Strange and light quark contributions to the nucleon mass from lattice QCD

Abstract

We determine the strangeness and light quark fractions of the nucleon mass by computing the quark line connected and disconnected contributions to the matrix elements ${m}_{q}⟨N|\overline{q}q|N⟩$ in lattice QCD, using the nonperturbatively improved Sheikholeslami-Wohlert Wilson fermionic action. We simulate ${n}_{\mathrm{F}}=2$ mass degenerate sea quarks with a pion mass of about 285 MeV and a lattice spacing $a\ensuremath{\approx}0.073\text{ }\text{ }\mathrm{fm}$. The renormalization of the matrix elements involves mixing between contributions from different quark flavors. The pion-nucleon $\ensuremath{\sigma}$ term is extrapolated to physical quark masses exploiting the sea quark mass dependence of the nucleon mass. We obtain the renormalized values ${\ensuremath{\sigma}}_{\ensuremath{\pi}N}=(38\ifmmode\pm\else\textpm\fi{}12)\text{ }\text{ }\mathrm{MeV}$ at the physical point and ${f}_{{T}_{s}}={\ensuremath{\sigma}}_{s}/{m}_{N}=0.012(14{)}_{\ensuremath{-}3}^{+10}$ for the strangeness contribution at our larger than physical sea quark mass.