Pseudoscalar meson decay constants fK, fD and fDs, from Nf=2 twisted mass Lattice QCD
Abstract
We present the results of a lattice QCD calculation of the pseudoscalar meson decay constants fK, fD and fDs, performed with Nf=2 dynamical fermions. The simulation is carried out with the tree-level improved Symanzik gauge action and with the twisted mass fermionic action at maximal twist. With respect to our previous study (0709.4574 [hep-lat]), here we have analysed data at three values of the lattice spacing (a=0.10 fm, 0.09 fm, 0.07 fm) and performed the continuum limit, and we have included at a=0.09 fm data with a lighter quark mass (mpi = 260 MeV) and a larger volume (L = 2.7 fm), thus having at each lattice spacing L >= 2.4 fm and mpi*L >= 3.6. Our result for the kaon decay constant is fK=(157.5 +- 0.8|stat. +- 3.3|syst.) MeV and for the ratio fK/fpi=1.205 +- 0.006|stat. +- 0.025|syst., in good agreement with the other Nf=2 and Nf=2+1 lattice calculations. For the D and Ds meson decay constants we obtain fD=(205 +- 7|stat. +- 7|syst.) MeV, in good agreement with the CLEO-c experimental measurement and with other recent Nf=2 and Nf=2+1 lattice calculations, and fDs=(248 +- 3|stat. +- 8|syst.) MeV that, instead, is 2.3 sigma below the CLEO-c/BABAR experimental average, confirming the present tension between lattice calculations and experimental measurements.