Measurement of the 45Ca β spectrum in search of deviations from the theoretical shape

New limits on heavy sterile neutrino mixing inB8decay obtained with the Borexino detector

“…For masses m H < 1 MeV the most sensitive searches have looked for kinks in the electron spectra of decays and have constrained the sterile-electron mixing to jU eH j 2 < 10 À2 -10 À3 [14][15][16][17][18]. The agreement with expectations of ft values for superallowed pure Fermi beta transitions also limits the mixing of massive neutrino and electron flavor [19][20][21].…”

“…For masses up to m H % 6 MeV, an important bound is provided by ft values for superallowed Fermi decays (line 4 [21]) and by searches of kinks in the electron spectrum of decays of 20 F (line 5 [21]), 64 Cu (line 6 [14]), 45 Ca (line 7 [16]), 63 Ni (line 8 [18]) and 35 S (line 9 [18]). …”

Sterile Neutrinos

“…[206]. Exclusion regions from beta decay kinematics, shown as colored regions in the top part of the plot and labeled with the respective isotopes, dominate at masses between m 4 ∼ 10 eV and m 4 ∼ 1 MeV [211][212][213][214][215][216][217][218][219][220][221]. In this mass range, the mixing matrix element |U e4 | 2 is constrained to be below well below 10 −2 , with constraints reaching well below 10 −3 at keV-scale masses.…”

Measurement of $^{144}\rm{Pr}$ beta-spectrum with Si(Li) detectors for the purpose of determining the spectrum of electron antineutrinos

“…In case of semiconductor detectors there is a significant probability of back-scattering from the detector surface that depends on the detector material. The most widespread siliconbased semiconductors have the backscattering probability of the order of 10% for 100 keV electrons at normal incidence [4]. In case of electron energies above 1 MeV and high Z detector materials, it also becomes important to take the bremsstrahlung into account.…”