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Measurements of and productions in collisions at TeV with the ATLAS detector
No full textInternational audienceThis article presents measurements of boson pair production cross-sections at a center-of-mass energy of TeV, using 140 fb of proton-proton data collected with the ATLAS detector at the Large Hadron Collider. The analysis includes both inclusive production and production in association with two jets (), where one boson decays into a pair of charged leptons (), and the other decays into a neutrino pair. The measured fiducial cross-section of the inclusive production is fb, while for the production it is fb. Extrapolation of the cross-section to the full phase space, for bosons within the mass range ~GeV, yields pb. Differential cross-sections are presented for an extended set of kinematic observables. The results are found to be in good agreement with Standard Model predictions. Constraints on anomalous gauge boson self-interactions are derived using both the vertex function formalism and the effective field theory framework
Fast gas heating and peculiarities of temperature measurements by optical emission spectroscopy in nanosecond surface dielectric barrier discharge
No full textInternational audienceThe aim of this work is the experimental and theoretical study of nanosecond Surface dielectric barrier discharge (SDBD) parameters in atmospheric pressure air. Measurements of electric current and delivered energy, ICCD images of the discharge at all stages of its evolution, and gas heating in the discharge and near afterglow are performed. The paper presents the results of 2D numerical modeling of the nanosecond SDBD. The results of the calculations are compared with measured data on the dynamics of current, energy input and gas heating. Special attention is paid to the study of the spatial structure of the discharge, in particular, to the distribution of gas temperature and the second positive system emission intensity in the direction perpendicular to the surface of the dielectric. It is shown that the results of temperature measurements in SDBD using optical emission spectroscopy technique are severely influenced by this spatial structure. The parameters of a probe discharge of smaller amplitude, which is formed by a reflected pulse 500 ns after the main discharge, are also calculated. The possibility of using the second diagnostic pulse to measure the gas temperature in the afterglow discharge is discussed
LHAASO Detection of Ultra-High-Energy Gamma-Ray Emission toward the Giant Molecular Clouds
No full textInternational audienceThe -ray from Giant molecular clouds (GMCs) is regarded as the most ideal tool to perform in-situ measurement of cosmic ray (CR) density and spectra in our Galaxy. We report the first detection of -ray emissions in the very-high-energy (VHE) domain from the five nearby GMCs with a stacking analysis based on a 4.5-year -ray observation with the Large High Altitude Air Shower Observatory (LHAASO) experiment. The spectral energy distributions derived from the GMCs are consistent with the expected -ray flux produced via CR interacting with the ISM in the energy interval 1 - 100 TeV. In addition, we investigate the presence of the CR spectral `knee' by introducing a spectral break in the -ray data. While no significant evidence for the CR knee is found, the current KM2A measurements from GMCs strongly favor a proton CR knee located above 0.9 PeV, which is consistent with the latest measurement of the CR spectrum by ground-based experiments
Modeling Jovian Plasma‐Europa Interactions: Innovative Atmosphere and Ionosphere Depiction for JUICE Mission Insights
No full textInternational audienceThe JUpiter ICy moons Explorer (JUICE) mission, launched by the European Space Agency (ESA) in April 2023, aims to explore Jupiter and its icy moons, particularly focusing on Europa, Ganymede, and Callisto. This study uses the Latmos Hybrid Simulation (LatHyS) model to simulate Europa's plasma and field environment, emphasizing the upcoming JUICE flybys in July 2032. The LatHyS model, incorporating a detailed 3D exospheric model and a self‐consistent ionosphere, allows for comprehensive analysis of the moon‐plasma interactions at ion scales. Our simulations, validated against Galileo's E4 flyby data, demonstrate the model's accuracy in reproducing key features of the plasma environment and ionospheric dynamics. To characterize the system's response to neutral/ionospheric environment assumptions, we compare three simulations, with different neutral and ionosphere impacts, revealing the ionosphere's influence on the magnetic field intensity. Using an atmosphere derived from a planetary exosphere simulation model like EGM allows for the consideration of various asymmetries and multiple major neutral species, supporting further studies on ionospheric ion dynamics. Results highlight the complex interactions influenced by Europa's neutral and ionospheric conditions, providing insights for the anticipated JUICE observations. The measured signatures primarily depend on the interactions with the ionosphere along the spacecraft's trajectory and simulations show that a dense ionosphere deduced from radio occultation observations cannot reproduce the observed in situ signatures. The exosphere being a source for planetary ions, it was shown that it is significant to consider the spatial asymmetries in global interaction models in order to better account for its impact on the system
Dynamical Tidal Response of Schwarzschild Black Holes
No full textInternational audienceDynamical Love numbers capture the conservative response of an object to a time-dependent external tidal gravitational field. We compute the dynamical Love numbers of Schwarzschild black holes in general relativity within a point-particle effective field theory framework. In addition to the known logarithmic running, we compute the finite scheme-dependent contributions to the Love number couplings. We do this by matching the renormalized one-point function in the effective theory to the classical field profile computed in general relativity. On the general relativity side, we solve the Regge-Wheeler and Zerilli equations perturbatively in a small frequency expansion. In order to match on the effective field theory side we include gravitational interactions using the Born series and employ dimensional regularization to obtain a renormalized field profile
