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Statistical analysis and correction of the pile-up effect in MAPMT single photoelectron counting with the SPACIROC-3 ASIC: application to the Mini-EUSO experiment
No full textInternational audienceWe present a comprehensive study addressing pile-up effects in single photoelectron counting with R-11265 Hamamatsu multi-anode photomultiplier tubes (MAPMTs) equipped with the SPACIROC-3 ASIC. Extended dead time in the electronics causes saturation and quenching of the counting rate, an effect we counter by inverting the pile-up plot once the double pulse resolution is determined. Our work combines extensive numerical simulations with experimental validations to quantify the statistical uncertainties associated with the corrected event rates. We apply this methodology to the Mini-EUSO experiment onboard the International Space Station where machine learning techniques are employed to extract pixel-by-pixel double pulse resolutions from long-term photon count histograms. This integrated approach enables the accurate recovery of true photon fluxes essential for studying ELVES, meteors and other transient phenomena detected by Mini-EUSO
EMU and Euclid: Detection of a radio-optical galaxy clustering cross-correlation signal between the Evolutionary Map of the Universe and Euclid
No full textInternational audienceSynergies between large-scale radio-continuum and optical/near-infrared galaxy surveys are a powerful tool for cosmology. Cross-correlating these surveys can constrain the redshift distribution of radio sources, mitigate systematic effects, and place constraints on cosmological models. We perform the first measurement of the clustering cross-spectrum between radio-continuum sources in the Evolutionary Map of the Universe (EMU) survey and galaxies from the ESA Euclid satellite mission's Q1 release. Our goal is to detect and characterise the cross-correlation signal, test its robustness against systematic effects, and compare our measurements with theoretical predictions. We use data from the Australian SKA Pathfinder's EMU Main Survey, which overlaps with the Euclid Deep Field South. We generate two radio-source catalogues using different source finders to create galaxy maps. We measure the harmonic-space cross-correlation signal using a pseudo-spectrum estimator. The measured signal is compared to theoretical predictions based on a ΛCDM cosmology, using several models for the EMU source redshift distribution and bias. We report detection above 8σ of the cross-correlation signal consistent across all tested models and data sets. The measured cross-spectra from the two radio catalogues are in excellent agreement, demonstrating that the cross-correlation is robust against the choice of source-finding algorithm. The measured signal also agrees with theoretical models developed from previous cross-correlation studies and simulations. This pathfinder study establishes a statistically significant cross-correlation between EMU and Euclid. The robustness of the signal is a crucial validation of the methodology, paving the way for future large-scale analyses leveraging the full power of this synergy to constrain cosmological parameters and our understanding of galaxy evolution
The Ongoing Decline in Activity of Comet 103P/Hartley 2
No full textInternational audienceWe report photometric observations of Comet 103P/Hartley 2 during its 2023 apparition. Our campaign, conducted from August through December 2023, combined data from a global network of citizen astronomers coordinated by Unistellar and the Association Française d'Astronomie. Photometry was derived using an automated pipeline for eVscope observations in partnership with the SETI Institute and aperture photometry via AstroLab Stellar. We find that the comet's peak reduced brightness, measured at G min = 10.24 ± 0.47, continues a long-term fading trend since 1991. The decline in activity follows a per-apparition minimum magnitude increase of ∆G min = 0.59 ± 0.11 mag, corresponding to a ∼42% reduction in brightness each return. This trend implies that the comet's active fraction has declined by approximately an order of magnitude since 1991 and may indicate that Hartley 2 is no longer hyperactive by definition. The fading is consistent with progressive volatile depletion rather than orbital effects. These results offer insight into the evolutionary processes shaping Jupiter-family comets
Deep Learning Framework for Enhanced Neutrino Reconstruction of Single-line Events in the ANTARES Telescope
