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Multiplicities of charged hadrons produced in deep inelastic muon scattering off a 6 LiD target have been measured as a function of the DIS variables x Bj , Q 2 , W 2 and the final state hadron variables p T and z . The distributions are fitted with a single exponential function at low values of to determine the dependence of on x Bj , Q 2 , W 2 and z . The z -dependence of is shown to be a potential tool to extract the average intrinsic transverse momentum squared of partons, , as a function of x Bj and Q 2 in a leading order QCD parton model.

The first moments of the polarized valence parton distribution functions (PDFs) truncated to the wide Bjorken x region 0.004< x <0.7 are directly (without any fitting procedure) extracted in the next to leading order (NLO) QCD from both COMPASS and HERMES data on pion production in polarized semi-inclusive DIS (SIDIS) experiments. The COMPASS and HERMES data are combined in two ways and two scenarios for the fragmentation functions (FFs) are considered. Two procedures are proposed for an estimation of light sea quark contributions to the proton spin. Both lead to the conclusion that these contributions are compatible with zero within the errors.

The formulas directly connecting parton distribution functions (PDFs) and fragmentation functions (FFs) at the next to leading order (NLO) QCD with the same quantities at the leading order (LO) are derived. These formulas are universal, i.e. have the same form for all kinds of PDFs and FFs, differing only in the respective splitting functions entering there.

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.

This paper is an erratum to a previous paper (EPJC 73 (2013) 2531) published by C. Adolph et al. (The COMPASS Collaboration) using a data sample taken in 2004. In the course of the ongoing analysis of the more recent 2006 data sample, and following some additional hints we identified a problem in the analysis of the 2004 data presented in EPJC 73 (2013) 2531. The acceptance correction for the 2004 data sample did not properly account for the use of semi-inclusive triggers on top of the inclusive triggers.

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 first moments of the polarized valence parton distribution functions (PDFs) truncated to the wide Bjorken \\(x\\) region \\(0.004

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