Constraining new physics with a novel measurement of the $^{23}$Ne $β$-decay branching ratio

Abstract

Measurements of the beta-neutrino correlation coefficient (a βν ) in nuclear beta decay, together with the Fierz interference term (b F ), provide a robust test for the existence of exotic interactions beyond the Standard Model of Particle Physics. The extraction of these quantities from the recoil ion spectra in β-decay requires accurate knowledge, decay branching ratios, and high-precision calculations of higher order nuclear effects. Here, we report on a new measurement of the 23 Ne β-decay branching ratio, which allows a reanalysis of existing high-precision measurements. Together with new theoretical calculations of nuclear structure effects, augmented with robust theoretical uncertainty, this measurement improves on the current knowledge of a βν in 23 Ne by an order of magnitude, and strongly constrains the Fierz

A formalism to assess the accuracy of nuclear-structure weak interaction effects in precision β-decay studies

“…In addition, contemporary precision β-decay experiments are aimed at a level of 10 −3 . In the following we tried to keep corrections that may become useful for this accuracy, leaning also on our experience with interpreting this formalism for 6 He [17] and 23 Ne [18]. Therefore, we refer to anything beyond the leading order, but still varying around 10 −3 relative to it, as a next-to-leading order (NLO) correction include ths NLO corrections and neglect its squared value, which we label as a nextto-next-to-leading order (NNLO) correction.…”

“…Thus, as an order of magnitude one can use NM ≡ max( EFT , model , conv ) (NM is nuclear model). Estimating NM should be done case by case (see 6 He [17] and 23 Ne [18] as examples). We note that a recent effort to calculate β-decays ab initio up to A = 100 has reached precision of the order of 10% of the Gamow-Teller strength [27].…”

“…New β-decay experiments are designed to have a per-mil level accuracy [6]. Such new efforts include, for example, studying the decays of 6 He, 16 N, and [17][18][19][20][21][22][23] Ne isotopes at SARAF accelerator (Israel) [7,8], 6 He decay studies at the National Superconducting Cyclotron Laboratory (USA) [9][10][11], Laboratoire Physique Corpusculaire de CAEN (France) [6], the University of Washington CENPA (USA) by the He6-CRES Collaboration [12], and more (for an overview of ongoing and planned experiments see [6,13]). However, deviations from the simplistic textbook formulae are also due to finite momentum transfer, radiative corrections, and nuclear structure effects (see e.g., [14,15] and references therein).…”

Translationally invariant matrix elements of general one-body operators

“…The β-decays are sensitive to interference of currents of SM particles and hypothetical BSM physics [4][5][6][7][8]. The potential of using β-decay observables as the precision frontier for BSM searches has led to the deployment of several experimental efforts [9][10][11][12]. However, discovering deviations from the SM predictions demands also high-precision theoretical calculations [13][14][15].…”

Nuclear ab initio calculations of 6He β-decay for beyond the Standard Model studies

“…Importantly, this indirectly induces a linear dependence of this observable upon BSM corrections, beyond the naive quadratic dependence of a βν . Consequently, ∼ 10 −4 experimental precision on this observable would entail tighter BSM constraints [52].…”