No full textInternational audienceWe present the -fit algorithm designed to improve the reconstruction of neutrino events detected by a single line of the ANTARES underwater telescope, usually associated with low energy neutrino events ( 100 GeV). -Fit is a neural network model that relies on deep learning and combines several advanced techniques in machine learning --deep convolutional layers, mixture density output layers, and transfer learning. This framework divides the reconstruction process into two dedicated branches for each neutrino event topology --tracks and showers-- composed of sub-models for spatial estimation --direction and position-- and energy inference, which later on are combined for event classification. Regarding the direction of single-line events, the -Fit algorithm significantly refines the estimation of the zenithal angle, and delivers reliable azimuthal angle predictions that were previously unattainable with traditional -fit methods. Improving on energy estimation of single-line events is a tall order; -Fit benefits from transfer learning to efficiently integrate key characteristics, such as the estimation of the closest distance from the event to the detector. -Fit also takes advantage from transfer learning in event topology classification by freezing convolutional layers of the pretrained branches. Tests on Monte Carlo simulations and data demonstrate a significant reduction in mean and median absolute errors across all reconstructed parameters. The improvements achieved by -Fit highlight its potential for advancing multimessenger astrophysics and enhancing our ability to probe fundamental physics beyond the Standard Model using single-line events from ANTARES data
Search for higgsinos in compressed mass spectra using low-momentum tracks in collisions at TeV with the ATLAS detector
No full textInternational audienceThis paper presents two searches for the electroweak production of higgsinos with compressed mass spectra using 140 fb of TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider. Events are required to feature an energetic jet, large missing transverse momentum, and at least one low-momentum charged particle that serves as a candidate higgsino decay product. In the first search, targeting higgsino mass splittings in the range of 0.3-1 GeV, the higgsinos are expected to predominantly decay into pions that are identified as low-momentum charged particles with large transverse impact parameters due to the long higgsino lifetime ((0.1-1 mm)). The second search targets larger mass splittings in the range of 1-3 GeV, where the higgsinos are expected to decay promptly into low-momentum leptons, one of which is identified by dedicated low-momentum electron or muon taggers based on neural networks utilising tracking and calorimeter information. No significant excess above the Standard Model prediction is observed in either search and the results are used to set lower limits on the masses of the higgsino-like charginos and neutralinos within a simplified model. Together, these searches exclude chargino masses below 126 GeV at 95% confidence level for mass splittings between the chargino and lightest neutralino in the range of 0.3-2 GeV, representing the first ATLAS constraints in this parameter space and surpassing the limits previously set by the LEP experiments
A group of merging galaxies falling onto Abell 2142
No full textGalaxy clusters produce a very hostile environment to galaxies, whose gas gets stripped by ram-pressure, suffer galaxy interactions and witness quenching of their star formation. Clusters continue their growth not only through galaxy accretion but also through galaxy group infall, such as Abell 2142, directly connected to the cosmic web. Our goal is to study the physical and dynamical state of the most conspicuous infalling group, on a filament projected at 1.3 Mpc from the Abell 2142 center. The galaxy group is the leading edge of a spectacular trailing X-ray tail, 700 kpc in length, of hot gas stripped by ram-pressure. The infalling galaxies are not yet quenched, and they are ideal objects to study the transformation processes due to the cluster environment. We use integral field spectroscopy from MaNGA to derive stellar and gas kinematics, and MegaCam for ugr photometry. Stellar populations (with age and metallicity) are obtained through full-spectrum fitting using Nburst. The gas kinematics and excitation are derived from the line emission of Hα, [NII], [OIII] and Hβ. The group contains four galaxies, of which two are merging, and partly superposing on the line of sight. With a simple parametric model for each velocity field, we succeed in disentangling the contribution of each galaxy, and derive their physical state and kinematics. The galaxies are perturbed and intra-group gas is observed as tidal tails and loops. They are mainly disks in rotation, although some regions reveal elevated dispersion, typical of out of equilibrium gas. All galaxies show sustained star formation, with a global star formation rate of 45 M ⊙ /yr. We conclude that the long X-ray tail must have come from the hot intra-group medium, present before the group infall, and does not correspond to the ram-pressure stripping of the galaxy gas. The galaxy interactions and merging within the group are still enhancing the star formation, from the galaxy disks, which are still rich in dense gas.</div
