Simulating the β<sup>+</sup> Decay Spectrum of <sup>22</sup>Na[3<sup>+ </sup>→ 2<sup>+</sup>]
ORAL
Abstract
The β+ decay of 22Na(3+), characterized by a Q-value of 1568.79(14) keV and a dominant transition (99.944(14)%) to the 2+ state of 22Ne, which itself promptly decays to 0+ state via
an E2 transition, offers a unique platform for probing physics beyond the Standard Model. In particular, the Fierz interference term b, which modifies the shape of the β spectrum
and is sensitive to exotic scalar or tensor couplings, remains poorly constrained. The last measurement of b in 22Na dates to the 1960s [1] and suffers from underestimated systematic
uncertainties. The 1960s measurement remains a key input into the CKM matrix element Vud estimate from a global analysis of 0+ → 0+ beta decays [2].
We performed a series of high-resolution simulations of the 22Na β+ decay spectrum using the Beta Spectrum Generator (BSG) toolkit, incorporating relativistic kinematics,
phase space factors, and shape corrections for values of b up to its projected sensitivity. The simulations also account for beta-electron asymmetry and the neutrino-electron correlation.
Special attention was given to modifications of the β+ spectrum introduced by background contributions from 7Be and 3H. The positron spectra were computed with 10 eV energy steps
to resolve fine features, and we propagated statistical uncertainties through normalization and spectrum analysis using a custom Python pipeline. Our goal is to characterize how
variations in b affect the spectrum shape, particularly in the low-energy region where the Fierz term contributes most significantly.
This simulation effort is part of a broader feasibility study toward a future experimental remeasurement of the 22Na β+ spectrum, potentially using a novel embedded-source technique
in a high-purity Germanium semiconductor detector. While detector modeling and full experimental planning are ongoing, this work establishes a rigorous foundation for assessing
the spectral sensitivity to b and refining the design criteria needed to reach a sensitivity of b < 0.01 (90% C.L.).
an E2 transition, offers a unique platform for probing physics beyond the Standard Model. In particular, the Fierz interference term b, which modifies the shape of the β spectrum
and is sensitive to exotic scalar or tensor couplings, remains poorly constrained. The last measurement of b in 22Na dates to the 1960s [1] and suffers from underestimated systematic
uncertainties. The 1960s measurement remains a key input into the CKM matrix element Vud estimate from a global analysis of 0+ → 0+ beta decays [2].
We performed a series of high-resolution simulations of the 22Na β+ decay spectrum using the Beta Spectrum Generator (BSG) toolkit, incorporating relativistic kinematics,
phase space factors, and shape corrections for values of b up to its projected sensitivity. The simulations also account for beta-electron asymmetry and the neutrino-electron correlation.
Special attention was given to modifications of the β+ spectrum introduced by background contributions from 7Be and 3H. The positron spectra were computed with 10 eV energy steps
to resolve fine features, and we propagated statistical uncertainties through normalization and spectrum analysis using a custom Python pipeline. Our goal is to characterize how
variations in b affect the spectrum shape, particularly in the low-energy region where the Fierz term contributes most significantly.
This simulation effort is part of a broader feasibility study toward a future experimental remeasurement of the 22Na β+ spectrum, potentially using a novel embedded-source technique
in a high-purity Germanium semiconductor detector. While detector modeling and full experimental planning are ongoing, this work establishes a rigorous foundation for assessing
the spectral sensitivity to b and refining the design criteria needed to reach a sensitivity of b < 0.01 (90% C.L.).
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Publication: [1] H. Wenninger, J. Stiewe, and H. Leutz. The 22Na positon spectrum. Nuclear Physics A, 109(3):561–576, 1968.<br>[2] J.C. Hardy and I.S. Towner. Superallowed 0+ → 0+ nuclear beta decays: 2014 critical survey, with precise results for vud and CKM unitarity. Phys. Rev. C, 91(2):025501, 2015.
Presenters
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Swarup Bhattarai
Mississippi State University
Authors
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Swarup Bhattarai
Mississippi State University
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Maruf Abubakar
Mississippi State University
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Jeff Allen Winger
Mississippi State University
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Prajwal T MohanMurthy
Massachusetts Institute of Technology