Search for deexcitations of 178m2Hf isomer induced by some inelastic Dark Matter candidates at the Gran Sasso underground laboratory

AbstraktAbstract

The 2(nd) isomeric state of Hf-178 has high energy of 2.446 MeV, and big half-life of 31 yr related to its high spin 16(+). Normally it decays spontaneously to the ground state of Hf-178 by isomeric transition with emission of cascade of gamma quanta with energies up to similar to 600 keV. Possible interactions of Hf-178m2 with some given inelastic Dark Matter (iDM) candidates could lead to emission of gamma rays with higher energies (> 1 MeV) from the excited levels of Hf-178 which are not populated in its usual decay. The search for such gamma rays was performed deep underground at the Gran Sasso National Laboratory of the INFN in measurements of Hf-178m2 source with an activity of similar or equal to 63 Bq with two ultra-low-background HPGe gamma spectrometers over cumulative 1170 h. This is the first Hf-178m2 measurements in the low-background conditions which allowed the enhancement of the sensitivity - in the framework of the models considered here - to hypothesized iDM induced decay at energies > 600 keV thanks to reduced natural radioactive background. Improved Tau(1/2) limits for several hypothesized iDM induced transitions were set, up to the level of lim Tau(1/2) similar to 10(7) yr, higher (or competitive) than those known previously.

The 2(nd) isomeric state of Hf-178 has high energy of 2.446 MeV, and big half-life of 31 yr related to its high spin 16(+). Normally it decays spontaneously to the ground state of Hf-178 by isomeric transition with emission of cascade of gamma quanta with energies up to similar to 600 keV. Possible interactions of Hf-178m2 with some given inelastic Dark Matter (iDM) candidates could lead to emission of gamma rays with higher energies (> 1 MeV) from the excited levels of Hf-178 which are not populated in its usual decay. The search for such gamma rays was performed deep underground at the Gran Sasso National Laboratory of the INFN in measurements of Hf-178m2 source with an activity of similar or equal to 63 Bq with two ultra-low-background HPGe gamma spectrometers over cumulative 1170 h. This is the first Hf-178m2 measurements in the low-background conditions which allowed the enhancement of the sensitivity - in the framework of the models considered here - to hypothesized iDM induced decay at energies > 600 keV thanks to reduced natural radioactive background. Improved Tau(1/2) limits for several hypothesized iDM induced transitions were set, up to the level of lim Tau(1/2) similar to 10(7) yr, higher (or competitive) than those known previously.