ɳ, ɳ' mesons from lattice QCD in fully physical conditions

Abstract

We determine masses and mixing parameters of the ɳ and ɳ' meson in lattice QCD. The calculations are carried out on a set of 13 ETMC gauge ensembles with Nf = 2+1+1 (maximally) twisted-mass Clover-improved quarks. These ensemble cover four values of the lattice spacing ɑ = 0.057 fm,...,0.092 fm and pion masses from 140 to 360 MeV, including three ensembles at physical quark masses and six ensembles with Mπ < 200 MeV. The strange-quark contribution is treated in a mixed-action approach using Osterwalder–Seiler fermions to avoid complications due to flavor mixing in the heavy quark sector and to enable the use of the one-end trick in the computation of strange quark-disconnected diagrams. With the strange-quark mass tuned to its physical value and several ensembles having close-to-physical light-quark mass, uncertainties related to the chiral extrapolations are reduced significantly compared to earlier studies. Physical results are computed with fully controlled systematics from a combined chiral, continuum and infinite-volume extrapolation, and a full error budget is obtained from model averages over of various fit ansätze and data cuts. Our results for the masses are given by Mɳ = 551 (16) MeV and Mɳ' = 972 (20) MeV, respectively, where statistical and systematic errors have been added in quadrature. For the mixing angle and decay-constant parameters the Feldmann–Kroll–Stech scheme is employed to compute them from pseudoscalar matrix elements in the quark-flavor basis. For the mixing angle we obtain Φphys = 39.3 (2.0)° and our results for the decay-constant parameters are given by f i phys = 138.6 (4.4) MeV and f s phys = 170.7 (3.3) MeV.