The gluon polarisation in the nucleon was measured using open charmproduction by scattering 160 GeV/c polarised muons off longitudinally polarisedprotons or deuterons. The data were taken by the COMPASS collaboration between2002 and 2007. A detailed account is given of the analysis method that includesthe application of neural networks. Several decay channels of D^0 mesons areinvestigated. Longitudinal spin asymmetries of the D meson productioncross-sections are extracted in bins of D^0 transverse momentum and energy. Atleading order QCD accuracy the average gluon polarisation is determined as(Delta g/G)^LO=-0.06 +/- 0.21 (stat.) +/- 0.08 (syst.) at the scale ~13(GeV/c)^2 and an average gluon momentum fraction ~ 0.11. For the first time,the average gluon polarisation is also obtained at next-to-leading order QCDaccuracy as (Delta g/G)^NLO = -0.13 +/- 0.15 (stat.) +/- 0.15 (syst.) at thescale ~ 13 (\GeV/c)^2 and ~ 0.20.

We present a determination of the gluon polarisation Delta g/g in the nucleon, based on the longitudinal double-spin asymmetry of DIS events with a pair of large transverse-momentum hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon beam scattering off a polarised ^6LiD target. The gluon polarisation is evaluated by a Neural Network approach for three intervals of the gluon momentum fraction x_g covering the range 0.04 < x_g < 0.27. The values obtained at leading order in QCD do not show any significant dependence on x_g. Their average is Delta g/g = 0.125 +/- 0.060 (stat.) +/- 0.063 (syst.) at x_g=0.09 and a scale of mu^2 = 3 (GeV/c)^2.

The photon detectors based on MPGD (MicroPattern Gaseous Detector) represent the new generation of gaseous photon detectors. We report about an R&D programme dedicated to study both the principles and the engineering aspects of photon detectors based on Thick GEMs (THGEM) electron multipliers coupled to a CsI photoconverting coating. The goal is the development of a gaseous detector of single UV photons, able to stably operate at high gain and high rate, to provide good time resolution and insensitive to magnetic field to be used in the Cherenkov imaging counter RICH-1 of the COMPASS experiment at CERN SPS.

The COMPASS Collaboration at CERN has measured the transverse spin azimuthal asymmetry of charged hadrons produced in semi-inclusive deep inelastic scattering using a 160 GeV positive muon beam and a transversely polarised NH_3 target. The Sivers asymmetry of the proton has been extracted in the Bjorken x range 0.003 0.03. The asymmetry is different from zero and positive also in the low x region, where sea-quarks dominate. The kinematic dependence of the asymmetry has also been investigated and results are given for various intervals of hadron and virtual photon fractional energy. In contrast to the case of the Collins asymmetry, the results on the Sivers asymmetry suggest a strong dependence on the four-momentum transfer to the nucleon, in agreement with the most recent calculations.

A measurement of the azimuthal asymmetry in dihadron production in deep-inelastic scattering of muons on transversely polarised proton (NH3) targets is presented. They provide independent access to the transversity distribution functions through the measurement of the Collins asymmetry in single hadron production. The data were taken in the year 2010 with the COMPASS spectrometer using a 160 GeV/c muon beam of the CERN SPS, increasing by a factor of about four the overall statistics with respect to the previously published data taken in the year 2007. The measured sizeable asymmetry is in good agreement with the published data. An approximate equality of the Collins asymmetry and the dihadron asymmetry is observed, suggesting a common physical mechanism in the underlying fragmentation.

AbstractA search is made for charged Higgs bosons predicted by Two-Higgs-Doublet extensions of the Standard Model (2HDM) using electron-positron collision data collected by the OPAL experiment at $\sqrt{s}=189\mbox{--}209\ \mbox{GeV}$, corresponding to an integrated luminosity of approximately 600 pb−1. Charged Higgs bosons are assumed to be pair-produced and to decay into $\mathrm{q} \bar{\mathrm{q}}$, τντ or AW±. No signal is observed. Model-independent limits on the charged Higgs-boson production cross section are derived by combining these results with previous searches at lower energies. Under the assumption $\mathrm{BR} (\mathrm{H}^{\pm} \to \tau\nu_{\tau}) + \mathrm{BR} (\mathrm{H}^{\pm} \to \mathrm{q} \bar{\mathrm{q}}) = 1$, motivated by general 2HDM type II models, excluded areas on the $[m_{\mathrm{H}^{\pm}} , \mathrm{BR} (\mathrm {H}^{\pm} \to \tau\nu_{\tau})]$ plane are presented and charged Higgs bosons are excluded up to a mass of 76.3 GeV at 95 % confidence level, independent of the branching ratio BR(H±→τντ). A scan of the 2HDM type I model parameter space is performed and limits on the Higgs-boson masses $m_{\mathrm{H}^{\pm}}$ and mA are presented for different choices of tanβ.

