Form factors of the D→π and D→K semileptonic decays with Nf=2 twisted mass lattice QCD

We present lattice results for the vector and scalar form factors of the semileptonic decays D → π lνl and D → Klνl in the physical range of values of squared four momentum transfer q2 , obtained with N f = 2 maximally twisted Wilson fermions simulated at three different lat- tice spacings (a ≃ 0.102 fm , 0.086 fm , 0.068 fm ) with pion masses as light as 270 MeV and mπ L 4. The form factors are extracted using a double ratios strategy, which allows a good statistical accuracy and is independent of the vector current renormalization constant. The chiral/continuum extrapolation is performed through a simultaneous fit in the three variables (mπ , q2 , a) using HMChPT formulae with additional O(a2 ) terms that parametrically account for the lattice spacing dependence. Our results are in very good agreement with the experimental data in the full q2 range for both D → π lνl and D → Klνl . At zero momentum transfer we obtain f D→π (0) = 0.65(6)stat (6)syst and f D→K (0) = 0.76(5)stat (5)syst , where the systematic error does not include the effects of quenching the strange and the charm quarks. Our findings are in good agreement with recent lattice calculations at N f = 2 + 1.