HAL-CEA
Not a member yet
145450 research outputs found
Sort by
The Lund -jet plane
No full textInternational audienceWe compute the primary Lund plane density for jets initiated by a massive () quark to single logarithmic accuracy in Quantum Chromodynamics (QCD). In order to capture mass effects, we consider quasi-collinear factorisation and we include contributions from the running of the QCD coupling and from collinear evolution, in a variable flavour-number scheme. Furthermore, the resummation of soft logarithms, including clustering effects, is performed numerically, keeping the full dependence on the -quark mass. While our all-order results can be applied to both hadron and lepton colliders, we present, as first phenomenological application, the resummed calculation of the Lund plane density in collisions at , matched to tree-level matrix elements
Cygnus X-3: A variable petaelectronvolt gamma-ray source
No full textInternational audienceWe report the discovery of variable -rays up to petaelectronvolt from Cygnus X-3, an iconic X-ray binary. The -ray signal was detected with a statistical significance of approximately 10 by the Large High Altitude Air Shower Observatory (LHAASO). Its intrinsic spectral energy distribution (SED), extending from 0.06 to 3.7 PeV, shows a pronounced rise toward 1 PeV after accounting for absorption by the cosmic microwave background radiation. The detected month-scale variability,together with a 3.2 evidence for orbital modulation, suggests that the PeV -rays originate within, or in close proximity to, the binary system itself. The observed energy spectrum and temporal modulation can be naturally explained by -ray production through photomeson processes in the innermost region of the relativistic jet, where protons need to be accelerated to tens of PeV energies
Hadron Physics Opportunities at FAIR
No full textInternational audienceThis White Paper outlines a coordinated, decade-spanning programme of hadron and QCD studies anchored at the GSI/FAIR accelerator complex. Profiting from intense deuteron, proton and pion beams coupled with high-rate capable detectors and an international theory effort, the initiative addresses fundamental questions related to the strong interaction featuring confinement and dynamical mass generation. This includes our understanding of hadron-hadron interactions and the composition of hadrons through mapping the baryon and meson spectra, including exotic states, and quantifying hadron structure. This interdisciplinary research connects topics in the fields of nuclear, heavy-ion, and (nuclear) astro (particle) physics, linking, for example, terrestrial data to constraints on neutron star structure. A phased roadmap with SIS100 accelerator start-up and envisaged detector upgrades will yield precision cross sections, transition form factors, in-medium spectral functions, and validated theory inputs. Synergies with external programmes at international accelerator facilities worldwide are anticipated. The programme is expected to deliver decisive advances in our understanding of non-perturbative (strong) QCD and astrophysics, and high-rate detector and data-science technology
Combination of searches for nonresonant Higgs boson pair production in proton-proton collisions at = 13 TeV
No full textInternational audienceThis paper presents a combination of searches for the nonresonant production of Higgs boson pairs (HH) in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data set was collected by the CMS experiment at the LHC from 2016 to 2018 and corresponds to a total integrated luminosity of 138 fb. The observed (expected) upper limit on the inclusive HH production cross section relative to the standard model (SM) prediction is found to be 3.5 (2.5). Assuming all other Higgs boson couplings are equal to their SM values, the Higgs boson trilinear self-coupling modifier is constrained in the range 1.35 6.37 at 95% confidence level. Similarly, for the coupling modifier , which governs the interaction between two vector bosons and two Higgs bosons, we have excluded = 0 at more than 5 standard deviations for all values of . At 95% confidence level assuming other couplings are equal to their SM values, is constrained in the range 0.64 1.40. This work also studies HH production in several new physics scenarios, using the Higgs effective field theory (HEFT) framework. The HEFT framework is further exploited to study various ultraviolet complete models with an extended Higgs sector and set constraints on specific parameters. An extrapolation of the results to the integrated luminosity expected after the high-luminosity upgrade of the LHC is reported as well
Tara Polaris expeditions: Sustained decadal observations of the coupled Arctic system in rapid transition
No full textThe coupled Arctic system is in rapid transition and is set to undergo further dramatic changes over the coming decades. These changes will lead most likely to an ice-free ocean in summer, expected before mid-century. The Arctic will become more strongly influenced by atmospheric and oceanographic processes characteristic of mid-latitudes, increasing the prevalence of contaminants and new biological species. This ongoing transition of the Arctic to a new state necessitates systematic monitoring of all sentinels (variables that make an essential contribution to characterizing the Earth's state) to improve our understanding of the system, enhance forecasting and support knowledge-based decisions. Here, we describe a sustained multi-decadal observation program to be implemented on the Tara Polar Station between 2026 and 2046. The monitoring program is designed as a series of year-long drift expeditions, called Tara Polaris, in the central Arctic Ocean, covering all seasons. The multidisciplinary data will bridge ecological, geochemical, biological, and physical parameters and processes in the atmosphere, sea ice and ocean. In addition, data collected with consistent methodologies over a 20-year period will make it possible to distinguish long-term trends from seasonal and interannual variability. In this paper, we discuss specific measurement challenges in each compartment (i.e., atmosphere, sea ice and ocean) along key sentinels and the most pressing scientific questions to be addressed. The expected outcomes of the Tara Polaris program will enable us to understand and quantify the main feedbacks of the coupled Arctic system, with their seasonal and interannual trends and spatial variability.</div
