References - Bogoliubov Laboratory of Theoretical Physics - JINR

OVERVIEW OF RECENT HERMES RESULTS
V.A. Korotkov
(on behalf of the HERMES Collaboration)
Institite for High Energy Physics, Protvino, Russia
E-mail: Vladislav.Korotkov@ihep.ru
Abstract
An overview of recent HERMES results is presented. The review topics include:
the nucleon structure function F2(x), the polarized structure function g2(x), the
search for a two-photon exchange effects in polarized DIS, the Collins and Sivers
asymmetries, the azimuthal asymmetries in hadron electro-production off unpolarized
target, and strange quark distributions, S(x) andΔS(x).
1 Introduction
The HERMES experiment at DESY was designed to investigate the spin structure of
the nucleon with a clear motivation to study/resolve the “Proton Spin Puzzle”. The
“Puzzle” originated due to a measurement by the European Muon Collaboration of the
quark spin contribution to the proton spin, which appeared to be surprisingly small [1].
Twelve years of running by the HERMES experiment, from 1995 to 2007, has led to many
exciting, unexpected results. New fields of investigations gained importance, such as the
study of the third twist-2 quark distribution function of the nucleon, so-called transversity,
the study of Transverse Momentum Dependent distribution and fragmentation functions,
the study of Generalized Parton Distributions. This paper presents part of the results
obtained by the HERMES Collaboration in the past two years based on inclusive and semiinclusive
DIS measurements only. Measurements of exclusive reactions are presented in
other contributions of the HERMES Collaboration at this Workshop.
The HERMES experiment studies the scattering of a longitudinally polarized lepton beam
(e + or e − ) of 27.6 GeV off a transversely/longitudinally polarized or unpolarized gas
target internal to the HERA storage ring. Scattered leptons and coincident hadrons were
detected by the HERMES spectrometer [2]. Leptons were identified with an efficiency
exceeding 98% and a hadron contamination of less than 1%. The HERMES dual-radiator
ring-imaging Čerenkov detector allows full hadron identification in the momentum range
2 ÷ 15 GeV.
2 Inclusive DIS
Structure function F2(x). During its data-taking, HERMES collected about 58 million
DIS events with (un)polarized hydrogen and deuterium targets. This statistics is highly
competitive with respect to other fixed target DIS experiments, and motivates a new
extraction of structure function F2(x) performed by HERMES in the same kinematic
domain explored by its polarized measurements. Extraction of such a function requires
the experimental data are corrected for detector smearing and radiative effects with an
unfolding procedure [3], and a precise knowledge of the luminosity [2]. To extend the
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