Measurement of the Neutron Lifetime by Counting Trapped Protons in a Cold Neutron Beam

Abstract

A measurement of the neutron lifetime ${\tau }_n$ performed by the absolute counting of in-beam neutrons and their decay protons has been completed. Protons confined in a quasi-Penning trap were accelerated onto a silicon detector held at a high potential and counted with nearly unit efficiency. The neutrons were counted by a device with an efficiency inversely proportional to neutron velocity, which cancels the dwell time of the neutron beam in the trap. The result is ${\tau }_n=(886.6\pm 1.2[\mathrm{stat}]\pm 3.2[\mathrm{sys}])$ s, which is the most precise measurement of the lifetime using an in-beam method. The systematic uncertainty is dominated by neutron counting, in particular the mass of the deposit and the ${}^6$Li({\it{n,t}}) cross section. The measurement technique and apparatus, data analysis, and investigation of systematic uncertainties are discussed in detail.

71 pages, 20 figures, 9 tables; submitted to PRC

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