München 2006 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 15: Elektromagnetische und Hadronische Sonden

HK 15.2: Vortrag

Dienstag, 21. März 2006, 14:30–14:45, F

Measurement of Δ S in the nucleon at HERMES from semi-inclusive DIS — •Shaojun Lu — II. Physikalisches Institut, Justus-Liebig-Universität, Giessen, Germany

The polarization of the strange quarks in the proton is of particular interest, because an explanation of the small net contribution to the nucleon spin from the quark spins under the assumption of SU(3) symmetry implies a signifcant negative value for this quantity. Such a value would explain the violation of the Ellis-Jaffe sum rule in inclusive Deep-inelastic scattering (DIS). However, recent results from HERMES for a flavor decomposition of quark helicity distributions based on semi-inclusive DIS suggest that the strange sea is zero or slightly positive.

The total strange quark helicity density Δ S(x) = Δ s(x) + Δ s(x) carries no isospin. It can be extracted from measurements of scattering off deuterium alone which is isoscalar. Effectively, measurements of the inclusive spin asymmetries provide an estimate of the helicity density of the non-strange sea. Using the spin asymmetries measured for charged kaons as the second experimental data set it is possible to extract directly Δ S(x). Furthermore, by measuring directly the charged kaon multiplicities at HERMES kinematics, the fragmentation functions relevent to the extraction procedure can be obtained without resort to other experiments. The results of a direct leading-order extraction of Δ S(x) using this approach will be presented.