S. Petrarca

Glueball masses and string tension in lattice QCD

We study glueball masses in lattice QCD. We present the first numerical determination of the mass of the lowest spin 2 state in the scaling region, and find that it is close to the lowest spin 0 state. We present very precise results for the string tension and for the spin 0 state, obtained by analyzing a large set of operators. We find that finite size effects are significant.

A New evaluation of the t ---> cH decay width in the standard model

The t->cH decay width has been computed in the standard model with a light Higgs boson. The corresponding branching fraction has been found to be in the range B(t->cH) ~ 10^{-13} - 10^{-14} for M_Z < m_H < 2 M_W. Our results correct the numerical evaluation usually quoted in the literature.

The Kaon B-parameter and K-π and K-ππ transition amplitudes on the lattice

We present the results of a computation of the K0−K0 and ΔI = 32 K−π and K−ππ amplitudes in lattice QCD. The numerical simulation has been done using the standard one-plaquette action and Wilson fermions, in the quenched approximation. Combining the tesults obtained at β = 6 on a 102 × 20 × 40 lattice with 30 configurations with those at β = 6.2 on a 163 × 48 lattice with 15 configurations, we have obtained for the kaon B-parameterBK0 − K0 = 0.65 ± 0.15 at μ = 3 GeV. We have also evaluated the ΔI = 32K−π and K−π weak hamiltonian matrix elements. The relevant renormalized operator O4 has been found to satisfy soft-pion theorems and chiral lagrangian relations at the 30% level, and this makes us confident about our results. We find (〈K+|HW|π+π0〉/mK) = (7 ± 2) × 10−8 to be compared with the experimental value of 3.7 × 10−8.

Inclusive beauty decays and the spectator model

Abstract A complete updated analysis of the branching ratios of inclusive b decays in a pure parton picture with inert spectator light quark(s) is presented. In view of recent data that indicate a rather small value for the average semileptonic decay fraction. particular attention is devoted to evaluating the central value and the range of theoretical errors for this quantity. We find that, while the data are marginally consistent with the spectator model, there are perhaps indications for a moderate non-spectator contribution. We discuss possible terms of this kind and argue that the ratio τ − τ 0 should probably be around its present upper limit.

Measuring the SUSY breaking scale at the LHC in the slepton NLSP scenario of GMSB models

We report a study on the measurement of the SUSY breaking scale √F in the framework of gauge-mediated supersymmetry breaking (GMSB) models at the LHC. The work is focused on the GMSB scenario where a stau is the next-to-lightest SUSY particle (NLSP) and decays into a gravitino with lifetime cτNLSP in the range 0.5 m to 1 km. We study the identification of long-lived sleptons using the momentum and time of flight measurements in the muon chambers of the ATLAS experiment. A realistic evaluation of the statistical and systematic uncertainties on the measurement of the slepton mass and lifetime is performed, based on a detailed simulation of the detector response. Accessible range and precision on √F achievable with a counting method are assessed. Many features of our analysis can be extended to the study of different theoretical frameworks with similar signatures at the LHC.

Heavy flavour weak transitions on the lattice

Abstract The pseudoscalar meson decay constant and the B parameter of charmed mesons are calculated by Monte Carlo simulation of lattice QCD, with Wilson fermions and in the quenched approximation. The combined results on two lattices, 10 2 × 20 × 40 and 16 3 × 48, at β = 6 and β = 6.2 respectively, yield ƒ D = 194±15 and ƒ F = 215±17 , and B D D = 0.82±0.10 at μ = 3 GeV. Within the non-relativistic quark model, predictions for the b system can be obtained by extrapolation of the previous results: ƒ B d ⋍120 MeV , ƒ B s ⋍150 MeV . We have also computed the hyperfine splitting and photon coupling of the charmonium system: M (1 − )− M (0 − ) = 50±10 MeV (experiment 117 MeV), (ƒ J/ψ ) − ⋍0.100 (experiment 0.125).

Non-perturbative renormalization of two-quark operators with an improved lattice fermion action

Abstract We determine the renormalization constants of two-quark operators for the clover action on the lattice, using chiral Ward identities. These renormalization constants are required for the determination of physical quantities, such as fπ, fϱ−1 and the quark masses from lattice calculations. Our results show that at β=6.0, with a sample of eighteen gauge configurations, it is possible to determine the renormalization constants with an error of a few percent.

GLUEBALL MASSES AND THE LOOP LOOP CORRELATION-FUNCTIONS

Abstract We analyse the pure gauge lattice QCD by measuring loop-loop correlation functions on a 12 3 ×32 lattice at β =5.9. We select a set of operators given by the smearing procedure. We obtain a good estimate of the mass of the 0 ++ state and for the string tension, and upper bounds for the masses of the 2 ++ and the 1 +− states.

On the Possible Detection of Massive Stable Exotic Particles at the LHC

The possible detection of massive quasi-stable exotic particles at the high luminosity hadronic colliders is discussed. In this decade, the LHC, now under preparation, has the best opportunity to observe them at the TeV scale. The present design of the ATLAS detector, that has been almost irreversibly decided, may turn out to be flexible enough to allow the detection of this interesting class of exotic particles. The trigger acceptance, the track reconstruction and the particle identification are studied. The necessity of a good measurement of the ionization loss in the muon sector of the detectors is recommended.

Theta dependence of the vacuum energy in the SU(3) gauge theory from the lattice

We report on a precise computation of the topological charge distribution in the SU(3) Yang-Mills theory. It is carried out on the lattice with high statistics Monte Carlo simulations by employing the definition of the topological charge suggested by Neubergers fermions. We observe significant deviations from a Gaussian distribution. Our results disfavor the