Search for a Neutrino with a Mass of 0.01–1.0 MeV in Beta Decays of 144Ce–144Pr Nuclei

Search for Light Exotic Fermions in Double-Beta Decays

“…This opens the possibility to observe a double-β decay final state in which a standard neutrino is replaced by a sterile neutrino (νN ββ decay): (A, Z) → (A, Z + 2) + 2e + ν + N , with a modified spectrum due to the sterile neutrino mass. This is indeed the same principle as the one used in kink searches with single-β decays [11][12][13][14][15], which currently provide the strongest laboratory bounds in our mass range of interest [2,3,16,17]. As we will see, the presence of light exotic fermions does not create a kink in the total double-β energy spectrum but still creates a continuous distortion that is detectable by 0νββ decay experiments.…”

“…The left panel shows the projected upper limits on the active-sterile mixing, parametrized as sin 2 θ, as a function of the sterile neutrino mass. We also show in the plot the current limits from single-β decay experiments [2,3,16,17] and from solar neutrinos [39]. As can be seen from the plot, the sensitivity of current double-β decay experiments is weaker than the existing limits, but only by a factor of a few.…”

“…The experimental constraints are displayed through a band covering a range of sensitivities that goes from the most optimistic scenario (systematic uncertainty smaller than statistical uncertainty), till a conservative scenario (systematic uncertainty at the level of past analyses). Existing sterile neutrino constraints from single-β decay experiments [2,3,16,17] and solar neutrinos [39] are shown in the background. The right panel shows the median upper limit on the coupling constant between Z2-odd fermion and the neutrinos assuming the effective interaction in Eq.…”

Search for exotic physics in double-β decays with GERDA Phase II

“…For low masses, the distribution of the decay into sterile neutrinos becomes indistinguishable from the SM 2νββ decay distribution, where two anti-neutrino are emitted. Existing bounds on the sterile neutrino mixing from β decay experiments [75][76][77][78] and solar neutrinos [79] are also shown in figure 5. The limits obtained in this work are still not competitive, but they demonstrate the potential of double-β decay experiments to search for sterile neutrino, with larger exposure data sets and good control of the systematic uncertainties.…”

Ab initio calculation of the $β$ decay spectrum of $^6$He

“…Measurements of spectra of purely Gamow-Teller transitions, such as the decay of 6 He to 6 Li, aim to push the constraint on the Fierz interference term induced by tensor and pseudoscalar currents to the level b < 10 −3 [37,38], probing tensor currents at the 10 TeV mass scale. In addition, modifications to the shape of the β spectrum can reveal the existence of sterile neutrinos, with minimal or non-minimal interactions [39][40][41][42][43][44].…”