Search

A set of measurements of azimuthal asymmetries in the production of pairs of identified hadrons in deep-inelastic scattering of muons on transversely polarised 6LiD (deuteron) and NH3 (proton) targets is presented. All available data collected in the years 2002–2004 and 2007/2010 with the COMPASS spectrometer using a muon beam of 160 GeV=c at the CERN SPS were analysed. The asymmetries provide access to the transversity distribution functions via a fragmentation function that in principle may be independently obtained from e+e- annihilation data. Results are presented, discussed and compared to existing measurements as well as to model predictions. Asymmetries of pi+pi- pairs measured with the proton target as a function of the Bjorken scaling variable are sizeable in the range x > 0:032, indicating non-vanishing transversity distribution and di-hadron interference fragmentation functions. As already pointed out by several authors, the small asymmetries of pi+pi- measured on the 6LiD target can be interpreted as indication for a cancellation of u and d-quark transversity distributions. A set of measurements of azimuthal asymmetries in the production of pairs of identified hadrons in deep-inelastic scattering of muons on transversely polarised $^6$LiD (deuteron) and NH$_3$ (proton) targets is presented. All available data collected in the years 2002-2004 and 2007/2010 with the COMPASS spectrometer using a muon beam of 160 GeV/$c$ at the CERN SPS were analysed. The asymmetries provide access to the transversity distribution functions via a fragmentation function that in principle may be independently obtained from $e^+e^-$ annihilation data. Results are presented, discussed and compared to existing measurements as well as to model predictions. Asymmetries of $\pi^{+}\pi^{-}$ pairs measured with the proton target as a function of the Bjorken scaling variable are sizeable in the range $x> 0.032$, indicating non-vanishing transversity distribution and di-hadron interference fragmentation functions. As already pointed out by several authors, the small asymmetries of $\pi^{+}\pi^{-}$ measured on the $^6$LiD target can be interpreted as indication for a cancellation of $u$ and $d$-quark transversity distributions.

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive $\rho ^0$ meson muoproduction at COMPASS using 160~GeV/$c$ polarised $ \mu ^{+}$ and $ \mu ^{-}$ beams impinging on a liquid hydrogen target. The measurement covers the kinematic range 5.0~GeV/$c^2$ $< W