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Measurement of differential -channel single top (anti)quark production cross-sections at 13 TeV with the ATLAS detector
No full textInternational audienceThe production of single top quarks and top antiquarks via the -channel exchange of a virtual boson is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider. The full Run 2 data sample recorded with the ATLAS detector in the years 2015-2018 is used, corresponding to an integrated luminosity of 140 fb. The absolute and normalised production cross-sections are measured differentially as a function of the transverse momentum and absolute rapidity of the top quark and top antiquark. In addition, the ratio of top quark to top antiquark production cross-sections is measured. The measured distributions are compared with next-to-leading-order quantum chromodynamics predictions obtained with different combinations of matrix-element generators, parton-shower programs and proton parton distribution functions, as well as to next-to-next-to-leading-order calculations. Overall, good agreement is observed between the measurements and the theoretical predictions. For most measured distributions, the sensitivity to differences between the predictions is limited by the systematic uncertainties in the measurement. The measured differential distributions are also interpreted in an effective field theory approach to constrain the Wilson-Coefficient associated with a four-quark operator. The interpretation accounts for the effect of the selection efficiency, which is altered significantly by non-zero contributions from
The MeerKLASS UHF On-the-Fly Continuum Survey -- Data Release I
No full textInternational audienceWe present the first public data release (DR1) from the interferometric component of the MeerKAT Large Area Synoptic Survey (MeerKLASS) UHF survey, a legacy program demonstrating a novel on-the-fly (OTF) mapping technique. This release is based on 12 hours of early science observations covering approximately 800 deg of the southern sky. We describe the data processing pipeline developed to calibrate and image these fast-scanning observations, producing high-fidelity continuum images at a central frequency of 816 MHz. The resulting mosaic reaches an RMS sensitivity of 35 Jy beam in its deepest regions, with a typical angular resolution of . In these images, we identify radio sources. We validate the catalogue through cross-matching with external surveys, confirming sub-arcsecond astrometric accuracy and a robust flux density scale. We compute the differential source counts, finding excellent agreement with existing measurements and validating our end-to-end processing. The success of this pilot study serves as a crucial proof of concept for the OTF observing strategy, and the public release of the images and source catalogue provides a valuable resource for a wide range of astrophysical studies. This work paves the way for the full MeerKLASS OTF survey and future large-area survey projects with the SKA
The MeerKLASS On-the-Fly continuum survey: pipeline design and validation
No full textInternational audienceThe MeerKAT Large Area Synoptic Survey (MeerKLASS) is designed to map large areas of the Southern sky for cosmology using the single-dish HI intensity mapping (IM) technique, while simultaneously delivering a wide, high angular-resolution interferometric survey. We present the design and first results of the MeerKLASS On-the-Fly (OTF) continuum data, which exploits the visibilities recorded during fast, constant-elevation scans. This observing mode enables fast commensal imaging over several hundred of square degrees on a nightly basis. We describe the OTF survey strategy and pipeline, focusing on handling challenges introduced by the current MeerKAT fixed-delay correlation observing mode, which causes decorrelation (smearing). We implement a correction scheme based on time-dependent phase rotation, direction-dependent PSF modeling, and wide-band faceted deconvolution with \texttt{DDFacet}. Using UHF-band and pilot L-band data, we demonstrate the recovery of high-quality 2-second snapshot images and deep mosaics over hundreds of square degrees. After smearing correction we are able to achieve a resolution of arcsec and arcsec with an rms sensitivity of and in the UHF and L-band respectively. The full survey will cover at 544-1088 MHz, and after the delay tracking fix implemented we expect to reach at arcsec resolution. The continuum OTF data products will support diverse science goals, including galaxy and AGN evolution, diffuse cluster emission, large-scale structure and cosmology, rotation-measure synthesis, and transient searches. MeerKLASS-OTF thus establishes an efficient path to wide-area commensal surveys with MeerKAT and provides a key technical precursor for SKA-Mid
Searching for Cosmological Collider in the Planck CMB Data II: collider templates and Modal analysis
No full textInternational audienceSignatures of massive particles during inflation are highly informative targets for cosmological experiments. With recent progress on both theoretical and observational frontiers, we have reached the point where these novel signals of primordial non-Gaussianities (PNG) can be systematically tested with increasingly precise data. In this paper, we present the results of improved CMB data analysis for cosmological collider signals using Planck CMB data. To set the stage, we first construct a set of simplified but characteristic collider templates which are accurate over a broad range of particle masses, spins and sound speeds. In order to break degeneracies with single-field PNG, we propose an orthogonalization scheme such that the collider templates are uncorrelated with the highly constrained equilateral and orthogonal shapes. On this basis, we deploy the Modal bispectrum estimator for the Planck analysis and perform a systematic scan of parameters to search for the most significant collider signal. The maximum signal-to-noise ratio is found to be for massive spin-0 exchange after taking into account the look-elsewhere effect. In addition, we cross-validate the Modal analysis with the CMB-BEST pipeline, which demonstrates the consistency of results across the benchmark examples of collider templates. Given the low signal-to-noise ratio regime we find at the current stage of PNG observations, we believe the orthogonalization procedure provides an optimized strategy for future tests of the cosmological collider with the ability to rule out single field inflation
Ultramafic float rocks at Jezero crater (Mars): excavation of lower crustal rocks or mantle peridotites by impact cratering?
