Eur. Phys. J. C (2010) 67: 1-24
https://doi.org/10.1140/epjc/s10052-010-1282-x

Regular Article - Experimental Physics

Jet production in ep collisions at low Q ² and determination of α _s

¹ I. Physikalisches Institut der RWTH, Aachen, Germany
² Vinca Institute of Nuclear Sciences, Belgrade, Serbia
³ School of Physics and Astronomy, University of Birmingham, Birmingham, UK
⁴ Inter-University Institute for High Energies ULB-VUB, Brussels, Belgium
⁵ Universiteit Antwerpen, Antwerpen, Belgium
⁶ National Institute for Physics and Nuclear Engineering (NIPNE), Bucharest, Romania
⁷ Rutherford Appleton Laboratory, Chilton, Didcot, UK
⁸ Institute for Nuclear Physics, Cracow, Poland
⁹ Institut für Physik, TU Dortmund, Dortmund, Germany
¹⁰ Joint Institute for Nuclear Research, Dubna, Russia
¹¹ CEA, DSM/Irfu, CE-Saclay, Gif-sur-Yvette, France
¹² DESY, Hamburg, Germany
¹³ Institut für Experimentalphysik, Universität Hamburg, Hamburg, Germany
¹⁴ Max-Planck-Institut für Kernphysik, Heidelberg, Germany
¹⁵ Physikalisches Institut, Universität Heidelberg, Heidelberg, Germany
¹⁶ Kirchhoff-Institut für Physik, Universität Heidelberg, Heidelberg, Germany
¹⁷ Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovak Republic
¹⁸ Department of Physics, University of Lancaster, Lancaster, UK
¹⁹ Department of Physics, University of Liverpool, Liverpool, UK
²⁰ Queen Mary and Westfield College, London, UK
²¹ Physics Department, University of Lund, Lund, Sweden
²² CPPM, CNRS/IN2P3—Univ. Mediterranee, Marseille, France
²³ Departamento de Fisica Aplicada, CINVESTAV, Mérida, Yucatán, Mexico
²⁴ Departamento de Fisica, CINVESTAV, México City, Mexico
²⁵ Institute for Theoretical and Experimental Physics, Moscow, Russia
²⁶ Lebedev Physical Institute, Moscow, Russia
²⁷ Max-Planck-Institut für Physik, München, Germany
²⁸ LAL, Univ. Paris-Sud, CNRS/IN2P3, Orsay, France
²⁹ LLR, Ecole Polytechnique, CNRS/IN2P3, Palaiseau, France
³⁰ LPNHE, Universités Paris VI and VII, CNRS/IN2P3, Paris, France
³¹ Faculty of Science, University of Montenegro, Podgorica, Montenegro
³² Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic
³³ Faculty of Mathematics and Physics, Charles University, Praha, Czech Republic
³⁴ Dipartimento di Fisica, Università di Roma Tre and INFN Roma 3, Roma, Italy
³⁵ Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria
³⁶ Institute of Physics and Technology of the Mongolian Academy of Sciences, Ulaanbaatar, Mongolia
³⁷ Paul Scherrer Institut, Villigen, Switzerland
³⁸ Fachbereich C, Universität Wuppertal, Wuppertal, Germany
³⁹ Yerevan Physics Institute, Yerevan, Armenia
⁴⁰ DESY, Zeuthen, Germany
⁴¹ Institut für Teilchenphysik, ETH, Zürich, Switzerland
⁴² Physik-Institut der Universität Zürich, Zürich, Switzerland

^* e-mail: sschmitt@mail.desy.de

Received: 30 November 2009
Revised: 10 February 2010
Published online: 19 March 2010

Abstract

The production of jets is studied in deep-inelastic e ⁺ p scattering at low negative four momentum transfer squared 5<Q ²<100 GeV² and at inelasticity 0.2<y<0.7 using data recorded by the H1 detector at HERA in the years 1999 and 2000, corresponding to an integrated luminosity of 43.5 pb⁻¹. Inclusive jet, 2-jet and 3-jet cross sections as well as the ratio of 3-jet to 2-jet cross sections are measured as a function of Q ² and jet transverse momentum. The 2-jet cross section is also measured as a function of the proton momentum fraction ξ. The measurements are well described by perturbative quantum chromodynamics at next-to-leading order corrected for hadronisation effects and are subsequently used to extract the strong coupling α _s .