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J. M. F. dos Santos

Publications and source records attributed to J. M. F. dos Santos.

At least 19 recordsLinked to original sources
arXiv2026

Detector Performance and Dark Matter Sensitivity of CYGNO with HFO-1234ze Gas Admixtures

The CYGNO project develops optical time projection chambers for directional dark matter searches, using a He:CF4 (60:40) gas mixture at atmospheric pressure and a triple-GEM amplification stage. We investigate the addition of 1-10% HFO-1234ze as a hydrogen-containing additive with low global warming potential. The charge response and scintillation light yield are studied with the MANGO prototype, complemented by secondary-scintillation spectroscopy of the baseline mixture and mixtures containing 1% and 2.5% HFO. Increasing the HFO concentration shifts the charge-response curves towards higher GEM voltages and strongly suppresses the scintillation emission in both the ultraviolet and visible bands. We use the measured optical response to estimate the impact on projected spin-independent WIMP-nucleon and spin-dependent WIMP-proton exclusion limits for a CYGNO-like directional detector. Under the assumed detector-response model, the higher optical energy threshold largely outweighs the benefit of the additional light target, although a 1% HFO admixture retains a limited advantage for low-mass spin-dependent interactions. An idealized fixed-threshold benchmark is also considered to illustrate the potential of the modified target composition without the optical threshold penalty.

physics.ins-det↗
arXiv2026

Demonstrating topological identification capabilities of the NEXT experiment at low pressure

The NEXT-100 detector is a high-pressure xenon time projection chamber utilising electroluminescence amplification for sub-1% FWHM energy resolution and topological discrimination, two key attributes required to achieve the NEXT programme's overarching goal of detecting neutrinoless double beta decay ($0 νββ$). The detector has completed its first physics run at the Laboratorio Subterráneo de Canfranc (LSC), with xenon at a pressure of $\sim$4 bar. In this paper we report on the first validation of NEXT-100's topological performance and present the first topological analysis conducted at low pressure within the detector programme. A Monte Carlo study characterising the effects of pressure on track topology is presented, with qualitative agreement observed in data. We then demonstrate the topological discrimination capabilities for $0νββ$-like events from $^{208}$Tl decays using a cut-based method considered the 'baseline' in NEXT's topological programme, upon which all future analyses will improve. The analysis described applies a set of selection cuts before implementing a background discrimination algorithm that yields a reported signal efficiency for double-electron tracks and background acceptance for single-electron tracks of 75.6 $\pm$ 1.9 (stat.) $^{+3.4}_{-4.1}$ (syst.) % and 14.7 $\pm$ 0.4 (stat.) $^{+0.7}_{-0.8}$ (syst.) %. These results demonstrate the excellent topological discrimination capabilities of the NEXT-100 detector in line with NEXT-White, which achieved a signal efficiency and background acceptance of 71.6 $\pm$ 1.5 (stat.) $\pm$ 0.3 (syst.) % and 20.6 $\pm$ 0.4 (stat.) $\pm$ 0.3 (syst.) % respectively.

hep-ex↗
arXiv2026

Detection of scintillation light in noble gases with wavelength-shifting optical fibers

Wavelength-shifting (WLS) techniques enable particle detectors based on noble gases, whose scintillation light is predominantly emitted in the vacuum-ultraviolet. We investigate WLS fibers coated with tetraphenyl butadiene (TPB) for scintillation light detection in gaseous xenon and argon at pressures up to 8.5 bar, motivated by future high-pressure xenon time-projection chambers of the NEXT program. Two detector configurations are studied: an elongated high-pressure vessel with four PTFE panels equipped with WLS fibers read by temperature-stabilized SiPMs, and a compact box-shaped detector operated at 1 bar Xe with WLS fibers read out by PMTs. Both operate with continuous gas purification. The detector response is characterized using cosmic muons and alpha particles from a $^{241}$Am source. With the SiPM setup, we measure a light collection efficiency (LCE) of ${1.18 \pm 0.01~\mathrm{(sta.)}~^{+0.07}_{-0.09}~\mathrm{(sys.)}~\%}$ for xenon and ${1.07 \pm 0.01~\mathrm{(sta.)}~^{+0.06}_{-0.08}~\mathrm{(sys.)}~\%}$ for argon. With PMT readout, we measure a LCE of ${0.45 \pm 0.01~\mathrm{(sta.)} \pm 0.05~\mathrm{(sys.)}~\%}$ in xenon, in agreement with the SiPM result once photon detection efficiency is accounted for. Average scintillation waveforms in xenon and argon are studied to assess the time structure of the emitted light. Cosmic-muon measurements yield a mean energy required to produce a scintillation photon $45\pm7~\mathrm{(sta.)}~^{+4}_{-5}~\mathrm{(sys.)}~\mathrm{eV}$ at 1.5 bar, in agreement with the literature. The results demonstrate that TPB-coated WLS fiber systems can reliably detect scintillation light in high-pressure gaseous noble detectors, with a LCE representing an upper limit for realistic large-scale TPCs, where additional photon losses from materials and fiber attenuation are expected.

