Novel Search for HeavyνMixing from theβ+Decay ofK38

Abstract

A new technique, full neutrino momentum reconstruction, is used to set limits on the admixture of heavy neutrinos into the electron neutrino. We measure coincidences between nuclear recoils and positrons from the beta decay of trapped radioactive atoms and deduce the neutrino momentum. A search for peaks in the reconstructed recoil time-of-flight spectrum as a function of positron energy is performed. The admixture upper limits range from 4 x 10(-3) to 2 x 10(-2) and are the best direct limits for neutrinos (as opposed to antineutrinos) for the mass region of 0.7 to 3.5 MeV.

A White Paper on keV sterile neutrino Dark Matter

“…The information from side-band integration from lower resolution calorimetry and the slow variation in the shape predicted by heavy sterile neutrinos would provide important independent confirmation of the heavy sterile neutrino hypothesis over the full production phase space of the β-decay spectrum. The mass (m s ) of the unobserved sterile neutrino can be determined in principle from a single β-decay event, if one can reconstruct its energy and full momentum from the measured observables, namely the full momenta k and p of the emitted electron and the recoiling daughter, assuming that the parent nucleus was at rest [917][918][919][920].…”

Proposed experiments to detect keV-range sterile neutrinos using energy-momentum reconstruction of beta decay or K-capture events

“…It is clear that in preference to attempting to detect a small sterile neutrino event population within a much larger population of standard neutrino events, it would be preferable to isolate the individual sterile neutrino events as a separate population. This is the objective of the principle of full energy-momentum reconstruction already outlined in section 1 above and the subject of [3][4][5][6][7][8]. Two variations of this are possible, using either beta decay or K-capture nuclides, and are shown in figure 7.…”

“…Top of this list is 131 Cs, which is also considered one of the best prospects for achieving an MOT source with 10 8 -10 10 atoms, and will therefore be assessed in more detail in the remainder of this section. The special case of 7 Be, which has particularly simple kinematics, with no x-ray but a single low energy Auger electron trigger, will be discussed in section 9.…”

“…This idea was also foreshadowed 50 years earlier by measurements of atomic recoil energy to establish the form of the weak interaction [5]. Mass reconstruction was subsequently used by Hindi et al [6], using K-capture in 37 Ar to set relative sterile neutrino coupling limits ∼10 −2 in the mass range 370-640 keV, and by Trinczek et al [7] using beta decay of 38m K to set coupling limits ∼10 −2 in the mass range 0.7-3.5 MeV. But for the reasons discussed below in section 2, there was increasing interest in the possible existence of sterile neutrinos at much lower masses ∼5-10 keV, and lower coupling levels <∼10 −6 , leading Bezrukov and Shaposhnikov [8] to investigate the possibility of more precise reconstruction of tritium beta decay events, together with higher event rates, in order to reach these lower values.…”

Precision measurements of beta-decay correlation parameters from trapped atoms and ions

“…just like the neutron. The TRINAT collaboration has a mature program performing precision β -decay experiments using a magneto-optical trap [1,2,3,4]. We have developed the ability to trap and highly-polarize 37 K using atomic techniques, and have recently taken data for the firstever measurement of the β -asymmetry parameter, A β , from laser-cooled atoms.…”