Atmospheric sounding using Earth-based occultations
No full textInternational audienceThe observation of Earth-based stellar occultations by solar system planets and satellites has been used for decades to retrieve information on the physical properties of their atmospheres. From the variations of the stellar flux during ingress and egress and, in some favourable cases, from the central flash, one can infer the vertical density, pressure and temperature profiles around the half-light level (typically in the range of a few μbars), as well as zonal wind regimes and the presence of hazes. Earth-based occultations have been successfully applied to all planets and satellites surrounded by an atmosphere, and have delivered unique and significant information that are often complementary to the results obtained by planetary space missions. The great improvement of the stellar catalogues provided by the Gaia astrometric space mission has drastically enlarged the capabilities of the stellar occultation method, which appears especially promising for probing the tenuous atmospheres of distant objects of the solar system. This article is part of the theme issue ‘Major advances in planetary sciences thanks to stellar occultations’
Spectral survey of the diffuse gas toward BL Lac in the <i>Q</i> band
No full textInternational audienceContext. The chemical composition of diffuse interstellar clouds is not fully established. They host an active chemistry despite their relatively low density and the ubiquitous presence of far-UV radiation. Aims. To further explore the chemical composition of diffuse clouds, we performed a spectral scan toward the bright radio source BL Lac in the Q band (from 32 to 50 GHz) using the Yebes 40 m telescope. Methods. Yebes observations were performed interleaving frequency switching and position switching integrations toward BL Lac, using a spectral resolution of 38 kHz. The data were reduced with the CLASS software. Results. We achieved an unprecedented sensitivity on the continuum of 0.02-0.07%, allowing for the detection of very faint absorption features. We confirm previous detections of HCS + , C 3 H, C 3 H + , CH 3 CN, and HC 3 N in diffuse clouds and report new detections of CCS, C 4 H, CH 3 CHO, H 2 CCO, HNCO, and H 2 CS along the line of sight to BL Lac, with abundances relative to H 2 from a few 10 -11 to a few 10 -10 . We compiled molecular detections toward diffuse clouds to obtain the chemical inventory of a typical diffuse interstellar cloud.Conclusions. The chemical inventory of diffuse interstellar clouds includes complex organic species with up to four heavy atoms. These species are efficiently formed in the diffuse interstellar gas and reach abundances similar to those measured in dense photodissociation regions, pointing to similar gas-phase chemical processes.</div
Differential cross-section measurements of coherent production of singly and doubly resonant top-quark in events with one lepton at = 13 TeV with the ATLAS detector
No full textInternational audienceThis paper presents differential cross-section measurements of events containing a charged lepton, missing transverse momentum, two -jets, and two light jets, consistent with the final state. The analysis is based on 140 fb of proton-proton collision data at = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider (2015-2018). Differential cross-sections are unfolded at particle level for a range of kinematic observables and in three kinematic regions. Both regions and observables are optimised for sensitivity to the interference between produced with singly and doubly resonant top quarks. Results are compared with various theoretical predictions. Significant discrepancies are observed in regions sensitive to the interference between singly and doubly resonant top-quark production. The unfolded results provide new information about the modelling of interference and off-shell effects of the final state, improving the understanding of top-quark production mechanisms and providing new inputs for future Monte Carlo generator development
Modeling of N2-H2 DC discharges for ammonia production
No full textInternational audienceIn this work we present the on-going validation of a kinetic model for nitrogen-hydrogen plasmas, highlighting the significance of plasma-surface interactions in ammonia production
Constraining the TeV gamma-ray emission of SN 2024bch, a possible type IIn-L from a red supergiant progenitor - Multiwavelength observations and analysis of the progenitor
No full textInternational audienceWe present very high-energy optical photometry and spectroscopic observations of SN 2024bch in the nearby galaxy NGC 3206 (∼20 Mpc). We used gamma-ray observations performed with the first Large-Sized Telescope (LST-1) of the Cherenkov Telescope Array Observatory (CTAO) and optical observations with the Liverpool Telescope (LT) combined with data from public repositories to evaluate the general properties of the event and the progenitor star. No significant emission above the LST-1 energy threshold for this observation (∼100 GeV) was detected in the direction of SN 2024bch, and we computed an integral upper limit on the photon flux of Fγ(> 100 GeV)≤3.61 × 10−12 cm−2 s−1 based on six nonconsecutive nights of observations with the LST-1, between 16 and 38 days after the explosion. Employing a general model for the gamma-ray flux emission, we found an upper limit on the mass-loss-rate to wind-velocity ratio of Ṁ/uw ≤ 10−4 M⊙/ yr s/km, although gamma-gamma absorption could potentially have skewed this estimation, effectively weakening our constraint. From spectro-photometric observations we found progenitor parameters of Mpr = 11 – 20 M⊙ and Rpr = 531 ± 125 R⊙. Finally, using archival images from the Hubble Space Telescope, we constrained the luminosity of the progenitor star to log (Lpr/L⊙) ≤ 4.82 and its effective temperature to Tpr ≤ 4000 K. Our results suggest that SN 2024bch is a type IIn-L supernova that originated from a progenitor star consistent with a red supergiant. We show how the correct estimation of the mass-loss history of a supernova will play a major role in future multiwavelength observations.Key words: supernovae: general / supernovae: individual: SN 2024bch / gamma rays: genera