[Show abstract][Hide abstract] ABSTRACT: We make a quenched lattice simulation of hadron spectroscopy at beta=6.2 with the Wilson action non-perturbatively improved. With respect to the unimproved case, the estimate of the lattice spacing is less influenced by the choice of input hadron masses. We study also the effects of using an improved quark mass in the fits to the dependence of hadron masses upon quark masses.
Physics Letters B 03/1998; 422(1-4). DOI:10.1016/S0370-2693(98)00041-0 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: η′-τ splitting in full QCD can be estimated extrapolating from negative to positive flavour numbers. Our results show a flavour dependence consistent with the Witten Veneziano formula based on the U(1) anomaly.
[Show abstract][Hide abstract] ABSTRACT: We perform an extrapolation from negative to positive flavour numbers of full QCD lattice estimates of the η′ mass. The extrapolations are carried out by keeping ϱ and π masses at fixed values. We find an η′-π splitting which shows a flavour dependence consistent with the Witten-Veneziano formula based on the U(1) anomaly. The quantitative splitting is consistent with the estimates made in the quenched approximation.
Nuclear Physics B 11/1996; 480(1-480):381-394. DOI:10.1016/S0550-3213(96)00468-3 · 3.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study the dynamical flavour dependence of the lattice estimates of the heavy meson decay constant in the static limit. We perform the analysis by considering negative flavour numbers and by extrapolating the results to positive values. We observe a sizeable flavour dependence which increases the quenched estimates.
Physics Letters B 08/1996; 382(4-382):398-402. DOI:10.1016/0370-2693(96)00697-1 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A method based on the Monte Carlo inversion of the Dirac operator on the lattice provides low noise results for the correlations entering the definition of the heavy meson decay constant in the static limit. The method is complementary to the usual method of smeared sources, avoids the systematic error arising from optimizing the size of the smearing volume ans is more efficient for the values of lattice parameters that we have explored.
Physics Letters B 08/1996; 382(4-382):393-397. DOI:10.1016/0370-2693(96)00567-9 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study dynamical fermion effects in lattice QCD at finite temperature. The method adopted is basically the extrapolation from negative flavour numbers already tested at zero temperature and based on the simulation of local bosonic theories, with an essential difference. With an appropriate choice of the boundary conditions on the bosonic fields, called “bermions”, it is possible to separate the Z3 breaking contribution of fermion loops to the effective action from the one conserving Z3: the former is simulated exactly at a fixed positive and even flavour number, while the extrapolation from negative flavour numbers is made only on the Z3 invariant part of the action. We test this approach by comparing our results on a 163 × 2 lattice with those from a hopping parameter expansion and our results on a 163 × 4 lattice with those of direct Monte Carlo simulations including the fermion determinant.
Physics Letters B 07/1996; 387(4-387):829-834. DOI:10.1016/0370-2693(96)01115-X · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We calculate the effects of including dynamical fermion loops in the lattice QCD estimates of meson decay constants, by extrapolating the results from negative flavour numbers after a suitable matching of the pion and rho mass. For moderately light quarks, the values of the decay constants not corrected for the renormalization constants increase with respect to their quenched values. Comment: 9 pages, uuencoded PS file, 2 figures included
Physics Letters B 10/1995; 367(1-4). DOI:10.1016/0370-2693(95)01467-5 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Perturbative cross section for direct Bc meson production in gluon gluon scattering is calculated and compared with other existing results. Predictions for hadronic Bc production at Tevatron and LHC are presented and the main sources of uncertainties are discussed.
Physics Letters B 09/1995; 357(4-357):659-665. DOI:10.1016/0370-2693(95)00908-4 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We estimate the effects of dynamical fermions by extrapolating to positive
flavour numbers the results from negative values obtained by adding to the pure
gauge sector a fermion action where the fields obey a Bose statistics: the
Nuclear Physics B 08/1995; 455(1-2-455):274-286. DOI:10.1016/0550-3213(95)00489-F · 3.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We propose to replace ordinary propagators in lattice operator correlations entering the determination of hadron masses with space-time smeared propagators. These are defined as the inverse of the quadratic operator in the fermion action times its hermitian conjugate. We obtain a cleaner determination of hadron masses, comparable to the effect of using smeared operators. Comment: PS file replaced with uuencoded PS file, 9 pages with 5 figures included
Physics Letters B 02/1995; 353(2-3). DOI:10.1016/0370-2693(95)00575-6 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We discuss the formulation in euclidean space of the effective theory for heavy quarks at non-zero velocity, which is necessary for the implementation of the Isgur-Wise limit in lattice QCD simulations. In this theory the energy spectrum is unbounded from below and, even at the tree level, an ultraviolet cut-off on spatial momenta must be introduced. The continuum limit of the effective quark propagator in configuration space does not exist. It is however possible, at least in the non-interacting case, to construct sensible correlation functions in time and in spatial momenta. The application of the theory to lattice simulations seems very problematic.
Physics Letters B 11/1992; 294(2-294):281-285. DOI:10.1016/0370-2693(92)90695-Z · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Theoretical predictions on decay properties of the simplest particle containing more than one heavy quark, the pseudoscalar
+, are presented. Some channels that should present a distinctive signature are discussed in more detail.
Zeitschrift für Physik C 12/1991; 51(4). DOI:10.1007/BF01565579
[Show abstract][Hide abstract] ABSTRACT: The pseudoscalar meson Bc is the simplest particle containing more than one heavy quark of different flavours. Its production cross sections at accelerators presently running or in project are estimated using the HERWIG parton shower Monte Carlo code.
Physics Letters B 08/1991; 266(1-2-266):142-146. DOI:10.1016/0370-2693(91)90757-H · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Monte Carlo estimates of the B(sub c) production cross sections, at different high energy accelerators, are presented. The attention is focussed on mesons formed by a bottom antiquark and a charmed quark. In all the considered cases, the estimated fraction F(sub B(sub C)) varies between 0.0001 and 0.002, according to the values assumed for several parameters governing the hadronization phase in the HERWIG Monte Carlo code. The HERWIG Monte Carlo code contains simutators of quantum chromodynamics parton shower, including interference and azimuthal correlations. These parameters should be tuned to actual data for the predictions to become sharper.
[Show abstract][Hide abstract] ABSTRACT: Theoretical predictions in decay properties of the simplest particle containing more than one heavy quark, the pseudoscalar meson, are presented. Some channels that should present a distinctive signature are discussed. The investigation is carried out by applying a quantum chromodynamics corrective effective hamiltonian and operator matrix elements evaluated in the vacuum insertion approximation and in the large N(sub c) limit. The results of inclusive decays predict the contribution to the total rate of different decay mechanisms to be 37 percent from C-spectator decays, 45 percent from (bar-b)-spectator, and 18 percent from c(bar-b) annihilation.