Speaker
Andrea Bressan
(INFN Trieste)
Description
The CERN COMPASS experiment is on the floor collecting data since 2002; in the years
2002,
2003, and 2004 data were collected using a 160 GeV polarized muon beam and a 6LiD
polarized target. In about 20% of the running time the target polarisation was
oriented transversely with respect to the muon beam direction to measure transverse
spin effects in semi inclusive deep inelastic scattering, one of the main objectives
of the COMPASS spin program.
Here the results for the Collins and the Sivers asymmetries, both for unidentified
and identified
hadrons (pi+, pi−, K± and K0) from the whole data sample are presented, together with
the projected statistical error for the proton run foreseen in 2007. The measured
asymmetries on the 6LiD target are small and compatible with zero within the few
percent statistical errors, an important result which can be interpreted as
cancellation between u and d quark in the deuteron and which allows to better
constrain the parton distribution functions.
Author
Andrea Bressan
(INFN Trieste)
