Publications (476)63.06 Total impact
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Article: Leading and Next-to-Leading Order Gluon Polarisation in the Nucleon and Longitudinal Double Spin Asymmetries from Open Charm Muoproduction
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ABSTRACT: The gluon polarisation in the nucleon was measured using open charm production by scattering 160 GeV/c polarised muons off longitudinally polarised protons or deuterons. The data were taken by the COMPASS collaboration between 2002 and 2007. A detailed account is given of the analysis method that includes the application of neural networks. Several decay channels of D^0 mesons are investigated. Longitudinal spin asymmetries of the D meson production cross-sections are extracted in bins of D^0 transverse momentum and energy. At leading 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 <mu^2> ~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 QCD accuracy as (Delta g/G)^NLO = -0.13 +/- 0.15 (stat.) +/- 0.15 (syst.) at the scale <mu^2> ~ 13 (\GeV/c)^2 and ~ 0.20.11/2012; -
Article: D* and D Meson Production in Muon Nucleon Interactions at 160 GeV/c
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ABSTRACT: 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 < Q^2 < 10 (GeV/c)^2 and 3x10^-5< x_Bj < 0.1. The study is based on 8100 events where a D^0 or anti D^0 is detected subsequently to a D*+ or D*- decay, and on 34000 events, where only a D^0 or anti D^0 is detected. Kinematic distributions of D*, D and K*_2 are given as a function of their energy E, transverse momentum p_T, energy fraction z, and of the virtual photon variables nu, Q^2 and x_Bj. Semi-inclusive differential D* production cross-sections are compared with theoretical predictions for D* production via photon-gluon fusion into open charm. The total observed production cross-section for D*+/- mesons with laboratory energies between 22 and 86 GeV is 1.9 nb. Significant cross-section asymmetries are observed between D*+ and D*- production for nu<40 GeV and z>0.6.European Physical Journal C 11/2012; 72(12). · 3.63 Impact Factor -
Article: Exclusive rho^0 muoproduction on transversely polarised protons and deuterons
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ABSTRACT: The transverse target spin azimuthal asymmetry A_UT in hard exclusive production of rho^0 mesons was measured at COMPASS by scattering 160 GeV/c muons off transversely polarised protons and deuterons. The measured asymmetry is sensitive to the nucleon helicity-flip generalised parton distributions E^q, which are related to the orbital angular momentum of quarks in the nucleon. The Q^2, x_B and p_t^2 dependence of A_UT is presented in a wide kinematic range. Results for deuterons are obtained for the first time. The measured asymmetry is small in the whole kinematic range for both protons and deuterons, which is consistent with the theoretical interpretation that contributions from GPDs E^u and E^d approximately cancel.07/2012; -
Article: Measurement of the Cross Section for High-p_T Hadron Production in Scattering of 160 GeV/c Muons off Nucleons
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ABSTRACT: The cross section for production of charged hadrons with high transverse momenta in scattering of 160 GeV/c muons off nucleons at low photon virtualities has been measured at the COMPASS experiment at CERN. The results, which cover transverse momenta from 1.1 to 3.6 GeV/c, are compared to a next-to-leading order perturbative Quantum Chromodynamics (NLO pQCD) calculation in order to evaluate the applicability of pQCD to this process in the kinematic domain of the experiment. The shape of the calculated differential cross section as a function of transverse momentum is found to be in good agreement with the experimental data, but the normalization is underestimated by NLO pQCD. This discrepancy may point towards the relevance of terms beyond NLO in the pQCD framework. The dependence of the cross section on the pseudo-rapidity and on the charge of the hadrons is also discussed.07/2012; -
Article: Experimental investigation of transverse spin asymmetries in muon-p SIDIS processes: Collins asymmetries
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ABSTRACT: 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 Collins asymmetry of the proton was extracted in the Bjorken x range 0.003<x<0.7. These new measurements confirm with higher accuracy previous measurements from the COMPASS and HERMES collaborations, which exhibit a definite effect in the valence quark region. The asymmetries for negative and positive hadrons are similar in magnitude and opposite in sign. They are compatible with model calculations in which the u-quark transversity is opposite in sign and somewhat larger than the d-quark transversity distribution function. The asymmetry is extracted as a function of Bjorken $x$, the relative hadron energy $z$ and the hadron transverse momentum p_T^h. The high statistics and quality of the data also allow for more detailed investigations of the dependence on the kinematic variables. These studies confirm the leading-twist nature of the Collins asymmetry.05/2012; -
Article: Experimental investigation of transverse spin asymmetries in muon-p SIDIS processes: Sivers asymmetries
