Speaker
Description
We present preliminary COMPASS results on pion and kaon multiplicities produced in semi-inclusive deep inelastic scattering of 160 GeV muons off a pure proton (LH2) target. The results constitute a data set of more than 600 points for pions and 600 for kaons, covering a large x, Q2 and z domain in a fine binning with W>5 GeV2. The results from the sum of the z-integrated multiplicities M(π+) + M(π-) and M(K+) + M(K-) are presented versus x and compared to earlier COMPASS results on a deuteron target and to other experiments.
In addition, we show the K-/K+ as well as pbar/p multiplicity ratios measured for hadrons carrying a large fraction z of the virtual-photon energy, 0.5 < z <1, using an isoscalar 6LiD target. The ratios can be obtained with lower systematic errors. For values of z larger than 0.8, the results contradict expectations obtained using the formalism of (next-to-) leading order perturbative quantum chromodynamics. In particular the data show a strong dependence upon the missing mass Mx, not expected from the calculations. The results suggest that additional corrections to the formalism may be required to take into account the phase space available for hadronization.
