Lepton Physics Department

https://lpd.kinr.kyiv.ua/

The Department was established in 1986 on the base of Low-background Systems Department of the Special Design Technological Bureau, Institute for Nuclear Research and was headed by late Yu. G. Zdesenko, Prof., Corresponding Member of the National Academy of Sciences of Ukraine.

(Acting Head — F. A. Danevich, Ph.D., Dr.Sc.)

• Investigation of rare or forbidden processes in nuclear and particle physics.
• Search for neutrinoless double beta decay (investigations are carried out in Solotvina Underground Laboratory as well as in the underground laboratories abroad: Gran Sasso (Italy), Frejus (France), Kamioka (Japan)).
• Study of rare (T_1/2 > 10¹⁵ yr.) alpha and beta decays of atomic nuclei.
• Search for exotic phenomena beyond the Standard Model (electron stability and electric charge non-conservation, nucleon and di-nucleon decay, charge non-conserving beta decay, violation of the Pauli principle, transition of nuclei to super-dense state, nuclear decays with cluster emission, and others).

• Construction of Solotvina Underground Laboratory in 1984. The Laboratory is situated in Transcarpathian region of Ukraine (salt mine 430 m underground with total area near 1000 m²). Due to low radioactive contamination of salt, the γ background in the Laboratory is 10-100 times lower than in other underground laboratories; cosmic ray flux is reduced by a factor of 10⁴.
• First observation of the two-neutrino 2β decay of ¹¹⁶Cd (T_1/2 = 2.9 ± 0.4 ×10¹⁹ yr) in Solotvina Underground Laboratory with help of isotopically enriched ¹¹⁶CdWO₄ scintillators.
• The most stringent half-life limits on the neutrinoless modes of ¹¹⁶Cd 2β decay. The value of the lim T_1/2 = 1.7×10²³ yr is fifth world result (after ⁷⁶Ge, ¹³⁶Xe, ¹³⁰Te, ¹⁰⁰Mo) for T_1/2 limits, determined for all known 2β candidates, and corresponds to the upper limit on the Majorana neutrino mass <m_ν> ≤ 1.7 eV.
• The best half-life limit for neutrinoless mode of ⁷⁶Ge 2β decay (T_1/2 ≥ 2.5 × 10²⁵ yr) was obtained by analysis of the Heidelberg-Moscow and IGEX experiments, which lead to the most stringent limit on the Majorana neutrino mass: <m_ν> ≤ 0.3 eV.
• Priority results were obtained in 2β decay investigations of other nuclei: ⁴⁰Ca, ⁴⁶Ca, ⁷⁶Ge, ⁸²Se, ⁹⁴Zr, ⁹⁶Zr, ¹⁰⁰Mo, ¹⁰⁶Cd, ¹⁰⁸Cd, ¹¹⁴Cd, ¹³⁰Te, ¹³⁶Ce, ¹³⁸Ce, ¹⁴²Ce, ¹⁶⁰Gd, ¹⁸⁰W, ¹⁸⁶W, ¹⁹⁶Hg.
• First observation of natural radioactivity of tungsten (¹⁸⁰W alpha decay with T_1/2 = 1.1^+0.9_–0.5 × 10¹⁸ yr). Due to this process, tungsten has the lowest specific activity (~2 decays per year per 1 g of element) among all known natural alpha active elements.
• First observation of natural radioactivity of europium (¹⁵¹Eu alpha decay with T_1/2 = 5⁺¹¹_–3 × 10¹⁸ yr).
• The spectrum shape of 4^th forbidden non-unique β decay of ¹¹³Cd was measured for the first time, and more precise value of T_1/2 was determined (T_1/2 = 7.7 ± 0.3 × 10¹⁵ yr).
• The most stringent to-date limits on the electron stability with respect to its disappearance or decay into weak interacting particles (neutrino, Majoron, and others): τ_e ≥ 2.4 × 10²⁴ yr.
• The best limits on the proton (τ_p > 3.5 × 10²⁸ yr) and di-nucleon (τ_nn > 4.9 × 10²⁵ yr, τ_np > 2.1 × 10²⁵ yr, τ_pp > 5.0 × 10²⁵ yr) decays into invisible channels were set, and the best bound on the proton decay independent on channel was established: τ_p ≥ 4.0×10²³ yr.

See more details on the web site of the Department: https://lpd.kinr.kyiv.ua/