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First measurement of prompt and non-prompt D⁎+ vector meson spin alignment in pp collisions at <math altimg="si1.svg"><msqrt><mrow><mi>s</mi></mrow></msqrt><mo linebreak="goodbreak" linebreakstyle="after">=</mo><mn>13</mn></math> TeV
No full textInternational audienceThis letter reports the first measurement of spin alignment, with respect to the helicity axis, for D⁎+ vector mesons and their charge conjugates from charm-quark hadronisation (prompt) and from beauty-meson decays (non-prompt) in hadron collisions. The measurements were performed at midrapidity (|y|<0.8) as a function of transverse momentum (pT) in proton–proton (pp) collisions collected by ALICE at the centre-of-mass energy s=13TeV. The diagonal spin density matrix element ρ00 of D⁎+ mesons was measured from the angular distribution of the D⁎+→D0(→K−π+)π+ decay products, in the D⁎+ rest frame, with respect to the D⁎+ momentum direction in the pp centre of mass frame. The ρ00 value for prompt D⁎+ mesons is consistent with 1/3, which implies no spin alignment. However, for non-prompt D⁎+ mesons an evidence of ρ00 larger than 1/3 is found. The measured value of the spin density element is ρ00=0.455±0.022(stat.)±0.035(syst.) in the 5<pT<20GeV/c interval, which is consistent with a Pythia 8 Monte Carlo simulation coupled with the EvtGen package, which implements the helicity conservation in the decay of D⁎+ meson from beauty mesons. In non-central heavy-ion collisions, the spin of the D⁎+ mesons may be globally aligned with the direction of the initial angular momentum and magnetic field. Based on the results for pp collisions reported in this letter it is shown that alignment of non-prompt D⁎+ mesons due to the helicity conservation coupled to the collective anisotropic expansion may mimic the signal of global spin alignment in heavy-ion collisions
Review of Neutrino Experiments Searching for Astrophysical Neutrinos
No full textInternational audienceOver the last two decades, we have intensified our search for a ghost particle, with the hope that it would provide us with information on the darkest places of our Universe. This quest has been conducted from the deep caves of the Earth, up to the upper layers of our atmosphere, and from one Pole to another. In this review, I will summarize the odyssey of the search for astrophysical neutrinos. I will focus on the recent discoveries and technical developments that led us to the point where we stand now. I will highlight the different types of neutrino detectors, and their performances enabling the discovery of high-energy astrophysical neutrinos, and the understanding of their sources behind. Finally, I will present some possible paths to the remaining uncharted territory of the ultra-high-energy neutrino astronomy
Can we reach suitable Tb purity for medical applications using theGd(d,n) reaction?
No full textInternational audienceTerbium is a chemical element that has several radioactive isotopes with suitable physical characteristics to be used in medical applications either for imaging or for therapy. This makes terbium a promising element to implement the theranostic approach. For therapeutic applications, 161Tb (T1/2 = 6.89 d) is suitable for targeted β-therapy. The main production route is through neutron capture reaction in nuclear reactors. In this work, we explored an alternative production route, the 160Gd(d,n)161Tb reaction. We have measured its production cross-section as well as those of possible co-produced contaminants, with a special focus on 160Tb (T1/2 = 72.3 d). To achieve this, cross-section measurements were made from natural gadolinium target. Production yields of 10.3 MBq/μA/h for the 161Tb and 1.5 MBq/μA/h for the 160Tb were obtained at 20 MeV. A161Tb radionuclidic purity of 86% was achieved over the 8 MeV–20 MeV energy range. The co-production of other terbium isotopes limits the interest of using higher energies. Based on the limited purity of 161Tb using the 160Gd(d,n)161Tb reaction, we conclude that it is not a production route suitable for medical applications. Although, this may be reconsidered when mass separation technique with high efficiency will be available. •161Tb is well suited to implement the theranostic approach (Tb family).•Study of an alternative 161Tb production route using accelerators.•Cross section measurements using the stacked foils technique and gamma spectrometry.•Production yield calculations for 161Tb and 160Tb and comparison to literature.•Optimisation of 161Tb purity knowing the co-production of 160Tb contaminant
J/ production at midrapidity in pPb collisions at TeV
No full textInternational audienceThe production of inclusive, prompt and non-prompt J/ψ was studied for the first time at midrapidity (−1.37 2 GeV/c. The study of the J/ψ mesons in the dielectron channel used for the first time in ALICE online single-electron triggers from the Transition Radiation Detector, providing a data sample corresponding to an integrated luminosity of 689 ± 13 μb. The proton-proton reference cross section for inclusive J/ψ was obtained based on interpolations of measured data at different centre-of-mass energies and a universal function describing the p-differential J/ψ production cross sections. The p-differential nuclear modification factors R of inclusive, prompt, and non-prompt J/ψ are consistent with unity and described by theoretical models implementing only nuclear shadowing.[graphic not available: see fulltext
Synthèse de microparticules de silicates riches en césium par interaction de combustible en fusion avec du béton : simulation expérimentale de phénomènes présents lors de l’accident de Fukushima Daiichi
