Properties of the weakly non-ideal Bose gas are considered without suggestion on the C-number representation of the creation and annihilation operators with zero momentum. The “density–density” ...correlation function and the one-particle Green's function of the degenerate Bose gas are calculated based on the self-consistent Hartree–Fock approximation. It is shown that the single-particle excitation spectrum has a gap associated with the particle density in the “condensate”. At the same time, the pole in the “density–density” Green function determines the phonon–roton excitation spectrum which is identical to that discovered by Bogolyubov for collective excitations (“bogolons”).
An exact relation has been obtained for the spectral distribution of the energy of radiation in thermodynamic equilibrium with a system of charged nonrelativistic particles. The difference from the ...Planck formula is unambiguously determined by the transverse permittivity of a medium, which takes into account not only frequency dispersion but also spatial dispersion.
This paper presents a direct measurement of the decay width of the top quark using
events in the lepton+jets final state. The data sample was collected by the ATLAS detector at the LHC in ...proton-proton collisions at a centre-of-mass energy of 8 TeV and corresponds to an integrated luminosity of 20.2 fb
. The decay width of the top quark is measured using a template fit to distributions of kinematic observables associated with the hadronically and semileptonically decaying top quarks. The result,
for a top-quark mass of 172.5 GeV, is consistent with the prediction of the Standard Model.
Additional jet activity in dijet events is measured using Formula: see text collisions at ATLAS at a centre-of-mass energy of Formula: see text, for jets reconstructed using the Formula: see text ...algorithm with radius parameter Formula: see text. This is done using variables such as the fraction of dijet events without an additional jet in the rapidity interval bounded by the dijet subsystem and correlations between the azimuthal angles of the dijet s. They are presented, both with and without a veto on additional jet activity in the rapidity interval, as a function of the scalar average of the transverse momenta of the dijet s and of the rapidity interval size. The double differential dijet cross section is also measured as a function of the interval size and the azimuthal angle between the dijet s. These variables probe differences in the approach to resummation of large logarithms when performing QCD calculations. The data are compared to powheg, interfaced to the pythia 8 and herwig parton shower generators, as well as to hej with and without interfacing it to the ariadne parton shower generator. None of the theoretical predictions agree with the data across the full phase-space considered; however, powheg+pythia 8 and hej+ariadne are found to provide the best agreement with the data. These measurements use the full data sample collected with the ATLAS detector in Formula: see textFormula: see text collisions at the LHC and correspond to integrated luminosities of Formula: see text and Formula: see text for data collected during 2010 and 2011, respectively.
This paper presents the combinations of single-top-quark production cross-section measurements by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at s\ \sqrt{s} \ = 7 ...and 8 TeV corresponding to integrated luminosities of 1.17 to 5.1 fb−1 at s\ \sqrt{s} \ = 7 TeV and 12.2 to 20.3 fb−1 at s\ \sqrt{s} \ = 8 TeV. These combinations are performed per centre-of-mass energy and for each production mode: t-channel, tW, and s-channel. The combined t-channel cross-sections are 67.5 ± 5.7 pb and 87.7 ± 5.8 pb at s\ \sqrt{s} \ = 7 and 8 TeV respectively. The combined tW cross-sections are 16.3 ± 4.1 pb and 23.1 ± 3.6 pb at s\ \sqrt{s} \ = 7 and 8 TeV respectively. For the s-channel cross-section, the combination yields 4.9 ± 1.4 pb at s\ \sqrt{s} \ = 8 TeV. The square of the magnitude of the CKM matrix element Vtb multiplied by a form factor fLV is determined for each production mode and centre-of-mass energy, using the ratio of the measured cross-section to its theoretical prediction. It is assumed that the top-quark-related CKM matrix elements obey the relation |Vtd|, |Vts| ≪ |Vtb|. All the |fLVVtb|2 determinations, extracted from individual ratios at s\ \sqrt{s} \ = 7 and 8 TeV, are combined, resulting in |fLVVtb| = 1.02 ± 0.04 (meas.) ± 0.02 (theo.). All combined measurements are consistent with their corresponding Standard Model predictions.
This paper presents combinations of inclusive and differential measurements of the charge asymmetry (AC) in top quark pair tt¯ events with a lepton+jets signature by the ATLAS and CMS Collaborations, ...using data from LHC proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. The data correspond to integrated luminosities of about 5 and 20 fb−1 for each experiment, respectively. The resulting combined LHC measurements of the inclusive charge asymmetry are ACCHC7 = 0.005 ± 0.007 (stat) ± 0.006(syst) at 7 TeV and ACCHC8 = 0.0055 ± 0.0023 (stat) ± 0.0025 (syst) at 8 TeV. These values, as well as the combination of AC measurements as a function of the invariant mass of the tt¯ system at 8 TeV, are consistent with the respective standard model predictions.
Possibility for coexistence of a phonon and one-particle spectra in \({}^4He\) at all temperatures including temperatures below the \(\lambda\) - point is shown. An approach developed to consider the ...problem of the weakly imperfect Bose gas results in the existence of a gap in the one-particle (one-atom) excitation spectrum below the transition point. Thus, the microscopic model of He II turns out to differ both from the model initially suggested by Landau and from the Bogolyubov model accepted at present. Analysis of the experimental data obtained by measuring enthalpy and the part of helium atoms condensed in the state with the momentum \(p=0\) enabled to estimate the size of the gap. It turned out to be approximately equal to 0.31 K at zero temperature.
Properties of the weakly non-ideal Bose gas are considered without suggestion on C-number representation of the creation and annihilation operators with zero momentum. The "density-density" ...correlation function and the one-particle Green function of the degenerated Bose gas are calculated on the basis of the self-consistent Hartree-Fock approximation. It is shown that the spectrum of the one-particle excitations possesses a gap whose value is connected with the density of particles in the "condensate". At the same time, the pole in the "density-density" Green function determines the phonon-roton spectrum of excitations which exactly coincides with one discovered by Bogolyubov for the collective excitations (the "bogolons").
The problem of anomalous diffusion in momentum space is considered for plasma-like systems on the basis of a new collision integral, which is appropriate for consideration of the probability ...transition function (PTF) with long tails in momentum space. The generalized Fokker-Planck equation for description of diffusion (in momentum space) of particles (ions, grains etc.) in a stochastic system of light particles (electrons, or electrons and ions, respectively) is applied to the evolution of the momentum particle distribution in a plasma. In a plasma the developed approach is also applicable to the diffusion of particles with an arbitrary mass relation, due to the small characteristic momentum transfer. The cases of an exponentially decreasing in momentum space (including the Boltzmann-like) kernel in the PT-function, as well as the more general kernels, which create the anomalous diffusion in velocity space due to the long tail in the PT-function, are considered. Effective friction and diffusion coefficients for plasma-like systems are found.
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