arXiv subjects

T. Papaevangelou

Publications and source records attributed to T. Papaevangelou.

At least 19 recordsLinked to original sources

arXiv2026

Construction, commissioning, and performance of the ENUBET demonstrator

A final full-size prototype of the instrumented decay tunnel of ENUBET, referred to as the Demonstrator, was constructed and its performance was tested during the 2022, 2023 and 2024 beam test campaigns at the CERN East Area facility. We demonstrate the full scalability of this specialized longitudinal sampling calorimeter technology, based on iron absorbers and scintillator tiles readout by wavelength-shifting fibers and SiPMs. In addition, we evaluate the channel-by- channel response and the performance in terms of electron energy resolution, linearity, and particle identification capabilities, using charged particle beams with energies up to 5 GeV. A comparison with the predictions of a GEANT4 simulation of the prototype is also presented. The results meet the requirements for neutrino monitoring through lepton identification in the decay tunnel and validate the ENUBET full simulation. Although some limitations have been identified, they can be readily addressed in future developments.

hep-ex↗

arXiv2026

A Novel Hadronic Calorimeter With A Direct Neutron Readout

A neutron-sensitive sampling calorimeter based on alternating lead absorber and gadolinium-loaded liquid scintillator layers is investigated using detailed Geant4 Monte Carlo simulations. In addition to the conventional prompt calorimetric signal, the proposed detector records delayed energy from neutron moderation and capture, providing direct information on the neutron component of hadronic showers. A six-layer Pb/LAB-Gd calorimeter exposed to 10~GeV protons is studied to characterize its neutron response and evaluate its impact on calorimetric performance. The delayed deposited energy is found to be almost perfectly proportional to the neutron-capture multiplicity, providing a direct calibration of the neutron-sensitive signal. Event-by-event analyses further reveal a clear relationship between the prompt calorimetric response and the delayed neutron observable, demonstrating that the latter contains substantial information on the invisible hadronic energy. Exploiting this correlation through a simple nonlinear event-by-event correction improves the prompt-energy resolution from 21.8% to 13.3% without rejecting events. Furthermore, the analysis of events with similar neutron multiplicities indicates that neutron-production fluctuations constitute a major contribution to the overall hadronic energy resolution. These results demonstrate the potential of gadolinium-loaded sampling calorimeters to recover part of the invisible hadronic energy and significantly improve hadronic energy reconstruction and energy resolution.

physics.ins-det↗

arXiv2026

Advances in photocathode development for PICOSEC Micromegas precise-timing detectors

The PICOSEC Micromegas detector is a~precise-timing gaseous detector that combines a Cherenkov radiator, a~semi-transparent photocathode and a Micromegas amplification stage, targeting time resolutions of tens of picoseconds for minimum ionising particles (MIPs). Initial single-pad prototypes achieved time resolutions of $σ<25$ ps, demonstrating strong potential for High Energy Physics (HEP) applications and beyond. The objective of this paper is a comprehensive characterisation of photocathodes, with a strong focus on robust materials while preserving excellent timing performance. The study includes laboratory measurements of optical and resistive properties, along with beam tests using 150 GeV/$c$ muons to evaluate the time resolution and photoelectron yield for various photocathodes. The best performance was obtained by a 5 nm Cesium Iodide (CsI) photocathode, reaching $σ= 10.9 \pm 0.3$ ps with more than 30 extracted photoelectrons, representing the most precise time resolution achieved by PICOSEC Micromegas to date. Metallic and carbon-based photocathodes, including Titanium (Ti), Boron Carbide (B$_4$C) and Diamond-Like Carbon (DLC), were also tested, with Ti and B$_4$C emerging as the most promising alternatives, achieving $σ\approx 30$ ps with about 5 extracted photoelectrons. These results demonstrate that improved robustness can be achieved while maintaining excellent time resolution, supporting the feasibility of using the PICOSEC Micromegas concept in future experiments.

physics.ins-det↗

arXiv2026

Performance Optimization and Characterization of 7-pad Resistive PICOSEC Micromegas Detectors

