arXiv subjects

Nazario Tantalo

Publications and source records attributed to Nazario Tantalo.

59 records · Page 4Linked to original sources

arXiv2007

Lattice calculations for B and K mixing

The bag parameters and the decay constants of neutral B and K mesons were among the non-perturbative hadronic inputs to the classical CKM Unitarity Triangle Analysis. Thanks to the big amount of experimental information collected in the last few years at the B-factories and by the CDF collaboration, these matrix elements are now among the outputs of the unitarity fits, once the validity of the Standard Model has been postulated. Lattice calculations of the mixing amplitudes are still needed in order to make a test of the theory, provided that their statistical and systematic errors are under control at the level of a few percent. Here we review some of the recent lattice calculations of these quantities.

hep-ph↗

arXiv2006

m_b and f_Bs from a combination of HQET and QCD

We compute the mass of the b-quark and the B_s meson decay constant in quenched lattice QCD using a combination of HQET and the standard relativistic QCD Lagrangian. We start from a small volume, where one can directly deal with the b-quark, and compute the evolution to a big volume, where the finite size effects are negligible through step scaling functions which give the change of the observables when L is changed to 2L. In all steps we extrapolate to the continuum limit, separately in HQET and in QCD for masses below m_b. The point m_b is then reached by an interpolation of the continuum results. With r_0=0.5 fm and the experimental B_s and K masses we find f_Bs=191(6) MeV and the renormalization group invariant mass M_b=6.89(11) GeV, translating into m_b(m_b)=4.42(7) GeV in the MS-bar scheme.

hep-lat↗

arXiv2004

Non leptonic two-body decay amplitudes from finite volume calculations

We discuss the quantization of the energy levels of two-particle scattering states in a finite volume in the case of Bloch-type boundary conditions. A generalization of the Luescher quantization condition is obtained that can be used in order to calculate the scattering phases, resulting for example by the strong elastic interaction of two pions, at fixed physical momentum transfers on a sequence of volumes of growing sizes. We also give a generalization of the Lellouch-Luescher formula to be used to extract the physical decay rate for a kaon decaying into two pions below the inelastic threshold from finite volume calculations. The formula is valid up to corrections exponentially vanishing in the volume. By using this formula the calculation can in principle be performed on different finite volumes of growing sizes in order to keep under control the corrections.

hep-lat↗

arXiv2004

Remarks on the discretization of physical momenta in lattice QCD

The calculation on the lattice of cross--sections, form--factors and decay rates associated to phenomenologically relevant physical processes is complicated by the spatial momenta quantization rule arising from the introduction of limited box sizes in numerical simulations. A method to overcome this problem, based on the adoption of two distinct boundary conditions for two fermions species on a finite lattice, is here discussed and numerical results supporting the physical significance of this procedure are shown.

hep-lat↗

arXiv2003

Heavy quark masses from finite volume effects

I discuss the results of a new calculation of the charm and bottom quark masses in the quenched approximation and in the continuum limit of lattice QCD. The work has been done by the APE group at the ``Tor Vergata'' University making use of the step scaling method, previously introduced to deal with two scale problems, that allows to take the continuum limit of the lattice data. We have computed the RGI quark masses and then we have connected the results to the MSbar scheme. The continuum numbers are m_b^{RGI} = 6.73(16) GeV for the b-quark and m_c^{RGI} = 1.681(36) GeV for the c-quark, corresponding respectively to m_b^{MSbar}(m_b^{MSbar}) = 4.33(10) GeV and m_c^{MSbar}(m_c^{MSbar}) = 1.319(28) GeV. The latter result, in agreement with current estimates, is for us a check of the method.

hep-lat↗