Paper detail

New limits on neutrino decay from the Glashow resonance of high-energy cosmic neutrinos

Discovering neutrino decay would be strong evidence of physics beyond the Standard Model. Presently, there are only lax lower limits on the lifetime $τ$ of neutrinos, of $τ/m \sim 10^{-3}$ s eV$^{-1}$ or worse, where $m$ is the unknown neutrino mass. High-energy cosmic neutrinos, with TeV-PeV energies, offer superior sensitivity to decay due to their cosmological-scale baselines. To tap into it, we employ a promising method, recently proposed, that uses the Glashow resonance $\barν_e + e \to W$, triggered by $\barν_e$ of 6.3 PeV, to test decay with only a handful of detected events. If most of the $ν_1$ and $ν_2$ decay into $ν_3$ en route to Earth, no Glashow resonance would occur in neutrino telescopes, because the remaining $ν_3$ have only a tiny electron-flavor content. We turn this around and use the recent first detection of a Glashow resonance candidate in IceCube to place new lower limits on the lifetimes of $ν_1$ and $ν_2$. For $ν_2$, our limit is the current best. For $ν_1$, our limit is close to the current best and, with the imminent detection of a second Glashow resonance, will vastly surpass it.