physics.ins-det↗
arXiv2026

Radon-induced backgrounds in the NEXT-100 experiment

The NEXT-100 detector at the LSC aims at the first competitive search for the \bbnonu decay using a high-pressure \Xe{136} electroluminescent time projection chamber. The first low-background run of NEXT-100 at 3.95 bar has been devoted to the measurement of the radon-induced backgrounds impacting this search. The contributions from both the internal and external airborne radon have been evaluated. The internal \Rn{222} activity is found to be (0.95$\pm$0.04(stat)$\pm$0.09(sys)) Bq/m$^3$, while no traces of \Rn{220} have been observed. Most of the \Rn{222} progeny plate-out on the surface of the cathode of the detector, leading to a rate of Rn-induced \Bi{214} of (0.97$\pm$0.05(stat)$\pm$0.10(sys)) Hz for visible energies above 400 keV. The corresponding background index in the \bbnonu region of interest is evaluated as (7.3$\pm$1.5(stat)$\pm$0.8(sys))$\times10^{-4}$ counts/(keV$\cdot$kg$\cdot$yr) after selection of the fully contained events. This background index is reduced to $\sim$4$\times10^{-5}$ counts/(keV$\cdot$kg$\cdot$yr) by applying a topological selection requiring only one double-electron-like track in the events. This value is one order of magnitude below the total radiogenic background expectation in NEXT-100. By analyzing the correlation of the airborne radon activity and the measured rate of events in NEXT-100, it is concluded that the detector operates in a virtually radon-free environment thanks to the radon abatement system of the LSC.

hep-ex↗
arXiv2026

He-CF4-CH4 ternary mixtures as target gas for the CYGNO directional dark matter experiment

The CYGNO collaboration is advancing a high-resolution optical Time Projection Chamber (TPC) for directional dark matter searches and solar neutrino spectroscopy at LNGS. The detector uses a He-40%CF4 gas mixture at atmospheric pressure and a triple-GEM cascade for ionization signal amplification. Scintillation light from GEM electron avalanches is read out using sCMOS cameras, enabling high sensitivity to interactions in the few keV range, alongside precise ionization event tracking and particle identification. This study investigates the effects of adding 3-10% methane to the He-40%CF4 mixture. Methane improves the electrical stability of the TPC, allowing for higher GEM voltages before discharge onset, which compensates for its scintillation quenching and leads to enhanced overall scintillation yield. Compared to prior studies performed with isobutane, methane demonstrates a lower quenching effect on visible and UV photons while maintaining good energy resolution. Importantly, the inclusion of methane lowers the dark matter detection threshold by providing a lighter target and extending track lengths of light nuclear recoils, thus enhancing directional discrimination. These results establish methane as a promising additive for optimizing CYGNO's performance in detecting low-mass dark matter candidates.

physics.ins-det↗
arXiv2026

Simulation of the CYGNO Gaseous TPC Optical Readout

Gaseous Time Projection Chambers with Optical Readout are sensitive detectors suitable for 3D measurement of low-energy O(1 keV) particles and are proposed for detecting rare events such as Dark Matter particle interactions. The CYGNO collaboration is developing such a detector with a high spatial and energy resolution, leveraging an innovative optical readout system. A reliable simulation of the detector response is needed to properly assess the physics reach of this technique and to better understand the performance of the detector in the development phase. Such a simulation cannot entirely rely on existing software packages; indeed, none of the available tools is capable of properly and reliably treating the different phenomena occurring in the detector, from the primary interaction in the gas volume throughout the whole detector response model, including charge transport, light production and propagation, and the response of the optical sensors. In this paper, we present a modeling of the detector response tuned on the CYGNO Optical TPC case; a description of the method is reported together with comparisons with experimental data from the LIME prototype to demonstrate the simulation performances.

physics.ins-det↗
arXiv2026

Upgrade of the Trigger and Data Acquisition System for Continuous Imaging and Multi-Camera Operation in CYGNO

