Elementary particle

Particle physics

Physics

Particle decay

Perturbation theory (quantum mechanics)

Isospin

Acoustics

Lattice (music)

Quark

Chiral perturbation theory

Physical Review Letters

The leading-order electromagnetic and strong isospin-breaking corrections to the ratio of ${K}_{\ensuremath{\mu}2}$ and ${\ensuremath{\pi}}_{\ensuremath{\mu}2}$ decay rates are evaluated for the first time on the lattice, following a method recently proposed. The lattice results are obtained using the gauge ensembles produced by the European Twisted Mass Collaboration with ${N}_{f}=2+1+1$ dynamical quarks. Systematic effects are evaluated and the impact of the quenched QED approximation is estimated. Our result for the correction to the tree-level ${K}_{\ensuremath{\mu}2}/{\ensuremath{\pi}}_{\ensuremath{\mu}2}$ decay ratio is $\ensuremath{-}1.22(16)%$, to be compared to the estimate of $\ensuremath{-}1.12(21)%$ based on chiral perturbation theory and adopted by the Particle Data Group.

First Lattice Calculation of the QED Corrections to Leptonic Decay Rates