We present a comprehensive characterization of resistive PICOSEC Micromegas detector prototypes, tested under identical conditions, constant drift gap, field configurations, and photocathode at the CERN SPS H4 beam line. This work provides a proof of concept for the use of resistive layer technology in gaseous timing detectors, demonstrating that robustness can be improved without compromising the excellent timing performance of PICOSEC Micromegas. Different resistive architectures and values were explored to optimize stability and ensure reliable long-term operation in challenging experimental environments. The prototype with a 10MΩ resistive layer achieved the best overall performance, with a timing resolution of 22.900 {\pm} 0.002 ps and a spatial resolution of 1.190 {\pm} 0.003 mm, while charge sharing across multiple pads enabled combined timing resolutions below 28 ps. A lower-resistivity (200kΩ) configuration exhibited enhanced charge spread, leading to minor systematic offsets in reconstructed pad centers, yet maintained robust timing and spatial performance. Capacitive charge-sharing architectures improved spatial resolution in some regions but suffered from signal attenuation and nonuniform charge distributions, resulting in slightly degraded timing (33.300 {\pm} 0.002 ps) and complex localization patterns. Mechanical precision, particularly readout planarity and photocathode alignment, was identified as critical for uniform detector response. These studies benchmark the potential of resistive layers for gaseous timing detectors and provide a foundation for scalable designs with optimized timing and spatial resolution across diverse experimental applications.

physics.ins-det↗

arXiv2026

Optical readout of MPGDs with solid wavelength shifters

Optical readout of MicroPattern Gaseous Detectors (MPGDs) makes use of the high granularity of imaging sensors to achieve good spatial resolution for radiation imaging and particle detection. CF4 is widely used as a scintillating gas because its emission lies in the visible range, where optical sensors are most sensitive. However, to reduce reliance on greenhouse gas, such as CF4, which also has limited availability, alternative gas mixtures emitting scintillation light in the ultraviolet range can be used in combination with wavelength shifters. We investigate the spatial resolution achievable with optically read out Gaseous Electron Multipliers (GEMs) and Micromegas when using solid wavelength shifter layers such as Tetraphenyl butadiene (TPB). TPB coatings on the anode of glass Micromegas achieve the best spatial resolution of 0.22 mm owing to the minimal distance between the origin of the scintillation light and the wavelength shifter. Nevertheless, TPB layers were also shown to achieve moderate spatial resolution in combination with optically read out GEMs.

physics.ins-det↗

arXiv2026

Timing performance of large prototype based on $\upmu$RWELL- PICOSEC detector technology with $10 \times 10\ \mathrm{cm}^{2}$ active area

The $\upmu$RWELL-PICOSEC detector, which combines a $\upmu$RWELL gaseous amplification structure with a Cherenkov radiator and photocathode, is a novel approach to acheive fast and precise timing in gaseous detectors. With timing precision at the level of tens of picoseconds, this technology is particularly suited for time-of-flight (TOF) applications in particle physics and potentially medical imaging. Beam tests with a 150~GeV/$c$ muon beam have been carried out on a large-area (10~$\times$~10~cm$^{2}$) prototype equipped with a cesium iodide (CsI) photocathode. Using an oscilloscope-based single-channel readout, timing measurements on two individual pads of the detector have yielded resolutions of $\approx$ 48 ps and $\approx$ 52 ps under different biasing conditions respectively.

physics.ins-det↗

arXiv2026

Spatial resolution improvement of PICOSEC Micromegas precise timing detectors

The combination of a Cherenkov radiator with a semi-transparent photocathode and a Micromegas based amplification stage allows PICOSEC Micromegas detectors to achieve a time resolution of better than 15ps. While tileable prototypes with 10x10 channels feature 1x1 cm^2 readout pads, finer readout granularity can be used to improve the spatial resolution. We report on the study of high readout granularity PICOSEC Micromegas prototypes which achieve around 0.5mm spatial resolution with 3.5mm large pads. No significant improvement was found when readout pad size was further reduced to 2.2mm. The timing resolution of the leading pad was found to be slightly degraded but remained better than 20ps for a medium granularity prototype. The achieved spatial resolution can enable PICOSEC Micromegas to be used as precise timing and moderate resolution tracking detector simultaneously.

physics.ins-det↗

arXiv2026

Design and Performance of a 96-channel Resistive PICOSEC Micromegas Detector for ENUBET

