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HK: Fachverband Physik der Hadronen und Kerne
HK 23: Elektromagnetische und Hadronische Sonden
HK 23.5: Talk
Tuesday, March 11, 2008, 12:15–12:30, 1C
Lambda polarization in transverse running at COMPASS — •Teresa Negrini for the COMPASS collaboration — Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn
COMPASS is a fixed target experiment on the SPS M2 beamline at CERN. Its target can be polarised both longitudinally and transversely with respect to the polarised 160 GeV/c µ+ beam. In 2002, 2003, and 2004, 20% of the beam-time was spent in the transverse configuration using a 6LiD target, allowing the measurement of transversity effects.
The measurement of the transverse spin quark distribution functions ΔTq(x) is an important part of the physics program of the COMPASS experiment. The transversity distributions, being chiral-odd objects, are not directly accessible in inclusive deep-inelastic scattering (DIS), but require the presence of another chiral-odd object. At COMPASS, ΔTq(x) can be measured in semi-inclusive deep-inelastic scattering (SIDIS), where this additional object is provided by the fragmentation functions.
The most promising channels for the measurement of the transversity distributions in SIDIS are the Collins effect, the azimuthal asymmetries in two hadrons production and the spin transfer to the Lambda hyperons. In this presentation the semi-inclusive Lambda production mechanism will be shown, demonstrating the connection between the measured polarization and ΔTq(x). Preliminary results for the Lambda polarization as a function of the Bjorken x variable, based on the full COMPASS statistics with transverse spin target configuration, are presented.