Measurement of the Neutron Lifetime Using a Proton Trap

We report a new measurement of the neutron decay lifetime by the absolute counting of in-beam neutrons and their decay protons. Protons were confined in a quasi-Penning trap and counted with a silicon detector. The neutron beam fluence was measured by capture in a thin ${}^6\mathrm{L}\mathrm{i}\mathrm{F}$ foil detector with known absolute efficiency. The combination of these simultaneous measurements gives the neutron lifetime: ${\tau }_n=(886.8\pm 1.2[\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}]\pm 3.2[\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}])\mathrm{s}$. The systematic uncertainty is dominated by uncertainties in the mass of the ${}^6\mathrm{L}\mathrm{i}\mathrm{F}$ deposit and the ${}^6\mathrm{L}\mathrm{i}(n,t)$ cross section. This is the most precise measurement of the neutron lifetime to date using an in-beam method.