The PICOSEC-Micromegas (PICOSEC-MM) detector is a fast gaseous detector that achieves picosecond-level timing by coupling a Cherenkov radiator, typically an MgF2 crystal, to a Micromegas-based photodetector with a photocathode. This configuration allows the fast photoelectron-induced signal to suppress the intrinsic time jitter of gaseous detectors, enabling sub-20 ps timing precision while preserving the robustness and scalability of micro-pattern gaseous detector technologies. The 96-pad PICOSEC-MM detector is a large-area demonstrator optimized for precision timing in high-energy physics, building on research and development insights from earlier 7-pad resistive prototypes to validate scalability, uniformity, and robustness for the ENUBET project. It employs a 2.5 nm diamond-like carbon photocathode and a Micromegas board with a surface resistivity of 10 megaohms per square, and was characterized using 150 GeV/c muons at the CERN SPS beamline, with one-third of the active area instrumented per run. A dedicated alignment procedure for multi-pad PICOSEC-MM systems was used to reconstruct pad centers and merge measurements across regions, yielding a timing resolution of 43 ps and uniform signal arrival time distributions over the tested area. Mechanical flatness was identified as a key factor, with planarity tolerances within 10 micrometers required to maintain good timing resolution, and the successful operation of the 96-pad demonstrator confirms the scalability of the PICOSEC-MM concept toward robust, high-granularity, picosecond-level gaseous timing detectors for monitored neutrino beam experiments such as ENUBET.

physics.ins-det↗

arXiv2025

Signal Processing and Machine Learning Algorithms for Precise Timing with PICOSEC Micromegas Detectors

High particle rates in current and future experiments make pile-up phenomena a critical issue for extracting useful information. In this context, timing can be important as the 4$^{\mathrm{th}}$ dimension parameter for triggering or event reconstruction. The PICOSEC-Micromegas detector has been shown to offer precise timing of the order of tens of\,ps. In this work, novel signal processing algorithms are being developed and evaluated to demonstrate the technology's ability for online precise timing. We propose, an algorithm based on Artificial Neural Networks (ANN). This algorithm uses a model to train the ANN. The performance of the different algorithms is evaluated using experimental data, resulting in a timing resolution of 18.3 $\pm$ 0.6\,ps, comparable to the standard analysis based on the Constant Fraction Discrimination technique. Additionally, an alternative algorithm using the charge of the pulse exceeding a threshold as a parameter to correct for systematic effects is reported.

physics.ins-det↗

arXiv2025

Spatial resolution studies with the BabyIAXO Micromegas prototype

The spatial resolution of the Micromegas prototype developed for the BabyIAXO experiment was evaluated using a low-energy X-ray beam at the SOLEIL synchrotron facility. BabyIAXO, currently under construction, aims to search for hypothetical solar axions. A key component of the experiment is a low-background X-ray detector with high efficiency in the 1-10 keV energy range and stringent background rejection capabilities. Achieving a spatial resolution on the order of, or better than, 1 mm is critical for accurately reconstructing signal shapes and positions, and for effectively discriminating between signal and background events. Therefore, a precise characterization of the detector's spatial resolution is essential to validate its suitability for the experiment. This study involved scanning the IAXO-D1 Micromegas detector under various beam energies, positions, and drift field configurations to evaluate their influence on spatial resolution. A resolution of approximately 100 $μ$m at 6 keV was achieved, confirming the strong potential of this technology for application in the final BabyIAXO setup.

physics.ins-det↗

arXiv2025

Search for solar axions produced through the axion-electron coupling $g_{ae}$ using a new GridPix detector at CAST

We present a search for solar axions produced through the axion-electron coupling $(g_{ae})$ using data from a novel 7-GridPix detector installed at the CERN Axion Solar Telescope (CAST). The detector, featuring ultra-thin silicon nitride windows and multiple veto systems, collected approximately 160 hours of solar tracking data between 2017-2018. Using machine learning techniques and the veto systems, we achieved a background rate of $1.06\times 10^{-5}\,\text{keV}^{-1}\text{cm}^{-2}\text{s}^{-1}$ at a signal efficiency of about $80\,\%$ in the $0.2$-$8\,\text{keV}$ range. Analysis of the data yielded no significant excess above background, allowing us to set a new upper limit on the product of the axion-electron and axion-photon couplings of $g_{ae}\cdot g_{aγ} < 7.35\times 10^{-23}\,\text{GeV}^{-1}$ at $95\,\%$ confidence level. This result improves upon the previous best helioscope limit and demonstrates the potential of GridPix technology for rare event searches. Additionally, we derived a limit on the axion-photon coupling of $g_{aγ} < 9.0\times 10^{-11}\,\text{GeV}^{-1}$ at $95\,\%$ CL, which, while not surpassing CAST's best limit, provides complementary constraints on axion models.

