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  • EUROPEAN PHYSICAL JOURNAL C  (94)
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  • 1
    Language: English
    In: The European Physical Journal C, 2011, Vol.71(9), pp.1-11
    Description: We extend a known method to integrate out the strange quark in three flavour chiral perturbation theory to the context of an arbitrary number of flavours. As an application, we present the explicit formulæ to one-loop accuracy for the heavy quark mass dependency of the low-energy constants after decreasing the number of flavours by one while integrating out the heaviest quark in N -flavour chiral perturbation theory.
    Keywords: High Energy Physics - Phenomenology ; High Energy Physics - Lattice;
    ISSN: 1434-6044
    E-ISSN: 1434-6052
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  • 2
    Language: English
    In: The European Physical Journal C, 2010, Vol.70(1), pp.39-49
    Description: 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 $p_{h}^{T}$ 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.
    Keywords: Questions And Answers ; Universities And Colleges;
    ISSN: 1434-6044
    E-ISSN: 1434-6052
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  • 3
    Language: English
    In: European Physical Journal C, 2017, Vol. 77(4)
    Description: Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality Q(2) 〉 1 ( GeV/c)(2). The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon beam impinging on a polarised (LiD)-Li-6 target. By analysing the full range in hadron transverse momentum p(T), the different pT-dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation Delta g/g is evaluated at leading order in pQCD at a hard scale of mu(2) = 〈 Q(2) 〉 = 3( GeV/c)(2). It is determined in three intervals of the nucleon momentum fraction carried by gluons, x(g), covering the range 0.04〈 x(g)〈 0.28 and does not exhibit a significant dependence on xg. The average over the three intervals, 〈 Delta g/g 〉 = 0.113 +/- 0.038(stat) +/- 0.036( syst) at 〈 x(g) 〉 approximate to 0.10, suggests that the gluon polarisation is positive in the measured x(g) range.
    Keywords: Natural Sciences ; Physical Sciences ; Subatomic Physics ; Naturvetenskap ; Fysik ; Subatomär Fysik
    ISSN: 1434-6044
    E-ISSN: 14346052
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  • 4
    Language: English
    In: The European Physical Journal C, 2018, Vol.78(11), pp.1-13
    Description: Single hadron azimuthal asymmetries of positive and negative hadrons produced in muon semi-inclusive deep inelastic scattering off longitudinally polarised deuterons are determined using the 2006 COMPASS data and also combined all deuteron COMPASS data. For each hadron charge, the dependence of the azimuthal asymmetry on the hadron azimuthal angle $$\phi $$ ϕ is obtained by means of a five-parameter fitting function that besides a $$\phi $$ ϕ -independent term includes four modulations predicted by theory: $$\sin \phi $$ sin ϕ , $$\sin 2 \phi $$ sin 2 ϕ , $$\sin 3\phi $$ sin 3 ϕ and $$\cos \phi $$ cos ϕ . The amplitudes of the five terms have been extracted, first, for the hadrons in the whole available kinematic region. In further fits, performed for hadrons from a restricted kinematic region, the $$\phi $$ ϕ -dependence is determined as a function of one of three variables (Bjorken- x , fractional energy of virtual photon taken by the outgoing hadron and hadron transverse momentum), while disregarding the others. Except the $$\phi $$ ϕ -independent term, all the modulation amplitudes are very small, and no clear kinematic dependence could be observed within experimental uncertainties.
    Keywords: Physics ; Elementary Particles, Quantum Field Theory ; Nuclear Physics, Heavy Ions, Hadrons ; Quantum Field Theories, String Theory ; Measurement Science and Instrumentation ; Astronomy, Astrophysics and Cosmology ; Nuclear Energy ; Physics;
    ISSN: 1434-6044
    E-ISSN: 1434-6052
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  • 5
    Language: English
    In: The European Physical Journal C, 2012, Vol.72(12), pp.1-17
    Description: The production of D ∗ and D mesons in inelastic scattering of 160 GeV/c muons off a 6 LiD 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 . 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±0.4) nb. Significant cross-section asymmetries are observed between D ∗+ and D ∗− production for ν 〈40 GeV and z 〉0.6.