The CYGNO experiment employs an optical readout to image particle interactions in a gaseous Time Projection Chamber (TPC), combining cameras and photomultiplier tubes (PMTs) to achieve high spatial resolution and timing information. This approach enables detailed track reconstruction but poses significant challenges for data acquisition, particularly in view of the next experimental phase, CYGNO-04, which will operate multiple cameras simultaneously. In this paper, we present an upgrade of the CYGNO Trigger and Data Acquisition (T-DAQ) system, developed starting from the LIME configuration and validated on the MANGO prototype. The upgrade introduces a continuous imaging acquisition mode, substantially reducing the camera dead time, together with an extended trigger time-tagging scheme that provides a robust global time reference for PMT signals. A synchronous multi-camera DAQ architecture is also implemented and tested, enabling coordinated operation of multiple optical sensors without a master camera. The performance of the upgraded system is validated through dedicated tests, demonstrating stable continuous acquisition, reliable time-tagging, and consistent synchronization across multiple cameras. These results establish a solid and scalable foundation for the CYGNO-04 DAQ and represent a key step toward efficient data acquisition in future large-scale optical TPC detectors.

physics.ins-det↗
arXiv2026

Characterization of field cage and cathode for low radioactivity operation with the CYGNO experiment

Dark matter, which is considered to account for approximately the 27% of the Universe's energy-mass content, remains an open issue in modern particle physics along with its composition. The CYGNO Experiment aims to exploit an innovative approach applied to the direct detection search of low energy nuclear recoils possibly induced by cold particle-like dark matter candidates. CYGNO employs a directional detector based on a Time Projection Chamber (TPC) filled with a He:CF$_{4}$ gas mixture and equipped with an optical readout. Currently, the CYGNO Collaboration is constructing the detector demonstrator, CYGNO-04, in Hall F at Laboratori Nazionali del Gran Sasso (LNGS). This 0.4 m$^3$ detector has the goal of proving the scalability of the technology and assessing the physics and radiopurity capabilities. Given the low radioactivity requirements, especially in internal components such as field cage and cathode, the reduction of material while keeping the correct electrical behavior is paramount. In this paper, we present the validation of several internal components, mainly focusing on the field cage material and support structure. The tests included geometrical asymmetries in the electric field response, collection efficiency as well as measurement of known physical quantities. A preferred configuration is found with a structure based on Nylon material which supports a PET or Kapton sheet with copper strips deposited on.

physics.ins-det↗
arXiv2026

Electroluminescence Yield Measurements in Xenon Gas with the NEXT-DEMO++ Detector

The NEXT-DEMO++ detector, a high-pressure xenon gas time projection chamber serving as a prototype for the NEXT-100 experiment, was used to measure the electroluminescence (EL) yield as a function of reduced electric field ($E/p$) across pressures from 2.0 to 9.4 bar, utilizing the 41.5 keV de-excitation peak of $^{83m}$Kr. These measurements were made to examine the pressure dependence of the slope of the reduced EL yield $Y/p$, which has shown inconsistencies in the literature. The reduced yield was fitted with a linear model, revealing a modest ($\sim$5%) change in slope, beginning around 5 bar and increasing with pressure up to 9.4 bar.

physics.ins-det↗
arXiv2026

Fast reconstruction-based ROI triggering via anomaly detection in the CYGNO optical TPC

Optical-readout Time Projection Chambers (TPCs) produce megapixel-scale images whose fine-grained topological information is essential for rare-event searches, but whose size challenges real-time data selection. We present an unsupervised, reconstruction-based anomaly-detection strategy for fast Region-of-Interest (ROI) extraction that operates directly on minimally processed camera frames. A convolutional autoencoder trained exclusively on pedestal images learns the detector noise morphology without labels, simulation, or fine-grained calibration. Applied to standard data-taking frames, localized reconstruction residuals identify particle-induced structures, from which compact ROIs are extracted via thresholding and spatial clustering. Using real data from the CYGNO optical TPC prototype, we compare two pedestal-trained autoencoder configurations that differ only in their training objective, enabling a controlled study of its impact. The best configuration retains (93.0 +/- 0.2)% of reconstructed signal intensity while discarding (97.8 +/- 0.1)% of the image area, with an inference time of approximately 25 ms per frame on a consumer GPU. The results demonstrate that careful design of the training objective is critical for effective reconstruction-based anomaly detection and that pedestal-trained autoencoders provide a transparent and detector-agnostic baseline for online data reduction in optical TPCs.

physics.ins-det↗
arXiv2026

The CYGNO experiment: a gaseous TPC with optical readout for rare events searches

