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Jet-like correlations with respect to K and () in pp and Pb-Pb collisions at = 5.02 TeV
No full textInternational audienceTwo-particle correlations with , /, and charged hadrons as trigger particles in the transverse momentum range 8{3 GeV/ as expected from strong in-medium energy loss, while an enhancement develops at low on both the near and away sides, reaching and 2.7 respectively. These findings are in good agreement with previous ALICE measurements from two-particle correlations triggered by neutral pions (–h) and charged hadrons (h–h) in Pb–Pb collisions at TeV. Moreover, the correlations with mesons and / baryons as trigger particles are compared to those of inclusive charged hadrons. The results are compared with the predictions of Monte Carlo models
Neutron emission in ultraperipheral Pb-Pb collisions at = 5.02 TeV
No full textInternational audienceIn ultraperipheral collisions (UPCs) of relativistic nuclei without overlap of nuclear densities, the two nuclei are excited by the Lorentz-contracted Coulomb fields of their collision partners. In these UPCs, the typical nuclear excitation energy is below a few tens of MeV, and a small number of nucleons are emitted in electromagnetic dissociation (EMD) of primary nuclei, in contrast to complete nuclear fragmentation in hadronic interactions. The cross sections of emission of given numbers of neutrons in UPCs of Pb208 nuclei at sNN=5.02 TeV were measured with the neutron zero degree calorimeters (ZDCs) of the ALICE detector at the LHC, exploiting a similar technique to that used in previous studies performed at sNN=2.76 TeV. In addition, the cross sections for the exclusive emission of one, two, three, four, and five forward neutrons in the EMD, not accompanied by the emission of forward protons, and thus mostly corresponding to the production of Pb207,206,205,204,203, respectively, were measured for the first time. The predictions from the available models describe the measured cross sections well. These cross sections can be used for evaluating the impact of secondary nuclei on the LHC components, in particular, on superconducting magnets, and also provide useful input for the design of the Future Circular Collider (FCC-hh)
Measurements of the groomed jet radius and momentum splitting fraction with the soft drop and dynamical grooming algorithms in pp collisions at = 5.02 TeV
No full textInternational audienceThis article presents measurements of the groomed jet radius and momentum splitting fraction in pp collisions at = 5.02 TeV with the ALICE detector at the Large Hadron Collider. Inclusive charged-particle jets are reconstructed at midrapidity using the anti-k algorithm for transverse momentum GeV/c. We report results using two different grooming algorithms: soft drop and, for the first time, dynamical grooming. For each grooming algorithm, a variety of grooming settings are used in order to explore the impact of collinear radiation on these jet substructure observables. These results are compared to perturbative calculations that include resummation of large logarithms at all orders in the strong coupling constant. We find good agreement of the theoretical predictions with the data for all grooming settings considered.[graphic not available: see fulltext
Dosimetric environment and first results of the studies on the physicochemical and biological mechanisms of FLASH hadrontherapy at the ARRONAX cyclotron
No full textInternational audienc
First measurement of <math altimg="si1.svg"><msubsup><mrow><mi mathvariant="normal">Ω</mi></mrow><mrow><mi mathvariant="normal">c</mi></mrow><mrow><mn mathvariant="normal">0</mn></mrow></msubsup></math> production in pp collisions at <math altimg="si2.svg"><msqrt><mrow><mi>s</mi></mrow></msqrt><mo linebreak="goodbreak" linebreakstyle="after">=</mo><mn>13</mn></math> TeV
No full textInternational audienceThe inclusive production of the charm–strange baryon Ωc0 is measured for the first time via its hadronic decay into Ω−π+ at midrapidity (|y|<0.5) in proton–proton (pp) collisions at the centre-of-mass energy s=13 TeV with the ALICE detector at the LHC. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 2<pT<12GeV/c. The pT dependence of the Ωc0-baryon production relative to the prompt D0-meson and to the prompt Ξc0-baryon production is compared to various models that take different hadronisation mechanisms into consideration. In the measured pT interval, the ratio of the pT-integrated cross sections of Ωc0 and prompt Λc+ baryons multiplied by the Ω−π+ branching ratio is found to be larger by a factor of about 20 with a significance of about 4σ when compared to e+e− collisions
Interactions des espèces issues de la radiolyse du milieu eau/NaOH pH ≈ 9 avec le Np (+V) : Spéciation et Hydrolyse
No full textNeptunium (Np) is one of the minor actinides present in the spent fuel from nuclearpower plants. Np is the main species and considered as an ultimate waste, which, in the future, will be stored in a deep geological repository. However, to reduce uncertainties on the reliability of the project, particularly the possibility of infiltration of water into the waste package, further investigations are required. Presence of radionuclides inside the package leads to radiolysis phenomenon, inducing the production of radicals and molecular species. Water and these new formed species can interact with actinides and thus change their chemical behavior (speciation, hydrolysis, complexation…). In this context, the goal of the researches described in this report is to studyfundamentally the impact of radiation (α and γ) on the Np chemistry, especially in alkali medium. First of all, the elaboration of a protocol to prepare Np solutions was developped in order to obtain only one species in solution. The study of water/NaOH pH ≈ 9 solutions radiolysis allowed to determine radiolytic formation yields of H2 and H2O2 for each type of radiation. Comparison of these yields with those obtained with the presence of Np led to deduce redox mechanisms involved in the system. Thus, at low doses ( 10 kGy), Np(+IV) is oxidized to Np (+V). The characterization of these Np species by UV-VIS-Nir, XANES and EXAFS allowed to better understand the role of radiolysis on Np speciation in the conditions of nuclear waste storage.Le Neptunium (Np) est l’un des actinides