B-physics from N f = 2 tmQCD: the Standard Model and beyond

We present a lattice QCD computation of the b -quark mass, the B and B s decay constants, the B -mixing bag prameters for the full four-fermion operator basis as well as determinations for ξ and f Bq √(B_i^(q) ) extrapolated to the continuum limit and to the physical pion mass. We used N f = 2 twisted mass Wilson fermions at four values of the lattice spacing with pion masses ranging from 280 to 500 MeV. Extrapolation in the heavy quark mass from the charm to the bottom quark region has been carried out on ratios of physical quantities computed at nearby quark masses, exploiting the fact that they have an exactly known infinite mass limit. Our results are m b ( m b , MS ) = 4 . 29(12) GeV, f Bs = 228(8) MeV, f B = 189(8) MeV and f Bs /f B = 1 . 206(24). Moreover with our results for the bag-parameters we find ξ = 1 . 225(31), B_1^(s) / B_1^(d) . = 1 . 01(2), f Bd √(B_1^(d) ) = 216(10) MeV and 1 f Bs √(B_1^(s) ) = 262(10) MeV. We also computed the bag parameters for the complete basis of the four-fermion operators which are required in beyond the SM theories. By using these results for the bag parameters we are able to provide a refined Unitarity Triangle analysis in the presence of New Physics, improving the bounds coming from B ( s ) − B_(s) mixing.