Abstract
Hermes collected a wealth of data using the 27.6 GeV polarized Hera lepton beam and various pure, polarized and unpolarized, gaseous targets. This unique data set opens the door to various measurements sensi- tive to the multi-dimensional structure of the nucleon. Among them are two-hadron production in semi-inclusive deep-inelastic scattering on a transversely polarized target, providing access to different transverse-momentum- dependent distribution and fragmentation functions in a way complementary to single-hadron production. Also transverse-target single-spin asymmetries in inclusive electroproduction of charged pions and kaons have been recently extracted, complementing data from proton-proton collisions, where large, so far unexplained, asym- metries have been observed. From inclusive measurements on various nuclear targets, the Λ polarization is extracted, also here complementing measurements in proton-proton collisions.
Highlights
The Hermes experiment at Desy in Hamburg (Germany) collected data from 1995 until 2007 using the 27.6 GeV Hera lepton beam
Longitudinally polarized electrons or positrons were scattered off stationary gaseous hydrogen, deuterium, helium, or heavier targets, with hydrogen longitudinally or transversely polarized or unpolarized, deuterium and helium longitudinally polarized or unpolarized, and the heavier targets unpolarized
Complementing measurements made in hadronhadron collisions and hadron production in semi-inclusive deep-inelastic scattering, here single-spin asymmetries in inclusive electroproduction of charged pions and kaons off a transversely polarized proton target are presented
Summary
The Hermes experiment at Desy in Hamburg (Germany) collected data from 1995 until 2007 using the 27.6 GeV Hera lepton beam. From data collected on the transversely polarized hydrogen data, transverse-target moments of two hadrons were extracted These provide access to distribution and fragmentation functions, in a way complementary to single-hadron production. Motivated by the unexplained large left-right asymmetries observed in, e.g., proton-proton collisions, with one of the protons transversely polarized, azimuthal singlespin asymmetries in inclusive electroproduction of pions and kaons off transversely polarized protons were extracted In two-hadron production transversity enters the cross section colinearly, through a direct product, whereas for single-hadron production transversemomentum-dependent convolution integrals enter the cross section, thereby largely complicating access to transversity
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