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High-temperature resistant boron nitride-based coatings for specialty silica optical fibers
No full textInternational audienceh-BN is well known for its thermal stability. h-BN coated silica optical fibers were manufactured. The coating solution is compatible with optical fiber drawing process, which allows the preparation of tens of meter of h-BN coated fibers. In addition, it is possible to use this coating material for the preparation of short length fiber samples in a post-production approach. Bentonite acts as a binder and allows the adhesion of h-BN to the silica optical fiber. The thermal stability of this protected optical fiber has been demonstrated over a short period of time (several hours) up to 900°C and over a long period of time (1500 h) up to 800°C in air. Moreover, the coated optical fiber can resist up to 1000°C in neutral atmosphere (tested over 6 h)
First polarisation measurement of coherently photoproduced J/ in ultra-peripheral PbPb collisions at = 5.02 TeV
No full textInternational audienceThe first measurement of the polarisation of coherently photoproduced J/ mesons in ultra-peripheral PbPb collisions, using data at TeV, is presented. The J/ meson is measured via its dimuon decay channel in the forward rapidity interval using the ALICE detector at the CERN LHC. An event sample corresponding to an integrated luminosity of 750 5% (syst) is analysed. Hadronic activity is highly suppressed since the interaction is mediated by a photon. The polar and azimuthal angle distributions of the decay muons are measured, and the polarisation parameters , , are extracted. The analysis is carried out in the helicity frame. The results are found to be consistent with a transversely polarised J/. These values are compared with previous measurements by the H1 and ZEUS experiments. The polarisation parameters of coherent J/ photoproduction in PbPb collisions are found to be consistent with the -channel helicity conservation hypothesis
Room temperature electron beam sensitive viscoplastic response of ultra-ductile amorphous olivine films
No full textInternational audienceThe mechanical properties of amorphous olivine (a-olivine) deformed at room temperature are investigated in situ in a TEM under uniaxial tension using a Push-to-Pull (PTP) device. Thin films of a-olivine were produced by pulsed laser deposition (PLD). With or without electron irradiation, a-olivine films deform plastically, with a gradual transition that makes impossible the determination of a precise threshold. The strength attains values up to 2.5 GPa. The increasing strain-rate in load control results in an apparent softening with stress drop. The fracture strain reaches values close to 30 % without e-beam irradiation. Under electron illumination at 200 kV, the strength is lower, around 1.7 GPa, while higher elongations close to 36 % are obtained. Alternating beam-off and beam-on sequences lead to exceptionally large fracture strains equal to 68 % at 200 kV and 139 % at 80 kV. EELS measurements were performed to characterize the interaction between the electron beam and a-olivine. At a voltage of 80 kV, radiolysis accompanied by oxygen release dominates whereas at high voltage (300 kV) the interaction is dominated by knock-on type defects. Radiolysis is also the main interaction mechanism at 200 kV with low exposition which corresponds to most of our in situ TEM deformation experiments. To interpret the mechanical data, a simple 1D model has been developed to rationalize the load transfer between the PTP device and the specimen. The strain-rate sensitivity is 6 to 10 times higher when a-olivine is deformed under electron irradiation
A new standard for the logarithmic accuracy of parton showers
No full textInternational audienceWe report on a major milestone in the construction of logarithmically accurate final-state parton showers, achieving next-to-next-to-leading-logarithmic (NNLL) accuracy for the wide class of observables known as event shapes. The key to this advance lies in the identification of the relation between critical NNLL analytic resummation ingredients and their parton-shower counterparts. Our analytic discussion is supplemented with numerical tests of the logarithmic accuracy of three shower variants for more than a dozen distinct event-shape observables in and Higgs decays. The NNLL terms are phenomenologically sizeable, as illustrated in comparisons to data
Impact and mitigation of spectroscopic systematics on DESI DR1 clustering measurements
No full textInternational audienceThe large scale structure catalogs within DESI Data Release 1 (DR1) use nearly 6 million galaxies and quasars as tracers of the large-scale structure of the universe to measure the expansion history with baryon acoustic oscillations and the growth of structure with redshift-space distortions. In order to take advantage of DESI's unprecedented statistical power, we must ensure that the galaxy clustering measurements are unaffected by non-cosmological density fluctuations. One source of spurious fluctuations comes from variation in galaxy density with spectroscopic observing conditions, lowering the redshift efficiency (and thus galaxy density) in certain areas of the sky. We measure the uniformity of the redshift success rate for DESI luminous red galaxies (LRG), bright galaxies (BGS) and quasars (QSO), complementing the detailed discussion of emission line galaxy (ELG) systematics in a companion paper (Yu et al., 2024). We find small but significant fluctuations of up to 3% in redshift success rate with the effective spectroscopic signal-to-noise, and create and describe weights that remove these fluctuations. We also describe the process to identify and remove data from certain poorly performing fibers from DESI DR1, and measure the stability of the redshift success rate with time. Finally, we find small but significant correlations of redshift success rate with position on the focal plane, survey speed, and number of exposures required, and show the impact of weights correcting these trends on the power spectrum multipoles and on cosmological parameters from BAO and RSD fits. These corrections change the best-fit parameters by of their statistical errors, and thus contribute negligibly to the overall DESI error budget
