Speaker
Description
The Cosmic Neutrino Background (C$\nu$B), a relic from the Big Bang predicted to consist of non-relativistic neutrinos at a present temperature of $\sim$1.95 K, has never been directly detected. Its experimental observation would provide the first direct evidence for non-relativistic neutrinos and open new avenues for probing neutrino masses and early-Universe cosmology. Among the most promising candidate nuclei for relic neutrino capture detection are $^{151}$Sm and $^{171}$Tm, owing to their low $\beta^-$ decay $Q$ values ($Q_{\beta^-} \approx 76.6 \pm 0.5$ keV and $96.5 \pm 1.0$ keV, respectively [1]) and favorable nuclear-structure properties [2, 3]. However, the currently adopted $Q$ values, derived from indirect mass-link chains and historical $\beta^-$ endpoint measurements [4], carry uncertainties at the $\sim$1 keV level. As shown by Kostensalo et al. [3], this is the dominant source of uncertainty in the predicted relic neutrino capture cross-sections, especially for $^{171}$Tm, translating into $\sim$10% variations in the estimated target mass required for detection experiments.
To overcome this limitation, we aim to measure the $Q_{\beta^-}$ values of $^{151}$Sm and $^{171}$Tm directly using the phase-imaging ion-cyclotron-resonance (PI-ICR) technique [5, 6] at the JYFLTRAP double Penning trap mass spectrometer at the IGISOL facility in the University of Jyväskylä, in June 2026. The PI-ICR method determines the cyclotron frequency ratio between the daughter and parent ions with a relative precision of $\Delta Q/M \sim 10^{-9}$, corresponding to a $Q$-value uncertainty of $\sim$100 eV for these heavy nuclei, an order-of-magnitude improvement over current values. The parent isotopes will be produced via light-ion induced fusion-evaporation reactions ($^{\text{nat}}$Nd($\alpha$,$xn$)$^{151}$Sm at 30 MeV and $^{\text{nat}}$Er($^3$He,$xn$)$^{171}$Tm at 24 MeV), while the stable daughter isobars $^{151}$Eu and $^{171}$Yb from a local discharge ion source will serve as references for the measurements. Advanced ion-cleaning methods, Ramsey-type excitations, and interleaved measurement cycles will be employed to suppress systematic effects arising from magnetic-field fluctuations, trap imperfections, and ion-ion interactions. The obtained $Q$ values will provide essential nuclear input data for next-generation C$\nu$B detection experiments.
References
[1] O. Mikulenko, Y. Cheipesh, V. Cheianov, A. Boyarsky, Eur. Phys. J. A 59, 216 (2023).
[2] V. Brdar, R. Plestid, N. Rocco, Phys. Rev. C 105, 045501 (2022).
[3] J. Kostensalo, J. Kotila, J. Suhonen, Phys. Lett. B 840, 137894 (2023).
[4] W. J. Huang et al., Chin. Phys. C 45, 030002 (2021).
[5] D. A. Nesterenko et al., Eur. Phys. J. A 54, 216 (2018).
[6] D. A. Nesterenko et al., Eur. Phys. J. A 57, 302 (2021).