Ponente
Descripción
Over the past few decades, modern physics has resolved many fundamental
questions about the nature and structure of the universe. Yet, the origin of dark
matter remains one of its most compelling open problems. Among the
proposed candidates, Weakly Interacting Massive Particles (WIMPs) stand out
as particularly promising, and a significant research effort has been devoted to
their direct detection. WIMPs are expected to produce nuclear recoil events at
energies of only a few keV, with extremely rare interaction rates.
To date, the only positive claim of a dark matter signal comes from the DAMA
experiment at LNGS, which has reported an annual modulation in its detection
rate for more than 20 years. Despite its potential impact, this result is difficult
to reconcile with the null findings of other, more sensitive direct detection
experiments within the standard WIMP interaction framework. This tension
suggests the possibility of target-dependent interactions and underscores the
need for independent verification using the same material as DAMA.
Because the DAMA signal is based on NaI(Tl) scintillating crystals, several
NaI(Tl)-based experiments—such as ANAIS and COSINE—have been conducted
in recent years, while others, including SABRE and PICOLON, are currently
under development. These experiments generally rely on conventional
photomultiplier tubes (PMTs), which present significant drawbacks: high dark
noise, modest photon detection efficiency (PDE), and intrinsic radioactivity.
In this context, we introduce ASTAROTH, a new NaI(Tl)-based detector that, to
our knowledge, demonstrates for the first time the replacement of PMTs with
large-area Silicon Photomultiplier (SiPM) matrices. SiPMs provide several
advantages over PMTs: higher PDE, negligible intrinsic radioactivity, and—when
cooled to cryogenic temperatures—dark noise suppression by nearly two orders
of magnitude.
The ASTAROTH project has developed a dedicated cryogenic system designed
to operate the detector stably at ~80 K. This setup features a custom cryostat
using a cryogenic fluid as coolant, along with front-end electronics specifically
engineered for cryogenic operation. Calibration with a pulsed laser was used to
measure the charge from single-photon events. Coupling the SiPM array to a
NaI(Tl) crystal, and using a 241Am source (59.5 keV gamma), we estimated a
light yield of 7.22 photoelectrons/keV. By applying a four-photon coincidence
requirement to reduce noise and isolate genuine scintillation events, we
achieved a detection threshold of ~0.5 keV.
Since NaI(Tl) crystals typically yield about 43 photoelectrons/keV, there
remains room for improvement. Work is ongoing in the next phase of theproject, ASTAROTH-Beyond, which aims to further enhance performance and
reduce the threshold toward the 100 eV level.
These results represent a significant milestone toward the realization of next-
generation dark matter experiments. With continued technological
advancements, SiPM-based detectors could surpass the sensitivity of
conventional PMT systems, opening the way for both an independent test of
the DAMA result and broader searches for dark matter.
