Direct neutrino mass measurement with HOLMES

by Sara Gamba

Thursday May 7, 2026, 2:00 PM → 3:00 PM Europe/Berlin

Seminarraum EG + zoom (IPE)

Sara Gamba is doctoral student at Dipartimento di Fisica, Università di Milano-Bicocca & Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Milano Bicocca, Milano, Italy. She works for the neutrino mass experiment HOLMES and is currently as visiting scientist at IPE.

The HOLMES experiment aims to measure the absolute mass of neutrinos with sub-eV sensitivity using low temperature microcalorimeters (TES) embedded with 163Ho, thus performing a calorimetric measurement. HOLMES will proceed in multiple phases. The first one marked a fundamental milestone for the overall project. Holmium was successfully implanted inside an array of 64 detectors, representing the first prototype of the final building block of the detector system. The embedded detectors, read out using the microwave multiplexing technique, performed remarkably well. The total activity was approximately 15 Bq, corresponding to about 0.5 ng of 163Ho. During the two physics runs, lasting two months, a high-statistics calorimetric spectrum of 163Ho was measured. Data-taking periods lasted between two and five consecutive days, with a duty cycle of 82% and a discarded event rate of less than 1%. In my presentation, I will report the results of the analysis of the data collected so far, which has led to the first neutrino mass limit of 27 eV at a 90% credible interval. 

The next stage of the project, called HOLMES+, aims to push the sensitivity frontier by scaling up detector arrays, optimizing readout techniques and implantation efficiency. The goal of HOLMES+ is to develop and test a new small prototype array of TESs with low Tc, implanted with high-activity 163Ho, reaching up to 30 Bq per detector. A novel readout system based on the new KICS chip will be fabricated and tested, alongside a state-of-the-art DAQ system based on RFSoC technology. Both of these upgrades will increase the bandwidth per channel and reduce readout costs by more than one order of magnitude. HOLMES+ will thus serve as a step toward the development of the final module for a final large scale Ho-based experiment with sensitivities of the order of O(50) meV.