Abstract
We calculate the nucleon isovector scalar charge in lattice QCD using overlap fermions on five ensembles of gauge configurations generated by the RBC/UKQCD collaboration using the domain-wall quark action with $2+1$ dynamical flavors. The five ensembles cover five pion masses, $m_\pi \approx$ 139, 171, 302, 337 and 371 MeV, and four lattice spacings, $a \approx $ 0.06, 0.08, 0.11 and 0.14 fm. Three to six valence quark masses are computed on each ensemble to investigate the pion mass dependence. The extrapolation to the physical pion mass, continuum and infinite volume limits is obtained by a global fit of all data to a formula originated from partially quenched chiral perturbation theory. The excited-states contamination is carefully analyzed with 3--5 sink-source separations and multi-state fits. Our final result, in the $\overline{\text{MS}}$ scheme at 2 GeV, is $g_{S}^{u-d}= 0.94 (10)_{stat}(8)_{sys}$, where the first error is the statistical error and the second is the systematic error.
Highlights
The nucleon scalar charge is a fundamental quantity in understanding the internal structure of nucleons and more importantly it is related to the search for new physics beyond the Standard Model (BSM)
Five ensembles covering five pion masses including one at the physical value, four lattice spacings in the range 0.06 fm–0.14 fm and five volumes are used in this work, and 3–6 valence pion masses are computed for each ensemble
This enables us to make a reliable extrapolation to the physical pion mass, continuum limit and infinitevolume limit
Summary
The nucleon scalar charge is a fundamental quantity in understanding the internal structure of nucleons and more importantly it is related to the search for new physics beyond the Standard Model (BSM). Five ensembles covering five pion masses including one at the physical value, four lattice spacings in the range 0.06 fm–0.14 fm and five volumes are used in this work, and 3–6 valence pion masses are computed for each ensemble. This enables us to make a reliable extrapolation to the physical pion mass, continuum limit and infinitevolume limit.
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