The Polarised Valence Quark Distribution from semi-inclusive DIS

The semi-inclusive difference asymmetry A^{h^{+}-h^{-}} for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002-2004 using a 160 GeV polarised muon beam scattered off a large polarised ^6LiD target and cover the range 0.006 < x < 0.7 and 1 < Q^2 < 100 (GeV/c)^2. In leading order QCD (LO) the asymmetry A_d^{h^{+}-h^{-}} measures the valence quark polarisation and provides an evaluation of the first moment of Delta u_v + Delta d_v which is found to be equal to 0.40 +- 0.07 (stat.) +- 0.05 (syst.) over the measured range of x at Q^2 = 10 (GeV/c)^2. When combined with the first moment of g_1^d previously measured on the same data, this result favours a non-symmetric polarisation of light quarks Delta u-bar = - Delta d-bar at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario Delta u-bar = Delta d-bar = Delta s-bar = Delta s.Comment: 7 pages, 3 figures, COMPASS, revised: details added, author list update

Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protons

Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise. © 2015

Performance of Multiplexed XY Resistive Micromegas detectors in a high intensity beam

We present the performance of multiplexed XY resistive Micromegas detectors tested in the CERN SPS 100 GeV/c electron beam at intensities up to 3.3 × 10 5e−/(s-cm2). So far, all studies with multiplexed Micromegas have only been reported for tests with radioactive sources and cosmic rays. The use of multiplexed modules in high intensity environments was not explored due to the effect of ambiguities in the reconstruction of the hit point caused by the multiplexing feature. For the specific mapping and beam intensities analyzed in this work with a multiplexing factor of five, more than 50% level of ambiguity is introduced due to particle pile-up as well as fake clusters due to the mapping feature. Our results prove that by using the additional information of cluster size and integrated charge from the signal clusters induced on the XY strips, the ambiguities can be reduced to a level below 2%. The tested detectors are used in the CERN NA64 experiment for tracking the incoming particles bending in a magnetic field in order to reconstruct their momentum. The average hit detection efficiency of each module was found to be 96% at the highest beam intensities. By using four modules a tracking resolution of 1.1% was obtained with 85% combined tracking efficiency.ISSN:0168-9002ISSN:1872-957

Particle identification with a combined hodoscope calorimeter

The differences in width and in deposited energy between electromagnetic and hadron showers developed by 18.5 and 38 GeV/c pions and electrons in a combined hodoscope detector composed of a GAMS-type electromagnetic calorimeter and a modular hadron calorimeter allow to reject pions or electrons to a level ≪ 0.1% keeping a detection efficiency larger than 90% when the other particle is selected. The hadron calorimeter helps to efficiently reject background in studies of multiphoton decays of neutral mesons with GAMS. © 1989.SCOPUS: le.jinfo:eu-repo/semantics/publishe

Measurement of the resolution of a combined hodoscope calorimeter at 18 GeV and 38 GeV

The energy and spatial resolution of a combined detector consisting of the Cherenkov photon calorimeter GAMS-2000 and the modular hadron calorimeter MHC-100 has been studied at 18.5 and 38 GeV incident pion energies at the IHEP accelerator. The energy resolution of the combined setup is substantially improved by applying a correction based on the analysis of the lateral development of hadron showers in GAMS and MHC. It is shown that the parameters of the correction depend only weakly on the hadron energy. The influence of the gap between both photon and hadron calorimeters on the combined detector characteristics is of less importance with increasing energy. © 1988.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Evidence for a 1.9 GeV meson decaying into ηη′

Evidence for a new meson decaying into ηη′ has been found in 38 GeV π-p charge-exchange interactions. The mass and the width of this meson are (1917 ± 15) MeV and (90-50+35) MeV, respectively. Possible spin and parity assignments are JPC = 0++, 1-+ or 2++, isospin and G-parity are IG = 0+. The t-dependence of the differential cross section follows an exponential behaviour exp(bt with a small slope: b = (2±1) (GeV/c)-2.Upper limits on its decay into ππ, ηη and KK exotic interpretation of this meson. © 1989.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Study of ωω systems produced in 38 GeV/c π- p collisions

The π- p→ωωn reaction has studied for the first time at the 70 GeV IHEP accelerator. The six photons from the decay of the two ω mesons were detected in GAMS-2000, a hodoscope multi-photon spectometer. Two resonances decaying into ωω,X (1640) and X(1960), have been observed. Their quantum numbers are JPC=2++, IG=0+. The reaction is dominated by the one-pion exchange mechanism. The production cross sections σ. BR(X→ωω) are 0.65±0.15 μb and 1.0±0.2 μb, respectively. © 1989.SCOPUS: ar.jinfo:eu-repo/semantics/publishe