Optimized Designs for Very Low Temperature Massive Calorimeters

TL;DR

This paper introduces a novel low-temperature calorimeter design with improved energy resolution and bandwidth matching, enabling better performance for dark matter and double beta decay experiments.

Contribution

The paper proposes a new detector design that enhances signal bandwidth and sensitivity, compatible with hygroscopic crystals, and demonstrates significant improvements in energy resolution.

Findings

Achieves 0.35 eV baseline resolution in an 80-mm Si detector

Enhances large-mass calorimeter resolution by up to 1000×

Provides intrinsic event timing resolution suitable for next-generation experiments

Abstract

The baseline energy-resolution performance for the current generation of large-mass, low-temperature calorimeters (utilizing TES and NTD sensor technologies) is $>2$ orders of magnitude worse than theoretical predictions. A detailed study of several calorimetric detectors suggests that a mismatch between the sensor and signal bandwidths is the primary reason for suppressed sensitivity. With this understanding, we propose a detector design in which a thin-film Au pad is directly deposited onto a massive absorber that is then thermally linked to a separately fabricated TES chip via an Au wirebond, providing large electron-phonon coupling (i.e. high signal bandwidth), ease of fabrication, and cosmogenic background suppression. Interestingly, this design strategy is fully compatible with the use of hygroscopic crystals (NaI) as absorbers. An 80-mm diameter Si light detector based upon these design principles, with potential use in both dark matter and neutrinoless double beta decay, has an estimated baseline energy resolution of 0.35 eV, 20$\times$ better than currently achievable. A 1.75 kg ZnMoO$_{4}$ large-mass calorimeter would have a 3.5 eV baseline resolution, 1000$\times$ better than currently achieved with NTDs with an estimated position dependence $\frac{\Delta E}{E}$ of 6$\times$10$^{-4}$. Such minimal position dependence is made possible by forcing the sensor bandwidth to be much smaller than the signal bandwidth. Further, intrinsic event timing resolution is estimated to be $\sim$170 $\mu$s for 3 MeV recoils in the phonon detector, satisfying the event-rate requirements of large $Q_{\beta \beta}$ next-generation neutrinoless double beta decay experiments. Quiescent bias power for both of these designs is found to be significantly larger than parasitic power loads achieved in the SPICA/SAFARI infrared bolometers.