arXiv subjects

M. Giammei

Publications and source records attributed to M. Giammei.

11 recordsLinked to original sources

arXiv2026

Characterization of the Low Energy Excess using a NUCLEUS Al$_{2}$O$_{3}$ detector

The NUCLEUS experiment aims to detect coherent elastic neutrino-nucleus scattering of reactor antineutrinos using low-threshold, gram-scale cryogenic calorimeters. Similar to other low-threshold experiments, NUCLEUS observes a sharp rise in the event rate below a few hundred eV, referred to as the low energy excess (LEE), whose origin remains yet unidentified. Building on results from the NUCLEUS testing and commissioning at the Technical University of Munich and from previous characterization campaigns, we present a comprehensive study of the background rate measured with a sapphire detector equipped with two transition-edge sensors under various experimental conditions. We find no evidence for a dependence of the LEE rate on the particle background level, whereas the results indicate that slower cooling-down procedures lead to lower initial LEE rates. The behavior of the LEE rate during the same cooldown is comparable across the measurements and is best described by a power law with a common exponent across datasets of $(-0.59 \pm 0.06)$, when time is expressed from the moment the detector reaches the 4 K temperature. These findings provide valuable guidance for future LEE mitigation strategies in the NUCLEUS experiment.

physics.ins-det↗

arXiv2026

Development and Commissioning of the Cryogenic Target Detectors for the Technical Run of the NUCLEUS Experiment

The NUCLEUS experiment aims to study coherent elastic neutrino-nucleus scattering (CE$ν$NS) of reactor electron antineutrinos at the Chooz nuclear power plant in France. In this work, the cryogenic target-detector module for the NUCLEUS Technical Run was developed and commissioned at the Technical University of Munich. The module comprises four gram-scale CaWO$_4$ detectors, each equipped with two Transition Edge Sensors (TES), providing a total target mass of 6.96 g. We present the design, integration, detector characterization, and X-ray-based energy calibration of these detectors. Across six characterized detectors, a mean baseline resolution of $\overlineσ_{\mathrm{BL}} = (2.79 \pm 0.60)\,\mathrm{eV}$ was achieved. The best-performing detector reached $σ_{\mathrm{BL}} = (2.16 \pm 0.02_{\mathrm{stat}})\,\mathrm{eV}$, surpassing the design goal by a factor of two and representing a state-of-the-art result for a cryogenic CaWO$_4$ detector. The target detector module was successfully operated simultaneously with the surrounding Cryogenic Outer Veto, which consists of six kg-scale Ge detectors for background discrimination, showing no measurable cross-talk. These results demonstrate the readiness of the target-detector system for the NUCLEUS Technical Run at Chooz and mark a key milestone in the development of cryogenic detectors for reactor-CE$ν$NS measurements.

physics.ins-det↗

arXiv2026

Prospect of the NUCLEUS Experiment at Chooz for Coherent Elastic Neutrino-Nucleus Scattering and New Physics Searches

The NUCLEUS experiment aims to measure coherent elastic neutrino-nucleus scattering (CE$ν$NS) at unprecedentedly low nuclear recoil energies using gram-scale cryogenic calorimeters operated at the Chooz nuclear power plant in France. Access to recoil energies at the $\mathcal{O}(10~\mathrm{eV})$ scale enables CE$ν$NS studies at extremely low momentum transfer and provides enhanced sensitivity to new physics. In this work, we present sensitivity projections for the upcoming NUCLEUS technical and physics runs, incorporating a data-driven treatment of the low-energy excess (LEE) observed during commissioning. We develop a likelihood framework that exploits reactor-power variation to disentangle signal and background in a low signal-to-background regime and to assess the impact of the dominant systematic uncertainties. For the Technical Run with a 7 g CaWO$_4$ target, we find competitive sensitivity to several scenarios beyond the Standard Model, which do not require a CE$ν$NS observation. For the Physics Run, assuming complete suppression of the LEE, we project a 4.7 $σ$ observation of CE$ν$NS with a statistical precision of about 20 % in 1 year, enabling a determination of the weak mixing angle at the lowest momentum transfer probed to date with CE$ν$NS and leading CE$ν$NS-based constraints on the neutrino charge radius and new mediator models.

hep-ex↗

arXiv2026

Background of the BULLKID detector array operated with moderate shield on surface

