HAL Mines Nantes
Not a member yet
7271 research outputs found
Sort by
QED corrections to the thermal neutrino interaction rate
No full textInternational audienceMotivated by precision computations of neutrino decoupling at MeV temperatures, we show how QED corrections to the thermal neutrino interaction rate can be related to the electron-positron spectral function as well as an effective vertex. The spectral function is needed both in a timelike and in a spacelike domain, and for both of its physical polarization states (transverse and longitudinal with respect to spatial momentum). Incorporating an NLO evaluation of this spectral function, an estimate of the vertex, and HTL resummation of scatterings mediated by soft Bose-enhanced -channel photons, we compute the interaction rate as a function of the neutrino momentum and flavour. Effects on the level are found, noticeably smaller than a previous estimate of a related quantity
Perspectives of a single-anode cylindrical chamber operating in ionization mode and high gas pressure
No full textInternational audienceAs part of the R2D2 (Rare Decays with Radial Detector) R&D, the use of a gas detector with a spherical or cylindrical cathode, equipped with a single anode and operating at high pressure, was studied for the search of rare phenomena such as neutrinoless double-beta decay. The presented measurements were obtained with a cylindrical detector, covering gas pressures ranging from 1 to 10 bar in argon and 1 to 6 bar in xenon, using both a point-like source of Po (5.3 MeV ) and a diffuse source of Rn (5.5 MeV ). Analysis and interpretation of the data were developed using the anodic current waveform. Similar detection performances were achieved with both gases, and comparable energy resolutions were measured with both sources. As long as the purity of the gas was sufficient, no significant degradation of the measured energy was observed by increasing the pressure. At the highest operating pressure, an energy resolution better than 1.5% full-width at half-maximum (FWHM) was obtained for both gaseous media, although optimal noise conditions were not reached
Assessing the chronic effect of the bioavailable fractions of radionuclides and heavy metals on stream microbial communities: A case study at the Rophin mining site
No full textInternational audienceThis study aimed to assess the potential impact of long-term chronic exposure (69 years) to naturally-occurring radionuclides (RNs) and heavy metals on microbial communities in sediment from a stream flowing through a watershed impacted by an ancient mining site (Rophin, France). Four sediment samples were collected along a radioactivity gradient (for 238U368 to 1710 Bq.Kg−1) characterized for the presence of the bioavailable fractions of radionuclides (226Ra, 210Po), and trace metal elements (Th, U, As, Pb, Cu, Zn, Fe).Results revealed that the available fraction of contaminants was significant although it varied considerably from one element to another (0 % for As and Th, 5–59 % for U). Nonetheless, microbial communities appeared significantly affected by such chronic exposure to (radio)toxicities. Several microbial functions carried by bacteria and related with carbon and nitrogen cycling have been impaired. The high values of fungal diversity and richness observed with increasing downstream contamination (H′ = 4.4 and Chao1 = 863) suggest that the community had likely shifted toward a more adapted/tolerant one as evidenced, for example, by the presence of the species Thelephora sp. and Tomentella sp. The bacterial composition was also affected by the contaminants with enrichment in Myxococcales, Acidovorax or Nostocales at the most contaminated points.Changes in microbial composition and functional structure were directly related to radionuclide and heavy metal contaminations, but also to organic matter which also significantly affected, directly or indirectly, bacterial and fungal compositions. Although it was not possible to distinguish the specific effects of RNs from heavy metals on microbial communities, it is essential to continue studies considering the available fraction of elements, which is the only one able to interact with microorganisms
System-size dependence of the hadronic rescattering effect at energies available at the CERN Large Hadron Collider
