Lattice calculation of the R-ratio smeared with Gaussian kernels

Abstract

The ratio ( ) of the cross-sections for + − → hadrons and + − → + − is a valuable energy-dependent probe of the hadronic sector of the Standard Model. Moreover, the experimental measurements of ( ) are the inputs of the dispersive calculations of the leading hadronic vacuum polarization contribution to the muon − 2 and these are in significant tension with direct lattice calculations and with the muon − 2 experiment.In this talk we discuss the results of our first-principles lattice study of ( ). By using a recently proposed method for extracting smeared spectral densities from Euclidean lattice correlators, we have calculated ( ) convoluted with Gaussian kernels of different widths and central energies up to 2.5 GeV. Our theoretical results have been compared with the KNT19 [1] compilation of experimental results smeared with the same Gaussian kernels and a tension (about three standard deviations) has been observed for ∼ 600 MeV and central energies around the -resonance peak.