The electron capture in 163Ho experiment – ECHo

Abstract

Abstract. Neutrinos, and in particular their tiny but non-vanishing masses, can be considered one of the doors towards physics beyond the Standard Model. Precision measurements of the kinematics of weak interactions, in particular of the 3 H β-decay and the 163 Ho electron capture (EC), represent the only model independent approach to determine the absolute scale of neutrino masses. The electron capture in 163 Ho experiment, ECHo, is designed to reach sub-eV sensitivity on the electron neutrino mass by means of the analysis of the calorimetrically measured electron capture spectrum of the nuclide 163 Ho. The maximum energy available for this decay, about 2.8 keV, constrains the type of detectors that can be used. Arrays of low temperature metallic magnetic calorimeters (MMCs) are being developed to measure the 163 Ho EC spectrum with energy resolution below 3 eV FWHM and with a time resolution below 1 μs. To achieve the sub-eV sensitivity on the electron neutrino mass, together with the detector optimization, the availability of large ultra-pure 163 Ho samples, the identification and suppression of background sources as well as the precise parametrization of the 163 Ho EC spectrum are of utmost importance. The high-energy resolution 163 Ho spectra measured with the first MMC prototypes with ion-implanted 163 Ho set the basis for the ECHo experiment. We describe the conceptual design of ECHo and motivate the strategies we have adopted to carry on the present medium scale experiment, ECHo-1K. In this experiment, the use of 1 kBq 163 Ho will allow to reach a neutrino mass sensitivity below 10 eV/c 2 . We then discuss how the results being achieved in ECHo-1k will guide the design of the next stage of the ECHo experiment, ECHo-1M, where a source of the order of 1 MBq 163 Ho embedded in large MMCs arrays will allow to reach sub-eV sensitivity on the electron neutrino mass.

Effective neutrino masses in KATRIN and future tritium beta-decay experiments

“…Since the description of the beta spectrum via the effective neutrino mass is still valid for KATRIN and Project 8, the posterior distributions of effective neutrino masses should be very suggestive for future experiments. Our results in this section can also be used for the electron-capture experiments ECHo [12], HOLMES [13] and NuMECS [14], if CPT is assumed to be conserved in the neutrino sector. For the similar analysis relevant for the effective neutrino masses in β and 0νββ decays, see Refs.…”

“…In this work, we focus only on tritium beta-decay experiments. Similar analyses of the effective neutrino mass can be performed for the electron-capture decays of holmium, namely, e − + 163 Ho → ν e + 163 Dy, which are and will be investigated in the ECHo[12] and HOLMES[13], NuMECS[14] experiments.…”

Highly efficient isotope separation and ion implantation of 163Ho for the ECHo project

“…The ECHo 10 mm × 5 mm detector chips is composed of an array of 64 metallic magnetic calorimeters (MMCs) with Au absorbers on top, 180 µm × 180 µm each [1]. Prior to 163 Ho ion implantation, the array must be prepared to protect the substrate and in particular the sensitive superconducting circuits from being destroyed by the impinging 163 Ho ions and possible electric charging up.…”

MetroMMC: Electron-Capture Spectrometry with Cryogenic Calorimeters for Science and Technology

“…Radionuclides that decay by electron capture (EC) play an important role in many fields such as nuclear medicine, nuclear waste disposal, geo-and cosmo-chronology (see, e.g., [1,2] and references therein) and even for testing the standard model of particle physics in various ways, e.g., in neutrino physics [3][4][5][6]. Activity standards of EC nuclides are being used to calibrate γ -ray or X-ray detectors which requires accurate knowledge of the photon emission intensities of the respective radionuclides.…”