Precise determination of electron-capture Q value of Sn 113 decay related to electron neutrino mass measurements

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A high-precision measurement of the electron-capture (EC) decay Q value for the ground-state-to-groundstate (gs-to-gs) transition of 113 Sn to 113 In has been performed using the JYFLTRAP double Penning trap mass spectrometer.Employing the phase-imaging ion-cyclotron-resonance technique, the isomeric state of 113 Sn at 77.389(19) keV was resolved, and the cyclotron frequency ratio measured between the isomer 113m Sn and the daughter nucleus 113 In.This yielded an isomer-to-ground-state Q value of 1116.64(19)keV and gs-to-gs Q value of 1039.25(19)keV.The atomic mass excess of 113 Sn was determined as -88327.87(27)keV/c 2 , in excellent agreement with the Atomic Mass Evaluation 2020 (AME2020) but with a sixfold precision improvement.Using nuclear energy-level data for 113 In, we identified two low Q-value transitions of the ground state of 113 Sn to excited states of 113 In at 1024.280(50) keV (Q * EC = 14.97(20) keV, second forbidden non-unique) and 1029.650(50)keV (Q * EC = 9.60(20) keV, allowed).The allowed transition exhibits small energy differences (∆ L1 = 5.58(20) keV, ∆ L2 = 5.87(20) keV) from L1 and L2 shell binding energies, enhancing endpoint events.Partial half-lives and energy-release spectra were calculated using the self-consistent Dirac-Hartree-Fock-Slater (DHFS) method (including exchange, overlap, shake-up, and shake-off corrections) together with the nuclear shell model, show enhanced endpoint sensitivity for the allowed transition to the state at 1029.650 keV.Including subthreshold atomic states in the spectral function enhances the EC rate near the zero-neutrino-momentum region by a factor of five, enabling new approaches for low Q-value EC reactions in neutrino-mass studies.