Speaker
Dr
Achim Hillenbrand
(DESY)
Description
The analysis of transverse momentum dependent quark distribution functions (TMDs), which are related to spin orbit correlations of the quarks within the nucleon, is an active field of research.
One way to gather information about TMDs on the experimental side is the measurement of azimuthal single-spin asymmetries (SSA) A^h_UT in semi-inclusive deep-inelastic scattering (SIDIS) of longitudinally polarized (L) electrons and positrons off a transversely polarized (T) proton target. The lepton beam can be considered unpolarized (U) as the recorded data is balanced with respect to the beam helicity states. A Fourier analysis of these asymmetries yields components which can be interpreted as convolutions in transverse momentum space of transverse-momentum dependent distribution and fragmentation functions. Two of these components provide leading-twist signals for the naive time reversal odd Sivers functions and the chiral-odd transversity function. The final results on these single-spin asymmetry amplitudes are presented.
Furthermore, azimuthal single-spin asymmetries A^h_UT have been extracted for the first time from inclusive hadron production using the same beam and target setup. These measurements are complementary to the well known large left-right asymmetries A_N in transversely polarized proton-proton scattering, but represent a much cleaner channel, involving just one proton quark field. The measurement of these asymmetries provide a test for the validity of TMD factorization, which is largely accepted for the SIDIS case involving two scales (small pt and large Q2), but
is still under debate for processes involving one large scale (pt), like inclusive DIS.
Primary author
Dr
Achim Hillenbrand
(DESY)
