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

Abstract

A measurement of the neutron lifetime τ 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 τ n = (886.6 ± 1.2[stat] ± 3.2[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(n,t) cross section. The measurement technique and apparatus, data analysis, and investigation of systematic uncertainties are discussed in detail.

Experimental limits on neutron disappearance into another braneworld

“…When measuring τ n with the beam method, one really measures the beta decay channel: one measures the absolute proton activity of a cold neutron beamline. Byrne et al [31] measured the rate of proton production of a well-defined section of a cold neutron beam at the ILL and have reported a neutron lifetime of τ n = 889.2 ± 4.8 s. Using the same improved technique, Nico et al [32] measured τ n = 886.3 ± 3.4 s. The two independent results can be combined: Next we consider the UCN trap experiments [33,[35][36][37] performed at the ultracold neutron beamline PF2 at the Institut Laue Langevin, using UCN traps coated with fluorinated polyether oil (Fomblin). We also consider the experiment [34] performed at the Saint Petersburg Institute of Nuclear Physics using a trap coated with solid Oxygen.…”

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].…”

Radiativeβdecay of the free neutron

“…The experimental method utilized a superconducting, solenoid magnet and charged-particle detection scheme previously applied to measure both the neutron lifetime and the electron-antineutrino angular correlation coefficient, which are described elsewhere [20][21][22]. The cold neutron beam enters parallel to the 4.6 T field produced by the magnet, as illustrated in Fig.…”