Pseudoscalar decay constants of kaon and D-mesons from N f = 2 twisted mass Lattice QCD

Abstract

We present the results of a lattice QCD calculation of the pseudoscalar meson decay constants f π, f K, f D and f D, performed with N f = 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. We have considered for the final analysis three values of the lattice spacing, a 0.10 fm, 0.09 fm and 0.07 fm, with pion masses down to m π ≃270MeV. Our results for the light meson decay constants are f K = 158.1(2.4)MeV and f Kf π = 1.210(18). From the latter ratio, by using the experimental determination of Γ(K → μ μ(γ))/ Γ(π→ μ μ(γ)) and the average value of V ud from nuclear beta decays, we obtain V us = 0.2222(34), in good agreement with the determination from semileptonic K l3 decays and the unitarity constraint. For the D and D s meson decay constants we obtain f D = 197(9)MeV, f Ds= 244(8)MeV and f Ds fD = 1.24(3). Our result for f D is in good agreement with the CLEO experimental measurement. For f Ds our determination is smaller than the PDG 2008 experimental average but in agreement with a recent improved measurement by CLEO at the 1.4σ level. © 2009 SISSA.