    Keywords: Physics;
    ISSN: 1434-6044
    E-ISSN: 1434-6052
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  • 6
    Language: English
    In: The European Physical Journal C, 2010, Vol.68(1), pp.119-123
    Description: The European Physical Journal C—Particles and Fields—publishes scientific manuscripts of relevance to the scientific community following careful and strict peer reviewing and, whenever appropriate and necessary, through discussion with the authors, so as to optimise scientific content and style of presentation prior to publication. In some cases significant disagreement between authors and referees (and/or editors) of the journal cannot be resolved despite all efforts and best of intentions. While the journal—notwithstanding any appeals—retains the right to reject such manuscripts, the editors of this journal may decide, in cases deemed of exceptional interest and potential significance for the field, to accept the manuscript for publication, to amend it by “comments” of the editor(s) in charge and, if appropriate, by a “reply” of the authors of the commented manuscript. The present comment is on “Study of multi-muon events produced in interactions at TeV” by T. Aaltonen et al. (the CDF Collaboration, Eur. Phys. J. C, 2010, doi:).
    Keywords: Nurses ; Editors ; Universities And Colleges;
    ISSN: 1434-6044
    E-ISSN: 1434-6052
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  • 7
    Language: English
    In: The European Physical Journal C, 2010, Vol.68(1), pp.109-118
    Description: We report the results of a study of multi-muon events produced at the Fermilab Tevatron collider and acquired with the CDF II detector using a dedicated dimuon trigger. The production cross section and kinematics of events in which both muon candidates are produced inside the beam pipe of radius 1.5 cm are successfully modeled by known processes which include heavy flavor production. In contrast, we are presently unable to fully account for the number and properties of the remaining events, in which at least one muon candidate is produced outside of the beam pipe, in terms of the same understanding of the CDF II detector, trigger, and event reconstruction.
    Keywords: Nurses -- Analysis ; Particle Accelerators -- Analysis ; Detection Equipment -- Analysis;
    ISSN: 1434-6044
    E-ISSN: 1434-6052
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  • 8
    Language: English
    In: The European Physical Journal C, 2014, Vol.74(10), pp.1-20
    Description: Invariant yields of neutral pions at midrapidity in the transverse momentum range $$0.6 〈 {p_\mathrm{T}} 〈 12\,{\mathrm {GeV}}/$$ 0.6 〈 p T 〈 12 GeV / c measured in Pb–Pb collisions at $${\sqrt{s_\mathrm{{NN}}}} =2.76$$ s NN = 2.76 TeV are presented for six centrality classes. The pp reference spectrum was measured in the range $$0.4 〈 {p_\mathrm{T}} 〈 10\,{\mathrm {GeV}}/$$ 0.4 〈 p T 〈 10 GeV / c at the same center-of-mass energy. The nuclear modification factor, $$R_\mathrm{{AA}}$$ R AA , shows a suppression of neutral pions in central Pb–Pb collisions by a factor of up to about $$8{-}10$$ 8 - 10 for $$5 \lesssim {p_\mathrm{T}} \lesssim 7\,{\mathrm {GeV}}/$$ 5 ≲ p T ≲ 7 GeV / c. The presented measurements are compared with results at lower center-of-mass energies and with theoretical calculations.
