Köln 2004 – scientific programme

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PV: Plenarvorträge

PV XXIV

PV XXIV: Plenary Talk

Friday, March 12, 2004, 09:30–10:00, P

Newest results from HERMES — •Delia Hasch — INFN-LNF, Frascati, Italy

At HERMES the 27.6 GeV longitudinally polarised electron or positron beam in the HERA storage ring is incident on polarised atomic gas targets as well as on several nuclear targets. The primary goal of the HERMES experiment is the study of the spin structure of the nucleon. Two pieces remain completely unmeasured - the transverse spin distribution of quarks in the nucleon, described by the transversity (h₁), and the contribution of the orbital angular momentum of quarks and gluons. HERMES has measured transverse single-spin asymetries in deep-inelastic scattering providing for the first time a direct access to the transversity h₁ as well as to the time-odd distribution function f₁^⊥ (Sivers function). The quark’s orbital angular momentum contribution to the nucleon spin can be studied via hard exclusive processes within the formalism of generalised parton distributions. New results on exclusive meson production will be reported.

HERMES furthermore studies the production and transport of hadrons in cold nuclear matter. Measurements of possible absorbtion and fragmentation function modification for π, K, p and p are presented. Links between cold and hot nuclear matter are discussed too.