Speaker
Description
The absolute value of the neutrino mass 𝑚𝜈remains one of the key missing pieces in the Standard Model. Its value plays a fundamental role in shaping the formation of large-scale structures in the Universe. The only model-independent method to determine 𝑚𝜈relies on direct kinematic measurements of the electrons emitted in beta decay processes. Current experimental approaches fall into two categories: spectrometers and calorimeters. Spectrometer-based experiments have set the most stringent limits so far - most notably KATRIN, which has reached a sensitivity of 0.45 eV and is progressing toward its design goal of 0.2 eV. However, spectrometers have reached practical limits in size and complexity, and the external-source configuration inherently introduces systematic effects
such as energy-loss corrections.
Calorimetric experiments avoid these issues by embedding the source within the active volume of low-temperature detectors, thereby measuring the full energy released in the decay except the neutrino’s share. Their main challenge is balancing the large statistics required for competitive sensitivity with the need to suppress pile-up, which can otherwise dominate the background in the region of interest. Achieving this balance demands distributing the total activity among a large array of detectors and equipping them with a highly efficient multiplexed readout system.
HOLMES is a calorimetric experiment designed to measure the electron capture decay of 163Ho for neutrino mass determination. After successfully demonstrating the readout of transition-edge sensors (TESs) using SQUID-based microwave multiplexing (μmux), HOLMES is now targeting a more scalable and bandwidth-efficient solution for future large-scale deployments. This new approach is based on kinetic inductance current sensors (KICS), a novel technique exploiting nonlinear superconducting microresonators to achieve high multiplexing factors.
In parallel with the development of KICS, HOLMES is transitioning from 100 mK TESs to new 40 mK TESs designed to mitigate the additional heat capacity introduced by the implanted 163Ho atoms.
In this contribution, after outlining the HOLMES experiment along with its current status and challenges, I will present recent progress on the development of the KICS-based readout scheme and the new low-𝑇𝑐 TES detectors.