Monday, August 20, 2007

CERN Courier highlights work of Prof. Reinhard Schumacher and collaborators

Work of Prof. Reinhard Schumacher and collaborators has been recently highlighted in the CERN Courier. A continuing mystery in nuclear and particle physics is the large polarization observed in the production of Λ hyperons in high-energy, proton–proton interactions. These effects were first reported in the 1970s in reactions at incident proton momenta of several hundred GeV/c, where experiments measured surprisingly strong hyperon polarizations of around 30%. Although the phenomenology of these reactions is now well known, the inability to distinguish between various competing theoretical models has hampered the field.

Two new measurements from the US Department of Energy's Jefferson Lab in Virginia are now challenging existing ideas on quark spin dynamics through studies of beam-recoil spin transfer in the electro- and photoproduction of K⁺Λ final states from an unpolarized proton target. Analyses of the two experiments in Hall B at Jefferson Lab using the CLAS spectrometer have provided extensive results of spin transfer from the polarized incident photon (real or virtual) to the final state Λ hyperon.

The results indicate that the Λ polarization is predominantly in the direction of the spin of the incoming photon, independent of the centre-of-mass energy or the production angle of the K⁺. Moreover, the photoproduction data show that, even where the transferred Λ polarization component along the photon direction is less than unity, the total magnitude of the polarization vector is equal to unity. Since these observations are not required by the kinematics of the reaction (except at extreme forward and backward angles) there must be some underlying dynamical origin.

For more information, see the  article in the CERN Courier.