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Measurement of K(892) production in inelastic pp collisions at the LHC
No full textInternational audienceThe first results on K⁎(892)± resonance production in inelastic pp collisions at LHC energies of s=5.02, 8, and 13 TeV are presented. The K⁎(892)± has been reconstructed via its hadronic decay channel K⁎(892)→±KS0+π± with the ALICE detector. Measurements of transverse momentum distributions, pT-integrated yields, and mean transverse momenta for charged K⁎(892) are found to be consistent with previous ALICE measurements for neutral K⁎(892) within uncertainties. For pT>1 GeV/c the K⁎(892)± transverse momentum spectra become harder with increasing centre-of-mass energy from 5.02 to 13 TeV, similar to what previously observed for charged kaons and pions. For pT<1 GeV/c the K⁎(892)± yield does not evolve significantly and the abundance of K⁎(892)± relative to K is rather independent of the collision energy. The transverse momentum spectra, measured for K⁎(892)± at midrapidity in the interval 0 <pT<15 GeV/c, are not well described by predictions of different versions of PYTHIA 6, PYTHIA 8 and EPOS-LHC event generators. These generators reproduce the measured pT-integrated K⁎±/K ratios and describe well the momentum dependence for pT<2 GeV/c
Production of and in jets in p–Pb collisions at =5.02 TeV and pp collisions at =7 TeV
No full textInternational audienceThe production of Λ baryons and KS0 mesons (V0 particles) was measured in p–Pb collisions at sNN=5.02 TeV and pp collisions at s=7 TeV with ALICE at the LHC. The production of these strange particles is studied separately for particles associated with hard scatterings and the underlying event to shed light on the baryon-to-meson ratio enhancement observed at intermediate transverse momentum (pT) in high multiplicity pp and p–Pb collisions. Hard scatterings are selected on an event-by-event basis with jets reconstructed with the anti-kT algorithm using charged particles. The production of strange particles associated with jets pT,jetch>10 and pT,jetch>20 GeV/c in p–Pb collisions, and with jet pT,jetch>10 GeV/c in pp collisions is reported as a function of pT. Its dependence on angular distance from the jet axis, R(V0,jet), for jets with pT,jetch>10 GeV/c in p–Pb collisions is reported as well. The pT-differential production spectra of strange particles associated with jets are found to be harder compared to that in the underlying event and both differ from the inclusive measurements. In events containing a jet, the density of the V0 particles in the underlying event is found to be larger than the density in the minimum bias events. The Λ/KS0 ratio associated with jets in p–Pb collisions is consistent with the ratio in pp collisions and follows the expectation of jets fragmenting in vacuum. On the other hand, this ratio within jets is consistently lower than the one obtained in the underlying event and it does not show the characteristic enhancement of baryons at intermediate pT often referred to as “baryon anomaly” in the inclusive measurements
Development of a Xe calibration source for nEXO
No full textInternational audienceWe study a possible calibration technique for the nEXO experiment using a Xe electron capture source. nEXO is a next-generation search for neutrinoless double beta decay (0νββ) that will use a 5-tonne, monolithic liquid xenon time projection chamber (TPC). The xenon, used both as source and detection medium, will be enriched to 90% in Xe. To optimize the event reconstruction and energy resolution, calibrations are needed to map the position- and time-dependent detector response. The 36.3 day half-life of Xe and its small Q-value compared to that of Xe 0νββ would allow a small activity to be maintained continuously in the detector during normal operations without introducing additional backgrounds, thereby enabling in-situ calibration and monitoring of the detector response. In this work we describe a process for producing the source and preliminary experimental tests. We then use simulations to project the precision with which such a source could calibrate spatial corrections to the light and charge response of the nEXO TPC
Forward rapidity J/ψ production as a function of charged-particle multiplicity in pp collisions at = 5.02 and 13 TeV
No full textInternational audienceThe production of J/ψ is measured as a function of charged-particle multiplicity at forward rapidity in proton-proton (pp) collisions at center-of-mass energies = 5.02 and 13 TeV. The J/ψ mesons are reconstructed via their decay into dimuons in the rapidity interval (2.5 < y < 4.0), whereas the charged-particle multiplicity density (dN/dη) is measured at midrapidity (|η| < 1). The production rate as a function of multiplicity is reported as the ratio of the yield in a given multiplicity interval to the multiplicity-integrated one. This observable shows a linear increase with charged-particle multiplicity normalized to the corresponding average value for inelastic events (dN/dη/〈dN/dη〉), at both the colliding energies. Measurements are compared with available ALICE results at midrapidity and theoretical model calculations. First measurement of the mean transverse momentum (〈p〉) of J/ψ in pp collisions exhibits an increasing trend as a function of dN/dη/〈dN/dη〉 showing a saturation towards high charged-particle multiplicities.[graphic not available: see fulltext