The CYGNO collaboration is developing a novel strategy for directional Dark Matter searches based on a gaseous Time Projection Chamber (TPC). The detector is optimized for the exploration of light (0.5-50 GeV) WIMPs-like particles and employs a He/CF4 gas mixture at atmospheric pressure, sensitive to both spin-dependent and spin-independent interactions. A key feature of the project is its optical readout, which relies on photon detection rather than charge collection. In CYGNO detectors, electrons released by ionizing tracks drift toward an amplification stage of three Gas Electron Multipliers (GEMs). The electron avalanches generate scintillation light that is captured by scientific CMOS (sCMOS) cameras for high-resolution two-dimensional imaging and by Photomultiplier Tubes (PMTs) that provide a precise time profile along the drift direction. This allows a 3D event reconstruction, detailed energy deposition mapping, and effective topology and head-to-tail discrimination. Building on the achievements of the 50 L prototype (LIME), which successfully operated underground at LNGS, the next step is the deployment of a 0.4 m3 demonstrator, CYGNO-04, to be completed in 2026. The demonstrator will validate scalability and confirm the advantages of the proposed technique. Recent results from LIME highlight strong progress in 3D tracking and particle identification. The current status of CYGNO-04 and its role in advancing the program will be presented as well.

physics.ins-det↗
arXiv2026

Trigger Optimization and Event Classification for Dark Matter Searches in the CYGNO Experiment Using Machine Learning

The CYGNO experiment employs an optical-readout Time Projection Chamber (TPC) to search for rare low-energy interactions using finely resolved scintillation images. While the optical readout provides rich topological information, it produces large, sparse megapixel images that challenge real-time triggering, data reduction, and background discrimination. We summarize two complementary machine-learning approaches developed within CYGNO. First, we present a fast and fully unsupervised strategy for online data reduction based on reconstruction-based anomaly detection. A convolutional autoencoder trained exclusively on pedestal images (i.e. frames acquired with GEM amplification disabled) learns the detector noise morphology and highlights particle-induced structures through localized reconstruction residuals, from which compact Regions of Interest (ROIs) are extracted. On real prototype data, the selected configuration retains (93.0 +/- 0.2)% of reconstructed signal intensity while discarding (97.8 +/- 0.1)% of the image area, with ~25 ms per-frame inference time on a consumer GPU. Second, we report a weakly supervised application of the Classification Without Labels (CWoLa) framework to data acquired with an Americium--Beryllium neutron source. Using only mixed AmBe and standard datasets (no event-level labels), a convolutional classifier learns to identify nuclear-recoil-like topologies. The achieved performance approaches the theoretical limit imposed by the mixture composition and isolates a high-score population with compact, approximately circular morphologies consistent with nuclear recoils.

physics.ins-det↗
arXiv2026

First Optical Observation of Negative Ion Drift at Surface Pressure

We report the first observation of Negative Ion Drift (NID) at surface pressure of $900 \pm 7$ mbar at Laboratori Nazionali del Gran Sasso in a He:CF$_4$:SF$_6$ mixture using an optically read out Time Projection Chamber (TPC) within the CYGNO/INITIUM project. We present the first PMT waveform analysis in the NID regime, interpreting the temporal light pattern through a model that combines track geometry and charge transport. The inferred drift velocities correspond to mobilities of O(cm$^2$ V$^{-1}$ s$^{-1}$), consistent with negative ion transport. The observed linear scaling of the time extension mean with drift distance reveals the presence of a faster minority charge carrier population in addition to the dominant SF$_6^-$ species, drifting at a $\sim$25\% higher velocity under external inputs. These results demonstrate multi-species negative ion drift operation at surface pressure in a He:CF$_4$:SF$_6$ mixture and open a concrete path toward large scale, low diffusion optical TPCs for rare event searches.

physics.ins-det↗
arXiv2026

Production of GEM-like structures for cryogenic applications, using laser-cutting techniques

A novel concept for electroluminescence (EL) structures was recently proposed. In it, a wavelength-shifting material is deposited inside the holes of GEM-like structures which, after suitable optical treatment of its electrodes, improves the light collection and detection efficiency in noble gas TPCs. This new development directly addresses problems related with the scalability of future dual-phase TPCs for rare-event searches, matching (and potentially exceeding) the performance of conventional EL techniques. We report the newest developments on the production of such structures using laser-based techniques, namely the manufacture of a first batch of the so-called FAT-GEMs. This process allows low-cost and reproducible manufacturing of a high volume of such structures. In addition to the detailed description of the production, we present a performance assessment in pure argon, at a gas density close to the one expected in LAr conditions. An energy resolution of 23.5$\pm$1~\% (FWHM) at 5.9~keV was obtained, indicating a consistent improvement over previous batch. The optical treatment of the electrode surfaces has been greatly simplified and modestly improved, while charging-up effects arising from the use of laminates eliminated.

