Peter Berglund, Jaakko Koivuniemi and Kenneth Gustafsson (HIP)
Duration: 1998 - 31.12.2003
After confirmation of the original EMC result by experiments at CERN and SLAC it is now firmly established that the spin content of the nucleon is not entirely due to the quark spins. Competing explanations exist for this result. In the gluon interpretation it is the polarised glue Delta G which lowers the quark's contribution to the nucleon spin, whereas in an alternative model negatively polarised strange quarks are responsible.
Several ways exist in which a new muon experiment can resolve these ambiguities in interpretation. The probability that a quark spin in a transversely polarised nucleon is oriented parallel or antiparallel to the nucleon spin can in principle be measured in deep-inelastic scattering. Such a measurement requires a transversely polarised target and the knowledge of the spin dependent fragmentation functions for the transverse case.
During the run 2003, 270 TBytes of data was recorded. The D0 and D* peaks were seen for the first time. They are needed to determine the gluon contribution to the nucleon spin. The properties of the COMPASS spectrometer are better understood, but the signal-to noise ratio did not yet allow to determine the gluon polarization with desired accuracy.
Publication
Ball, J., Baum, G., Berglund, P., Daito, I., Doshita, N., Gautheron, F., Goertz, St., Harmsen, J., Hasegawa, T., Heckmann, J., Horikawa, N., Iwata, T., Kisselev, Yu., Koivuniemi, J., Kondo, K., Le Goff, J.M., Magnon, A., Meier, A., Meyer, W., Radtke, E., Reicherz, G., and Takabayashi, N., First results of the large COMPASS 6LiD polarized target, Nuclear Instruments and Methods in Physics Research A, 498 (2003), pp 101-111