Mauro Papinutto

B-parameters of the complete set of matrix elements of (ΔB = 2) operators from the lattice

We compute on the lattice the “bag” parameters of the five ∆B = 2 operators of the supersymmetric basis, by combining their values determined in full QCD and in the static limit of HQET. The extrapolation of the QCD results from the accessible heavy-light meson masses to the B-meson mass is constrained by the static result. The matching of the corresponding results in HQET and in QCD is for the first time made at NLO accuracy in the MS(NDR) renormalization scheme. All results are obtained in the quenched approximation. PACS: 11.15.Ha (Lattice gauge theory), 12.38.Gc (Lattice QCD calculations), 13.75Lb (Meson-meson interactions), 14.40.Nd (Bottom mesons), 12.39.Hg (Heavy quark effective theory)

Dynamical twisted mass fermions with light quarks

We present results of dynamical simulations with 2 flavours of degenerate Wilson twisted mass quarks at maximal twist in the range of pseudo scalar masses from 300 to 550 MeV. The simulations are performed at one value of the lattice spacing a \lesssim 0.1 fm. In order to have O(a) improvement and aiming at small residual cutoff effects, the theory is tuned to maximal twist by requiring the vanishing of the untwisted quark mass. Precise results for the pseudo scalar decay constant and the pseudo scalar mass are confronted with chiral perturbation theory predictions and the low energy constants F, \bar{l}_3 and \bar{l}_4 are evaluated with small statistical errors.

B_d-Bbar_d Mixing and the B_d -> J/psi K_s Asymmetry in General SUSY Models

Abstract We present a next-to-leading order determination of the gluino-mediated SUSY contributions to B d – B d mixing and to the CP asymmetry a J / ψK s in the framework of the mass-insertion approximation. Using hadronic matrix elements recently computed on the lattice, we obtain improved constraints on the squark-mass splittings.

B(d) - anti-B(d) mixing and the B(d) ---> J / psi K(s) asymmetry in general SUSY models

Abstract We present a next-to-leading order determination of the gluino-mediated SUSY contributions to B d – B d mixing and to the CP asymmetry a J / ψK s in the framework of the mass-insertion approximation. Using hadronic matrix elements recently computed on the lattice, we obtain improved constraints on the squark-mass splittings.

Light quark masses and pseudoscalar decay constants from Nf = 2 lattice QCD with twisted mass fermions

We present the results of a lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants with Nf = 2 dynamical fermions. The simulation is carried out at a single value of the lattice spacing with the twisted mass fermionic action at maximal twist, which guarantees automatic (a)-improvement of the physical quantities. Quark masses are renormalized by implementing the non perturbative RI-MOM renormalization procedure. Our results for the light quark masses are mud(2 GeV) = 3.85±0.12±0.40 MeV, ms(2 GeV) = 105±3±9 MeV and ms/mud = 27.3±0.3±1.2. We also obtain fK = 161.7±1.2±3.1 MeV and the ratio fK/fπ = 1.227±0.009±0.024. From this ratio, by using the experimental determination of Γ(K → μμ(γ))/Γ(π → μμ(γ)) and the average value of |Vud| from nuclear beta decays, we obtain |Vus| = 0.2192(5)(45), in agreement with the determination from Kl3 decays and the unitarity constraint.

Simulation of QCD with N f = 2 + 1 flavors of non-perturbatively improved Wilson fermions

A bstractWe describe a new set of gauge configurations generated within the CLS effort. These ensembles have Nf = 2 + 1 flavors of non-perturbatively improved Wilson fermions in the sea with the Lüscher-Weisz action used for the gluons. Open boundary conditions in time are used to address the problem of topological freezing at small lattice spacings and twisted-mass reweighting for improved stability of the simulations. We give the bare parameters at which the ensembles have been generated and how these parameters have been chosen. Details of the algorithmic setup and its performance are presented as well as measurements of the pion and kaon masses alongside the scale parameter t0.

Non-perturbative renormalization of static-light four-fermion operators in quenched lattice QCD

We perform a non-perturbative study of the scale-dependent renormalization factors of a multiplicatively renormalizable basis of ¢B = 2 parity-odd four-fermion op- erators in quenched lattice QCD. Heavy quarks are treated in the static approximation with various lattice discretizations of the static action. Light quarks are described by non- perturbatively O(a) improved Wilson-type fermions. The renormalization group running is computed for a family of Schrodinger functional (SF) schemes through finite volume techniques in the continuum limit. We compute non-perturbatively the relation between the renormalization group invariant operators and their counterparts renormalized in the SF at a low energy scale. Furthermore, we provide non-perturbative estimates for the matching between the lattice regularized theory and all the SF schemes considered.

Renormalization constants of quark operators for the non-perturbatively improved Wilson action

We present the results of an extensive lattice calculation of the renormalization constants of bilinear and four-quark operators for the non-perturbatively O(a)-improved Wilson action. The results are obtained in the quenched approximation at four values of the lattice coupling by using the non-perturbative RI/MOM renormalization method. Several sources of systematic uncertainties, including discretization errors and final volume effects, are examined. The contribution of the Goldstone pole, which in some cases may affect the extrapolation of the renormalization constants to the chiral limit, is non-perturbatively subtracted. The scale independent renormalization constants of bilinear quark operators have been also computed by using the lattice chiral Ward identities approach and compared with those obtained with the RI-MOM method. For those renormalization constants the non-perturbative estimates of which have been already presented in the literature we find an agreement which is typically at the level of 1%.We present the results of an extensive lattice calculation of the renormalization constants of bilinear and four-quark operators for the non-perturbatively (a)-improved Wilson action. The results are obtained in the quenched approximation at four values of the lattice coupling by using the non-perturbative RI/MOM renormalization method. Several sources of systematic uncertainties, including discretization errors and final volume effects, are examined. The contribution of the Goldstone pole, which in some cases may affect the extrapolation of the renormalization constants to the chiral limit, is non-perturbatively subtracted. The scale independent renormalization constants of bilinear quark operators have been also computed by using the lattice chiral Ward identities approach and compared with those obtained with the RI-MOM method. For those renormalization constants the non-perturbative estimates of which have been already presented in the literature we find an agreement which is typically at the level of 1%.

Axial nucleon form factors from lattice QCD

We present results on the nucleon axial form factors within lattice QCD using two flavors of degenerate twisted mass fermions. Volume effects are examined using simulations at two volumes of spatial length L=2.1 fm and L=2.8 fm. Cut-off effects are investigated using three different values of the lattice spacings, namely a=0.089 fm, a=0.070 fm and a=0.056 fm. The nucleon axial charge is obtained in the continuum limit and chirally extrapolated to the physical pion mass enabling comparison with experiment.

BK-parameter from Nf=2 twisted mass lattice QCD

We present an unquenched N{sub f}=2 lattice computation of the B{sub K} parameter which controls K{sup 0}-K{sup 0} oscillations. A partially quenched setup is employed with two maximally twisted dynamical (sea) light Wilson quarks, and valence quarks of both the maximally twisted and the Osterwalder-Seiler variety. Suitable combinations of these two kinds of valence quarks lead to a lattice definition of the B{sub K} parameter which is both multiplicatively renormalizable and O(a) improved. Employing the nonperturbative RI-MOM scheme, in the continuum limit and at the physical value of the pion mass we get B{sub K}{sup RGI}=0.729{+-}0.030, a number well in line with the existing quenched and unquenched determinations.