Publications (646)990.56 Total impact

Dataset: 1s2.00370269391909986main

Dataset: democrite00010443
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ABSTRACT: The energy loss spectrum of 180 GeV muons has been measured with the 5.6 m long finely segmented Module 0 of the ATLAS hadron Tile Calorimeter at the CERN SPS. The differential probability dP/dv per radiation length of a fractional energy loss v = ΔΕμ/Εμ has been measured in the range 0.025 ≤ v ≤ 0.97; it is compared with theoretical predictions for energy losses due to bremsstrahlung, production of electronpositron pairs, and energetic knockon electrons. The iron elastic form factor correction ΔelFe = 1.63 ± 0.17stat ± 0.23Syst±0.200.14theor to muon bremsstrahlung in the region of no screening of the nucleus by atomic electrons has been measured for the first time, and is compared with different theoretical predictions. 

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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 crosssections 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 nexttoleading 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.  [Show abstract] [Hide abstract]
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 3×10−5<x Bj <0.1. The study is based on 8100 events where a D 0 or \(\bar{D}^{0}\) is detected subsequently to a D ∗+ or D ∗− decay, and on 34000 events, where only a D 0 or \(\bar{D}^{0}\) is detected. Kinematic distributions of D ∗, D and \(K_{2}^{*} (1430)\) are given as a function of their energy E, transverse momentum p T , energy fraction z, and of the virtual photon variables ν, Q 2 and x Bj . Semiinclusive differential D ∗ production crosssections are compared with theoretical predictions for D ∗ production via photon–gluon fusion into open charm. The total observed production crosssection for D ∗± mesons with laboratory energies between 22 and 86 GeV is (1.9±0.4) nb. Significant crosssection asymmetries are observed between D ∗+ and D ∗− production for ν<40 GeV and z>0.6.  [Show abstract] [Hide abstract]
ABSTRACT: The COMPASS Collaboration at CERN has investigated the π γ → π π π+ reaction at centerofmomentum energy below five pion masses, sqrt[s]<5m(π), 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/c2. Using partialwave analysis techniques, the scattering intensity of Coulomb production described in terms of chiral dynamics and its dependence on the 3πinvariant mass m(3π)=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.  [Show abstract] [Hide abstract]
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 helicityflip 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.  [Show abstract] [Hide abstract]
ABSTRACT: Along with π 0 and η mesons, a resonance structure in the invariant mass spectrum of two photons atM γγ = 360 ± 7 ± 9 MeV is observed in dC interactions at momentum 2.75 GeV/c per nucleon. This resonance structure is not observed in pC collisions at the beam momentum 5.5 GeV/c. The result obtained in the reaction dC is confirmed by the second experiment carried out on the deuteron beam at momentum 3.83 GeV/c per nucleon with a copper target. Some other checks of the observed effect are presented.  [Show abstract] [Hide abstract]
ABSTRACT: The COMPASS Collaboration at CERN has measured the transverse spin azimuthal asymmetry of charged hadrons produced in semiinclusive 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 uquark transversity is opposite in sign and somewhat larger than the dquark 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 leadingtwist nature of the Collins asymmetry.  [Show abstract] [Hide abstract]
ABSTRACT: The COMPASS Collaboration at CERN has measured the transverse spin azimuthal asymmetry of charged hadrons produced in semiinclusive 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 spinorbit 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 seaquarks 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 fourmomentum transfer to the nucleon, in agreement with the most recent calculations.  [Show abstract] [Hide abstract]
ABSTRACT: A nonperturbative method for calculating functional integrals is proposed. Only Gaussian quadratures and only those types of diagrams which occur in the standard perturbation theory are used for the formulation of this method. The proposed approach is used for the consideration of the φ2k anharmonic oscillator in the strong coupling limit. 
Article: Transverse spin effects in hadronpair production from semiinclusive deep inelastic scattering
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ABSTRACT: First measurements of azimuthal asymmetries in hadronpair production in deepinelastic scattering of muons on transversely polarised ^6LiD (deuteron) and NH_3 (proton) targets are presented. The data were taken in the years 20022004 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 nonvanishing uquark transversity and twohadron interference fragmentation functions. The small asymmetries measured on the ^6LiD target can be interpreted as indication for a cancellation of u and dquark transversities. 
Article: Leading order determination of the gluon polarisation from DIS events with highp_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 doublespin asymmetry of DIS events with a pair of large transversemomentum 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. 
Article: ANALYSIS OF SERIES CONVERGENCE IN VARIATIONAL PERTURBATION THEORY AND GAUSSIAN EFFECTIVE POTENTIAL
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ABSTRACT: The properties of convergence are studied for the series in the variational perturbation theory for the φ4(d) model. The nonperturbative Gaussian effective potential is derived from a more general approach, the variational perturbation theory. Various versions of the variational procedure are explored and the preference of the anharmonic variational procedure in view of convergence of the obtained series is argued.  [Show abstract] [Hide abstract]
ABSTRACT: The InönüWigner contraction from the Lorentz group O(2,1) to the Euclidean group E(2) is used to relate the separation of variables in the LaplaceBeltrami operators on the two corresponding homogeneous spaces. We consider the contractions on four levels: the Lie algebra, the commuting sets of second order operators in the enveloping algebra o(2,1), the coordinate systems and some eigenfunctions of the LaplaceBeltrami operators.  [Show abstract] [Hide abstract]
ABSTRACT: The COMPASS collaboration at CERN has investigated the \pi^ \gamma > \pi^ \pi^ \pi^+ reaction at centerofmomentum 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 quasireal photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, t' < 0.001 (GeV/c)^2. Using partialwave analysis techniques, the scattering intensity of Coulomb production described in terms of chiral dynamics and its dependence on the 3\piinvariant 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.  [Show abstract] [Hide abstract]
ABSTRACT: We propose a method by which it is possible to go beyond the scope of quantum chromodynamics perturbation theory. By using a new small parameter we formulate a systematic nonperturbative expansion and derive a renormalization βfunction in quantum chromodynamics. 
Article: Measurements of Cross Sections and Charged Pion Spectra in ProtonCarbon Interactions at 31 GeV/c
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ABSTRACT: Interaction cross sections and charged pion spectra in p+C interactions at 31 GeV/c were measured with the large acceptance NA61/SHINE spectrometer at the CERN SPS. These data are required to improve predictions of the neutrino flux for the T2K long baseline neutrino oscillation experiment in Japan. A set of data collected during the first NA61/SHINE run in 2007 with an isotropic graphite target with a thickness of 4% of a nuclear interaction length was used for the analysis. The measured p+C inelastic and production cross sections are 257.2 + 1.9 + 8.9 mb and 229.3 + 1.9 + 9.0 mb, respectively. Inclusive production cross sections for negatively and positively charged pions are presented as a function of laboratory momentum in 10 intervals of the laboratory polar angle covering the range from 0 up to 420 mrad. The spectra are compared with predictions of several hadron production models.
Publication Stats
5k  Citations  
990.56  Total Impact Points  
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Institutions

19702012

Joint Institute for Nuclear Research
 Bogoliubov Laboratory of Theoretical Physics
Dubno, MO, Russia


2007

Bielefeld University
Bielefeld, North RhineWestphalia, Germany


19942004

Bergische Universität Wuppertal
Wuppertal, North RhineWestphalia, Germany 
University of Grenoble
Grenoble, RhôneAlpes, France


19932003

University of Milan
 Department of Physics
Milano, Lombardy, Italy


2001

Università di Pisa
Pisa, Tuscany, Italy


19911998

University of Padova
Padua, Veneto, Italy