    Keywords: Physics ; Elementary Particles, Quantum Field Theory ; Nuclear Physics, Heavy Ions, Hadrons ; Quantum Field Theories, String Theory ; Measurement Science and Instrumentation ; Astronomy, Astrophysics and Cosmology ; Nuclear Energy ; Physics;
    ISSN: 1434-6044
    E-ISSN: 1434-6052
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  • 9
    Language: English
    In: The European Physical Journal C, 2016, Vol.76(4), pp.1-13
    Description: We report on the inclusive production cross sections of $${\mathrm{J}/\psi }$$ J / ψ , $${\psi (\mathrm{2S})}$$ ψ ( 2 S ) , $$\mathrm{\Upsilon }$$ Υ (1S), $$\mathrm{\Upsilon }$$ Υ (2S) and $$\mathrm{\Upsilon }$$ Υ (3S), measured at forward rapidity with the ALICE detector in $$\mathrm{pp}$$ pp collisions at a center-of-mass energy $$\sqrt{s}=8$$ s = 8  TeV. The analysis is based on data collected at the LHC and corresponds to an integrated luminosity of 1.23 pb $$^{-1}$$ - 1 . Quarkonia are reconstructed in the dimuon-decay channel. The differential production cross sections are measured as a function of the transverse momentum $${p_\mathrm{T}}$$ p T and rapidity y , over the $${p_\mathrm{T}}$$ p T ranges $$0〈{p_\mathrm{T}}〈20$$ 0 〈 p T 〈 20  GeV/ c for $${\mathrm{J}/\psi }$$ J / ψ , $$0〈{p_\mathrm{T}}〈12$$ 0 〈 p T 〈 12  GeV/ c for all other resonances, and for $$2.5〈y〈4$$ 2.5 〈 y 〈 4 . The cross sections, integrated over $${p_\mathrm{T}}$$ p T and y , and assuming unpolarized quarkonia, are $$\sigma _{{\mathrm{J}/\psi }} = 8.98\pm 0.04\pm 0.82$$ σ J / ψ = 8.98 ± 0.04 ± 0.82   $$\upmu $$ μ b, $$\sigma _{{\psi (\mathrm{2S})}} = 1.23\pm 0.08\pm 0.22$$ σ ψ ( 2 S ) = 1.23 ± 0.08 ± 0.22   $$\upmu $$ μ b, $$\sigma _{\mathrm{\Upsilon }\mathrm{(1S)}} = 71\pm 6\pm 7$$ σ Υ ( 1 S ) = 71 ± 6 ± 7  nb, $$\sigma _{\mathrm{\Upsilon }\mathrm{(2S)}} = 26\pm 5\pm 4$$ σ Υ ( 2 S ) = 26 ± 5 ± 4  nb and $$\sigma _{\mathrm{\Upsilon }\mathrm{(3S)}} = 9\pm 4\pm 1$$ σ Υ ( 3 S ) = 9 ± 4 ± 1  nb, where the first uncertainty is statistical and the second one is systematic. These values agree, within at most $$1.4\sigma $$ 1.4 σ , with measurements performed by the LHCb collaboration in the same rapidity range.
    Keywords: Regular Article - Experimental Physics;
    ISSN: 1434-6044
    E-ISSN: 1434-6052
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  • 10
    Language: English
    In: The European Physical Journal C, 2016, Vol.76(5), pp.1-16
    Description: Measurements of charged jet production as a function of centrality are presented for  p–Pb  collisions recorded at $$\sqrt{s_\mathrm {NN}}= 5.02$$ s NN = 5.02 TeV with the ALICE detector. Centrality classes are determined via the energy deposit in neutron calorimeters at zero degree, close to the beam direction, to minimise dynamical biases of the selection. The corresponding number of participants or binary nucleon–nucleon collisions is determined based on the particle production in the Pb-going rapidity region. Jets have been reconstructed in the central rapidity region from charged particles with the anti- $$k_\mathrm {T}$$ k T algorithm for resolution parameters $$R = 0.2$$ R = 0.2 and $$R = 0.4$$ R = 0.4 in the transverse momentum range 20 to 120 GeV/ c . The reconstructed jet momentum and yields have been corrected for detector effects and underlying-event background. In the five centrality bins considered, the charged jet production in  p–Pb   collisions is consistent with the production expected from binary scaling from pp collisions. The ratio of jet yields reconstructed with the two different resolution parameters is also independent of the centrality selection, demonstrating the absence of major modifications of the radial jet structure in the reported centrality classes.
    Keywords: Regular Article - Theoretical Physics;
    ISSN: 1434-6044
    E-ISSN: 1434-6052
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