directorate for support and for the hospitality which they extend to the non-DESY members of the collaboration.
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This project is co-funded by the European Social Fund (75%) and National Resources (25%)—(EPEAEK II)–PYTHAGORAS II.
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Supported by the Bundesministerium für Bildung und Forschung, FRG, under contract numbers 05 H1 1GUA/1, 05 H1 1PAA/1, 05 H1 1PAB/9, 05 H1 1PEA/6, 05 H1 1VHA/7 and 05 H1 1VHB/5.
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Supported by the UK Particle Physics and Astronomy Research Council, and formerly by the UK Science and Engineering Research Council.
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Supported by FNRS-FWO-Vlaanderen, IISN-IIKW and IWT and by Interuniversity Attraction Poles Programme, Belgian Science Policy.
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Partially Supported by Polish Ministry of Science and Higher Education, grant PBS/DESY/70/2006.
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Supported by VEGA SR grant No. 2/7062/27.
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Supported by the Swedish Natural Science Research Council.
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Supported by CONACYT, México, grant 400073-F.
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Supported by the Deutsche Forschungsgemeinschaft.
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Supported by the Ministry of Education of the Czech Republic under the projects LC527 and INGO-1P05LA259.
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Supported by the Swiss National Science Foundation.
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Supported by a scholarship of the World Laboratory Björn Wiik Research Project.