arXiv subjects

V. V. Kobychev

Publications and source records attributed to V. V. Kobychev.

At least 19 recordsLinked to original sources

arXiv2026

The CROSS experiment: detector construction, background projection, and sensitivity to $^{100}$Mo $0\nu2\beta$ decay

The CROSS experiment to search for neutrinoless double-beta ($0\nu2\beta$) decay in $^{100}$Mo with the help of an array of scintillating cryogenic calorimeters, containing 4.9 kg of $^{100}$Mo, has been ongoing in a low-background setup at the Canfranc underground laboratory (Spain) since mid-November 2025. In this paper, we present the construction of the CROSS detector and the description of Geant4-based Monte Carlo simulations of expected background in the region of interest. The simulations predict the background index in a 100-keV-wide interval centered at the $Q$-value of $^{100}$Mo (3034 keV) on the level of 3.2(5) $\times$ 10$^{-3}$ cnts/keV/kg/yr. Taking into account an 18% deadtime induced by the muon veto cut and a typical 90% duty cycle of the facility, such background level would allow to reach the world-leading sensitivity to $^{100}$Mo $0\nu2\beta$ decay (lim $T_{1/2} \sim 4 \times 10^{24}$ yr) in 1 year of data taking. Considering conservatively a factor 3 (10) worse background index due to unpredictable radioactive contamination of construction materials and/or detector performance, a 2-yr-long operation of the CROSS array would be still compatible with the best (competitive) sensitivity to $0\nu2\beta$ decay in $^{100}$Mo.

physics.ins-det↗

arXiv2026

Gamma spectrometry with CsI(Tl), NaI(Tl) and CdWO4 scintillation crystals using a silicon photomultiplier

This study investigated using of silicon photomultiplier (SiPM) for scintillation {\gamma}-spectrometry with CdWO4, CsI(Tl), and NaI(Tl) crystal scintillators. At room temperature, CsI(Tl) crystal scintillator provides the best performance, while the achievable energy resolution is lower compared to that obtained with conventional photomultiplier tube (PMT) with green-enhanced photocathode. These findings highlight the potential of SiPMs as a compact and cost-effective alternative to PMTs in nuclear physics applications, particularly for light portable spectrometers, such as radiation monitoring systems based on small unmanned aerial vehicles.

physics.ins-det↗

arXiv2026

Solar axion searches with RES-NOVA: projected sensitivity and first prototype limit

RES-NOVA is a cryogenic experiment based on PbWO4 scintillating bolometers produced from archaeological lead, originally designed to detect coherent elastic neutrino-nucleus scattering (CEvNS) from galactic core-collapse supernovae. We show that the same high-density, high-Z absorbers and sub-keV energy resolution make RES-NOVA an appealing probe of solar axions. We compute the expected signal from the Primakoff, ABC (atomic recombination and de-excitation, Bremsstrahlung, Compton), longitudinal-plasmon (LP), and 57Fe nuclear-line components of the solar axion flux, folded through the inverse-Primakoff and axioelectric detection channels in PbWO4, which probe the axion couplings to photons (g_a-gamma), electrons (g_ae), and nucleons (g_aN), respectively. We derive projected sensitivities for a 1 ton*y exposure of the RES-NOVA demonstrator in the (g_ae,g_a-gamma), (g_ae,g_aN), and (g_a-gamma,g_aN) planes. The projected reach in g_ae approaches that of XENONnT to within a factor of ~2, despite a background roughly four orders of magnitude higher, thanks to the large target mass, the high-Z enhancement of the axioelectric and inverse-Primakoff cross sections, and the sub-keV energy resolution. Because the inverse-Primakoff constraint on g_a-gamma relies on absorption rather than coherent conversion, it is independent of the axion mass, unlike bounds from magnetic helioscopes. We complement these projections with the first solar-axion exclusion limit obtained on real data with a 13 g PbWO4 prototype grown from archaeological lead, using a background-model-independent optimum-interval analysis. These results establish RES-NOVA as a promising multi-coupling probe of solar axions, with simultaneous sensitivity to g_ae, g_a-gamma and g_aN that is complementary to existing helioscope and direct-detection searches.