Implementation and first results of the KM3NeT real-time core-collapse supernova neutrino search
No full textInternational audienceThe KM3NeT research infrastructure is unconstruction in the Mediterranean Sea. KM3NeT will study atmospheric and astrophysical neutrinos with two multi-purpose neutrino detectors, ARCA and ORCA, primarily aimed at GeV–PeV neutrinos. Thanks to the multi-photomultiplier tube design of the digital optical modules, KM3NeT is capable of detecting the neutrino burst from a Galactic or near-Galactic core-collapse supernova. This potential is already exploitable with the first detection units deployed in the sea. This paper describes the real-time implementation of the supernova neutrino search, operating on the two KM3NeT detectors since the first months of 2019. A quasi-online astronomy analysis is introduced to study the time profile of the detected neutrinos for especially significant events. The mechanism of generation and distribution of alerts, as well as the integration into the SNEWS and SNEWS 2.0 global alert systems, are described. The approach for the follow-up of external alerts with a search for a neutrino excess in the archival data is defined. Finally, an overview of the current detector capabilities and a report after the first two years of operation are given
Chemistry and speciation of protactinium – a first principles study
No full textNational audienceIt is of fundamental interest to understand and predict the chemistry of rare radioelements. In this work, we focus on protactinium (Z = 91), an element that is located in between thorium and uranium in the periodic table. It might be considered as an unpredictable actinide, because it be-haves differently than any other actinide and in particular its immediate neighbours. For instance, in solution, the +V oxidation state dominates, and related complexes display a mono-oxo bond (thorium would not while uranium would display trans-di-oxo bonds). For a first study, we start with two series of protactinium(V) complexes of similar nature, that have been already experimentally investigated, and that successively form in sulfuric acid and oxalic acidic media [1-3]. As experimental information, we may rely on the structure of one of the complexes, determined by EXAFS, and on apparent formation constants. Based on this in-formation, research hypotheses and a preliminary methodological study, we aim at revealing the structure and coordination of all the complexes and at defining a computational strategy to derive relative complexation constants (corresponding to ligand-exchange reactions). For instance, if the formed 1:1, 1:2 and 1:3 (Pa:L) complexes all mutually have similar natures, we may simply de-rive the relative complexation constants from the global formation constants of both the relevant complexes. Note that owing to the few available computational studies of protactinium complex-es and to the near degeneracy of the protactinium 5f and 6d shells, this study may prove to be quite challenging.From our computational models, geometry optimizations performed both in the gas phase and in solution lead to a first view on the actual coordination sphere of protactinium(V). It involves an oxygen atom from the Pa=O mono-oxo bond and also oxygen atoms from the bidentate sulfate and oxalate ligands, and in some cases from additional water molecules. The exchange formation constants are deduced and found to be in fair agreement with experiment for the reactions involving two or three bidentate ligands; i.e. when the ligands nearly fill by themselves the coordination sphere.[1]Le Naour C. et al. (2019) Radiochim. Acta, 107, 979-991.[2]Le Naour C. et al. (2005) Inorg. Chem. 44, 9542.[3]Mendes M. et al. (2010) Inorg. Chem. 49, 9962-9971.<br
Total Absorption Spectroscopy of Fission Fragments Relevant for Reactor Physics and Nuclear Structure and Astrophysics
No full textInternational audienceThe accurate determination of reactor antineutrino spectra remains a very hot research topic, where new questions have emerged in recent years. Indeed, after the “reactor anomaly” – a deficit of measured antineutrinos at short baseline reactor experiments with respect to spectral predictions – the three international reactor neutrino experiments Double Chooz, Daya Bay and Reno have evidenced spectral distortions in their measurements with respect to the same spectral predictions. This puzzle is called the “shape anomaly”. Recently summation calculations of reactor antineutrino spectra based on the use of nuclear data have obtained the best agreement to date with the reactor neutrino flux measurements at the level of 2% thanks to a decade of Total Absorption Gamma-ray Spectroscopy (TAGS) measurements at the radioactive beam facility of the University of Jyväskylä in two experimental campaigns. A selection of the results obtained so far is presented
DONJON5/CLASS coupled simulations of MOX/UO heterogeneous PWR core
