A search for rare and induced nuclear decays in hafnium

Abstract

A measurement of hafnium foil using a modified ultra-low-background high purity detector with optimized sample-to-detector geometry was performed at Laboratori Nazionale del Gran Sasso. Radiopurity of the stock Hf foil was studied in detail, in addition to an analysis of data collected over 310 days to search for rare processes that can occur in natural Hf isotopes. Firstly, limits on alpha decays of all natural Hf isotopes to the first excited state of the daughter nuclides were established in the range of 10 16 -10 18 a (90% C.L.). Secondly, a search for modes of double electron capture and electron capture with positron emission in 174 Hf was performed, yielding half-life limits 10 16 -10 18 a (90% C.L.). Lastly, novel dark matter-induced nuclear excitations in hafnium isotopes were investigated. For dark matter with 1 TeV/c 2 mass, leading limits on the inelastic dark matter-nucleon cross section are set for mass splittings in the range 428 keV < δ < 473 keV.

Pushing the frontier of WIMPy inelastic dark matter: journey to the end of the periodic table

“…Slightly higher splittings can be reached by considering the 36.20 keV transition. We also set limits on inelastic dark matter by employing Hf rare decay measurements in a similar approach [63], which yields less stringent bounds compared with osmium owing to relatively higher transition energies and less massive nuclei. We also propose to detect inelastic dark matter by investigating the deexcitation gamma yield of a mercurycontaining compound.…”

“…Hf. Rare decay of hafnium isotopes were also investigated at the LNGS by measuring the internal background of 55.38 grams of Hf foil using modified HPGe detector [63]. Low-background data was been collected over 310.6 days.…”

“…This means that, for a given transition, there is no danger of the signal being lost outside of the analysis region of interest. Previously, we have performed such an analysis in the context of a search for rare decays of Hf [63] and set stronger bounds on IDM mass splittings than previously-reported results from direct detection experiments. In this paper, we extend our approach, using previously-published data collected within low-background measurements with Hf and Os metal samples, along with the limits derived from bolometeric measurements using CaWO 4 and PbWO 4 scintillating crystals.…”

“…Bounds on IDM derived accordingly are shown in Figure 5. For constraints from individual Hf isotope, see [63]. We do not include 187 Os 74.4 keV excitation in the analysis since the measured B(E2) is subject to large uncertainty.…”

Earth-catalyzed detection of magnetic inelastic dark matter with photons in large underground detectors

“…Dark matter that scatters inelastically off nuclei is one of the most promising weakly interacting massive particle (WIMP) candidates [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] that can substantially evade experimental constraints from direct detection [15][16][17]. Over the past several years, research has continued along several lines, including: astrophysical implications such as heating up neutron stars [18]; detection prospects at IceCube [19]; detection of large inelastic splittings from collisional de-excitation [20][21][22]; a local enhancement of dark matter flux due to stronglyinteracting dark matter slowing down through multiple-scattering off the atmosphere and/or Earth [20]; detection of light dark matter that scatters inelastically [23] and through the Migdal effect [24]; new bounds from heavy element nuclear recoil or nuclear excitation with very low background runs of detectors [17]; cosmic-ray upscattered inelastic dark matter in the presence of a light mediator [25] as well as pseudo-Dirac dark matter through a light mediator [26]; inelastic Dirac dark matter [27]; the detection of luminous dark matter when the dark matter is itself light enough to be amenable to detection by sub-eV resolution solid-state detectors [28]; production of gamma-rays for indirect detection [29]; formation of compact objects from inelastic dark matter cooling [30]; direct searches at the LHC or beam-dump experiments [31][32]...…”