ArcAdiA

First lattice QCD Study of the Σ- --> n axial and vector form factors with SU(3) breaking corrections

Sun, 31 Dec 2006 23:00:00 GMT

First lattice QCD Study of the Σ- --> n axial and vector form factors with SU(3) breaking corrections Guadagnoli, Diego; Lubicz, Vittorio; Papinutto, Mauro; Simula, Silvano 2007 Nuclear Physics B 761 63-91 We present the first quenched lattice QCD study of the form factors relevant for the hyperon semileptonic decay Σ−→nℓν. The momentum dependence of both axial and vector form factors is investigated and the values of all the form factors at zero-momentum transfer are presented. Following the same strategy already applied to the decay K0→π−ℓν, the SU(3)-breaking corrections to the vector form factor at zero-momentum transfer, f1(0), are determined with great statistical accuracy in the regime of the simulated quark masses, which correspond to pion masses above ≈0.7 GeV. Besides f1(0) also the axial to vector ratio g1(0)/f1(0), which is relevant for the extraction of the CKM matrix element Vus, is determined with significant accuracy. Due to the heavy masses involved, a polynomial extrapolation, which does not include the effects of meson loops, is performed down to the physical quark masses, obtaining f1(0)=−0.948±0.029 and g1(0)/f1(0)=−0.287±0.052, where the uncertainties do not include the quenching effect. Adding a recent next-to-leading order determination of chiral loops, calculated within the Heavy Baryon Chiral Perturbation Theory in the approximation of neglecting the decuplet contribution, we obtain f1(0) = −0.988 ± 0.029(lattice) ± 0.040(HBChPT). Our findings indicate that SU(3)-breaking corrections are moderate on both f1(0) and g1(0). They also favor the experimental scenario in which the weak electricity form factor, g2(0), is large and positive, and correspondingly the value of |g1(0)/f1(0)| is reduced with respect to the one obtained with the conventional assumption g2(q2)=0 based on exact SU(3) symmetry.

Kaon oscillations in the Standard Model and Beyond using Nf=2 dynamical quarks

Wed, 31 Dec 2008 23:00:00 GMT

Kaon oscillations in the Standard Model and Beyond using Nf=2 dynamical quarks Bertone, Valerio; Dimopoulos, Petros; Frezzotti, Roberto; Gimenez, Vicent; Lubicz, Vittorio; Mescia, Federico; Palao, David; Papinutto, Mauro; Rossi, Giancarlo; Simula, Silvano; Vladikas, Anastassios 2009 1-7 We compute non-perturbatively the B-parameters of the complete basis of four-fermion operators needed to study the Kaon oscillations in the SM and in its supersymmetric extension. We perform numerical simulations with two dynamical maximally twisted sea quarks at three values of the lattice spacing on configurations generated by the ETMC. Unwanted operator mixings and O(a) discretization effects are removed by discretizing the valence quarks with a suitable Osterwalder-Seiler variant of the Twisted Mass action. Operators are renormalized non-perturbatively in the RI/MOM scheme. Our preliminary result for BK(RGI) is 0.73(3)(3).

Dynamical twisted mass fermions with light quarks

Wed, 04 Jul 2007 22:00:00 GMT

Dynamical twisted mass fermions with light quarks Boucaud, Ph.; Dimopoulos, P.; Farchioni, F.; Frezzotti, R.; Gimenez, V.; Herdoiza, G.; Jansen, K.; Lubicz, Vittorio; Martinelli, G.; McNeile, C.; Michael, C.; Montvay, I.; Palao, D.; Papinutto, Mauro; Pickavance, J.; Rossi, G.C.; Scorzato, L.; Shindler, A.; Simula, Silvano; Urbach, C.; Wenger, U. 2007-07-05 Physics Letters B 650 304-311 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 <~ 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, l3 and l4 are evaluated with small statistical errors.