The COMPASS Collaboration at CERN has investigated the pi(-)gamma -> pi(-)pi(-)pi(+) reaction at center-of-momentum energy below five pion masses, root s < 5m(pi), embedded in the Primakoff reaction of 190 GeV pions impinging on a lead target. Exchange of quasireal photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, t' < 0.001 GeV2/c(2). Using partial-wave analysis techniques, the scattering intensity of Coulomb production described in terms of chiral dynamics and its dependence on the 3 pi-invariant mass m(3 pi) = root s were extracted. The absolute cross section was determined in seven bins of root s with an overall precision of 20%. At leading order, the result is found to be in good agreement with the prediction of chiral perturbation theory over the whole energy range investigated.

An R&D project is presented, aimed to develop a high performance gaseous detector of single photons, for the upgrade of the Ring Imaging Cherenkov Counter RICH-1 of the COMPASS Experiment at CERN SPS. The detector has to stably operate at high gain and high rate, to provide good time resolution and insensitivity to magnetic field, and to offer the possibility to cover very large areas at affordable cost. The proposed solution is based on the use of a novel and robust electron multiplier, the Thick GEM (THGEM), arranged in a multilayer architecture, where the first layer is coated with a photosensitive CsI film. A systematic study of the response of THGEMs with various geometrical and production parameters and in different conditions was performed, leading to the choice of a set of optimal parameters. Prototypes of THGEM-based photon detectors able to efficiently detect Cherenkov photons have been built, tested in laboratory and operated in test beam exercises with typical gain of 10(5) and time resolution better than 10 ns. The engineering aspects of building large area (600x600 mm(2)) THGEM-based photon detectors are presently being investigated. (C) 2012 Published by Elsevier B.V. Selection and/or peer review under responsibility of the organizing committee for TIPP 11.

The production of D ∗ and D mesons in inelastic scattering of 160 GeV/c muons off a 6LiD target has been investigated with the COMPASS spectrometer at CERN for 0.003 (GeV/c)2"0.6."

search is made for charged Higgs bosons predicted by Two-Higgs-Doublet extensions of the Standard Model (2HDM) using electron-positron collision data collected by the OPAL experiment at √(s)=189209 , corresponding to an integrated luminosity of approximately 600 pb −1 . Charged Higgs bosons are assumed to be pair-produced and to decay into qq̅ , τν τ or AW ± . No signal is observed. Model-independent limits on the charged Higgs-boson production cross section are derived by combining these results with previous searches at lower energies. Under the assumption BR (H^±→τν_τ) + BR (H^±→qq̅) = 1 , motivated by general 2HDM type II models, excluded areas on the [m_H^± , BR (H^±→τν_τ)] plane are presented and charged Higgs bosons are excluded up to a mass of 76.3 GeV at 95

An R&D project was started to develop a gaseous detector of single UV photons, able to stably operate at high gain and high rate, and to provide good time resolution and insensitivity to magnetic field, as required by the next generation of Ring Imaging Cherenkov Counters. The detector is based on the use of a novel and robust electron multiplier, the THGEM, arranged in a multilayer architecture, where the first layer is coated with a photosensitive CsI film. A systematic study of the response of single layer THGEMs with various geometries and different conditions was performed and several small photon detector prototypes have been built, tested in laboratory and operated in test beam exercises during 2009 and 2010 at the CERN H4 beam line. Evidence for the efficient detection of Cherenkov photons has been obtained, with stable operation in the test beam environment; the typical gain was about 10 5 and the time resolution was better than 10 ns.

Hadronic event shape distributions from e + e − annihilation measured by the OPAL experiment at centre-of-mass energies between 91 GeV and 209 GeV are used to determine the strong coupling α S . The results are based on QCD predictions complete to the next-to-next-to-leading order (NNLO), and on NNLO calculations matched to the resummed next-to-leading-log-approximation terms (NNLO + NLLA). The combined NNLO result from all variables and centre-of-mass energies is while the combined NNLO + NLLA result is The completeness of the NNLO and NNLO + NLLA results with respect to missing higher order contributions, studied by varying the renormalization scale, is improved compared to previous results based on NLO or NLO + NLLA predictions only. The observed energy dependence of α S agrees with the QCD prediction of asymptotic freedom and excludes the absence of running.

COMPASS RICH-1 is a large size gaseous Imaging Cherenkov Detector providing hadron identification in the range from 3 to 55 GeV/c, in the wide acceptance spectrometer of the COMPASS Experiment at CERN SPS. It uses a 3 m long C(4)F(10) radiator, a 21 m(2) large VUV mirror surface and two kinds of photon detectors: MAPMTs and MWPCs with CsI photocathodes, covering a total of 5.5 m(2). It is in operation since 2002 and its performance has increased in time thanks to progressive optimization and mostly to a major upgrade which was implemented in 2006. The main characteristics of COMPASS RICH-1 components are described and some specific aspects related to the radiator gas system, the mirror alignment, the MWPC electrical stability and the readout electronics are discussed. Some key features of the event reconstruction and the PID analysis are presented together with results from the COMPASS RICH-1 performance characterization study. (C) 2010 Elsevier B.V. All rights reserved.

