Dortmund 2006 – scientific programme

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T: Teilchenphysik

T 201: Strukturfunktionen

T 201.4: Group Report

Tuesday, March 28, 2006, 14:50–15:10, HG2-HS2

Transverse spin effects at COMPASS — •Rainer Joosten — Helmholtz Institut für Strahlen- und Kernphysik,Rheinische Friedrich-Wilhelms-Universität Bonn

The cross-section for deep inelastic scattering off spin 1/2 hadrons can be parametrised in leading order in terms of three quark distribution functions: the helicity averaged distribution q(x), the longitudinal helicity distribution Δq(x) and the transverse spin distribution Δ_Tq(x). This last function, referred to as transversity, is chiral-odd and can only be measured in combination with another chiral-odd function. At COMPASS, Δ_Tq(x) can be measured in semi-inclusive measurements, requiring the partial detection of the hadronic products. It can be measured in combination with the chiral-odd Collins fragmentation-function H₁^⊥(z) producing an asymmetry in the azimuthal production angle of the hadron which depends on the Collins angle ϕ_C = ϕ_h−ϕ_S′, where ϕ_S′ is the spin angle of the fragmenting quark. A second probe is the measurement of two hadron production introducing the chiral odd interference fragmentation function H₁^{< −0.3 em )}(z). Here, an asymmetry is expected in the azimuthal angle of the hadron plane which depends on ϕ_R−ϕ_S′, where ϕ_R is the angle of the hadron plane in the lepton scattering plane. COMPASS is a fixed target experiment on the SPS M2 beamline at CERN. Its ⁶LiD target can be polarised both longitudinally and transversally with respect to the polarised 160 GeV/c µ⁺ beam. In 2002 – 2004, 20% of the beam-time was spent in the transverse configuration, allowing the measurement of transversity effects. Present results of the analysis of one and two hadron production will be reported. (This work is supported by the BMBF)