Physical-mass calculation of $\rho(770)$ and $K^*(892)$ resonance parameters via $\pi \pi$ and $K \pi$ scattering amplitudes from lattice QCD

Abstract

We present our study of the $\rho(770)$ and $K^*(892)$ resonances from lattice quantum chromodynamics (QCD) employing domain-wall fermions at physical quark masses. We determine the finite-volume energy spectrum in various momentum frames and obtain phase-shift parameterizations via the L\"uscher formalism, and as a final step the complex resonance poles of the $\pi \pi$ and $K \pi$ elastic scattering amplitudes via an analytical continuation of the models. By sampling a large number of representative sets of underlying energy-level fits, we also assign a systematic uncertainty to our final results. This is a significant extension to data-driven analysis methods that have been used in lattice QCD to date, due to the two-step nature of the formalism. Our final pole positions, $M+i\Gamma/2$, with all statistical and systematic errors exposed, are $M_{K^{*}} = 893(2)(8)(54)(2)~\mathrm{MeV}$ and $\Gamma_{K^{*}} = 51(2)(11)(3)(0)~\mathrm{MeV}$ for the $K^*(892)$ resonance and $M_{\rho} = 796(5)(15)(48)(2)~\mathrm{MeV}$ and $\Gamma_{\rho} = 192(10)(28)(12)(0)~\mathrm{MeV}$ for the $\rho(770)$ resonance. The four differently grouped sources of uncertainties are, in the order of occurrence: statistical, data-driven systematic, an estimation of systematic effects beyond our computation (dominated by the fact that we employ a single lattice spacing), and the error from the scale-setting uncertainty on our ensemble.