mineurs présents dans le combustible usé issu des centrales nucléaires. Ce dernier est majoritaire et considéré comme un déchet ultime qui, à l’avenir, sera stocké en couche géologique profonde. Cependant, pour réduire les incertitudes sur la fiabilité du projet, notamment sur la possibilité d’une pénétration de l’eau jusqu’au colis, des investigations semblent nécessaires. La présence de radionucléides au sein des déchets nucléaires conduit à un phénomène de radiolyse provoquant la production d’espèces radicalaires ou moléculaires. L’eau et ces espèces peuvent interagir avec les actinides présents et ainsi jouer sur leurs comportements chimiques (spéciation, hydrolyse, complexation…). Selon ce contexte, le but des travaux de recherche décrits dans ce manuscrit est d’étudier de manière fondamentale, l’impact des rayonnements (γ et α) sur la chimie du Np notamment en milieu alcalin. Tout d’abord, l’élaboration d’un protocole de préparation des solutions de Np a dû être établi afin d’obtenir une seule espèce en solution. Ensuite, l’étude du milieu eau/NaOH pH ≈ 9 a permis de déterminer les rendements radiolytiques en H2 et H2O2 pour chaque type de rayonnement. La comparaison de ces derniers avec ceux obtenus en présence de Np a conduit à la déduction de mecanismes d’oxydo-réduction. Ainsi, à faibles doses (10 kGy), il se réoxyde en Np (+V). Les caractérisations des espèces obtenues par UV-Vis-NIR, XANES et EXAFS sont également menées et permettent de mettre en évidence le rôle de la radiolyse dans la spéciation du Np en conditions de stockage des déchets nucléaires
Structure and Properties of Water in a New Model of the 10-Å Phase: Classical and Ab Initio Atomistic Computational Modeling
No full textInternational audienceThe 10-Å phase is an important member of the family of dense hydrous magnesium silicates (DHMSs) that play a major role in the water budget in the Earth’s upper mantle. Its nominal composition is usually written as Mg3Si4O10(OH)2·xH2O, and its structure is often described as layers of talc with some amount of water present in the interlayer space. However, its actual structure and composition and the detailed mechanisms of retaining H2O molecules within the mineral are not yet sufficiently known. In particular, more recent spectroscopic and diffraction data indicate the presence of Si vacancies in the tetrahedral silicate sheets of the 10-Å phase leading to the formation of Q2-type Si sites terminated by silanol groups. These silanols are, in turn, hydrogen bonded to interlayer H2O molecules. Here, we use classical and ab initio molecular dynamics (MD) simulations to compare the structures and properties of ideal and defect models of the 10-Å phase under ambient conditions. For classical MD simulations, the most recent modification of the ClayFF force field is used, which can accurately account for the bending of Mg–O–H and Si–O–H angles in the mineral layers, including the structural defects. The crystal lattice parameters, elastic constants, structure, and dynamics of the interlayer hydrogen bonding network for the model 10-Å phase are calculated and compared with available experimental data. The results demonstrate that the inclusion of Si vacancies leads to better agreement with crystallographic data, elastic constants, and bulk and shear moduli compared to a simpler model based on the idealized talc structure. The results also clearly illustrate the importance of the explicit inclusion of Mg–O–H and Si–O–H angular bending terms for accurate modeling of the 10-Å phase. In particular, the properly constrained orientation of the silanol groups promotes the formation of strong hydrogen bonds with the interlayer H2O molecules.</jats:p
Inclusive photon production at forward rapidities in pp and p–Pb collisions at TeV
No full textInternational audienceA study of multiplicity and pseudorapidity distributions of inclusive photons measured in pp and p–Pb collisions at a center-of-mass energy per nucleon–nucleon collision of TeV using the ALICE detector in the forward pseudorapidity region 2.3 3.9 is presented. Measurements in p–Pb collisions are reported for two beam configurations in which the directions of the proton and lead ion beam were reversed. The pseudorapidity distributions in p–Pb collisions are obtained for seven centrality classes which are defined based on different event activity estimators, i.e., the charged-particle multiplicity measured at midrapidity as well as the energy deposited in a calorimeter at beam rapidity. The inclusive photon multiplicity distributions for both pp and p–Pb collisions are described by double negative binomial distributions. The pseudorapidity distributions of inclusive photons are compared to those of charged particles at midrapidity in pp collisions and for different centrality classes in p–Pb collisions. The results are compared to predictions from various Monte Carlo event generators. None of the generators considered in this paper reproduces the inclusive photon multiplicity distributions in the reported multiplicity range. The pseudorapidity distributions are, however, better described by the same generators
The C70XP injection line transverse distribution study and impact
No full textInternational audienceThe C70XP is a cyclotron operated for production of radionuclides in nuclear medicine, for research in physics, radio-chemistry and biology. It aims at providing high intensity beams to the various experiment for long or very short time runs. The beam transverse distribution, e,g. homogeneity and emittance, has a great impact on the experiments. The ion source and subsequently the injection line, which can hold 4 types of particles (HH+, D-,He2+ and H-), being the first stage of the accelerator defining the beam, are therefore of particular focus for the beam studies.Thus, a first study of the transverse beam distribution in the injection line has been measured with an Allison-type emittance-meter. Additionally, various simple shape collimators have been used and their impact has been measured in the extraction beam line. These studies have also been combined with multiple magnets tuning simulating various operating mode.A model of the injection line based on G4Beamline has been performed. The experimental and simulation results are given in this paper as well as the on-going studies for a potential future collimator