Köln 2004 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 17: Electromagnetic and Hadronic Probes II

HK 17.3: Vortrag

Dienstag, 9. März 2004, 16:30–16:45, B

Transverse Spin Physics at HERMES — •Ulrike Elschenbroich — University of Ghent, Department of Subatomic and Radiation Physics, Proeftuinstraat 86, B-9000 Ghent

The cross section for deep inelastic lepton scattering off spin 1/2 hadrons can be parameterised in terms of quark distribution functions. In leading order only three quark distribution functions survive the integration over transverse quark momenta: i.e. the unpolarised distribution q(x), the helicity distribution Δ q(x), and the so–called transversity function h₁^q(x).

The latter one is a chiral–odd object and cannot be measured in inclusive deep inelastic scattering. To access h₁^q(x), it has to be combined with e.g. the chiral–odd Collins fragmentation function H₁^{⊥ q}(z), which enters the cross section for scattering processes where also a produced hadron is detected in coincidence. This combination gives rise to a sine–dependence in the azimuthal hadron production angle. The same cross section contains also the combination of the well–known unpolarised fragmentation function D^q(z) and the distribution function f_1T^{⊥ q}(x) (Sivers function) which exhibits a different sine modulation. A non–vanishing Sivers function would indicate a non–zero orbital angular momentum of quarks in the hadron.

Latest results measured with the longitudinally and transversely polarised targets of the HERMES experiment at the HERA storage ring are presented.