No full textInternational audienceThe first measurements of K*(892)0 resonance production as a function of charged-particle multiplicity in Xe-Xe collisions at sNN=5.44 TeV and pp collisions ats=5.02 TeV using the ALICE detector are presented. The resonance is reconstructed at midrapidity (|y| < 0.5) using the hadronic decay channel K*0 →K±π∓. Measurements of transverse-momentum integrated yield, mean transverse-momentum, nuclear modification factor of K*0, and yield ratios of resonance to stable hadron (K*0/K) are compared across different collision systems (pp, p-Pb, Xe-Xe, and Pb-Pb) at similar collision energies to investigate how the production of K*0 resonances depends on the size of the system formed in these collisions. The hadronic rescattering effect is found to be independent of the size of colliding systems and mainly driven by the produced charged-particle multiplicity, which is a proxy of the volume of produced matter at the chemical freeze-out. In addition, the production yields of K*0 in Xe-Xe collisions are utilized to constrain the dependence of the kinetic freeze-out temperature on the system size using the hadron resonance gas–partial chemical equilibrium model
Measurement of (anti)alpha production in central Pb-Pb collisions at = 5.02 TeV
No full textInternational audienceIn this letter, measurements of (anti)alpha production in central (010%) PbPb collisions at a center-of-mass energy per nucleonnucleon pair of = 5.02 TeV are presented, including the first measurement of an antialpha transverse-momentum spectrum. Owing to its large mass, (anti)alpha production yields and transverse-momentum spectra are of particular interest because they provide a stringent test of particle production models. The averaged antialpha and alpha spectrum is included into a common blast-wave fit with lighter particles, indicating that the (anti)alpha also participates in the collective expansion of the medium created in the collision. A blast-wave fit including only protons, (anti)alpha, and other light nuclei results in a similar flow velocity as the fit that includes all particles. A similar flow velocity, but a significantly larger kinetic freeze-out temperature is obtained when only protons and light nuclei are included in the fit. The coalescence parameter is well described by calculations from a statistical hadronization model but significantly underestimated by calculations assuming nucleus formation via coalescence of nucleons. Similarly, the (anti)alpha-to-proton ratio is well described by the statistical hadronization model. On the other hand, coalescence calculations including approaches with different implementations of the (anti)alpha substructure tend to underestimate the data
gSeaGen code by KM3NeT: an efficient tool to propagate muons simulated with CORSIKA
No full textInternational audienceThe KM3NeT Collaboration has tackled a common challenge faced by the astroparticle physics community, namely adapting the experiment-specific simulation software to work with the CORSIKA air shower simulation output. The proposed solution is an extension of the open-source code gSeaGen, allowing for the transport of muons generated by CORSIKA to a detector of any size at an arbitrary depth. The gSeaGen code was not only extended in terms of functionalities but also underwent a thorough redesign of the muon propagation routine, resulting in a more accurate and efficient simulation. This paper presents the capabilities of the new gSeaGen code as well as prospects for further developments
Sensitivity studies of PWR MOX fuel management to the plutonium initial vector using Artificial Neural Networks
No full textInternational audienceThis paper presents new metamodels based on artificial neural networks trained on full core 3D depletion simulations performed with APOLLO2 and CRONOS2. They are used to estimate the irradiation cycle length, discharge burn-up of each fuel assembly type and radial power factor of a PWR loaded with 30% of MOX fuels, as a function of the initial plutonium composition. They allow to explore the impact of the plutonium isotopic vector on the reactor characteristics and can be used for scenarios studied for future fuel cycle. Some exclusion domains in the plutonium isotopic vector phase space are identified as a function of the cycle length. As an example, the potentialities of such fuel management for plutonium recycling from MOX spent fuel are studied
Multimuons in cosmic-ray events as seen in ALICE at the LHC
