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 ⁶LiF foil detector with known absolute efficiency. The combination of these simultaneous measurements gives the neutron lifetime: ${{τ}}ₙ=(886.8±{}1.2[stat]±{}3.2[syst]) s$. The systematic uncertainty is dominated by uncertainties in the mass of the $⁶LiF$ deposit and the $⁶Li(n,t)$ cross section. This is the most precise measurement of the neutron lifetime to date using an in-beam method.