Multiplicities of charged pions and unidentified charged hadrons from deep-inelastic scattering of muons off an isoscalar target

Multiplicities of charged pions and unidentified hadrons produced in deep-inelastic scattering were measured in bins of the Bjorken scaling variable $x$, the relative virtual-photon energy $y$ and the relative hadron energy $z$. Data were obtained by the COMPASS Collaboration using a 160 GeV muon beam and an isoscalar target ($^6$LiD). They cover the kinematic domain in the photon virtuality $Q^2$ > 1(GeV/c$)^2$, $0.004 < x < 0.4$, $0.2 < z < 0.85$ and $0.1 < y < 0.7$. In addition, a leading-order pQCD analysis was performed using the pion multiplicity results to extract quark fragmentation functions

Long term experience with CsI photocathodes in gas photon detectors

RICH-1 is a Cherenkov Imaging detector in operation at the COMPASS experiment at CERN SPS since 2001. MWPCs equipped with CsI photocathodes have been used as photon detectors, for the full detection area in the first years of operation, and for 75% of the area after a detector upgrade in 2006. The mean number of detected photons per particle has been extracted from the data collected during six years of COMPASS data taking. An indirect measurement of possible variations of the CsI quantum efficiency versus time is obtained from this analysis

Hybrid MPGD-based detectors of single photons for the upgrade of COMPASS RICH-1

A seven year-long R&D programme has been performed and the resulting detector architecture is a hybrid MPGD including two THick GEM (THGEM) multiplication stages followed a MICROMEGAS. The first THGEM board forms the photocathode support: its upper face is CsI coated. The properties of THGEM-based photocathodes have been studied in details. The two THGEM layers act as pre-amplification stages and, thanks to a staggered configuration, namely by the misalignment of the holes of the two THGEMs, the electron shower produced in the pre-amplification phase is distributed onto a larger surface portion of the following MICROMEGAS unit, where the final multiplication takes place: it is so possible to operate at gains as high as 105 and more even in radioactive environments. COMPASS RICH-1 is a large-size Cherenkov imaging counter with gaseous radiator for hadron identification up to 50 GeV/c. The construction of a set of large-size (unit size: 60 760 cm2) gaseous photon detectors based on the hybrid MPGD architecture for the upgrade of COMPASS RICH-1 is ongoing and the upgraded detector will be in operation in 2016. The R&D studies, the engineering aspects and the construction challenges are presented

Multiplicities of charged kaons from deep-inelastic muon scattering off an isoscalar target

Precise measurements of charged-kaon multiplicities in deep inelastic scattering were performed. The results are presented in three-dimensional bins of the Bjorken scaling variable x, the relative virtual-photon energy y, and the fraction z of the virtual-photon energy carried by the produced hadron. The data were obtained by the COMPASS Collaboration by scattering 160 GeV muons off an isoscalar 6LiD target. They cover the kinematic domain View the MathML source in the photon virtuality, 0.0045 GeV/c2 in the invariant mass of the hadronic system. The results from the sum of the z -integrated K+ and K 12 multiplicities at high x point to a value of the non-strange quark fragmentation function larger than obtained by the earlier DSS fit

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

Measurement of the n̄-Fe absorption cross section between 125 and 780 MeV/c

The n\u304-Fe absorption cross section sigma(nbarFe) has been measured at LEAR (the Low Energy Antiproton Ring at CERN) using tagged n\u304's produced in the p\u304p \u2192 n\u304n charge-exchange reaction. With incident p\u304 momenta of 875 and 545 MeV/c sigma(nbarFe) has been measured in the momentum interval between 125 and 780 MeV/c, in a region where only a few measurements presently exist. The overall statistical and systematic errors range from 20 to 5%; the normalisation error is less than 3%. The measured cross sections are well reproduced by a parametrisation a+b/p, with a = 0.680 \ub1 0.051 barn and b = 0.228 \ub1 0.024 barn\ub7GeV/c

A new measurement of the p̄p → n̄n charge-exchange differential cross-section at LEAR

We have measured the p̄p → n̄n charge-exchange differential cross-section at two incoming p̄ momenta (601.5 and 1202 MeV/c) at the CERN Low Energy Antiproton Ring. After reviewing the experimental method, the data analysis is fully detailed, and the results on the whole statistics available in the centre of mass forward hemisphere are given. A precision in the absolute normalisation of 2% and 4% at 601.5 and 1202 MeV/c respectively is achieved, while over most of the angular range the point-to-point error is lower than 1%. The forward peak associated with the nearby pion pole and a dip-bump structure are accurately measured. The “Chew” extrapolation to the pion-pole suggests a “low” value for the πNN coupling constant gc2