The novel and robust Thick GEM (THGEM) electron multiplier, coupled to a solid state photon converter, represents a promising option for instrumenting, at affordable costs, large areas with photon detectors, in particular, in Cherenkov imaging counters where single photons must be detected with high efficiency. The main goal of our project is to demonstrate the feasibility of reliable gaseous detector of single photons based on the use of THGEM multipliers, able to stably operate at high gain and high rate and to build and validate a large size prototype of such a detector. The project status and perspectives are reported; in particular attention is dedicated to the simulation and laboratory studies performed to understand the photo-electron extraction performance attainable using a solid state coated photo-cathode film onto a THGEM substrate.

The COMPASS experiment at the CERN SPS has studied the diffractive dissociation of negative pions into the π- π- π+ final state using a 190  GeV/c pion beam hitting a lead target. A partial wave analysis has been performed on a sample of 420,000 events taken at values of the squared 4-momentum transfer t' between 0.1 and 1  GeV2/c2. The well-known resonances a1(1260), a2(1320), and π2(1670) are clearly observed. In addition, the data show a significant natural-parity exchange production of a resonance with spin-exotic quantum numbers J(PC)=1-+ at 1.66  GeV/c2 decaying to ρπ. The resonant nature of this wave is evident from the mass-dependent phase differences to the J(PC)=2-+ and 1++ waves. From a mass-dependent fit a resonance mass of (1660±10(-64)(+0))  MeV/c2 and a width of (269±21(-64)(+42))  MeV/c2 are deduced, with an intensity of (1.7±0.2)% of the total intensity.

M.G. Alekseev, V.Yu. Alexakhin, Yu. Alexandrov, G.D. Alexeev, A. Amoroso, A. Austregesilo, B. Badełek, F. Balestra, J. Ball, J. Barth, G. Baum, Y. Bedfer, J. Bernhard, R. Bertini, M. Bettinelli, R. Birsa, J. Bisplinghoff, P. Bordalo, F. Bradamante, A. Bravar, A. Bressan, G. Brona, E. Burtin, M. P. Bussa, A. Chapiro, M. Chiosso, S. U. Chung, A. Cicuttin, M. Colantoni, M. L. Crespo, S. Dalla Torre, T. Dafni, S. Das, S. S. Dasgupta, O.Yu. Denisov, L. Dhara, V. Diaz, A.M. Dinkelbach, S. V. Donskov, N. Doshita, V. Duic, W. Dünnweber, A. Efremov, A. El Alaoui, P. D. Eversheim, W. Eyrich, M. Faessler, A. Ferrero, M. Finger, M. Finger, Jr., H. Fischer, C. Franco, J.M. Friedrich, R. Garfagnini, F. Gautheron, O. P. Gavrichtchouk, R. Gazda, S. Gerassimov, R. Geyer, M. Giorgi, B. Gobbo, S. Goertz, S. Grabmüller, O.A. Grajek, A. Grasso, B. Grube, R. Gushterski, A. Guskov, F. Haas, D. von Harrach, T. Hasegawa, J. Heckmann, F. H. Heinsius, R. Hermann, F. Herrmann, C. Heß, F. Hinterberger, N. Horikawa,18,x Ch. Höppner, N. d’Hose, C. Ilgner, S. Ishimoto,18,{ O. Ivanov, Yu. Ivanshin, T. Iwata, R. Jahn, P. Jasinski, G. Jegou, R. Joosten, E. Kabuß, D. Kang, B. Ketzer, G. V. Khaustov, Yu. A. Khokhlov, Yu. Kisselev, F. Klein, K. Klimaszewski, S. Koblitz, J. H. Koivuniemi, V. N. Kolosov, E. V. Komissarov,* K. Kondo, K. Königsmann, R. Konopka, I. Konorov, V. F. Konstantinov, A. Korzenev, A.M. Kotzinian, O. Kouznetsov, K. Kowalik, M. Krämer, A. Kral, Z. V. Kroumchtein, R. Kuhn, F. Kunne, K. Kurek, L. Lauser, J.M. Le Goff, A.A. Lednev, A. Lehmann, S. Levorato, J. Lichtenstadt, T. Liska, A. Maggiora, M. Maggiora, A. Magnon, G.K. Mallot, A. Mann, C. Marchand, J. Marroncle, A. Martin, J. Marzec, F. Massmann, T. Matsuda, A.N. Maximov,* W. Meyer, T. Michigami, Yu. V. Mikhailov, M.A. Moinester, A. Mutter, A. Nagaytsev, T. Nagel, J. Nassalski,* T. Negrini, F. Nerling, S. Neubert, D. Neyret, V. I. Nikolaenko, A.G. Olshevsky, M. Ostrick, A. Padee, R. Panknin, D. Panzieri, B. Parsamyan, S. Paul, B. Pawlukiewicz-Kaminska, E. Perevalova, G. Pesaro, D.V. Peshekhonov, G. Piragino, S. Platchkov, J. Pochodzalla, J. Polak, V. A. Polyakov, G. Pontecorvo, J. Pretz, C. Quintans, J.-F. Rajotte, S. Ramos, V. Rapatsky, G. Reicherz, D. Reggiani, A. Richter, F. Robinet, E. Rocco, E. Rondio, D. I. Ryabchikov, V.D. Samoylenko, A. Sandacz, H. Santos, M.G. Sapozhnikov, S. Sarkar, I. A. Savin, G. Sbrizzai, P. Schiavon, C. Schill, T. Schlüter, L. Schmitt,17,k S. Schopferer, W. Schröder, O.Yu. Shevchenko, H.-W. Siebert, L. Silva, L. Sinha, A.N. Sissakian, M. Slunecka, G. I. Smirnov, S. Sosio, F. Sozzi, A. Srnka, M. Stolarski, M. Sulc, R. Sulej, S. Takekawa, S. Tessaro, F. Tessarotto, A. Teufel, L. G. Tkatchev, S. Uhl, I. Uman, G. Venugopal, M. Virius, N.V. Vlassov, A. Vossen, Q. Weitzel, R. Windmolders, W. Wiślicki, H. Wollny, K. Zaremba, M. Zavertyaev, E. Zemlyanichkina, M. Ziembicki, J. Zhao, N. Zhuravlev, and A. Zvyagin

