f_B and f_Bs with maximally twisted Wilson fermions

Understand

We present a lattice QCD calculation of the heavy-light decay constants f_B and f_Bs performed with Nf=2 maximally twisted Wilson fermions, at four values of the lattice spacing.

• The decay constants have been also computed in the static limit and the results are used to interpolate the observables between the charm and the infinite-mass sectors, thus obtaining the value of the decay constants at the physical b quark mass.
• Our preliminary results are f_B=191(14) MeV, f_Bs=243(14) MeV, f_Bs/f_B=1.27(5).
• They are in good agreement with those obtained with a novel approach, recently proposed by our Collaboration (ETMC), based on the use of suitable ratios having an exactly known static limit.