Measurement of the Neutron Lifetime Using a Proton Trap

Abstract

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: ${\ensuremath{\tau}}_{n}=(886.8\ifmmode\pm\else\textpm\fi{}1.2[\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}]\ifmmode\pm\else\textpm\fi{}3.2[\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}])\text{ }\text{ }\mathrm{s}$. 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.