The Collins and Sivers asymmetries for charged hadrons produced in deeply inelastic scattering on transversely polarised protons have been extracted from the data collected in 2007 with the CERN SPS muon beam tuned at 160 GeV/c. At large values of the Bjorken x variable non-zero Collins asymmetries are observed both for positive and negative hadrons while the Sivers asymmetry for positive hadrons is slightly positive over almost all the measured x range. These results nicely support the present theoretical interpretation of these asymmetries, in terms of leading-twist quark distribution and fragmentation functions.
The exclusive production cross sections for and mesons have been measured in proton-proton reactions at p lab ϭ3.67 GeV/c. The observed / cross section ratio is (3.8Ϯ0.2 Ϫ0.9 ϩ1.2 )ϫ10 Ϫ3 . After phase space corrections, this ratio is enhanced by about an order of magnitude relative to naive predictions based upon the Okubo-Zweig-Iizuka ͑OZI͒ rule, in comparison to an enhancement by a factor ϳ3 previously observed at higher beam momenta. The modest increase of this enhancement near the production threshold is compared to the much larger increase of the / ratio observed in specific channels of p p annihilation experiments. Furthermore, differential cross section results are also presented which indicate that although the meson is predominantly produced from a 3 P 1 proton-proton entrance channel, other partial waves contribute significantly to the production mechanism at this beam momentum.
The COMPASS experiment at the CERN SPS has studied the diffractive dissociation of negative pions into the π- π- π+ final state using a 190 GeV/c pion beam hitting a lead target. A partial wave analysis has been performed on a sample of 420,000 events taken at values of the squared 4-momentum transfer t' between 0.1 and 1 GeV2/c2. The well-known resonances a1(1260), a2(1320), and π2(1670) are clearly observed. In addition, the data show a significant natural-parity exchange production of a resonance with spin-exotic quantum numbers J(PC)=1-+ at 1.66 GeV/c2 decaying to ρπ. The resonant nature of this wave is evident from the mass-dependent phase differences to the J(PC)=2-+ and 1++ waves. From a mass-dependent fit a resonance mass of (1660±10(-64)(+0)) MeV/c2 and a width of (269±21(-64)(+42)) MeV/c2 are deduced, with an intensity of (1.7±0.2)% of the total intensity.
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