hep-ex↗

arXiv2026

Probing large mass-splitting inelastic Dark Matter with RES-NOVA

Probing inelastic dark matter at large mass splittings requires heavy target nuclei, an extended recoil-energy range, and the high-velocity tail of the dark-matter distribution. We exploit these features with the RES-NOVA prototype detector, featuring a PbWO4 cryogenic calorimeter, produced from archaeological Pb and operated at the deep-underground laboratory of Gran Sasso of INFN (Italy), analyzing a 32.4 g day exposure over 2.5 keV - 1 MeV under both the Standard Halo Model (SHM) and a Large Magellanic Cloud (LMC)-motivated velocity distribution. We extend direct-detection constraints beyond the 330 keV reach of established technologies (e.g. Xe-based TPCs), probing splittings up to 510 (780) keV in the SHM (LMC) benchmark, while future exposures will probe new regions of the parameter space.

astro-ph.CO↗

arXiv2026

A study of neutrinoless double electron capture in $^{40}$Ca from the AMoRE experiment

The search for neutrinoless double electron capture ($0\nu\mathrm{2EC}$) provides a sensitive probe of lepton-number violation and the Majorana nature of neutrinos. We investigate the $0\nu\mathrm{2EC}$ decay of $^{40}$Ca using cryogenic detectors equipped with metallic magnetic calorimeters in the AMoRE-I experiment. The analysis is based on a physics dataset corresponding to a total exposure of 7.32 kg$\cdot$yr from thirteen $^{40}$Ca$^{100}$MoO$_4$ crystals. No significant excess is observed, and a lower limit on the half-life is obtained as $T^{0\nu}_{1/2} > 1.7 \times 10^{22}$ yr at 90$\%$ confidence level. An improved sensitivity is expected for the upcoming AMoRE-II experiment. These results demonstrate the potential of CaMoO$_4$ detectors to explore rare decay processes beyond the primary $^{100}$Mo $0\nu\beta\beta$ search program.

nucl-ex↗

arXiv2026

Neutrino NSI in archaeological Pb

Dark matter direct detection experiments can observe solar neutrinos via coherent elastic neutrino-nucleus scattering, making it possible to test new physics in the neutrino sector. In this article, we study the sensitivity of RES-NOVA, a novel cryogenic calorimetric experiment employing PbWO$_4$ crystals grown from archaeological lead, to neutrino non-standard interactions (NSI). We perform a sensitivity study for a benchmark setup with a nominal energy threshold of 1 keV and an exposure of 1 ton$\cdot$y, both for a conservative (only heat readout) and ideal (heat and scintillation) background rejection scenario. We find that, in its nominal configuration, while not being sensitive to Standard Model solar $\nu$ interactions, RES-NOVA can reach sensitivities to NSI at the level of current global fits. With moderate or significant improvements of the threshold down to $0.5$ keV and $0.2$ keV, RES-NOVA will be able to achieve sensitivities beyond NSI global fit results, testing new areas of the parameter space in the electron and tau sectors, $\varepsilon_{ee}$, $\varepsilon_{\tau\tau}$, and $\varepsilon_{e\tau}$. A similar improvement in sensitivities is expected when instead increasing the exposure to 10 ton$\cdot$y.

hep-ph↗

arXiv2026

Probing dark matter interactions with a RES-NOVA prototype cryogenic detector

We report on the operation of a 13 g PbWO$_4$ crystal, grown from archaeological Pb and operated as a cryogenic calorimeter in an underground environment. Read out with a Ge thermistor, the detector achieves a low energy threshold and, for the first time, enables the derivation of a dark matter exclusion limit using PbWO$_4$ as target material, for both spin-dependent interactions on neutrons and spin-independent interactions. Although limited in mass and not representative of the final RES-NOVA detector design, this prototype demonstrates effective control of mechanical vibrations and low-energy noise in a cryogenic system, which is a key requirement for rare-event searches. The experiment therefore provides a proof of principle for the RES-NOVA detection concept, validating the use of archaeological Pb-based PbWO$_4$ crystals, low-background operation, and robust data-analysis procedures. These results establish a solid technological and methodological foundation for future RES-NOVA detectors employing larger target masses and advanced thermal readout technologies.

physics.ins-det↗

arXiv2026

Simourg2.0 -- Geant4 application for simulation of nuclear detectors with simple geometries

