A new scheme to measure the electron-neutrino correlation - the case of $^{6}$He

Abstract

A novel experiment has been commissioned at the Weizmann Institute of Science for the study of weak interactions via a high-precision measurement of the beta-neutrino angular correlation in the radioactive decay of short-lived 6 He. The facility consists of a 14 MeV d + t neutron generator to produce atomic 6 He, followed by ionization and bunching in an electron beam ion source, and injection into an electrostatic ion beam trap. This ion trap has been designed for efficient detection of the decay products from trapped light ions. The storage time in the trap for different stable ions was found to be in the range of 0.6 to 1.2 s at the chamber pressure of ∼7×10 −10 mbar. We present the initial test results of the facility, and also demonstrate an important upgrade of an existing method [1] for production of light radioactive atoms, viz. 6 He, for the precision measurement. The production rate of 6 He atoms in the present setup has been estimated to be ∼ 1.45 × 10 −4 atoms per neutron, and the system efficiency was found to be 4.0±0.6%. An improvement to this setup is also presented for the enhanced production and diffusion of radioactive atoms for future use.

New physics searches in nuclear and neutron β decay

“…The system is actually being commissioned [312]. Storage times of ∼1.2 s for O + and CO + ions and of ∼0.6 s for 4 He + ions have been obtained and a first β spectrum has been observed as well [319].…”

Improved Limit on Tensor Currents in the Weak Interaction from $^8$Li $β$ Decay

“…The development of intense, low-energy beams of radioactive nuclei has greatly aided the current generation of β-ν angular correlation experiments with ion and atom traps [4][5][6][7][8]. Traps are an ideal tool for these measurements, as the nuclide of interest is held nearly at rest in a small, well-characterized volume at high vacuum.…”

“…The highest precision nuclear β-ν correlation limits on T currents were set from a corrected 6 He β-decay measurement from 1963: a βν = −0.3308 ± 0.0030 [9,10] and our previous 8 Li work: a βν = −0.3342±0.0038 [11], both of which involve Gamow-Teller decays. In 2019, a global analysis of available neutron and nuclear β-decay data estimated 0.003<|C T /C A |<0.078 (|C T /C A | 2 < ∼ 0.0061) [1] at 95.5% CL, with the assumption of right-handed couplings for tensor currents (C T = −C T and b F ierz = 0).…”

“…High-energy measurements at the Large Hadron Collider provide tensor-current limits that are comparable [12] or in the case of right-handed couplings, more stringent [1] than those achieved from β decay, although substantially different energy scales and assumptions are required. This Letter presents an improved limit on T contributions obtained from a high-precision study of 8 Li β decay performed with the Beta-decay Paul Trap (BPT) [14]. The experimental setup and data analysis are built upon our earlier efforts to study 8 Li [11,15].…”

Simultaneous Measurements of the Beta Neutrino Angular Correlation in $^{32}$Ar Pure Fermi and Pure Gamow-Teller Transitions using Beta-Proton Coincidences

“…Both techniques yield similar constraints on exotic couplings with ∆ã βν ∼ 5.10 −3 for pure F transitions [5,11], and ∆ã βν ∼ 3.10 −3 for pure GT ones [4,13]. Ongoing experimental programs aim today at precision levels of 10 −3 and below [14][15][16][17][18][19][20]. The present project targets a similar goal by improving by a factor 5 or more the most precise results previously obtained from the recoil energy broadening of beta-delayed protons in the decay of 32 Ar towards its isobaric analogue state in 32 Cl [11,21,22].…”