Euclid: Early Release Observations -- Unveiling the morphology of two Milky Way globular clusters out to their periphery
No full textInternational audienceAs part of the Euclid Early Release Observations (ERO) programme, we analyse deep, wide-field imaging from the VIS and NISP instruments of two Milky Way globular clusters (GCs), namely NGC 6254 (M10) and NGC 6397, to look for observational evidence of their dynamical interaction with the Milky Way. We search for such an interaction in the form of structural and morphological features in the clusters' outermost regions, which are suggestive of the development of tidal tails on scales larger than those sampled by the ERO programme. Our multi-band photometric analysis results in deep and well-behaved colour-magnitude diagrams that, in turn, enable an accurate membership selection. The surface brightness profiles built from these samples of member stars are the deepest ever obtained for these two Milky Way GCs, reaching down to mag~arcsec, which is about mag arcsec below the current limit. The investigation of the two-dimensional density map of NGC 6254 reveals an elongated morphology of the cluster peripheries in the direction and with the amplitude predicted by -body simulations of the cluster's dynamical evolution, at high statistical significance. We interpret this as strong evidence for the first detection of tidally induced morphological distortion around this cluster. The density map of NGC 6397 reveals a slightly elliptical morphology, in agreement with previous studies, which requires further investigation on larger scales to be properly interpreted. This ERO project thus demonstrates the power of Euclid in studying the outer regions of GCs at an unprecedented level of detail, thanks to the combination of large field of view, high spatial resolution, and depth enabled by the telescope. Our results highlight the future Euclid survey as the ideal data set to investigate GC tidal tails and stellar streams
A solvable non-unitary fermionic long-range model with extended symmetry
No full textInternational audienceWe define and study a long-range version of the XX model, arising as the free-fermion point of the XXZ-type Haldane-Shastry (HS) chain. It has a simple realisation via non-unitary fermions, based on the free-fermion Temperley-Lieb algebra, and may also be viewed as an alternating spin chain. Even and odd length behave very differently; we focus on odd length. The model is integrable, and we explicitly identify two commuting hamiltonians. While non-unitary, their spectrum is real by PT-symmetry. One hamiltonian is chiral and quadratic in fermions, while the other is parity-invariant and quartic. Their one-particle spectra have two linear branches, realising a massless relativistic dispersion on the lattice. The appropriate fermionic modes arise from 'quasi-translation' symmetry, which replaces ordinary translation symmetry. The model exhibits exclusion statistics, like for the isotropic HS chain, with even more 'extended symmetry' and larger degeneracies
Observation of the -ray Emission from W43 with LHAASO
No full textInternational audienceIn this paper, we report the detection of the very-high-energy (VHE, ) -ray emissions from the direction of the young star-forming region W43, observed by the Large High Altitude Air Shower Observation (LHAASO). The extended -ray source was detected with a significance of by KM2A and by WCDA, respectively. The angular extension of this -ray source is about 0.5 degrees, corresponding to a physical size of about 50 pc. We discuss the origin of the -ray emission and possible cosmic ray acceleration in the W43 region using multi-wavelength data. Our findings suggest that W43 is likely another young star cluster capable of accelerating cosmic rays (CRs) to at least several hundred TeV
Measurement of the inclusive cross sections for W and Z boson production in proton-proton collisions at = 5.02 and 13 TeV
No full textInternational audienceMeasurements of fiducial and total inclusive cross sections for W and Z boson production are presented in proton-proton collisions at = 5.02 and 13 TeV. Electron and muon decay modes ( = e or) are studied in the data collected with the CMS detector in 2017, in dedicated runs with reduced instantaneous luminosity. The data sets correspond to integrated luminosities of 298 6 pb at 5.02 TeV and 206 5 pb at 13 TeV. Measured values of the products of the total inclusive cross sections and the branching fractions at 5.02 TeV are (pp W+X)(W ) = 7300 10 (stat) 60 (syst) 140 (lumi) pb, and (pp Z+X)(Z ) = 669 2 (stat) 6 (syst) 13 (lumi) pb for the dilepton invariant mass in the range of 60-120 GeV. The corresponding results at 13 TeV are 20480 10 (stat) 170 (syst) 470 (lumi) pb and 1952 4 (stat) 18 (syst) 45 (lumi) pb. The measured values agree with cross section calculations at next-to-next-to-leading-order in perturbative quantum chromodynamics. Fiducial and total inclusive cross sections, ratios of cross sections of W and W production as well as inclusive W and Z boson production, and ratios of these measurements at 5.02 and 13 TeV are reported
The M2-M5 Mohawk
No full textInternational audienceWe show that the near-brane back-reaction of M2 branes ending on M5 branes has a rich "spike structure" that is determined by partitioning the numbers of M2 branes that are terminating on groups of M5 branes. The near-brane limit of the metric describing these branes has an AdS factor, implying the existence of a dual CFT. Each partition of the M2 and M5 charges among spikes gives rise to a different "mohawk" revealing a new layer of brane fractionation. We conjecture that all these mohawks are dual to ground states of near-brane-intersection CFT's. We show that the supergravity solutions describing these mohawks are part of the large families of AdS solutions described in [arXiv:1312.5477]. We identify precisely which of these families are relevant to brane intersections and show that the AdS invariance emerges from the self-similarity of the spikes