Simourg is a software based on the Geant4 toolkit and provides the Monte Carlo simulation of nuclear spectrometric setups with simple geometries for such applications as nuclear decay research, radiation safety, and nuclear medicine. With just a few command lines, users can define simple geometries, materials, and radiation sources to obtain reliable approximations for typical experimental setups. Simourg version 2.0, currently in its prerelease stage, introduces extended functionality for data extraction, geometry configuration, debugging, and visualization.

physics.ins-det↗

arXiv2025

The program Simourg for simulating the response functions of gamma detectors with simple geometries

The program Simourg (Simulator of Usually Requested Geometries) is based on the Geant4 toolkit and created for Monte Carlo simulation of gamma-ray spectrometric nuclear detectors with a simple axial symmetric geometry, which is typical for many tasks of studying the decay of long-lived nuclei and measuring the radioactivity of natural objects. The program is designed for quick estimation of the effectiveness and the response function of the detector to monoenergetic gamma quanta in the energy range from keV to several MeV.

physics.ins-det↗

arXiv2025

Muon veto system for the CROSS double-beta decay search experiment

In preparation to the CROSS experiment at the Canfranc underground laboratory (Spain) $-$ aiming to search for neutrinoless double-beta ($0\nu\beta\beta$) decay of $^{100}$Mo using low-temperature detectors with heat-scintillation readout $-$ we report on development of a dedicated muon veto system. The need for the muon veto in CROSS is caused by a comparatively high residual cosmic muon flux at the experimental site ($\sim$20 $\mu$/m$^2$/h), being a dominant background in the region of interest (ROI) at $\sim$3 MeV. Thus, we installed the muon veto system around the CROSS low-background setup, forming four lateral, one top, and four bottom sectors. In this paper we describe the design, construction and operation of the CROSS muon veto system, as well as its optimization and validation by comparing dedicated Monte Carlo (MC) simulations of muons with low-temperature measurements in the setup. We demonstrate a stable operation of the veto system with the average trigger rates compatible with MC simulations. Also, we investigated two muon trigger logics based on coincidences with either 2 sectors or a single sector of the veto. The MC study shows that, in combination with the multiplicity cut of thermal detectors, these trigger logics allow to reject 99.2\% and 99.7\% of muon-induced events in the ROI, respectively. Despite a comparatively high dead time ($\sim$18\%) introduced by coincidences with any of nine sectors of the veto $-$ the adopted strategy $-$ the muon-induced background in the ROI of the CROSS experiment can be reduced down to $\sim$2 $\times 10^{-3}$ cnts/keV/kg/yr, i.e., an acceptable level compatible with a high-sensitivity $0\nu\beta\beta$ decay search foreseen in CROSS.

physics.ins-det↗

arXiv2025

Search for spontaneous fission of plutonium and americium nuclides using gamma spectrometry

Spontaneous fission in americium and plutonium isotopes was investigated using high-resolution gamma spectrometry. This process was investigated through analysis of a certified PuO2 sample spectrum obtained from the IAEA database of reference spectra. Measurements were carried out with a HPGe detector, and detection efficiency calibration was performed by Monte Carlo simulations using GEANT4. There are no peaks observed that can be ascribed to beta decay of expected spontaneous-fission daughters. Thus, lower experimental limits on the partial half-lives for some spontaneous fission channels in 238-242Pu and 241Am were established. In many cases these limits have exceeded current theoretical predictions for cold fission done by S.B. Duarte et al., indicating the need to refine current models for the description of this process.

nucl-ex↗

arXiv2025

Cryogenic light detectors with thermal signal amplification for $0\nu\beta\beta$ search experiments

As a step towards the realization of cryogenic-detector experiments to search for neutrinoless double-beta decay (such as CROSS, BINGO, and CUPID), we investigated a batch of 10 Ge light detectors (LDs) assisted by Neganov-Trofimov-Luke (NTL) signal amplification. Each LD was assembled with a large cubic light-emitting crystal (45 mm side) using the recently developed CROSS mechanical structure. The detector array was operated at milli-Kelvin temperatures in a pulse-tube cryostat at the Canfranc underground laboratory in Spain. We achieved good performance with scintillating bolometers from CROSS, made of Li$_{2}$$^{100}$MoO$_4$ crystals and used as reference detectors of the setup, and with all LDs tested (except for a single device that encountered an electronics issue). No leakage current was observed for 8 LDs with an electrode bias up to 100 V. Operating the LDs at an 80 V electrode bias applied in parallel, we obtained a gain of around 9 in the signal-to-noise ratio of these devices, allowing us to achieve a baseline noise RMS of $O$(10 eV). Thanks to the strong current polarization of the temperature sensors, the time response of the devices was reduced to around half a millisecond in rise time. The achieved performance of the LDs was extrapolated via simulations of pile-up rejection capability for several configurations of the CUPID detector structure. Despite the sub-optimal noise conditions of the LDs (particularly at high frequencies), we demonstrated that the NTL technology provides a viable solution for background reduction in CUPID.

