Simulation Framework for Precision Studies of the Fierz Interference Term in the β⁺ decay of <sup>22</sup>Na
ORAL
Abstract
The β⁺ decay of 22Na (3⁺) → 22Ne (2⁺, 1.274 MeV) offers a sensitive probe for exotic scalar or tensor currents through the Fierz interference term b, which modifies the shape of the positron energy spectrum. The last direct measurement of b in 22Na, performed nearly six decades ago, underestimated systematic uncertainties yet remains an influential input to the global analysis of the CKM matrix element Vud.
This work develops a simulation framework to quantify how variations in b influence the observed β⁺ spectrum, including detector-response and background effects. Using the Beta Spectrum Generator (BSG) for relativistic kinematics and spectral corrections, coupled with Geant4-based modeling, we investigate the impact of photoelectric, Compton, pair-production, bremsstrahlung, nuclear scattering, and Rayleigh scattering processes on the reconstructed spectra combined with high-statistics simulations (10⁷–10⁸ events per configuration).
The resulting simulations establish a quantitative basis for assessing spectral sensitivity to b and identifying detectors configurations best suited for remeasurement of the ²²Na β⁺ spectrum using a high-purity germanium semiconductor detector. These studies provide essential groundwork for refining the design criteria needed to reach a sensitivity of b < 0.01 (90% C.L.), thereby constraining exotic scalar and tensor couplings with improved precision.
This work develops a simulation framework to quantify how variations in b influence the observed β⁺ spectrum, including detector-response and background effects. Using the Beta Spectrum Generator (BSG) for relativistic kinematics and spectral corrections, coupled with Geant4-based modeling, we investigate the impact of photoelectric, Compton, pair-production, bremsstrahlung, nuclear scattering, and Rayleigh scattering processes on the reconstructed spectra combined with high-statistics simulations (10⁷–10⁸ events per configuration).
The resulting simulations establish a quantitative basis for assessing spectral sensitivity to b and identifying detectors configurations best suited for remeasurement of the ²²Na β⁺ spectrum using a high-purity germanium semiconductor detector. These studies provide essential groundwork for refining the design criteria needed to reach a sensitivity of b < 0.01 (90% C.L.), thereby constraining exotic scalar and tensor couplings with improved precision.
*This work was supported by the Shackouls Honors College and the Department of Physics and Astronomy at Mississippi State University.
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Presenters
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Swarup Bhattarai
- Mississippi State University