[en] The T2K long-baseline neutrino oscillation experiment is running in Japan. The primary goals of the T2K are measurement of the mixing angle θ₁₃, and precise measurements of the mixing angle θ₂₃ and of the mass difference Δm²₂₃. The installation of the near detector complex was completed and first data were already registered. This article presents operation of the Side Muon Range Detector, a component of the Off-Axis near detector. Detector concept and implementation are presented, followed by a description of cosmic muon track reconstruction algorithm and finally current status. (author)

[en] An analytical model of preamplifier noise identification in a spectrometric system is presented in the article. It allows analysis of normal passive pulse shapers, general time-invariant systems as well as time-variant systems. An equivalent noise charge (ENC) is modeled as the sum of three components: (i) proportional to the amplifier shaping time, (ii) inversely proportional, and (iii) independent of the amplifier shaping time. The Least Squares Method for identifying the noise components of the spectrometric system was used; measured values of ENC were fitted to the theoretical dependence on peaking time ${\tau }_0$. Analytical formulas have been derived for the values of coefficients included in the dependence of ENC on the shaping time for $CR-{\left(RC\right)}^n$ shaping for any value of n. The conclusion of this analysis may be used for the optimization of spectrometric systems.

[en] Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality Q"2 > 1 (GeV/c)"2. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon beam impinging on a polarised "6LiD target. By analysing the full range in hadron transverse momentum p_T, the different p_T-dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation Δg/g is evaluated at leading order in pQCD at a hard scale of μ"2 = left angle Q"2 right angle = 3 (GeV/c)"2. It is determined in three intervals of the nucleon momentum fraction carried by gluons, x_g, covering the range 0.04 < x_g < 0.28 and does not exhibit a significant dependence on x_g. The average over the three intervals, left angle Δg/g right angle = 0.113 ± 0.038_(_s_t_a_t_._) ± 0.036_(_s_y_s_t_._) at left angle x_g right angle ∼ 0.10, suggests that the gluon polarisation is positive in the measured x_g range. (orig.)

[en] Single hadron azimuthal asymmetries of positive and negative hadrons produced in muon semi-inclusive deep inelastic scattering off longitudinally polarised deuterons are determined using the 2006 COMPASS data and also combined all deuteron COMPASS data. For each hadron charge, the dependence of the azimuthal asymmetry on the hadron azimuthal angle φ is obtained by means of a five-parameter fitting function that besides a φ-independent term includes four modulations predicted by theory: sin φ, sin 2φ, sin 3φ and cos φ. The amplitudes of the five terms have been extracted, first, for the hadrons in the whole available kinematic region. In further fits, performed for hadrons from a restricted kinematic region, the φ-dependence is determined as a function of one of three variables (Bjorken-x, fractional energy of virtual photon taken by the outgoing hadron and hadron transverse momentum), while disregarding the others. Except the φ-independent term, all the modulation amplitudes are very small, and no clear kinematic dependence could be observed within experimental uncertainties. (orig.)

[en] The COMPASS Collaboration at CERN has investigated the reaction π^-γ → π^-π^-π⁺ embedded in the Primakoff reaction of 190 GeV pions scattering in the Coulomb field of a lead target, π^-Pb → π^-π^-π⁺ Pb. Exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at momentum transfer below 0.001 (GeV/c)². Using a partial-wave analysis the amplitudes and relative phases of the a₂(1320) and π₂(1670) mesons have been extracted, and the Coulomb and the diffractive contributions have been disentangled. Measuring absolute production cross sections we have determined the radiative width of the a₂(1320) to be Γ₀(a₂(1320) → πγ) = (358 ± 6_stat ± 42_syst) keV. As the first measurement, Γ₀(π₂(1670) → πγ) = (181 ± 11_stat ± 27_syst) keV . (BR^PDG_f2π/BR_f2π) is obtained for the radiative width of the π₂(1670), where in this analysis the branching ratio BR^PDG_f2π = 0.56 has been used. We compare these values to previous measurements and theoretical predictions. (orig.)

[en] Large samples of Λ, Σ(1385) and Ξ(1321) hyperons produced in the deep-inelastic muon scattering off a ⁶LiD target were collected with the COMPASS experimental setup at CERN. The relative yields of Σ(1385)⁺, Σ(1385)^-, anti Σ(1385)^-, anti Σ(1385)⁺, Ξ(1321)^-, and anti Ξ(1321)⁺ hyperons decaying into Λ(anti Λ)π were measured. The ratios of heavy-hyperon to Λ and heavy-antihyperon to anti Λ were found to be in the range 3.8 % to 5.6 % with a relative uncertainty of about 10 %. They were used to tune the parameters relevant for strange particle production of the LEPTO Monte Carlo generator. (orig.)

[en] Multiplicities of charged hadrons produced in deep inelastic muon scattering off a ⁶LiD target have been measured as a function of the DIS variables x_Bj, Q², W² and the final state hadron variables p_T and z. The p_T² distributions are fitted with a single exponential function at low values of p_T² to determine the dependence of left angle p_T² right angle on x_Bj, Q², W² and z. The z-dependence of left angle p_T² right angle is shown to be a potential tool to extract the average intrinsic transverse momentum squared of partons, left angle k _{perpendicularto}² right angle, as a function of x_Bj and Q² in a leading order QCD parton model. (orig.)

[en] 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 p_h^T 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. (orig.)