Next-Generation Bolometers for 0νββ: Background Rejection Strategies from CUPID, CROSS, and BINGO.

by Hawraa Khalife (CEA Paris-Saclay)

Monday 16 Jun 2025, 16:00 → 17:00 Europe/Madrid

C7b-0-058 - Seminar (IFAE Main Building C7b)

The search for neutrinoless double-beta decay (0νββ) is a major experimental frontier in particle
physics, with the potential to unveil the Majorana nature of neutrinos and the violation of lepton
number conservation. Achieving sensitivity to half-lives beyond 1027 years, as required to probe
the Inverted Ordering of the neutrino mass hierarchy (and a significant part of the Normal one),

necessitates unprecedented background suppression and detector performance. Low-
temperature calorimetric techniques, particularly those based on bolometers, offer excellent

energy resolution and scalability, making them prime candidates for next-generation
experiments.
CUPID (CUORE Upgrade with Particle IDentification) represents the leading bolometric effort
aiming to search for the 0νββ decay of ^100Mo. It will deploy ~1600 scintillating Li2MoO4 crystals,
enriched in ^100Mo, each paired with a light detector for simultaneous heat and light readout.
This dual-channel detection enables powerful alpha background rejection through particle
identification. Building upon the CUORE infrastructure at LNGS, CUPID is currently in its design
finalization phase, supported by extensive R&D.
Complementary to CUPID, the CROSS project focuses on enhancing bolometer sensitivity to
surface background events. By applying thin metallic or superconducting films (e.g., Pd or Al-Pd)
onto the crystal surfaces, CROSS modifies the phonon propagation and enables pulse shape
discrimination between bulk and surface events. This innovation is critical for suppressing
surface-originating α and β backgrounds, a key limiting factor in existing bolometric detectors.
The BINGO project takes a holistic approach to background reduction, aiming to achieve a
background index as low as 10−5 counts/(keV·kg·yr) in the region of interest. In addition to dual
heat-light readout and surface coating strategies, BINGO introduces a new detector assembly
with minimized passive materials, improved light detector sensitivity via Neganov-Luke
amplification, and the integration of an active veto system using BGO scintillators with bolometric
readout.
Together, CUPID, CROSS, and BINGO represent a coherent research program addressing the
technological challenges that stand between current capabilities and the sensitivity required to
probe the Majorana nature of neutrinos. Their innovations in detector design, surface
background rejection, and cryogenic performance lay the groundwork for the future of 0νββ
searches.