[en] We give results for the B and the D meson spectrum using NRQCD on the lattice in the quenched approximation. The masses of radially and orbitally excited states are calculated as well as S-wave hyperfine and P-wave fine structure. Radially excited P states are observed for the first time. Radial and orbital excitation energies match well to experiment, as does the strange-nonstrange S-wave splitting. We compare the light and heavy quark mass dependence of various splittings to experiment. Our B results cover a range in lattice spacings of more than a factor of two. Our D results are from a single lattice spacing and we compare them to numbers in the literature from finer lattices using other methods. We see no significant dependence of physical results on the lattice spacing. (c) 2000 The American Physical Society

[en] Mass shifts Δm of particles in nuclear matter relative to their vacuum values are considered. A general formula relating Δm(E) (E is the particle energy) to the real part of the forward particle-nucleon scattering amplitude Ref(E) is presented and its applicability domain is formulated. The ρ-meson mass shift in nuclear matter is calculated at 2 approx-lt E_ρ approx-lt 7GeV for transversally and longitudinally polarized ρmesons. copyright 1997 The American Physical Society

[en] An approximate vacuum wave functional Ψ₀ is proposed for (2+1)-dimensional Yang-Mills theories. Using Ψ₀, one can compute the 0⁺⁺ glueball mass M_G in terms of the string tension. By using the idea of dimensional reduction, a prediction for M_G can be made in 3+1 dimensions. One finds M_G∼1.5 GeV. copyright 1997 The American Physical Society

[en] A systematic procedure to consistently formulate a field theoretical, QCD bound state problem with a fixed number of constituents is outlined. The approach entails applying the Hamiltonian flow equations, which are a set of continuous unitary transformations, to a QCD motivated Hamiltonian with a confining interaction. The method is developed in detail for gluodynamics in the Coulomb gauge to obtain an effective block-diagonal Hamiltonian appropriate to a reduced Fock space with a fixed number of dynamical gluons. Standard many-body techniques are used to numerically diagonalize this Hamiltonian in a constituent two gluon Fock space. The calculated gluon condensates and glueball masses are in good agreement with QCD sum rule and lattice results. (c) 2000 The American Physical Society

[en] We present lattice results for the spectrum of mesons containing one heavy quark and of baryons containing one or two heavy quarks. The calculation is done in the quenched approximation using the NRQCD formalism for the heavy quark. We analyze the dependence of the mass splittings on both the heavy and the light quark masses. Meson P-state fine structure and baryon hyperfine splittings are resolved for the first time. We fix the b quark mass using both M_B and M_Λb, and our best estimate is m_b^MS(m_b^MS)=4.35(10)(₊₂^-3)(20) GeV. The spectrum, obtained by interpolation to m_b, is compared with the experimental data. (c) 2000 The American Physical Society

[en] Using a sample of 9.6x10⁶BB(bar sign) meson pairs collected with the CLEO detector, we have fully reconstructed 135 B⁰→ψ^(') K_S⁰ and 526 B⁺→ψ^(')K⁺ candidates with very low background. We fitted the ψ^(')K invariant mass distributions of these B meson candidates and measured the masses of the neutral and charged B mesons to be M(B⁰)=5279.1±0.7[stat]±0.3[ syst] MeV/c² and M(B⁺)=5279.1±0.4[stat]±0.4[ syst] MeV/c². The precision is a significant improvement over previous measurements. (c) 2000 The American Physical Society

[en] The oscillation frequency Δm_d of B⁰B(bar sign)⁰ mixing is measured using the partially reconstructed semileptonic decay B(bar sign)⁰→l^-ν(bar sign)D^*+X. The data sample was collected with the CDF detector at the Fermilab Tevatron collider during 1992-1995 by triggering on the existence of two lepton candidates in an event, and corresponds to about 110 pb^-1 of p(bar sign)p collisions at √(s)=1.8 TeV. We estimate the proper decay time of the B(bar sign)⁰ meson from the measured decay length and reconstructed momentum of the l^-D^*+ system. The charge of the lepton in the final state identifies the flavor of the B(bar sign)⁰ meson at its decay. The second lepton in the event is used to infer the flavor of the B(bar sign)⁰ meson at production. We measure the oscillation frequency to be Δm_d=0.516±0.099_-0.035^+0.029 ps^-1, where the first uncertainty is statistical and the second is systematic. (c) 1999 The American Physical Society

[en] We propose an analogue of the familiar gap equation for the case of four-quark condensates at finite temperature. The condensates of interest correspond to scalar, vector, pseudoscalar, axial vector, and tensor Dirac structures. Working with correlators at zero chemical potential without factorization, we arrive at coupled equations for these four-quark condensates and the masses of certain light-quark mesons. We study the temperature dependence of the four-quark condensates and masses; in one of our models, factorization of the four-quark condensates is shown to be increasingly violated as the temperature is increased toward T_c. The 2⁺⁺ tensor mesons a₂(1320)-f₂(1270) are identified as especially sensitive probes of the four-quark condensates. (c) 2000 The American Physical Society

[en] The front form Hamiltonian for quantum chromodynamics, reduced to an effective Hamiltonian acting only in the q bar q space, is solved approximately. After coordinate transformation to usual momentum space and Fourier transformation to configuration space, a second order differential equation is derived. This retarded Schroedinger equation is solved by variational methods and semianalytical expressions for the masses of all 30 pseudoscalar and vector mesons are derived. In view of the direct relation to quantum chromodynamics without a free parameter, the agreement with experiment is remarkable, but the approximation scheme is not adequate for the mesons with one up or down quark. The crucial point is the use of a running coupling constant α_s(Q²), in a manner similar, but not equal to the one of Richardson in the equal usual-time quantization. Its value is fixed at the Z mass and the five flavor quark masses are determined by a fit to the vector meson quarkonia. copyright 1997 The American Physical Society

[en] A partial-wave analysis of 9082 ηπ⁺π^-n events produced in the reaction π^-p→ηπ⁺π^-n at 18.3 GeV/c has been carried out using data from experiment 852 at Brookhaven National Laboratory. The data are dominated by J^PC=0^-+ partial waves consistent with observation of the η(1295) and the η(1440). The mass and width of the η(1295) were determined to be 1282±5 MeV and 66±13 MeV, respectively, while the η(1440) was observed with a mass of 1404±6 MeV and a width of 80±21 MeV. Other partial waves of importance include the 1⁺⁺ and the 1^+- waves. Results of the partial wave analysis are combined with results of other experiments to estimate f₁(1285) branching fractions. These values are considerably different from current values determined without the aid of amplitude analyses. (c) 2000 The American Physical Society