hep-ex↗

arXiv2025

nuSCOPE: A short-baseline neutrino beam at CERN for high-precision cross-section measurements

A new generation of neutrino cross-section experiments at the GeV scale is crucial in the precision era of oscillation physics and lepton flavor studies. In this document, we present a novel neutrino beam design that leverages the experience and R&D achievements of the NP06/ENUBET and NuTag Collaborations and explore its potential implementation at CERN. This beam enables flux monitoring at the percent level and provides a neutrino energy measurement independent of final state particle reconstruction at the neutrino detector. As a result, it eliminates the two primary sources of systematic uncertainty in cross-section measurements: flux normalization and energy bias caused by nuclear effects. We provide a detailed description of the beam technology and instrumentation, along with an overview of its physics potential, with particular emphasis on cross-sections relevant to DUNE and Hyper-Kamiokande.

hep-ex↗

arXiv2025

The International Axion Observatory (IAXO): case, status and plans. Input to the European Strategy for Particle Physics

The International Axion Observatory (IAXO) is a next-generation axion helioscope designed to search for solar axions with unprecedented sensitivity. IAXO holds a unique position in the global landscape of axion searches, as it will probe a region of the axion parameter space inaccessible to any other experiment. In particular, it will explore QCD axion models in the mass range from meV to eV, covering scenarios motivated by astrophysical observations and potentially extending to axion dark matter models. Several studies in recent years have demonstrated that IAXO has the potential to probe a wide range of new physics beyond solar axions, including dark photons, chameleons, gravitational waves, and axions from nearby supernovae. IAXO will build upon the two-decade experience gained with CAST, the detailed studies for BabyIAXO, which is currently under construction, as well as new technologies. If, in contrast to expectations, solar axion searches with IAXO ``only'' result in limits on new physics in presently uncharted parameter territory, these exclusions would be very robust and provide significant constraints on models, as they would not depend on untestable cosmological assumptions.

hep-ph↗

arXiv2025

PICOSEC Micromegas Precise-timing Detectors: Development towards Large-Area and Integration

PICOSEC Micromegas (MM) is a precise timing gaseous detector based on a Cherenkov radiator coupled with a semi-transparent photocathode and an MM amplifying structure. The detector conceprt was successfully demonstrated through a single-channel prototype, achieving sub-25 ps time resolution with Minimum Ionizing Particles (MIPs). A series of studies followed, aimed at developing robust, large-area, and scalable detectors with high time resolution, complemented by specialized fast-response readout electronics. This work presents recent advancements towards large-area resistive PICOSEC MM, including 10 $\times$ 10 $\text{cm}^2$ area prototypes and a 20 $\times$ 20 $\text{cm}^2$ prototype, which features the jointing of four photocathodes. The time resolution of these detector prototypes was tested during the test beam, achieved a timing performance of around 25 ps for individual pads in MIPs. Meanwhile, customized electronics have been developed dedicated to the high-precision time measurement of the large-area PICOSEC MM. The performance of the entire system was evaluated during the test beam, demonstrating its capability for large-area integration. These advancements highlight the potential of PICOSEC MM to meet the stringent requirements of future particle physics experiments.