We present the operation with moderate radiation shield in a surface laboratory of BULLKID (BULky and Low-threshold Kinetic Inductance Detector), a cryogenic detector for searches of light Dark Matter or Coherent Elastic Neutrino-Nucleus Scattering. The detector consists of an array of 60 cubic silicon particle absorbers of 0.34 g each, sensed by cryogenic kinetic inductance detectors. The analysis presented focuses on data from 15 elements of the array, with two central units used to evaluate the background and with their surrounding elements used as veto. The low energy spectrum resulting from an exposure of 290 hours to ambient backgrounds, acquired with the use of external and internal radiation shields, is compatible with the simulations at the level of $(6.8\pm0.4\,{\rm stat.}\pm0.1\,{\rm syst.})\times10^4$ counts / keV kg days from 2 keV down to an energy of 600 eV. The region between 225 eV and 600 eV shows a rise in background in disagreement with the simulations, while not sharing some of the key traits of the low energy excess observed in other cryogenic experiments. The high energy spectrum shape is in overall agreement with the simulations and displays the typical particle-induced X-ray emission of the surrounding lead.

hep-ex↗

arXiv2026

Sensitivity enhancement techniques for cryogenic calorimeters in the NUCLEUS experiment

Phonon-mediated cryogenic calorimeters find application in rare event searches due to their intrinsically low energy threshold. Achieving the best sensitivity for this kind of detectors is crucial for signal identification, leading to various optimization techniques. In this work, we present two complementary methods to increase the sensitivity of cryogenic detectors read out by transition-edge sensors, developed and tested in the context of the NUCLEUS experiment. The first procedure maps the signal-to-noise ratio of the device across a wide range of operating points, to identify the configuration with maximal sensitivity to be used during data taking. The second method exploits the double readout of the detector, combining the information on different channels with a two-dimensional optimum filter analysis that effectively lowers the energy threshold. With both techniques at the same time, we obtained a baseline resolution of 2.94 $\pm$ 0.05 (stat) eV using a CaWO4 based detector, achieving a promising result in view of the first run of NUCLEUS at the experimental site.

physics.ins-det↗

arXiv2025

Particle background characterization and prediction for the NUCLEUS reactor CE$ν$NS experiment

NUCLEUS is a cryogenic detection experiment which aims to measure Coherent Elastic Neutrino-Nucleus Scattering (CE$ν$NS) and to search for new physics at the Chooz nuclear power plant in France. This article reports on the prediction of particle-induced backgrounds, especially focusing on the sub-keV energy range, which is a poorly known region where most of the CE$ν$NS signal from reactor antineutrinos is expected. Together with measurements of the environmental background radiations at the experimental site, extensive Monte Carlo simulations based on the Geant4 package were run both to optimize the experimental setup for background reduction and to estimate the residual rates arising from different contributions such as cosmic ray-induced radiations, environmental gammas and material radioactivity. The NUCLEUS experimental setup is predicted to achieve a total rejection power of more than two orders of magnitude, leaving a residual background component which is strongly dominated by cosmic ray-induced neutrons. In the CE$ν$NS signal region of interest between 10 and 100 eV, a total particle background rate of $\sim$ 250 d$^{-1}$kg$^{-1}$keV$^{-1}$ is expected in the CaWO$_4$ target detectors. This corresponds to a signal-to-background ratio $\gtrsim$ 1, and therefore meets the required specifications in terms of particle background rejection for the detection of reactor antineutrinos through CE$ν$NS.

physics.ins-det↗

arXiv2025

Commissioning of the NUCLEUS Experiment at the Technical University of Munich

The NUCLEUS experiment aims to detect coherent elastic neutrino-nucleus scattering of reactor antineutrinos on CaWO$_4$ targets in the fully coherent regime, using gram-scale cryogenic calorimeters. The experimental apparatus will be installed at the Chooz nuclear power plant in France, in the vicinity of two 4.25 GW$_{\text{th}}$ reactor cores. This work presents results from the commissioning of an essential version of the experiment at the shallow Underground Laboratory of the Technical University of Munich. For the first time, two cryogenic target detectors were tested alongside active and passive shielding systems. Over a period of two months all detector subsystems were operated with stable performance. Background measurements were conducted, providing important benchmarks for the modeling of background sources at the reactor site. Finally, we present ongoing efforts to upgrade the detector systems in preparation for a technical run at Chooz in 2026, and highlight the remaining challenges to achieving neutrino detection.

