D-s -> eta,eta ' semileptonic decay form factors with disconnected quark loop contributions

Abstract

We calculate for the first time the form factors of the semileptonic decays of the D-s meson to eta and eta ' using lattice techniques. As a by-product of the calculation we obtain the masses and leading distribution amplitudes of the eta and eta' mesons. We use N-f = 2 + 1 nonperturbatively improved clover fermions on configurations with a lattice spacing a similar to 0.075 fm. We are able to obtain clear signals for relevant matrix elements, using several noise reduction techniques, for both the connected and the disconnected contributions. This includes a new method for reducing the variance of pseudoscalar disconnected two-point functions. At zero momentum transfer, we obtain for the scalar form factors, vertical bar f(0)(Ds ->eta)vertical bar = 0.564(11) and vertical bar f(0)(Ds ->eta')vertical bar = 0.437(18) at M-pi approximate to 470 MeV, as well as vertical bar f(0)(Ds ->eta)vertical bar = 0.542(13) and vertical bar f(0)(Ds ->eta')vertical bar = 0.404(25) at M-pi approximate to 370 MeV, w here the errors are statistical only.