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ABSTRACT: 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<x<0.7. The new measurements have small statistical and systematic uncertainties of a few percent and confirm with considerably better accuracy the previous COMPASS measurement. The Sivers asymmetry is found to be compatible with zero for negative hadrons and positive for positive hadrons, a clear indication of a spin-orbit coupling of quarks in a transversely polarised proton. As compared to measurements at lower energy, a smaller Sivers asymmetry for positive hadrons is found in the region x > 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.05/2012; -
Article: Some special features in the filling of the Fermi sphere with quark quasiparticles
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ABSTRACT: The filling of the Fermi sphere with quarks treated as quasiparticles of the model Hamiltonian for four-fermion interaction is studied.Physics of Atomic Nuclei 04/2012; 73(7):1245-1253. · 0.57 Impact Factor -
Article: Measurement of the longitudinal spin transfer to Λ and hyperons in polarised muon DIS
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ABSTRACT: The longitudinal polarisation transfer from muons to Λand [`\varLambda]\bar{\varLambda} hyperons, DLL\varLambda([`\varLambda])D_{LL}^{\varLambda(\bar{\varLambda})} , has been studied in deep-inelastic scattering off an unpolarised isoscalar target at the COMPASS experiment at CERN. The spin transfers to Λand [`\varLambda]\bar{\varLambda} produced in the current fragmentation region exhibit different behaviours as a function of x and x F . The measured x and x F dependences of D LL Λ are compatible with zero, while DLL[`\varLambda]D_{LL}^{\bar{\varLambda}} tends to increase with x F , reaching values of 0.4–0.5. The resulting average values are D LL Λ = −0.012±0.047±0.024 and DLL[`\varLambda]D_{LL}^{\bar{\varLambda}} = 0.249±0.056±0.049. These results are discussed in the frame of recent model calculations.European Physical Journal C 04/2012; 64(2):171-179. · 3.63 Impact Factor -
Article: Progress in development of Nuclotron accelerator complex
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ABSTRACT: The Nuclotron superconducting synchrotron was constructed in 1987–1992 [1]; it is the world’s first synchrotron based on fast cycling “window frame” electromagnets with a superconducting coil. For a design field of dipole magnets of 2 T, the magnetic rigidity is 45 T m, which corresponds to the energy of heavy nuclei (for example, gold) of 4.5 GeV/nucleon. The Nuclotron accelerator complex is currently being upgraded (the Nuclotron-M project); this upgrade is considered a key part of the first stage of fulfilling the new Joint Institute for Nuclear Research (JINR) project: the Nuclotron-based Ion Collider fAcility and Multi-Purpose Detector (NICA/MPD). The most important task of this new project is the preparation of basic Nuclotron systems for its reliable operation as part of the NICA accelerator complex. Basic results of activity on the project, which started in 2007, are presented and the results of the last Nuclotron runs are analyzed.Physics of Particles and Nuclei Letters 04/2012; 7(7):442-445. -
Article: Towards light scalar meson structure
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ABSTRACT: The origin of the lightest scalar mesons is studied in the framework of the instanton liquid model of the QCD vacuum. The impact of phonon-like vacuum excitations on the σ-meson features is qualitatively analyzed. In particular, it is noticed that the changes produced in the scalar sector may unexpectedly become quite considerable in spite of insignificant values of corrections to the dynamical quark masses and then the medley of σ-meson and those excitations may reveal itself as broad resonance states of different masses.European Physical Journal C 04/2012; 61(1):61-68. · 3.63 Impact Factor -
Article: Sigma meson and phonon-like excitations of the instanton vacuum
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ABSTRACT: The possible nature of two experimentally observed scalar mesons that are widely spaced in mass and whose special features may be caused by the excitations of the instanton liquid considered as a model of the QCD vacuum. It is shown that mass changes in the scalar sector may prove to be unexpectably large, even though the scale of such corrections to the dynamical quark mass is relatively small. PACS numbers11.15.Kc–12.38.-AwPhysics of Atomic Nuclei 04/2012; 71(2):313-320. · 0.57 Impact Factor -
Article: Azimuthal asymmetries of charged hadrons produced by high-energy muons scattered off longitudinally polarised deuterons
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ABSTRACT: 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 phTp_{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.European Physical Journal C 04/2012; 70(1):39-49. · 3.63 Impact Factor -
Article: Relativistic nuclear physics at the Joint Institute for Nuclear Research
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ABSTRACT: The basic stages of the development of the Veksler and Baldin Laboratory of High Energies, Joint Institute for Nuclear Research, in Dubna are described briefly. Some experiments on the investigation of cumulative particle production and the new direction of investigation of the processes of hadron-nuclear and nuclear-nuclear interaction in which the quark structure of nuclei can be manifested—relativistic nuclear physics—are considered. Basic methodical and experimental results obtained at the synchrophasotron and Nuclotron are presented, ideas produced in collaboration with theoreticians of the Bogoliubov Laboratory of Theoretical Physics are discussed. An overview of investigations in the field of relativistic nuclear physics planned at the Nuclotron is given.Physics of Particles and Nuclei 04/2012; 38(4):407-446. · 0.52 Impact Factor -