physics.ins-det↗

arXiv2025

The ENUBET monitored neutrino beam and its implementation at CERN

The ENUBET project recently concluded the R&D for a site independent design of a monitored neutrino beam for high precision cross section measurements, in which the neutrino flux is inferred from the measurement of charged leptons in an instrumented decay tunnel. In this phase three fundamental results were obtained and will be discussed here: 1) a beamline not requiring a horn and relying on static focusing elements allows to perform a $ν_e$ cross section measurement in the DUNE energy range with 1% statistical uncertainty employing $10^{20}$ 400 GeV protons on target (pot) and a neutrino detector of the size of ProtoDUNE; 2) the instrumentation of the decay tunnel, based on a cost effective sampling calorimeter solution, has been tested with a large scale prototype achieving the performance required to identify positrons and muons from kaon decays with high signal-to-noise ratio; 3) the systematics budget on the neutrino flux is constrained at the 1% level by fitting the charged leptons observables measured in the decay tunnel. Based on these successful results ENUBET is now pursuing a study for a site dependent implementation at CERN in the framework of Physics Beyond Colliders. In this context a new beamline, able to enrich the neutrino flux at the energy of HK and to reduce by more than a factor 3 the needed pot, has been designed and is being optimized. The civil engineering and radioprotection studies for the siting of ENUBET in the North Area towards the two ProtoDUNEs are also in the scope of this work, with the goal of proposing a neutrino cross section experiment in 2026. The combined use of both the neutrino detectors and of the improved beamline would allow to perform cross section measurements with unprecedented precision in about 5 years with a proton request compatible with the needs of other users after CERN Long Shutdown 3.

hep-ex↗

arXiv2024

Photocathode characterisation for robust PICOSEC Micromegas precise-timing detectors

The PICOSEC Micromegas detector is a~precise-timing gaseous detector based on a~Cherenkov radiator coupled with a~semi-transparent photocathode and a~Micromegas amplifying structure, targeting a~time resolution of tens of picoseconds for minimum ionising particles. Initial single-pad prototypes have demonstrated a~time resolution below 25 ps, prompting ongoing developments to adapt the concept for High Energy Physics applications, where sub-nanosecond precision is essential for event separation, improved track reconstruction and particle identification. The achieved performance is being transferred to robust multi-channel detector modules suitable for large-area detection systems requiring excellent timing precision. To enhance the robustness and stability of the PICOSEC Micromegas detector, research on robust carbon-based photocathodes, including Diamond-Like Carbon (DLC) and Boron Carbide (B4C), is pursued. Results from prototypes equipped with DLC and B4C photocathodes exhibited a~time resolution of approximately 32 ps and 34.5 ps, respectively. Efforts dedicated to improve detector robustness and stability enhance the feasibility of the PICOSEC Micromegas concept for large experiments, ensuring sustained performance while maintaining excellent timing precision.

physics.ins-det↗

arXiv2024

A new upper limit on the axion-photon coupling with an extended CAST run with a Xe-based Micromegas detector

Hypothetical axions provide a compelling explanation for dark matter and could be emitted from the hot solar interior. The CERN Axion Solar Telescope (CAST) has been searching for solar axions via their back conversion to X-ray photons in a 9-T 10-m long magnet directed towards the Sun. We report on an extended run with the IAXO (International Axion Observatory) pathfinder detector, doubling the previous exposure time. The detector was operated with a xenon-based gas mixture for part of the new run, providing technical insights for future detector configurations in IAXO. No counts are detected in the 95% signal-encircling region during the new run, while 0.75 are expected. The new data improve the axion-photon coupling limit to 5.8$\times 10^{-11}\,$GeV$^{-1}$ at 95% C.L. (for $m_a \lesssim 0.02$ eV), the most restrictive experimental limit to date.

hep-ex↗

arXiv2024

An accurate solar axions ray-tracing response of BabyIAXO

BabyIAXO is the intermediate stage of the International Axion Observatory (IAXO) to be hosted at DESY. Its primary goal is the detection of solar axions following the axion helioscope technique. Axions are converted into photons in a large magnet that is pointing to the sun. The resulting X-rays are focused by appropriate X-ray optics and detected by sensitive low-background detectors placed at the focal spot. The aim of this article is to provide an accurate quantitative description of the different components (such as the magnet, optics, and X-ray detectors) involved in the detection of axions. Our efforts have focused on developing robust and integrated software tools to model these helioscope components, enabling future assessments of modifications or upgrades to any part of the IAXO axion helioscope and evaluating the potential impact on the experiment's sensitivity. In this manuscript, we demonstrate the application of these tools by presenting a precise signal calculation and response analysis of BabyIAXO's sensitivity to the axion-photon coupling. Though focusing on the Primakoff solar flux component, our virtual helioscope model can be used to test different production mechanisms, allowing for direct comparisons within a unified framework.

hep-ex↗