Stray field NMR: a powerful method to measure dynamics at the millisecond scale
No full textTransport properties in fluids and confined systems play a central role across a wide range of natural and technological contexts, from geology and environmental sciences to biology, energy storage, and membrane-based separation processes. Nuclear Magnetic Resonance (NMR) provides a unique, non-destructive means to probe these properties through speciesselective measurements of self-diffusion coefficients. While pulsed field gradient NMR (PFG-NMR) is routinely used, its access to diffusion times is typically limited to values no shorter than about 10 ms, restricting its applicability to systems with fast dynamics and long relaxation times. Diffusion NMR in a permanent magnetic field gradient (STRAFI) offers a complementary, multiscale approach, enabling diffusion measurements over an extended temporal window, from a few hundred microseconds to several tens of seconds. Despite its strong potential, this technique remains rarely implemented due to experimental and methodological challenges. In this work, we present a robust and versatile STRAFI-based methodology, including a specifically designed experimental setup, optimized pulse sequences, and rigorous data analysis, allowing accurate extraction of self-diffusion coefficients for a broad range of nuclei. The capabilities of the approach are illustrated through diverse applications, including the study of concentrated electrolytes using "NMR-exotic" nuclei ( 35 Cl, 79 Br/ 81 Br, 127 I, 17 O) and the characterization of micrometre-scale porosity in membrane
Hydration mechanisms in Roman seawater concrete: Archaeological analogue for validation of long-term ageing reactive transport model
No full textInternational audienceCement-based materials are considered for sealing plugs in deep geological disposal of radioactive waste. Ensuring their long-term durability is critical for safety over millennia. The Roman Concrete (RoC) project uses ancient Roman underwater concretes as analogues to validate reactive transport models for long-term ageing.This study focuses on hydration mechanisms in Roman concrete made with Phlegrean pozzolan, slaked lime, and seawater. Various techniques (XRD, SEM-EDS, NMR, nanoindentation, microtomography, ICP-OES, ion chromatography) were used to characterize hydration products. Casting underwater led to aragonite and brucite layers with a 60 GPa Young's modulus, protecting the concrete from further degradation. In the core, pozzolanicreactions produce C-(A)-S-H phases (Ca/Si = 1.2; Al/Si = 0.2) with a modulus of 12 GPa. HYTEC modeling confirmed the mechanism: incongruent pozzolan dissolution releases ions (K+, SiO₄ 4− , Al3+, Na+), promoting C-(A)-S-H formation and portlandite consumption
Approaching zero power: the role of the spontaneous fission in CROCUS
No full textInternational audienceIn this paper we investigate the impact of spontaneous fission when approaching zero power in uraniumfueled reactors, taking the CROCUS reactor as a case study. In the regime of very low power (i.e., in the milliwatt range), the contribution of neutrons produced by spontaneous fission from 238 U becomes nonnegligible, and must be included in the neutron balance. Through a series of dedicated experiments, we assess the influence of spontaneous fission on the CROCUS stability conditions, focusing in particular on the water level required to have a stationary neutron flux. Below a certain power threshold, the fission chains become sensitive to the extra neutrons added by spontaneous fission, and a steady state can be only sustained by inserting a negative reactivity. Furthermore, we characterize the effect of spontaneous fission on the axial neutron flux shape, by comparing the profiles obtained at sub-milliwatt and higher-power regimes, combining theoretical predictions with experimental data from a three-dimensional detection array
Traps and radio-frequency characterization of polysilicon layer on high resistivity silicon substrate
No full textInternational audienceIn this work, radio-frequency and traps properties of unintentionally doped polycrystalline silicon (polySi) deposited by low pressure chemical vapor deposition (LPCVD) on high resistivity silicon (HR-Si) substrate are characterized. Both volume (i.e. inside polySi) and interface traps (i.e. near polySi/HR-Si) are detected by photo-induced current transient spectroscopy (PICTS). A thermal budget of 900 ◦C during 2 h is sufficient to observe trap densities reduction near the polySi/HR-Si interface, affecting the RF performance of the fabricated substrates
Inundation flow velocities generated by tropical cyclones across atoll islands, derived from two centuries of megaclast deposits in French Polynesia
No full textInternational audienceUnderstanding potential flow velocities during high-energy marine inundation events is crucial for coastal risk assessment. However, modelling struggles to simulate wave energy dissipation across atoll island coastlines. Here, we examined coral reefblocks transported by past tropical cyclones to calculate the minimum flow velocities (MFVs) responsible. Fieldwork on 6 atolls in the Tuamotu archipelago (South Pacific) examined 196 reefblocks, some megaclasts exceeding 300 cubic metres in size. These blocks are scattered between the oceanside reef edge and the atoll lagoon over several hundred metres and suggest flow velocities much higher than those modelled in an assumed ‘extreme reference scenario’ (HS = 12 m). Through U/Th dating and by studying archives and historical aerial photos, the cyclones that moved these reefblocks were identified. Inundation flows generated by two recent cyclones (March and April 1983), two historical cyclones (1903 AD and 1906 AD) and one prehistorical cyclone (54–80 AD) were calculated (storms with swells 10–18.5 m in height). Calculations reveal that previous modelling underestimates flow velocities across atoll islands (inhabited areas) for two reasons: the underestimation of extreme swell heights and the unaccounted-for degradation of shoreline rubble ramparts. During a supercyclone (HS > 15 m), flows can exceed 3 m/s at 350 m from the reef edge and are capable of transporting 20-ton coral blocks. Findings have a wider significance to tropical coral reef coastlines beyond these atolls studied, where the presence of reefblocks can allow hindcasting of the characteristics of prehistorical cyclone inundations