Article: The isospin-symmetry-breaking effects in Ke4 decays
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ABSTRACT: The Fermi-Watson theorem is generalized to the case of two coupled channels with different masses and applied to final-state interaction inK e4 decays. The impact of the considered effect on the phase of ππ scattering is estimated and it is shown that it can be crucial for the scattering length extraction from experimental data on K e4 decays.Physics of Atomic Nuclei 04/2012; 73(6):961-964. · 0.57 Impact Factor -
Article: DViN-2 stationary inspection complex
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ABSTRACT: A DViN-2 stationary inspection complex has been designed and manufactured for identifying hidden explosives and drugs. The identification of hidden substances is based on the method of tagged neutrons. The source of the tagged neutron beam, which has an energy of 14.1 MeV produced in the reaction d + t → α + n, is a portable neutron generator with a built-in 9-channel silicon α detector. The DViN-2 makes it possible to identify hidden explosives and drugs with a mass of from 100 g to 50 kg in objects with dimensions from 50 to 400 mm in all three directions. The results of 76 experiments testify to the high efficiency of the DViN-2 in regards to identifying hidden explosives and drugs and it has a rather low probability of false actuations: the probability of identifying explosives and drugs is 94%, and that of false alarms rate is 3%. The time it takes to identify hidden substances, depending on their mass and the thickness of the shielding material layer, is 3–7 min for an average neutron beam intensity into a solid angle of 4π of 2 × 107s−1.Physics of Particles and Nuclei Letters 04/2012; 6(6):505-510. -
Article: The electromagnetic effects in Ke4 decay
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ABSTRACT: The final-state interaction of pions in K e4 decay allows to obtain the value of the isospin and angular-momentum-zero ππ scattering length a 00.We take into account the electromagnetic interaction of pions and isospin-symmetry-breaking effects caused by different masses of neutral and charged pions and estimate the impact of these effects on the procedure of scattering-length extraction from K e4 decays.Physics of Atomic Nuclei 04/2012; 73(6):937-940. · 0.57 Impact Factor -
Article: Properties of strongly interacting matter and the search for a mixed phase at the JINR nuclotron
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ABSTRACT: A physical program is formulated for new facilities opening in Dubna for the acceleration of heavy ions with an energy up to 5A GeV. PACS numbers12.38.-tPhysics of Particles and Nuclei Letters 04/2012; 5(1):1-6. -
Article: Transverse spin effects in hadron-pair production from semi-inclusive deep inelastic scattering
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ABSTRACT: First measurements of azimuthal asymmetries in hadron-pair production in deep-inelastic scattering of muons on transversely polarised ^6LiD (deuteron) and NH_3 (proton) targets are presented. The data were taken in the years 2002-2004 and 2007 with the COMPASS spectrometer using a muon beam of 160 GeV/c at the CERN SPS. The asymmetries provide access to the transversity distribution functions, without involving the Collins effect as in single hadron production. The sizeable asymmetries measured on the NH_ target indicate non-vanishing u-quark transversity and two-hadron interference fragmentation functions. The small asymmetries measured on the ^6LiD target can be interpreted as indication for a cancellation of u- and d-quark transversities.02/2012; -
Article: Leading order determination of the gluon polarisation from DIS events with high-p_T hadron pairs
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ABSTRACT: 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)^2.02/2012; -
Article: First Measurement of Chiral Dynamics in \pi^- \gamma -> \pi^- \pi^- \pi^+
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ABSTRACT: The COMPASS collaboration at CERN has investigated the \pi^- \gamma -> \pi^- \pi^- \pi^+ reaction at center-of-momentum energy below five pion masses, sqrt(s) < 5 m(\pi), embedded in the Primakoff reaction of 190 GeV pions impinging on a lead target. Exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, t' < 0.001 (GeV/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) = sqrt(s) were extracted. The absolute cross section was determined in seven bins of $\sqrt{s}$ 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.11/2011;
Top co-authors
Top Journals
Institutions
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1973–2012
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Joint Institute for Nuclear Research
Dubna, Moskovskaya, Russia
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2003
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The University of Georgia (Tbilisi)
Tbilisi, K'alak'i T'bilisi, Georgia
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1991
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Università degli studi di Udine
Udine, Friuli Venezia Giulia, Italy
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1985
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Yerevan State University
Yerevan, K'aghak' Yerevan, Armenia
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