Nucleon longitudinal spin structure at COMPASS

The nucleon spin structure is studied at COMPASS via the measurement of the spin dependent properties of deep inelastic muon-deuteron scattering. Both inclusive and semi-inclusive observables are investigated, with the emphasis put on the latter. This allows to access, in particular, the gluon polarization ($\Delta G/G$) and the flavor decomposition of the quark helicity distributions. Results from measurements with longitudinal target polarization are presented, as well as uncertainties expected from the first 3 years of data taking.Comment: 4 pages, 2 figures. Prepared for 10th International Baryons Conference (Baryons 2004). To be published with the conference proceedings in Nuclear Physics

Uzdužna spinska struktura pri COMPASSU

COMPASS is a fixed-target experiment at CERN\u27s Super-Proton-Synchrotron. Part of its physics program is dedicated to the spin structure of the nucleon, which it studies with a 160 GeV polarized muon beam and polarized targets. An overview of its measurements performed with longitudinal target polarization is given. In particular, recent results, concerning the gluon polarization, the separation of the contributions of the individual quark flavors and the test of the Bjorken sum rule, are presented.COMPASS su mjerenja na mirnoj meti pri super protonskom sinkrotronu u CERNu. Dio programa njegovih istraživanja posvećen je spinskoj strukturi nukleona što se proučava sa snopom polariziranih muona energije 160 GeV i polariziranim metama. Izlaže se pregled mjerenja izvedenih s uzdužno polarizaciranim metama. Posebice se izlažu nedavni ishodi za gluonsku polarizaciju, razdjela doprinosa pojedinačnih kvarkovskih okusa i provjera Bjorkenovog pravila suma

New pixelized Micromegas detector for the COMPASS experiment

New Micromegas (Micro-mesh gaseous detectors) are being developed in view of the future physics projects planned by the COMPASS collaboration at CERN. Several major upgrades compared to present detectors are being studied: detectors standing five times higher luminosity with hadron beams, detection of beam particles (flux up to a few hundred of kHz/mm^2, 10 times larger than for the present detectors) with pixelized read-out in the central part, light and integrated electronics, and improved robustness. Studies were done with the present detectors moved in the beam, and two first pixelized prototypes are being tested with muon and hadron beams in real conditions at COMPASS. We present here this new project and report on two series of tests, with old detectors moved into the beam and with pixelized prototypes operated in real data taking condition with both muon and hadron beams.Comment: 11 pages, 5 figures, proceedings to the Micro-Pattern Gaseous Detectors conference (MPGD2009), 12-15 June 2009, Kolympari, Crete, Greece Minor details added and language corrections don

New pixelized Micromegas detector with low discharge rate for the COMPASS experiment

New Micromegas (Micro-mesh gaseous detectors) are being developed in view of the future physics projects planned by the COMPASS collaboration at CERN. Several major upgrades compared to present detectors are being studied: detectors standing five times higher luminosity with hadron beams, detection of beam particles (flux up to a few hundred of kHz/mm^{2}, 10 times larger than for the present Micromegas detectors) with pixelized read-out in the central part, light and integrated electronics, and improved robustness. Two solutions of reduction of discharge impact have been studied, with Micromegas detectors using resistive layers and using an additional GEM foil. Performance of such detectors has also been measured. A large size prototypes with nominal active area and pixelized read-out has been produced and installed at COMPASS in 2010. In 2011 prototypes featuring an additional GEM foil, as well as an resistive prototype, are installed at COMPASS and preliminary results from those detectors presented very good performance. We present here the project and report on its status, in particular the performance of large size prototypes with an additional GEM foil.Comment: 11 pages, 5 figures, proceedings to the Micro-Pattern Gaseous Detectors conference (MPGD2011), 29-31 August 2011, Kobe, Japa

DISTO data on Kpp

The data from the DISTO Collaboration on the exclusive pp -> p K+ Lambda production acquired at T_p = 2.85 GeV have been re-analysed in order to search for a deeply bound K- pp (= X) state, to be formed in the binary process pp -> K+ X. The preliminary spectra of the DeltaM_{K+} missing-mass and of the M_{p Lambda} invariant-mass show, for large transverse-momenta of protons and kaons, a distinct broad peak with a mass M_X = 2265 +- 2 MeV/c^2 and a width Gamma_X = 118 +- 8 MeV/c^2.Comment: 8 pages, 4 figures. Talk presented at the "10th International Conference on Hypernuclear and Strange Particle Physics" (HYP-X), Tokai, Ibaraki, Japan, September 14th-18th, 2009. To appear in the proceeding

Indication of a deeply bound compact K-pp state formed in the pp -> p Lambda K+ reaction at 2.85 GeV

We have analyzed data of the DISTO experiment on the exclusive pp -> p Lambda K+ reaction at 2.85 GeV to search for a strongly bound compact K-pp (= X) state to be formed in the pp -> K+ + X reaction. The observed spectra of the K+ missing-mass and the p Lambda invariant-mass with high transverse momenta of p and K+ revealed a broad distinct peak with a mass M_X = 2265 +- 2 (stat) +- 5 (syst) MeV/c2 and a width Gamma_X = 118 +- 8 (stat) +- 10 (syst) MeV.Comment: 4 pages, 4 figure

K−^- Meson Production in the Proton-Proton Reaction at 3.67 GeV/c

The total cross section of the reaction $pp\to ppK^+K^-$ has been determined for proton--proton reactions with $p_{beam}=3.67 GeV/c$. This represents the first cross section measurement of the $pp \to ppK^-K^+$ channel near threshold, and is equivalent to the inclusive $pp\to ppK^-X$ cross section at this beam momentum. The cross section determined at this beam momentum is about a factor 20 lower than that for inclusive $pp\to ppK^+X$ meson production at the same CM energy above the corresponding threshold. This large difference in the $K^+$ and $K^-$ meson inclusive production cross sections in proton-proton reactions is in strong contrast to cross sections measured in sub-threshold heavy ion collisions, which are similar in magnitude at the same energy per nucleon below the respective thresholds.Comment: 12 pages, 3 figures Phys. Lett. B in prin

Production of η′\eta\prime Mesons in the pp→ppη′pp \to pp\eta\prime Reaction at 3.67 GeV/c

The ratio of the total exclusive production cross sections for $\eta\prime$ and $\eta$ mesons has been measured in the $pp$ reaction at $p_{beam}=3.67$ GeV/c. The observed $\eta\prime/\eta$ ratio is $(0.83\pm{0.11}^{+0.23}_{-0.18})\times 10^{-2}$ from which the exclusive $\eta\prime$ meson production cross section is determined to be $(1.12\pm{0.15}^{+0.42}_{-0.31})\mu b$. Differential cross section distributions have been measured. Their shape is consistent with isotropic $\eta\prime$ meson production.Comment: 14 pages, 5 figures, accepted by Phys.Lett.

SFE16, a low noise front-end integrated circuit dedicated to the read-out of large Micromegas detectors

Abstract A front-end BiCMOS ASIC was specially developed for the Micromegas detectors to be used in the Small Angle Tracker of the COMPASS experiment at CERN. Each of the 16 channels of this integrated circuit contains a low noise preamplifier with a 100 ns peaking time filter and a discriminator driving a low-level differential digital buffer. The design of the preamplifier and the choice of the shaping have been tuned to the detector signal shape in order to allow the operation of Micromegas even for very low multiplication gain values. Noise measurements show an equivalent noise charge of less than 1500 e-rms for a detector capacitance of 40pF. The measured performances of this ASIC associated or not with the detector are fully described in this paper

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