No full textInternational audienceALICE is a large experiment at the CERN Large Hadron Collider. Located 52 meters underground, its detectors are suitable to measure muons produced by cosmic-ray interactions in the atmosphere. In this paper, the studies of the cosmic muons registered by ALICE during Run 2 (2015--2018) are described. The analysis is limited to multimuon events defined as events with more than four detected muons () and in the zenith angle range ) obtained with QGSJET and SIBYLL is compatible with the data, while EPOS-LHC produces a significantly lower rate ( of the measured rate). For both QGSJET and SIBYLL, the rate is close to the data when the composition is assumed to be dominated by heavy elements, an outcome compatible with the average energy ~eV of these events. This result places significant constraints on more exotic production mechanisms
Physique des neutrinos avec les expériences SuperNEMO et SoLid
No full textThe Standard Model of particle physics describes elementary particles and their interactions with remarkable precision. Among these are neutrinos, leptons that exist in three flavors: electron, muon, and tau. Lacking an electric charge, neutrinos interact only through the weak interaction, making them very difficult to study. Certain properties of neutrinos, such as their extremely low mass or the possible indistinction between neutrinos and antineutrinos according to Majorana's theory, challenge the Standard Model. Flavor oscillations, where a neutrino changes type during its propagation, are also not fully explained by this model. It is also possible that a sterile neutrino, insensitive to all interactions described by the model, exists.The research presented in this Habilitation à Diriger des Recherches first focuses on the Majorana nature of the neutrino, with the study of neutrinoless double beta decay. The SuperNEMO experiment analyzes the decays of the 82-Se isotope at the Modane Underground Laboratory. A tracking detector reconstructs the emitted electrons, and a segmented calorimeter measures their energies. We will present the characteristics of the SuperNEMO demonstrator, its construction, and the initial performances of its calorimeter.Secondly, this habilitation addresses the search for a sterile neutrino at short range from a nuclear reactor, which could explain the observed anti-neutrino deficit compared to predictions. The SoLid experiment, conducted near the BR2 reactor in Mol, Belgium, seeks a signal of anti-neutrino oscillation. Thanks to its fine segmentation and hybrid use of scintillators, it actively mitigates background noise from atmospheric and natural radioactivity. We will present the motivations behind SoLid, its experimental principle, energy calibration, and its initial results.Le Modèle Standard de la physique des particules décrit avec une précision remarquable les particules élémentaires et leurs interactions. Parmi celles-ci, on trouve les neutrinos, des leptons qui existent sous trois saveurs : électron, muon et tau. Ne possédant pas de charge électrique, les neutrinos n'interagissent qu'à travers l'interaction faible, ce qui les rend très difficiles à étudier. Certaines propriétés des neutrinos, comme leur faible masse ou la possible indistinction entre neutrinos et antineutrinos selon la théorie de Majorana, défient le Modèle Standard. Les oscillations de saveurs, où un neutrino change de type durant sa propagation, ne sont pas entièrement expliquées dans ce modèle. Il est aussi possible qu'un neutrino stérile, insensible à toutes les interactions du modèle, existe.Les recherches présentées dans cette Habilitation à diriger des recherches concernent d'abord la nature Majorana du neutrino, avec l'étude de la double désintégration bêta sans émission de neutrinos. L'expérience SuperNEMO analyse les désintégrations de l'isotope 82-Se au Laboratoire Souterrain de Modane. Un détecteur de traces permet de reconstruire les électrons émis, et un calorimètre segmenté mesure leurs énergies. Nous présenterons les caractéristiques du démonstrateur SuperNEMO, sa construction et les premières performances de son calorimètre.Deuxièmement, cette habilitation aborde la recherche du neutrino stérile à courte distance d'un réacteur nucléaire, pouvant expliquer le déficit d'anti-neutrinos observé par rapport au prédictions. L’expérience SoLid, menée près du réacteur BR2 à Mol, en Belgique, cherche un signal d'oscillation d'anti-neutrinos. Grâce à sa fine segmentation et à l'utilisation hybride de scintillateurs, elle lutte contre les bruits de fond atmosphériques et radioactifs. Nous présenterons les motivations de SoLid, son principe expérimental, la calibration en énergie et ses premiers résultats