No full textInternational audienceBased on observation and data from meteorites and in situ scientific missions, experiments as well as models, the Martian mantle is assumed to share some compositional and mineralogical affinity with the terrestrial mantle. However, there might be subtle differences like the Martian mantle being more ferroan. Yet, we do not have any direct analysis of a Martian mantle rock to confirm this assumption. NASA’s Perseverance rover found olivine-rich boulder-sized float rocks on the upper Jezero fan (Mars). These boulders have an ultramafic composition and their mineralogy is dominantly composed of Fo73±3 olivine with high-Mg orthopyroxene, Cr-rich Ti-Fe oxides and minor plagioclase and high-Ca pyroxene. Microtextural and petrological analysis reveals that these minerals crystallized at equilibrium. In addition, these boulders are different from all the bedrocks analyzed by Perseverance along its traverse which are crustal igneous rocks and sediments. Comparing our data to Martian meteorites and available Mars bulk silicate models (BSM), we discuss that these boulders could represent primitive melts and/or lower crustal material, and we specifically hypothesize that they could be mantle peridotites. We propose that these putative mantle rocks could have been excavated by the succession of impacts from the shallow mantle or lower crust in the Isidis region where Jezero crater is located. These olivine-rich boulders could thereby constitute the first direct analysis of a Martian mantle rock
Multi-messenger observations of binary neutron star mergers: synergies between the next generation gravitational wave interferometers and wide-field, high-multiplex spectroscopic facilities
No full textInternational audienceThird-generation gravitational wave (GW) observatories such as the Einstein Telescope (ET) and Cosmic Explorer (CE) will detect hundreds of thousands of binary neutron star (BNS) mergers, reaching redshifts beyond . To fully exploit joint GW and electromagnetic (EM) detections, dedicated strategies and adapted EM facilities are essential. We investigate the role of Integral Field and Multi-Object Spectroscopy (IFS and MOS) with the Wide-field Spectroscopic Telescope (WST) on next generation GW multi-messenger (MM) observations. We consider simulations of BNS populations, their GW detections with ET(+CE), and their EM counterparts: kilonovae (KNe) and gamma-ray bursts (GRBs). We consider two strategies: one in synergy with wide-field photometric surveys, and a galaxy-targeted one exploiting WST high multiplexing. We estimate the number of galaxies in GW error volumes, and identify observational challenges and mitigation strategies. We find that WST can detect KNe up to and , and GRB afterglows beyond for . KN observations are best scheduled 12-24 hours post-merger. For poorly localised GRBs, WST IFS can aid the identification. Mini-IFUs and galaxy catalogues complete to are key to EM counterpart detection. Even at low , the number of galaxies can be huge-thousands at , tens of thousands at . Events at with localisation deg are golden cases for WST, requiring few exposures to target all galaxies. Detecting and characterising EM counterparts of BNS detected in the extended volume explored by next-generation interferometers will be challenging. We show that high-sensitivity, wide-field, high-multiplex spectroscopic facilities are powerful instruments to fully exploit the new multi-messenger science opportunities enabled by next generation GW detectors
SKA-Low simulations for a cosmic dawn/epoch of reionisation deep field
No full textInternational audienceWe present a realistic simulation of an SKA-Low cosmic dawn/epoch of reionisation (CD/EoR) observation, which can be used to further the development of foreground-mitigation approaches. The simulation corresponds to a deep (1000 h) integration pointing over the 106 MHz-196 MHz frequency range. The sky components include the CD/EoR signal, extragalactic foreground emission featuring strong (over 5 Jy at 150 MHz) out-of-field sources and in-field sources down to 1 microJy at 150 MHz, and Galactic emission from the GSM2016 model complemented with small-scales structure beyond its native deg resolution from a magneto-hydrodynamic simulation of the interstellar medium. Modeled errors include a partial de-mixing of the out-of-field sources, direction-dependent calibration errors leading to residual ionospheric effects, and direction-independent gain calibration errors, on top of thermal noise. Simulated observations are delivered as visibilities as well as imaging products with natural weighting. The true, uncorrupted, CD/EoR signal is also delivered, to allow an assessment of the efficacy of foreground-mitigation approaches. The codes used to generate these simulations are also delivered, so that new simulated datasets can be produced. This simulation has been the basis for the SKA Science Data Challenge 3a (SDC3a), which addressed foreground removal
