Electron-antineutrino spectrum from precision measurements of $^{144}$Pr-decay

TL;DR

This work achieves a high-precision determination of the beta spectrum from the ${}^{144}$Ce-${}^{144}$Pr source by employing two complementary Si(Li) beta-spectrometers, enabling a precise extraction of the nuclear shape factor $C(W)$ for the ground-state transition and a robust reconstruction of the electron antineutrino spectrum above the IBD threshold. The 4π setup yields $C(W)=1+(-0.0301 ext{(7)})W+(-0.101 ext{(6)})W^{-1}$, while the target-detector approach provides a consistent, independently derived shape-factor estimate. From the measured beta spectrum, the neutrino spectrum $N(E_ u)$ is obtained and used to compute the inverse beta decay cross section per decay as $\sigma_{144Pr}=(4.7344 ext{(stat)} ext{(syst)}) imes10^{-44} ext{ cm}^2$, with a detailed accounting of radiative, screening, and energy-scale corrections. These results yield a highly precise input for short-baseline sterile neutrino searches, enabling sensitivity to $m_4 o ext{~1 eV}$ and $ ext{sin}^2(2 heta_{14}) o ext{a few }10^{-3}$ in standard disappearance analyses, and represent the most accurate determination to date for this source.

Abstract

The $^{144}$Ce -- $^{144}$Pr electron antineutrino source is one of the most suitable radiochemical sources for experiments searching for the oscillations of active neutrinos to the light sterile state. In the current work the $β$-spectra of $^{144}\rm{Ce}$ -- ${^{144}\rm{Pr}}$ source have been measured by two types of $β$-spectrometers based on silicon Si(Li) detectors in order to determine the energy spectrum of electron anti-neutrino emitted in the $β$-decay of $\rm{^{144}Pr}$ nuclei. The nuclear shape factor of the ground state beta transition in ${^{144}\rm{Pr}}-{^{144}\rm{Nd}}$ has been obtained with high precision: $C(W) = 1 + (-0.0301 \pm 0.0007)W + (-0.101 \pm 0.006)W^{-1}$. The reduced cross section for the inverse beta decay reaction on hydrogen for the $\rm{{^{144}Pr}}$ electron anti-neutrino source has been defined as $\rm{(4.7344 \pm 0.0006_{stat} \pm 0.013_{syst}) \times 10^{-44}~cm^2 {decay}^{-1}}$ that provides sufficient sensitivity to search for a sterile neutrino with a mass of $m_4 \sim 1$~eV and a mixing angle $Sin^2(2θ_{14}) \sim 0.005$ using standard disappearance method.

Figures (9)

• Figure 1: Schematic representation of the spectrometers. A)"target - detector" spectrometer: 1 - Si(Li) full absorption detector, 2 - Si transmission detector, 3 - $\rm{^{144}Ce-^{144}Pr}$ source, 4 - tungsten collimator, 5 - Cu cold finger, 6 - vacuum cryostat. B) $4\pi-$spectrometer: 1,2 - Si(Li) full absorption detectors, 3 - $\rm{^{144}Ce-^{144}Pr}$ source, 4 - preamplifiers, 5 - bias voltage.
• Figure 2: Energy spectra in the ranges $(0.01-2.0)$ MeV measured by a Si(Li)-detector with a $\rm{^{207}Bi}$ source. The bottom insert shows the electron peaks corresponding to the internal conversion from K-, L- and M-shells while the $569.7$ keV nuclear level discharge. The nuclear levels of $\rm{^{207}Pb}$ are shown in the top inset.
• Figure 3: The spectrum of $\rm{^{207}Bi}$ measured in coincidence with transition detector (black) and simulated with Monte Carlo method (red). The lower plot shows the full absorption detector spectrum obtained without transition detector. The inset shows detector response functions for $\rm{^{144}Ce – ^{144}Pr}$ conversion electrons with energies 91.5 keV (1), 127 keV (2), 626 keV (3), 1446 keV (4) and 2145 keV (5) Ale2018.
• Figure 4: The measured spectrum of the $^{144}$Ce-$^{144}$Pr source with the spectrometer in the "target-detector" geometry. The fitting result is shown by red line. The difference is given in the units of standard deviations (SD).
• Figure 5: The spectrum of the allowed $\beta-$transition $\rm{{^{144}Pr~(0^-)} \rightarrow {^{144}Nd~(1^-)}}$ measured with the "target-detector" spectrometer and the fitting results.