physics.ins-det↗

arXiv2025

CUPID, the CUORE Upgrade with Particle IDentification

CUPID, the CUORE Upgrade with Particle IDentification, is a next-generation experiment to search for neutrinoless double beta decay ($0νββ$) and other rare events using enriched Li$_2$$^{100}$MoO$_4$ scintillating bolometers. It will be hosted by the CUORE cryostat located at the Laboratori Nazionali del Gran Sasso in Italy. The main physics goal of CUPID is to search for $0νββ$\ of $^{100}$Mo with a discovery sensitivity covering the full neutrino mass regime in the inverted ordering scenario, as well as the portion of the normal ordering regime with lightest neutrino mass larger than 10 meV. With a conservative background index of 10$^{-4}$ cnts/(keV$\cdot$kg$\cdot$yr), 240 kg isotope mass, 5 keV FWHM energy resolution at 3 MeV and 10 live-years of data taking, CUPID will have a 90\% C.L. half-life exclusion sensitivity of 1.8 $\cdot$ 10$^{27}$ yr, corresponding to an effective Majorana neutrino mass ($m_{ββ}$) sensitivity of 9--15 meV, and a $3σ$ discovery sensitivity of 1 $\cdot$ 10$^{27}$ yr, corresponding to an $m_{ββ}$ range of 12--21 meV.

physics.ins-det↗

arXiv2025

A new dark matter direct search based on archaeological Pb

The RES-NOVA project is an experimental initiative aimed at detecting neutrinos from the next galactic supernova using PbWO$_{4}$ cryogenic detectors, operated at low temperatures in a low-background environment. By utilizing archaeological lead (Pb) as the target material, RES-NOVA leverages its high radiopurity, large nuclear mass, and the natural abundance of $^{207}$Pb, making it well-suited for exploring both spin-independent and spin-dependent Dark Matter (DM) interactions via nuclear scattering. This work presents a background model developed for the RES-NOVA technology demonstrator and evaluates its implications for Dark Matter detection. Detailed calculations of nuclear matrix elements, combined with the unique properties of archaeological Pb, demonstrate RES-NOVA's potential as a complementary tool to existing direct detection experiments for studying Dark Matter interactions. The experiment will conduct DM searches over a broad mass range spanning 4 orders of magnitude, from sub-GeV/$c^2$ to TeV/$c^2$. In the most optimistic scenario, RES-NOVA is expected to probe DM-nucleon cross-sections down to 1$\times 10^{-43}$ cm$^2$ and 2$\times 10^{-46}$ cm$^2$ for candidates with masses of 2 GeV/$c^2$ and 20 GeV/$c^2$, respectively.

physics.ins-det↗

arXiv2025

Sensitivity of the CUPID experiment to $0\nu\beta\beta$ decay of $^{100}$Mo

CUPID is a next-generation bolometric experiment to search for neutrinoless double-beta decay ($0\nu\beta\beta$) of $^{100}$Mo using Li$_2$MoO$_4$ scintillating crystals. It will operate 1596 crystals at $\sim$10 mK in the CUORE cryostat at the Laboratori Nazionali del Gran Sasso in Italy. Each crystal will be facing two Ge-based bolometric light detectors for $\alpha$ rejection. We compute the discovery and the exclusion sensitivity of CUPID to $0\nu\beta\beta$ in a Frequentist and a Bayesian framework. This computation is done numerically based on pseudo-experiments. For the CUPID baseline scenario, with a background and an energy resolution of $1.0 \times 10^{-4}$ counts/keV/kg/yr and 5 keV FWHM at the Q-value, respectively, this results in a Bayesian exclusion sensitivity (90% c.i.) of $\hat{T}_{1/2} > 1.6 \times 10^{27} \ \mathrm{yr}$, corresponding to the effective Majorana neutrino mass of $\hat{m}_{\beta\beta} < \ 9.6$ -- $28 \ \mathrm{meV}$. The Frequentist discovery sensitivity (3$\sigma$) is $\hat{T}_{1/2}= 1.0 \times 10^{27} \ \mathrm{yr}$, corresponding to $\hat{m}_{\beta\beta}= \ 12$ -- $36 \ \mathrm{meV}$.