Sensitivity to low-mass WIMPs with an improved liquid argon ionization response model within the DarkSide programme
No full textInternational audienceDark matter detection experiments using liquid argon rely on a precise characterization of the ionization response to nuclear recoils, especially in the keV energy range relevant for light dark matter interactions. In this work, we present a comprehensive analysis that combines new measurements from the ReD setup, part of the DarkSide experimental program, with calibration data from DarkSide-50, as well as results from the ARIS and SCENE experiments. These combined datasets enable improved constraints on atomic screening effects in the modeling of the ionization response of liquid argon to nuclear recoils. By including the updated ionization model into the DarkSide-50 analysis framework, we obtain stronger exclusion limits on low-mass WIMP interactions, setting new world-leading constraints in the 1-3 GeV/c WIMP mass range. Finally, we recast the sensitivity projections for the upcoming DarkSide-20k detector, demonstrating a significantly enhanced discovery potential for low-mass dark matter candidates
Fast far-sidelobe modeling for centimeter to sub-millimeter astrophysical observations
No full textInternational audienceNext-generation centimeter to sub-millimeter telescopes require exquisite control over instrumental far-sidelobe response to accurately measure faint signals like the Cosmic Microwave Background B modes. Because existing electromagnetic modeling methods are computationally expensive, we developed a novel, diffraction-based beam modeling method for rapid and low-cost calculations. We applied this methodology to model the BICEP3 far-sidelobes and found good qualitative agreement with in situ beam measurements. Using this validated simulated beam, we calculated the sidelobe temperature pickup for a specific observation scenario: scanning near the slopes of Cerro Toco in the Atacama Desert. This rapid, predictive framework is most valuable as a tool for optimizing instrument baffling and identifying efficient scan strategies during the conceptual design phase
Precise Measurement of Cosmic Ray Light and Helium Spectra above 0.1 Peta-electron-Volt
No full textInternational audienceWe report a measurement of the cosmic ray helium energy spectrum in the energy interval 0.16 -- 13 PeV, derived by subtracting the proton spectrum from the light component (proton and helium) spectrum obtained with observations made by the Large High Altitude Air Shower Observatory (LHAASO) under a consistent energy scale. The helium spectrum shows a significant hardening centered at 1.1 PeV, followed by a softening at 7 PeV, indicating the appearance of a helium `knee'. Comparing the proton and helium spectra in the LHAASO energy range reveals some remarkable facts. In the lower part of this range, in contrast to the behavior at lower energies, the helium spectrum is significantly softer than the proton spectrum. This results in protons overtaking helium nuclei and becoming the largest cosmic ray component at 0.7 PeV. A second crossing of the two spectra is observed at 5 PeV, above the proton knee, when helium nuclei overtake protons to become the largest cosmic ray component again. These results have important implications for our understanding of the Galactic cosmic ray sources
Supersymmetry Breaking with Fields, Strings and Branes
No full textInternational audienceThe first part of this review tries to provide a self-contained view of supersymmetry breaking from the bottom-up perspective. We thus describe N=1 supersymmetry in four dimensions, the Standard Model and the MSSM, with emphasis on the ``soft terms'' that can link it to supergravity. The second part deals with the top-down perspective. It addresses, insofar as possible in a self-contained way, the basic setup provided by ten-dimensional strings and their links with supergravity, toroidal orbifolds, Scherk-Schwarz deformations and Calabi-Yau reductions, before focusing on a line of developments that is closely linked to our own research. Its key input is drawn from ten-dimensional non-tachyonic string models where supersymmetry is absent or non-linearly realized, and runaway ``tadpole potentials'' deform the ten-dimensional Minkowski vacua. We illustrate the perturbative stability of the resulting most symmetrical setups, which are the counterparts of circle reduction but involve internal intervals. We then turn to a discussion of fluxes in Calabi-Yau vacua and the KKLT setup, and conclude with some aspects of Cosmology, emphasizing some intriguing clues that the tadpole potentials can provide for the onset of inflation. The appendices collect some useful material on global and local N=1 supersymmetry, in components and in superspace, on string vacuum amplitudes, and on convenient tools used to examine the fluctuations of non-supersymmetric string vacua