A clean, bright, and versatile source of neutron decay products

Abstract

We present a case study on a new type of cold neutron beam station for the investigation of angular correlations in the beta-decay of free neutrons. With this beam station, called PERC, the 'active decay volume' lies inside the neutron guide, and the charged neutron decay products are magnetically guided towards the end of the neutron guide. Hence, the guide delivers at its exit a beam of decay electrons and protons, under well-defined and precisely variable conditions, which can be well separated from the cold neutron beam. In this way a general-purpose source of neutron decay products is obtained which can be used for various different experiments in neutron decay correlation spectroscopy. A gain in phase space density of several orders of magnitude can be achieved with PERC, as compared to existing neutron decay spectrometers. Neutron beam related background is separately measurable in PERC, and magnetic mirror effects on the charged neutron decay products and edge effects in the active neutron beam volume are both strongly suppressed. Therefore the spectra and angular distributions of the emerging decay particles will be distortion-free on the level of 10^-4, more than 10 times better than achieved today.Comment: 20 pages, 6 figure

Prospects for precision measurements in nuclear decay in the LHC era

“…The anticipated precision goals on δa/a of these experiments are of <1% for aCORN [87] <0.5% for aSPECT [86] and 0.1% for Nab [88]. Significant improvements in precision are also expected to be achieved with the PERC spectrometer [89] in the measurement of several correlation parameters. It is anticipated that the sensitivity goal is of about 10 −5 for those correlations not involving polarized neutrons.…”

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

“…Note that we calculate τ as per Eq. (20), assuming the central value for the superallowed 0 + → 0 + value of V ud = 0.97425 (22) [22].…”

“…Specifically, we would be able to determine the value of λ in an a measurement to 0.010% (equivalent to a 0.037% determination of a 0 ) and to 0.008% in an A measurement (0.032% determination of A 0 ). The stated goals on a and A in the upcoming PERC experiment [20] are to achieve statistical and systematic errors on the level of 0.03%.…”

“…The neutron lifetime is relatively insensitive to new scalar or tensor physics, because such new physics only enters quadratically in the Ξ parameter, noting Eq. (20). Therefore, we would expect a simultaneous fit to an {a, A, τ } data set in the presence of new scalar and tensor interactions to return a poor value for χ 2 min .…”

“…Of the future experimental plans reviewed in Refs. [11][12][13][14][15][16][17][18][19], the claim of ultimate precision rests with the PERC experiment [20], for a sensitivity of up to 10 −4 precision.…”