COMPASS results on proton longitudinal spin structure function g1 and quark fragmentation functions

We present a few recent highlights from the COMPASS experiment at CERN, related to the nucleon spin and structure: the proton spin structure function g(1)(P)(x) measured using 200 GeV polarized muons, together with a QCD fit of g(1) world data; pion and kaon multiplicities in DIS in view of constraining quark fragmentation functions. The statistical precision on g(1)(P) is improved by a factor of 2 at low x. A re-evaluation of the Bjorken sum rule based on COMPASS data alone confirms its validation within 9% accuracy. An NLO QCD fit to g(1) world data leads to a value of the quark spin contribution to the nucleon spin Delta Sigma, between 0.26 and 0.36 at Q(2) = 3 (GeV/c)(2), the size of the uncertainty being driven by the unknown shape of the polarized parton distributions. The results on pion and kaon multiplicities produced in DIS of muons off an isoscalar target constitute an impressive data set of more than 400 points in pi and 400 in K, covering a large kinematical domain in (x, z, Q(2)), which will be used in future NLO QCD fits to extract quark fragmentation functions into pi and K. A LO fit is performed to extract the favoured and unfavoured quark fragmentation functions into pions.