Simulation of irradiated hybrid planar pixels modules at fluences expected at HL-LHC
No full textInternational audienceSignal loss is the main limitation on tracking/vertexing performance due to radiation damage effect to hybrid pixel detectors when irradiated at fluences expected at High Luminosity LHC (HL-LHC). It is important to have reliable predictions on the charge collection performance after irradiation in order to predict operational voltage values and test tracking algorithms robustness. In this paper the validation of combined TCAD and Monte Carlo simulations of hybrid silicon planar pixels sensors will be presented. In particular different trapping models will be compared to identify the one giving the best predictions. Eventually predictions on the collected charge performance of planar pixels modules at HL-LHC will be discussed
A fast powerful X-ray transient from possible tidal disruption of a white dwarf
No full textInternational audienceStars getting close enough to black holes (BHs) can be torn apart by strong tidal forces, producing electromagnetic flares. To date, more than 100 tidal disruption events (TDEs) have been observed, each involving invariably normal gaseous stars whose debris falls onto the BH, sustaining the flares over years. White dwarfs (WDs), which are the most prevalent compact stars and a million times denser–and therefore tougher–than gaseous stars, can only be disrupted by intermediate-mass black holes (IMBHs) of 102–105 solar masses. WD-TDEs are considered to generate more powerful and short-lived flares, but their evidence has been lacking. Here we report observations of a fast and luminous X-ray transient EP250702a detected by Einstein Probe. Its one-day-long X-ray peak as luminous as 1047-49ergs-1showed strong recurrent flares with hard spectra extending to several tens of MeV gamma-rays, as detected by Fermi/GBM and Konus-Wind, indicating relativistic jet emission. The jet’s X-rays dropped sharply from 3×1049ergs-1 to around 1044ergs-1within 20 days (10 days in the source rest frame). These characteristics are inconsistent with any previously known transient phenomena. We suggest that this fast-evolving event over the unprecedentedly short timescale arises likely from disruption of a WD by an IMBH. At late times, a soft component progressively dominates the X-ray spectrum, reaching a luminosity as high as 1044 erg s−1, which is consistent with being extreme super-Eddington emission from an accretion disk expected to form in an IMBH-WD TDE. WD-TDEs open a new window for investigating the elusive IMBHs and their surrounding stellar environments, and they are prime sources of gravitational waves in the band of space-based interferometers
Possible favored great oxidation event scenario on exoplanets around M-stars with the example of TRAPPIST-1e
No full textInternational audienceThe Great Oxidation Event (GOE), which marked the transition from an anoxic to an oxygenated atmosphere, occurred 2.4 billion years ago on Earth, several hundreds of millions of years after the emergence of oxygenic photosynthesis. This long delay implies that specific conditions in terms of biomass productivity and burial were necessary to trigger the GOE. It could be a limiting factor for the development of oxygenated atmospheres on inhabited exoplanets. In this study, we explore the specificities of a terrestrial planet in the habitable zone of an M dwarf for a GOE. Using a 1D coupled photochemical-climate model, we simulate the atmospheric evolution of TRAPPIST-1e, an Earth-like exoplanet, exploring the effect of oxygen sources (biotic or abiotic). Our results show that the stellar energy distribution promotes O[Formula: see text] production at lower O[Formula: see text] concentrations compared to Earth, and the ozone layer on TRAPPIST-1e forms more efficiently. This lowers the threshold for atmospheric oxidation, suggesting that the GOE on TRAPPIST-1e would occur quickly after the rise of oxygenic photosynthesis, up to 1Gyrs earlier than on Earth, and would reach O[Formula: see text] enabling oxygenic respiration and thus the development of animals. We may question whether this is a general behavior around several M-stars. Furthermore, we discuss how the overproduction of ozone could make O[Formula: see text] detection possible using the James Webb Space Telescope, providing a potential method to observe oxygenation signatures on exoplanets in the near future. Previous studies predicted that for an Earth-like atmosphere O[Formula: see text] would require over 150 transits for detection, but our results show that significantly fewer transits could be needed