The inclusive double-spin asymmetry, A_1^p, has been measured at COMPASS in deepinelastic polarised muon scattering off a large polarised NH3 target. The data, collected in the year 2007, cover the range Q2 > 1 (GeV/c)^2, 0.004 < x < 0.7 and improve the statistical precision of g_1^p(x) by a factor of two in the region x < 0.02. The new proton asymmetries are combined with those previously published for the deuteron to extract the non-singlet spin-dependent structure function g_1^NS(x,Q2). The isovector quark density, Delta_q_3(x,Q2), is evaluated from a NLO QCD fit of g_1^NS. The first moment of Delta_q3 is in good agreement with the value predicted by the Bjorken sum rule and corresponds to a ratio of the axial and vector coupling constants g_A/g_V = 1.28+-0.07(stat)+-0.10(syst).

New photon detectors, based on the use of multi-anode photo-multiplier tubes coupled to individual lens telescopes and read out with a dedicated read-out electronics system, equip the central region of the Cherenkov imaging counter RICH-1 of the COMPASS experiment at CERN SPS. They are characterised by high photon yield, fast response and high rate capability and are successfully in operation since the 2006 COMPASS data taking. The photon detection system fully matches the expected performance.The design and construction of the photon detectors are described in detail. (C) 2010 Elsevier B.V. All rights reserved.

A search is performed for Higgs bosons decaying into invisible final states, produced in association with a Z(0) boson in e(+)e(-) collisions at energies between 183 and 209 GeV. The search is based on data samples collected by the OPAL detector at LEP corresponding to an integrated luminosity of about 660 pb(-1). The analysis aims to select events containing the hadronic decay products of the Z(0) boson and large missing momentum, as expected from Higgs boson decay into a pair of stable weakly interacting neutral particles, such as the lightest neutralino in the Minimal Supersymmetric Standard Model. The same analysis is applied to a search for nearly invisible Higgs boson cascade decays into stable weakly interacting neutral particles. No excess over the expected background from Standard Model processes is observed. Limits on the production of invisibly decaying Higgs bosons produced in association with a Z(0) boson are derived. Assuming a branching ratio BR(h(0) -> invisible) = 1, a lower limit of 108.2 GeV is placed on the Higgs boson mass at the 95% confidence level. Limits on the production of nearly invisibly decaying Higgs bosons are also obtained. (C) 2009 Elsevier B.V. All rights reserved.

The Collins and Sivers asymmetries for charged hadrons produced in deeply inelastic scattering on transversely polarised protons have been extracted from the data collected in 2007 with the CERN SPS muon beam tuned at 160 GeV/c. At large values of the Bjorken x variable non-zero Collins asymmetries are observed both for positive and negative hadrons while the Sivers asymmetry for positive hadrons is slightly positive over almost all the measured x range. These results nicely support the present theoretical interpretation of these asymmetries, in terms of leading-twist quark distribution and fragmentation functions.