No full textInternational audienceMost fuel cycle simulation tools are based either on fixed recipes or assembly calculations for reactor modeling. Due to the high number of calculations and extensive computational power requirements, full-core computations are often seen as not viable for this purpose. However, this leads to additional hypotheses and modeling biases, thus limiting the realism of the resulting fuel cycle. For several applications, the current modeling method is sufficient, but precise calculations of discharged fuel composition may require further refinements. CLASS (Core Library for Advanced Simulation Scenarios) is a dynamic fuel cycle simulation code developed since 2012 with reactor models based on neural networks to produce nuclear data and physical quantities. Past work has shown a first coupling between CLASS and DONJON5 to quantify neural networks approach biases. This work assesses the applicability of 3D full-core diffusion calculations using the DONJON5 code coupled with nuclear scenario simulations involving a realistic PWR core at equilibrium cycle conditions. DONJON5 interpolates burnup dependent diffusion coefficients and cross sections generated beforehand by DRAGON5, a deterministic lattice calculation tool. Whereas previous studies considered only homogeneous reactors (i.e. homogeneous assembly in terms of composition and enrichment as well as homogeneous core), the present contribution focuses on the integration of full-core calculations in CLASS for fuel cycles involving a MOX/UO2 PWR core (i.e. 1/3 MOx–2/3 UOx). The DONJON5 model considered in this work describes a core with critical boron concentration at each time step partially loaded with MOx heterogeneous assemblies composed of three enrichments. In fuel cycle calculations, the main issue is to adapt, in the fabrication stage, the fresh fuel composition for the reactor with regards to the isotopic composition of the available stocks. This work presents a fuel loading model based on power peaking factors minimization that respects irradiation cycle length, 235U enrichment as well as Pu concentration and fissile quality, hence, ensuring a more uniform power distribution in the core.</p
The Advanced Virgo+ status
No full textInternational audienceThe gravitational wave detector Advanced Virgo+ is currently in the commissioning phase in view of the fourth Observing Run (O4).The major upgrades with respect to the Advanced Virgo configuration are the implementation of an additional recycling cavity, the Signal Recycling cavity (SRC), at the output of the interferometer to broaden the sensitivity band and the Frequency Dependent Squeezing (FDS) to reduce quantum noise at all frequencies.The main difference of the Advanced Virgo + detector with respect to the LIGO detectors is the presence of marginally stable recycling cavities, with respect to the stable recycling cavities present in the LIGO detectors, which increases the difficulties in controlling the interferometer in presence of defects (both thermal and cold defects).This work will focus on the interferometer commissioning, highlighting the control challenges to maintain the detector in the working point which maximizes the sensitivity and the duty cycle for scientific data taking
Vers la Détection des Neutrinos issus de l’Explosion des Supernovae à Effondrement de Coeur avec les système PMT 3 pouces du détecteur JUNO
No full textCore-Collapse Supernovae (CCSN) are gigantic explosions that occur when a massive star comes to death. Thirty-five years ago, for the first time, two dozens of neutrinos from a CCSN (SN1987A) were detected, marking the beginning of a new era in the study of CCSN. JUNO is a 20 kton liquid scintillator (LS) detector currently under construction in China. Two photomultiplier tube (PMT) systems, the first one made of #18,000 20-inch PMTs and the second one made of #26,000 3-inch PMTs, will collect the light produced by the neutrino interactions in the LS. JUNO primary objectives are to determine the neutrino mass ordering and to precisely measure three oscillation parameters. Thanks to its huge detection volume, JUNO is also expected to detect a burst of a few hundreds to a few thousands of neutrinos from the next galactic CCSN. The present thesis focuses on various aspects of the detection of CCSN neutrino using the 3-inch PMT system of JUNO. Based on simulation data, the rate capabilities of the system are assessed, the events vertex and energy reconstruction algorithms developed as well as an analysis for energy spectra reconstruction are presented.Les supernovae à effondrement de coeur (SNEC) sont des explosions gigantesques qui se produisent à la fin de la vie d’une étoile massive. Il y a trente-cinq ans, pour la première fois, deux douzaines de neutrinos provenant d’une SNEC (SN1987A) ont été détectés, marquant le début d’une nouvelle air dans l’études des SNEC. JUNO est un détecteur à liquide scintillant (LS) actuellement en construction en Chine. Deux systèmes de tubes photomultiplicateurs (PMT), le premier constitué de #18,000 PMT de 20 pouces et le second constitué de #26,000 PMT de 3 pouces, collecteront la lumière produite par les interactions des neutrinos avec le LS. Les objectives primaires de JUNO sont de déterminer l’ordre des masses des neutrinos et de mesurer précisément trois paramètres d’oscillation. Grâce à son immense volume de détection, JUNO devrait également détecter une salve de quelques centaines à quelques milliers de neutrinos provenant de la prochaine SNEC galactique. Cette thèse se concentre sur divers aspects de la détection des neutrinos des SNEC avec le système PMT 3 pouces de JUNO. Basé sur des données de simulation, les performances de lecture du système sont évaluées, les algorithmes de reconstruction de la position et de l’énergie des évènements dévelopés ainsi qu’une analyse pour la reconstruction des spèctres en énergie sont présentés