nucl-ex↗

arXiv2025

Innovating Bolometers' Mounting: A Gravity-Based Approach

Cryogenic calorimeters, also known as bolometers, are among the leading technologies for searching for rare events. The CUPID experiment is exploiting this technology to deploy a tonne-scale detector to search for neutrinoless double-beta decay of $^{100}$Mo. The CUPID collaboration proposed an innovative approach to assembling bolometers in a stacked configuration, held in position solely by gravity. This gravity-based assembly method is unprecedented in the field of bolometers and offers several advantages, including relaxed mechanical tolerances and simplified construction. To assess and optimize its performance, we constructed a medium-scale prototype hosting 28 Li$_2$MoO$_4$ crystals and 30 Ge light detectors, both operated as cryogenic calorimeters at the Laboratori Nazionali del Gran Sasso (Italy). Despite an unexpected excess of noise in the light detectors, the results of this test proved (i) a thermal stability better than $\pm$0.5 mK at 10 mK, (ii) a good energy resolution of Li$_2$MoO$_4$ bolometers, (6.6 $\pm$ 2.2) keV FWHM at 2615 keV, and (iii) a Li$_2$MoO$_4$ light yield measured by the closest light detector of 0.36 keV/MeV, sufficient to guarantee the particle identification requested by CUPID.

physics.ins-det↗

arXiv2025

Improved limit on neutrinoless double beta decay of $^{100}$Mo from AMoRE-I

AMoRE searches for the signature of neutrinoless double beta decay of $^{100}$Mo with a 100 kg sample of enriched $^{100}$Mo. Scintillating molybdate crystals coupled with a metallic magnetic calorimeter operate at milli-Kelvin temperatures to measure the energy of electrons emitted in the decay. As a demonstration of the full-scale AMoRE, we conducted AMoRE-I, a pre-experiment with 18 molybdate crystals, at the Yangyang Underground Laboratory for over two years. The exposure was 8.02 kg$\cdot$year (or 3.89 kg$_{\mathrm{^{100}Mo}}\cdot$year) and the total background rate near the Q-value was 0.025 $\pm$ 0.002 counts/keV/kg/year. We observed no indication of $0νββ$ decay and report a new lower limit of the half-life of $^{100}$Mo $0νββ$ decay as $ T^{0ν}_{1/2}>2.9\times10^{24}~\mathrm{yr}$ at 90\% confidence level. The effective Majorana mass limit range is $m_{ββ}<$(210--610) meV using nuclear matrix elements estimated in the framework of different models, including the recent shell model calculations.

nucl-ex↗

arXiv2025

Development of MMC-based lithium molybdate cryogenic calorimeters for AMoRE-II

The AMoRE collaboration searches for neutrinoless double beta decay of $^{100}$Mo using molybdate scintillating crystals via low temperature thermal calorimetric detection. The early phases of the experiment, AMoRE-pilot and AMoRE-I, have demonstrated competitive discovery potential. Presently, the AMoRE-II experiment, featuring a large detector array with about 90 kg of $^{100}$Mo isotope, is under construction. This paper discusses the baseline design and characterization of the lithium molybdate cryogenic calorimeters to be used in the AMoRE-II detector modules. The results from prototype setups that incorporate new housing structures and two different crystal masses (316 g and 517 - 521 g), operated at 10 mK temperature, show energy resolutions (FWHM) of 7.55 - 8.82 keV at the 2.615 MeV $^{208}$Tl $γ$ line, and effective light detection of 0.79 - 0.96 keV/MeV. The simultaneous heat and light detection enables clear separation of alpha particles with a discrimination power of 12.37 - 19.50 at the energy region around $^6$Li(n, $α$)$^3$H with Q-value = 4.785 MeV. Promising detector performances were demonstrated at temperatures as high as 30 mK, which relaxes the temperature constraints for operating the large AMoRE-II array.

physics.ins-det↗