Eur. Phys. J. A (2025) 61: 281
https://doi.org/10.1140/epja/s10050-025-01744-w

Regular Article - Experimental Physics

High-precision Q-value measurement and evaluation of nuclear matrix elements for $_{}^{122}$Sn and $_{}^{124}$Sn neutrinoless double beta decays

¹ Accelerator Laboratory, Department of Physics, University of Jyväskylä, P.O. Box 35 (YFL), 40014, Jyvaskyla, Finland
² Department of Physics, Banaras Hindu University, 221005, Varanasi, Uttar Pradesh, India
³ International Centre for Advanced Training and Research in Physics, P.O. Box MG12, 077125, Bucharest-Mǎgurele, Romania
⁴ Finnish Institute for Educational Research, University of Jyväskylä, P.O. Box 35, 40014, Jyvaskyla, Finland

^a elina.k.kauppinen@jyu.fi
^b jouni.k.a.ruotsalainen@jyu.fi

Received: 21 July 2025
Accepted: 6 November 2025
Published online: 11 December 2025

Abstract

We have determined the decay energy (Q value) of the double beta decay of $_{}^{122}$Sn with the JYFLTRAP double Penning trap mass spectrometer using the Phase-Imaging Ion Cyclotron Resonance technique. Our new Q value, 373.58(12) keV, agrees with the literature value but is 20 times more precise. We also measured the Q value for the double beta decay of $_{}^{124}$Sn with unprecedented precision, 2293.542(83) keV. The Q values of $_{}^{122}$Sn and $_{}^{124}$Sn were used to calculate precisely the phase-space factors for the neutrinoless double beta ($0\nu \beta \beta$) decay mode of these nuclei. With the phase-space factor and our computed nuclear matrix elements (NMEs) we predict the $0\nu \beta \beta$-decay half-life of $_{}^{122}$Sn based on the recently extracted upper limit of the effective neutrino mass by the KamLAND-Zen experiment. We used three nuclear-structure frameworks to compute the NMEs, namely the proton-neutron quasiparticle random-phase approximation (pnQRPA), the microscopic interacting boson model (IBM-2), and a hybrid model exploiting both the pnQRPA and the nuclear shell model (NSM). We find that including the short-range components enhances the total NME in the IBM-2 model, making it significantly larger than the NMEs calculated with the pnQRPA and hybrid models. Nevertheless, for all models, the obtained half-lives are very long for $_{}^{122}$Sn ( $\approx {10}^{27}$–${10}^{29}$ years), making the observation of $0\nu \beta \beta$ decay of $_{}^{122}$Sn experimentally challenging. On the other hand, the hybrid-model calculated value of the NME for $_{}^{124}$Sn goes, interestingly enough, toward those previously computed by the NSM and the ab initio model.