Eur. Phys. J. C (2015) 75: 600
https://doi.org/10.1140/epjc/s10052-015-3825-7

Regular Article - Experimental Physics

Transverse-target-spin asymmetry in exclusive -meson electroproduction

The HERMES Collaboration

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 Department of Theoretical Physics, University of the Basque Country UPV/EHU, 48080, Bilbao, Spain
⁵ IKERBASQUE, Basque Foundation for Science, 48013, Bilbao, Spain
⁶ Nuclear Physics Laboratory, University of Colorado, Boulder, CO, 80309-0390, USA
⁷ DESY, 22603, Hamburg, Germany
⁸ DESY, 15738, Zeuthen, Germany
⁹ Joint Institute for Nuclear Research, 141980, Dubna, Russia
¹⁰ Physikalisches Institut, Universität Erlangen-Nürnberg, 91058, Erlangen, Germany
¹¹ Sezione di Ferrara, Istituto Nazionale di Fisica Nucleare, 44122, Ferrara, Italy
¹² Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, 44122, Ferrara, Italy
¹³ Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati, 00044, Frascati, Italy
¹⁴ Department of Physics and Astronomy, Ghent University, 9000, Gent, Belgium
¹⁵ II. Physikalisches Institut, Justus-Liebig Universität Gießen, 35392, Gießen, Germany
¹⁶ SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
¹⁷ Department of Physics, University of Illinois, Urbana, IL, 61801-3080, USA
¹⁸ Randall Laboratory of Physics, University of Michigan, Ann Arbor, MI, 48109-1040, USA
¹⁹ Lebedev Physical Institute, 117924, Moscow, Russia
²⁰ National Institute for Subatomic Physics (Nikhef), 1009 DB, Amsterdam, The Netherlands
²¹ B.P. Konstantinov Petersburg Nuclear Physics Institute, Gatchina, 188300, Leningrad Region, Russia
²² Institute for High Energy Physics, Protvino, 142281, Moscow Region, Russia
²³ Gruppo Collegato Sanità, Sezione di Roma, Istituto Nazionale di Fisica Nucleare, 00161, Rome, Italy
²⁴ Istituto Superiore di Sanità, 00161, Rome, Italy
²⁵ TRIUMF, Vancouver, BC, V6T 2A3, Canada
²⁶ Department of Physics, Tokyo Institute of Technology, Tokyo, 152, Japan
²⁷ Department of Physics and Astronomy, VU University, 1081 HV, Amsterdam, The Netherlands
²⁸ National Centre for Nuclear Research, 00-689, Warsaw, Poland
²⁹ Yerevan Physics Institute, 375036, Yerevan, Armenia

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

Received: 4 September 2015
Accepted: 1 December 2015
Published online: 17 December 2015

Abstract

Hard exclusive electroproduction of mesons is studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off a transversely polarized hydrogen target. The amplitudes of five azimuthal modulations of the single-spin asymmetry of the cross section with respect to the transverse proton polarization are measured. They are determined in the entire kinematic region as well as for two bins in photon virtuality and momentum transfer to the nucleon. Also, a separation of asymmetry amplitudes into longitudinal and transverse components is done. These results are compared to a phenomenological model that includes the pion pole contribution. Within this model, the data favor a positive transition form factor.