physics.ins-det↗
arXiv2026

Demonstration of Sub-Percent Energy Resolution in the NEXT-100 Detector

NEXT-100 is a high-pressure xenon time projection chamber with electroluminescent amplification, designed to operate with up to approximately 70.5 kg at 13.5 bar. It is the most recent detector developed by the NEXT collaboration to search for the neutrinoless double-beta decay ($ββ0ν$) of Xe-136. The NEXT gas TPC technology offers the best energy resolution near the Q-value of the decay ($Q_{ββ}$ = 2458 keV) among xenon detectors, which is set by design to be <1% FWHM. We report here the high-energy calibration of the detector using a Th-228 source, demonstrating linear response and an energy resolution of $(0.90 \pm 0.02)$% FWHM at the Tl-208 photopeak (2615 keV). This performance extrapolates to a resolution at the double-beta decay end-point of $R(Q_{ββ})$ = $(0.93 \pm 0.02)$% FWHM, confirming the detector's capability for precision energy measurement in the search for $ββ0ν$.

physics.ins-det↗
arXiv2026

First results of the NEXT-100 detector using $^{83m}$Kr decays

The NEXT collaboration is investigating the double beta decay of $^{136}$Xe using high-pressure gas electroluminescent time projection chambers, which provide excellent energy resolution together with a robust topological signature. Operating at the Laboratorio Subterráneo de Canfranc (LSC) and building on the success of the NEXT-White detector, the NEXT-100 apparatus began commissioning in May 2024 and started operation with xenon at a pressure of 4 bar in October 2024. We report here the first results obtained with NEXT-100 using low-energy calibration data from $^{83m}$Kr decays, which allow mapping of the detector response in the active volume and monitoring of its stability over time. After homogenizing the light response, we achieve an energy resolution of 4.37% FWHM at 41.5 keV for $^{83m}$Kr point-like energy deposits contained in a radius of 425 mm. In a fiducial region representing the operating conditions of NEXT-100 at 10 bar we obtain an improved energy resolution of 4.16% FWHM. These results are in good agreement with that obtained in NEXT-White, and an $E^{-1/2}$ extrapolation to $Q_{ββ}$ yields an energy resolution close to 0.5% FWHM, well below the 1% FWHM design target.

hep-ex↗
arXiv2025

The NEXT-100 Detector

The NEXT collaboration is dedicated to the study of double beta decays of $^{136}$Xe using a high-pressure gas electroluminescent time projection chamber. This advanced technology combines exceptional energy resolution ($\leq 1\%$ FWHM at the $Q_{ββ}$ value of the neutrinoless double beta decay) and powerful topological event discrimination. Building on the achievements of the NEXT-White detector, the NEXT-100 detector started taking data at the Laboratorio Subterráneo de Canfranc (LSC) in May of 2024. Designed to operate with xenon gas at 13.5 bar, NEXT-100 consists of a time projection chamber where the energy and the spatial pattern of the ionising particles in the detector are precisely retrieved using two sensor planes (one with photo-multiplier tubes and the other with silicon photo-multipliers). The detector has been operating at stable conditions using argon and xenon gases at $\sim$4 bar and drift fields of 74 V/cm and 118 V/cm, respectively. Alpha decays from the $^{222}$Rn chain have been used to test and monitor the stability of the detector, showing a constant electron lifetime in the drift volume. In this paper, in addition to reporting the results of the commissioning run, we provide a detailed description of the NEXT-100 detector, describe its assembly, and present the current estimation of the radiopurity budget.

physics.ins-det↗
arXiv2025

High Voltage Delivery and Distribution for the NEXT-100 Time Projection Chamber

A critical element in the realization of large liquid and gas time projection chambers (TPCs) is the delivery and distribution of high voltages into and around the detector. Such experiments require of order tens of kilovolts to enable electron drift over meter-scale distances. This paper describes the design and operation of the cathode feedthrough and high voltage distribution through the field cage of the NEXT-100 experiment, an underground TPC that will search for neutrinoless double beta decay $0νββ$. The feedthrough has been demonstrated to hold pressures up to 20~bar and sustain voltages as high as -65~kV, and the TPC is operating stably at its design high voltages. The system has been realized within the constraints of a stringent radiopurity budget and is now being used to execute a suite of sensitive double beta decay analyses.

physics.ins-det↗