Abstract
Single-spin asymmetries were investigated in inclusive electroproduction of charged pions and kaons from transversely polarized protons at the Hermes experiment. The asymmetries were studied as a function of the azimuthal angle ψ about the beam direction between the target-spin direction and the hadron production plane, the transverse hadron momentum PT relative to the direction of the incident beam, and the Feynman variable xF. The sinψ amplitudes are positive for π+ and K+, slightly negative for π− and consistent with zero for K−, with particular PT but weak xF dependences. Especially large asymmetries are observed for two small subsamples of events, where also the scattered electron was recorded by the spectrometer.
Highlights
HERMES Collaboration / Physics Letters B 728 (2014) 183–190 p Department of Physics, University of Illinois, Urbana, IL 61801-3080, USA q Randall Laboratory of Physics, University of Michigan, Ann Arbor, MI 48109-1040, USA r Lebedev Physical Institute, 117924 Moscow, Russia s National Institute for Subatomic Physics (Nikhef), 1009 DB Amsterdam, The Netherlands t K.P
Single-spin asymmetries were investigated in inclusive electroproduction of charged pions and kaons from transversely polarized protons at the Hermes experiment
The asymmetries were studied as a function of the azimuthal angle ψ about the beam direction between the target-spin direction and the hadron production plane, the transverse hadron momentum P T relative to the direction of the incident beam, and the Feynman variable xF
Summary
Single-spin asymmetries were investigated in inclusive electroproduction of charged pions and kaons from transversely polarized protons at the Hermes experiment. Transverse single-spin asymmetries (SSAs) observed in the azimuthal distributions of hadrons produced in high-energy electromagnetic and hadronic reactions (where either the projectile or the target nucleon is polarized transversely to the beam direction) are a window for our understanding of the nucleon structure and the process of hadronization in the framework of quantumchromodynamics (QCD). This Letter reports on the first measurement of azimuthal SSAs in inclusive electroproduction of charged pions and kaons off transversely polarized protons. It addresses a portion of this unexplored kinematic space. The sin ψ azimuthal dependence follows directly from the term S · (Ph × k) in the spindependent part of the cross section (see, e.g., Ref. [60]), with S being the target-spin vector, and k and Ph the three-momenta of the incident lepton and of the final-state hadron, respectively
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