Twisted mass QCD in the charm sector

We present preliminary results for the charm quark mass mc and the D and Ds mesons decay constants fD and fDs from a lattice QCD calculation with Nf = 2 dynamical fermions. We use the twisted mass fermionic action defined at maximal twist so that physical quantities are automatically O(a) improved. Two lattice spacings are considered. The charm quark mass has been renormalised in the RI-MOM scheme. After a matching to the MS scheme, we obtain from the simulation at a fine lattice (a ∼ 0.09 fm) mMS c (mc) = 1.481± 0.022± 0.092 GeV, fD = 205± 13± 17 MeV, fDs = 271± 6± 6 MeV and from the simulation at the finer lattice (a ∼ 0.07 fm) mMS c (mc) = 1.474± 0.041± 0.132 GeV, fD = 230 ± 31 ± 8 MeV and fDs = 264± 5± 8 MeV. We chose three renormalisation conditions to determine mc: the spread between the final results contributes to the systematic error. At both lattice spacings, particularly at the finer one, the error on mc is dominated by present uncertainty on the renormalisation constant ZP, which should be reduced before performing a reliable continuum limit.