hep-ex↗

arXiv2025

Sub-keV Electron Recoil Calibration for Macroscopic Cryogenic Calorimeters using a Novel X-ray Fluorescence Source

Percent-level calibration of cryogenic macro-calorimeters with energy thresholds below 100~eV are crucial for light Dark Matter (DM) searches and reactor neutrino studies based on coherent elastic neutrino-nucleus scattering (CEvNS). This paper presents a novel calibration source based on X-ray fluorescence (XRF) of light elements. It uses a $^{55}$Fe source to irradiate a two-staged target arrangement, emitting characteristic emission lines from 677\,eV to 6.5\,keV. We demonstrate the potential of this new XRF source to calibrate a 0.75 gram CaWO$_4$ crystal of the NUCLEUS and CRAB experiments. Additionally, we introduce CryoLab, an advanced analysis tool for cryogenic detector data, featuring robust methods for data processing, calibration, and high-level analysis, implemented in MATLAB and HDF5. We also present a phenomenological model for energy resolution, which incorporates statistical contributions, systematic effects, and baseline noise, enabling a novel approach to evaluating athermal phonon collection efficiency in macro-calorimeters based on transition edge sensors (TES).

physics.ins-det↗

arXiv2025

Decoupling Pulse Tube Vibrations from a Dry Dilution Refrigerator at milli-Kelvin Temperatures

With the rising adoption of dry dilution refrigerators across scientific and industrial domains, there has been a pressing demand for highly efficient vibration decoupling systems capable of operation at cryogenic temperatures in order to achieve the low vibration levels required for operation of sensitive equipment like cryogenic detectors or quantum devices. As part of the NUCLEUS experiment, a cryogenic spring pendulum has been engineered to effectively isolate pulse tube vibrations by establishing an autonomous frame of reference for the experimental volume, while sustaining temperatures below 10 mK. Attaining attenuation of up to two orders of magnitude within the region of interest of the NUCLEUS cryogenic detectors, we achieved displacement RMS values in the order of 1 nm in the axial direction and 100 pm radially, thereby reducing vibrations below typical environmental levels. Our successful detector operation across multiple cooldown cycles demonstrated negligible sensitivity to pulse tube induced vibrations, culminating in the achievement of an ultra-low $(6.22 \pm 0.07)$ eV baseline resolution on a gram-scale CaWO$_4$ cryogenic calorimeter during continuous pulse tube operation over the course of several weeks.

physics.ins-det↗

arXiv2024

Low-energy spectrum of the BULLKID detector array operated on surface

We present the first continuous operation in a surface lab of BULLKID, a detector for searches of light Dark Matter and precision measurements of the coherent and elastic neutrino-nucleus scattering. The detector consists of an array of 60 cubic silicon particle absorbers of 0.34 g each, sensed by cryogenic kinetic inductance detectors. The data presented focusses on one of the central elements of the array and on its surrounding elements used as veto. The energy spectrum resulting from an exposure of 39 hours to ambient backgrounds, obtained without radiation shields, is flat at the level of $(2.0\pm0.1\,{\rm stat.}\pm0.2\,{\rm syst.})\times10^6$ counts / keV kg days down to the energy threshold of $160\pm13$ eV. The data analysis demonstrates the unique capability of rejecting backgrounds generated from interactions in other sites of the array, stemming from the segmented and monolithic structure of the detector.

hep-ex↗

arXiv2022

BULLKID: Monolithic array of particle absorbers sensed by Kinetic Inductance Detectors

We introduce BULLKID, an innovative phonon detector consisting of an array of dices acting as particle absorbers sensed by multiplexed Kinetic Inductance Detectors (KIDs). The dices are carved in a thick crystalline wafer and form a monolithic structure. The carvings leave a thin common disk intact in the wafer, acting both as holder for the dices and as substrate for the KID lithography. The prototype presented consists of an array of 64 dices of 5.4x5.4x5 mm$^3$ carved in a 3" diameter, 5 mm thick silicon wafer, with a common disk 0.5 mm thick hosting a 60 nm patterned aluminum layer. The resulting array is highly segmented but avoids the use of dedicated holding structures for each unit. Despite the fact that the uniformity of the KID electrical response across the array needs optimization, the operation of 8 units with similar features shows, on average, a baseline energy resolution of $26\pm7$ eV. This makes it a suitable detector for low-energy processes such as direct interactions of dark matter and coherent elastic neutrino-nucleus scattering.

physics.ins-det↗