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The LHCb experiment has been taking data at the Large Hadron Collider (LHC) at CERN since the end of 2009. One of its key detector components is the Ring-Imaging Cherenkov (RICH) system. This provides charged particle identification over a wide momentum range, from 2–100 GeV/ c . The operation and control, software, and online monitoring of the RICH system are described. The particle identification performance is presented, as measured using data from the LHC. Excellent separation of hadronic particle types ( π , K, p) is achieved.

Azimuthal asymmetries in semi-inclusive production of positive ( h + ) and negative hadrons ( h − ) have been measured by scattering 160 GeV muons off longitudinally polarised deuterons at CERN. The asymmetries were decomposed in several terms according to their expected modulation in the azimuthal angle φ of the outgoing hadron. Each term receives contributions from one or several spin and transverse-momentum-dependent parton distribution and fragmentation functions. The amplitudes of all φ -modulation terms of the hadron asymmetries integrated over the kinematic variables are found to be consistent with zero within statistical errors, while the constant terms are nonzero and equal for h + and h − within the statistical errors. The dependencies of the φ -modulated terms versus the Bjorken momentum fraction x , the hadron fractional momentum z , and the hadron transverse momentum were studied. The x dependence of the constant terms for both positive and negative hadrons is in agreement with the longitudinal double-spin hadron asymmetries, measured in semi-inclusive deep-inelastic scattering. The x dependence of the sin  φ -modulation term is less pronounced than that in the corresponding HERMES data. All other dependencies of the φ -modulation amplitudes are consistent with zero within the statistical errors.

The production of D ∗ and D mesons in inelastic scattering of 160 GeV/c muons off a 6 LiD target has been investigated with the COMPASS spectrometer at CERN for 0.003 (GeV/c) 2 < Q 2 <10 (GeV/c) 2 and 3×10 −5 < x Bj <0.1. The study is based on 8100 events where a D 0 or is detected subsequently to a D ∗+ or D ∗− decay, and on 34000 events, where only a D 0 or is detected. Kinematic distributions of D ∗ , D and are given as a function of their energy E , transverse momentum p T , energy fraction z , and of the virtual photon variables ν , Q 2 and x Bj . Semi-inclusive differential D ∗ production cross-sections are compared with theoretical predictions for D ∗ production via photon–gluon fusion into open charm. The total observed production cross-section for D ∗± mesons with laboratory energies between 22 and 86 GeV is (1.9±0.4) nb. Significant cross-section asymmetries are observed between D ∗+ and D ∗− production for ν <40 GeV and z >0.6.

The longitudinal polarisation transfer from muons to Λ  and  hyperons, , has been studied in deep-inelastic scattering off an unpolarised isoscalar target at the COMPASS experiment at CERN. The spin transfers to Λ  and  produced in the current fragmentation region exhibit different behaviours as a function of x and x F . The measured x and x F dependences of D LL Λ are compatible with zero, while tends to increase with x F , reaching values of 0.4–0.5. The resulting average values are D LL Λ = −0.012±0.047±0.024 and = 0.249±0.056±0.049. These results are discussed in the frame of recent model calculations.

The longitudinal polarisation transfer from muons to and $\\bar{\\varLambda}$ hyperons, $D_{\\varLambda(\\bar{\\varLambda})}$ , has been studied in deep-inelastic scattering off an unpolarised isoscalar target at the COMPASS experiment at CERN. The spin transfers to and $\\bar{\\varLambda}$ produced in the current fragmentation region exhibit different behaviours as a function of x and x sub(F ). The measured x and x sub(F )dependences of D sub(LL ) super( )are compatible with zero, while $D_{\\bar{\\varLambda}}$ tends to increase with x sub(F ), reaching values of 0.4-0.5. The resulting average values are D sub(LL ) super( )= -0.012c0.047c0.024 and $D_{\\bar{\\varLambda}}$ = 0.249c0.056c0.049. These results are discussed in the frame of recent model calculations.

The longitudinal double spin asymmetry A1ρ for exclusive leptoproduction of ρ0 mesons, μ+N→μ+N+ρ, is studied using the COMPASS 2002 and 2003 data. The measured reaction is incoherent exclusive ρ0 production on polarised deuterons. The Q2 and x dependence of A1ρ is presented in a wide kinematical range, 3×10-3

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