Darmstadt 2008 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 16: Elektromagnetische und Hadronische Sonden

HK 16.6: Talk

Tuesday, March 11, 2008, 10:00–10:15, 1C

Transverse target spin asymmetries in semi-inclusive production of K⁰-mesons at COMPASS — •Andreas Richter — for the COMPASS collaboration — Physikalisches Institut, Universität Erlangen-Nürnberg, 91058 Erlangen, Germany

COMPASS is a fixed target experiment at the CERN M2 external beamline using a 160 GeV/c polarised µ⁺ beam. In 2002-04 COMPASS had collected physics data with a polarised ⁶LiD target. This deuterium target can be both longitudinally or transversely polarised with respect to the µ⁺ beam. The transverse configuration allows the measurement of transverse spin effects. For having a full description of the spin structure of the nucleon at quark level at leading twist it is necessary to know all three quark distribution functions, namely the unpolarised distribution function q(x), the helicity distribution function Δ q(x) and the transverse spin distribution function Δ_T q(x), the so-called Transversity. One possibility to extract the transverse spin distribution is the measurement of the Collins effect in the fragmentation in semi-inclusive deep inelastic scattering on a transversely polarised target. Beside the asymmetries in the production of charged pions and kaons also the Collins asymmetry for the neutral K⁰ was measured. Like for the analysis of the charged hadrons in addition the Sivers effect was studied. This effect will measure the correlation of the transverse momentum of an unpolarised quark in a transversely polarised nucleon and the transverse polarisation of the nucleon. The results for both asymmetries for the fragmentation into K⁰ will be presented. Supported by the BMBF.