Eur. Phys. J. C (2012) 72: 1921
https://doi.org/10.1140/epjc/s10052-012-1921-5

Regular Article - Experimental Physics

Measurement of the virtual-photon asymmetry A ₂ and the spin-structure function g ₂ of the proton

¹ Physics Division, Argonne National Laboratory, Argonne, IL, 60439-4843, USA
² Sezione di Bari, Istituto Nazionale di Fisica Nucleare, 70124, Bari, Italy
³ School of Physics, Peking University, Beijing, 100871, China
⁴ Nuclear Physics Laboratory, University of Colorado, Boulder, CO, 80309-0390, USA
⁵ DESY, 22603, Hamburg, Germany
⁶ DESY, 15738, Zeuthen, Germany
⁷ Joint Institute for Nuclear Research, 141980, Dubna, Russia
⁸ Physikalisches Institut, Universität Erlangen-Nürnberg, 91058, Erlangen, Germany
⁹ Sezione di Ferrara, Istituto Nazionale di Fisica Nucleare, 44100, Ferrara, Italy
¹⁰ Dipartimento di Fisica, Università di Ferrara, 44100, Ferrara, Italy
¹¹ Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, 00044, Frascati, Italy
¹² Department of Physics and Astronomy, Ghent University, 9000, Gent, Belgium
¹³ Physikalisches Institut, Universität Gießen, 35392, Gießen, Germany
¹⁴ SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
¹⁵ Department of Physics, University of Illinois, Urbana, IL, 61801-3080, USA
¹⁶ Randall Laboratory of Physics, University of Michigan, Ann Arbor, MI, 48109-1040, USA
¹⁷ Lebedev Physical Institute, 117924, Moscow, Russia
¹⁸ National Institute for Subatomic Physics (Nikhef), 1009 DB, Amsterdam, The Netherlands
¹⁹ Petersburg Nuclear Physics Institute, Gatchina, 188300, Leningrad Region, Russia
²⁰ Institute for High Energy Physics, Protvino, 142281, Moscow Region, Russia
²¹ Institut für Theoretische Physik, Universität Regensburg, 93040, Regensburg, Germany
²² Sezione di Roma, Gruppo Collegato Sanità and Istituto Superiore di Sanità, Istituto Nazionale di Fisica Nucleare, 00161, Roma, Italy
²³ TRIUMF, Vancouver, British Columbia, V6T 2A3, Canada
²⁴ Department of Physics, Tokyo Institute of Technology, Tokyo, 152, Japan
²⁵ Department of Physics and Astronomy, VU University, 1081 HV, Amsterdam, The Netherlands
²⁶ National Centre for Nuclear Research, 00-689, Warsaw, Poland
²⁷ Yerevan Physics Institute, 375036, Yerevan, Armenia

^* e-mail: gunar.schnell@desy.de

Received: 23 December 2011
Revised: 17 February 2012
Published online: 13 March 2012

Abstract

A measurement of the virtual-photon asymmetry A ₂(x,Q ²) and of the spin-structure function g ₂(x,Q ²) of the proton are presented for the kinematic range 0.004<x<0.9 and 0.18 GeV²<Q ²<20 GeV². The data were collected by the HERMES experiment at the HERA storage ring at DESY while studying inclusive deep-inelastic scattering of 27.6 GeV longitudinally polarized leptons off a transversely polarized hydrogen gas target. The results are consistent with previous experimental data from CERN and SLAC. For the x-range covered, the measured integral of g ₂(x) converges to the null result of the Burkhardt–Cottingham sum rule. The x ² moment of the twist-3 contribution to g ₂(x) is found to be compatible with zero.