References - Bogoliubov Laboratory of Theoretical Physics - JINR

4 Summary
Since the end of data-taking in 2007, the HERMES Collaboration has continued in refining
the quality of and analyzing data.
The large statistics of inclusive DIS events collected by HERMES with hydrogen and deuterium
targets allowed to perform a new measurement of the structure function F2(x) for
proton and deuteron. The data cover a new still unexplored region and are in agreement
with world data in the overlap region. A measurement of the spin-dependent structure
function of the proton g2(x) is performed. This is the first measurement of HERMES
where both, longitudinal polarization of the beam and transverse polarization of the target
are important. The results are in agreement with the most accurate data obtained
by the E155 experiment and do not show any evidence, within the statistical accuracy,
of a contribution of the twist-3 part ¯g2(x). A search of the two-photon exchange effects
using the transversely polarized hydrogen target gave no evidence within the uncertainty,
at the level of 10 −3 .
The final result on the extraction of the Sivers amplitudes from semi-inclusive production
of pions and charged kaons using unpolarized lepton beam and transversely polarized hydrogen
target was obtained. The results obtained based on a small part of the collected
statistics are confirmed on the full data sample and new results on the amplitudes for
production of neutral pions and charged kaons are presented. The amplitudes for positive
kaons is larger then for positive pions. Azimuthal asymmetries for semi-inclusive production
of positive and negative hadrons with unpolarized hydrogen and deuterium targets
were studied. The different behaviour of positive and negative hadrons can be considered
as an evidence of a non-zero Boer-Mulders distribution function. Strange quark distributions,
S(x) andΔS(x), were measured using production of charged kaons off deuterium
target. The measured shape of xS(x) is in a contradiction with known parameterizations.
The strange helicity distribution is consistent with zero.
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