Physical-mass calculation of ρ(770) and K^*(892) resonance parameters via π π and K π scattering amplitudes from lattice QCD

We present our study of the ρ(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 π π and K π 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+iΓ/2, with all statistical and systematic errors exposed, are M_K* = 893(2)(8)(54)(2)~MeV and Γ_K* = 51(2)(11)(3)(0)~MeV for the K^*(892) resonance and Mρ = 796(5)(15)(48)(2)~MeV and Γρ = 192(10)(28)(12)(0)~MeV for the ρ(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.