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 6LiF foil detector with known absolute efficiency. The combination of these simultaneous measurements gives the neutron lifetime: tau(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.

Framework for maximum likelihood analysis of neutronβdecay observables to resolve the limits of theV−Alaw

“…The existing tension between the latter, "in beam" experiments and the former, "bottle" experiments [17,22] -though there is also tension between the results of the most precise bottle experiments [17,22] -make the observation intriguing. However, the most precise in-beam neutron lifetime experiment [61,62] counts decay protons, rather than electrons, so that our numerical analysis is not directly relevant. Indeed, in such experiments, there are no threshold effects, and the entire proton recoil spectrum is empirically accessible [61,62].…”

“…However, the most precise in-beam neutron lifetime experiment [61,62] counts decay protons, rather than electrons, so that our numerical analysis is not directly relevant. Indeed, in such experiments, there are no threshold effects, and the entire proton recoil spectrum is empirically accessible [61,62]. On the other hand, experimental concepts which detect the decay electrons have been under development [63,64].…”

Measurement of the neutron lifetime by counting trapped protons in a cold neutron beam

“…This paper describes a measurement of the neutron lifetime by counting beam neutrons and trapped protons [9]. It presents a refined analysis of the data and treatment of the systematic effects.…”

“…[3] [7] [ 9] beam UCN bottle Storage ring Neutron decay can be used to determine the CKM matrix element |V ud | with high precision in a fashion that is free of some of the theoretical uncertainties present in 0 + → 0 + nuclear decays, which are still used for the most precise determination of |V ud |. Neutron decay is the system that offers the best prospect of a significant improvement in the direct determination of |V ud |.…”

Testing the Unitarity of the CKM Matrix With a Space-Based Neutron Decay Experiment

“…This was mainly due to the difficulty in determining the experimental systematics involved in the various experiments. But since that time experiments have improved to yield accuracies as low as in the 0.1% range [17]- [24]. This yielded a 2004 world average of [8] τ n = (885.7 ± 0.8) s.…”