No full textOn March 11, 2011, a powerful earthquake and tsunami caused the nuclear accident at the Fukushima Daiichi power plant in Japan. During the course of the accident, radioactive releases occurred towards the land in Japan and into the Pacific Ocean. Among these radioactive releases, Cs-bearing microparticles (CsMP) of amorphous silica were identified as a significant pollution source. This unprecedented form of radioactive pollution is highly insoluble, and its behavior in the environment could be significantly different from previously anticipated forms of cesium releases. Several hypotheses have been put forward by the scientific community to explain the process of their formation. This aspect holds significant importance in enhancing our comprehension of the accident's progression and assessing the necessity of considering them within the source term of a hypothetical future incident. An experiment aiming to reproduce a small-scale corium-concrete interaction has been conducted and has confirmed that this phenomenon is capable of producing CsMP. A detailed analysis of the experimental aerosols revealed the presence of micrometer-sized and nanometer-sized particles, with similar chemical composition, consisting of an amorphous silica matrix and containing nano-inclusions. Finally, a generation mechanism has been suggested to explain the origin of CsMP.Le 11 mars 2011, un puissant séisme et un tsunami ont provoqué l’accident nucléaire de la centrale de Fukushima Daiichi au Japon. Durant le déroulement de l’accident, des rejets radioactifs ont eu lieu vers les terres au Japon et vers l’Océan Pacifique. Parmi ces rejets radioactifs, des microparticules de silice amorphe contenant du césium radioactif (CsMP) ont été identifiées, et ce, en proportion significative et jusqu’à plusieurs centaines de kilomètres. Cette forme de pollution radioactive inédite est très peu soluble et son évolution dans l’environnement pourrait être significativement différente des formes jusqu’ici anticipées pour les rejets de césium. Plusieurs propositions ont été avancées par la communauté scientifique pour expliquer leur processus de formation. Il s’agit d’une donnée importante pour avoir une meilleure compréhension du déroulement de l’accident et savoir si elles doivent être prises en compte dans le terme source d’un nouvel accident hypothétique. Une expérience visant à reproduire une interaction corium-béton à petite échelle a été mise en place et a permis de valider que ce phénomène était en mesure de produire des CsMP. Une analyse détaillée des aérosols expérimentaux a permis d’observer des particules micrométriques et nanométriques, de composition chimique proche, constituées d’une matrice en silice amorphe et contenant des nano-inclusions cristallines. Finalement, un mécanisme de génération a été proposé pour expliquer l’origine des CsMP
Closing in on critical net-baryon fluctuations at LHC energies: Cumulants up to third order in Pb–Pb collisions
No full textInternational audienceFluctuation measurements are important sources of information on the mechanism of particle production at LHC energies. This article reports the first experimental results on third-order cumulants of the net-proton distributions in Pb–Pb collisions at a center-of-mass energy sNN=5.02 TeV recorded by the ALICE detector. The results on the second-order cumulants of net-proton distributions at sNN=2.76 and 5.02 TeV are also discussed in view of effects due to the global and local baryon number conservation. The results demonstrate the presence of long-range rapidity correlations between protons and antiprotons. Such correlations originate from the early phase of the collision. The experimental results are compared with HIJING and EPOS model calculations, and the dependence of the fluctuation measurements on the phase-space coverage is examined in the context of lattice quantum chromodynamics (LQCD) and hadron resonance gas (HRG) model estimations. The measured third-order cumulants are consistent with zero within experimental uncertainties of about 4% and are described well by LQCD and HRG predictions
Symmetry plane correlations in Pb-Pb collisions at TeV
No full textInternational audienceA newly developed observable for correlations between symmetry planes, which characterize the direction of the anisotropic emission of produced particles, is measured in Pb–Pb collisions at = 2.76 TeV with ALICE. This so-called Gaussian Estimator allows for the first time the study of these quantities without the influence of correlations between different flow amplitudes. The centrality dependence of various correlations between two, three and four symmetry planes is presented. The ordering of magnitude between these symmetry plane correlations is discussed and the results of the Gaussian Estimator are compared with measurements of previously used estimators. The results utilizing the new estimator lead to significantly smaller correlations than reported by studies using the Scalar Product method. Furthermore, the obtained symmetry plane correlations are compared to state-of-the-art hydrodynamic model calculations for the evolution of heavy-ion collisions. While the model predictions provide a qualitative description of the data, quantitative agreement is not always observed, particularly for correlators with significant non-linear response of the medium to initial state anisotropies of the collision system. As these results provide unique and independent information, their usage in future Bayesian analysis can further constrain our knowledge on the properties of the QCD matter produced in ultrarelativistic heavy-ion collisions
Observation of flow angle and flow magnitude fluctuations in Pb-Pb collisions at <math><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>5.02</mn><mspace width="0.16em"/><mi>TeV</mi></mrow></math> at the CERN Large Hadron Collider
No full textInternational audienceThis Letter reports on the first measurements of transverse momentum dependent flow angle Ψn and flow magnitude vn fluctuations determined using new four-particle correlators. The measurements are performed for various centralities in Pb–Pb collisions at a center-of-mass energy per nucleon pair of sNN = 5.02 TeV with ALICE at the CERN Large Hadron Collider. Both flow angle and flow magnitude fluctuations are observed in the presented centrality ranges and are strongest in the most central collisions and for a transverse momentum pT>2GeV/c. Comparison with theoretical models, including iEBE-VISHNU, MUSIC, and AMPT, show that the measurements exhibit unique sensitivities to the initial state of heavy-ion collisions
Temperature effect of U(VI) retention on the Callovo-Oxfordian clay rock
No full textInternational audienceIn the context of management of the radioactive waste in deep geological formations, the effect of temperature (20–80 °C) on U(VI) adsorption by Callovo-Oxfordian claystone (COx) was studied. A step-by-step approach was followed, starting with the single mineral, illite, followed by an increase in the complexity of the system, through the analysis of the clay fraction and the natural samples of the Callovo-Oxfordian formation. Depending on the study conditions, and the speciation of U(VI) in solution (hydrolysed species, carbonate species and presence of ternary U(VI)-Ca(Mg)‑carbonate complexes), the temperature effect was either negligible, or positive (where the increase in temperature favours retention). The most important positive effect was observed for the U(VI)/COx system in the presence of ternary complexes. The data were modelled considering an existing sorption model at 20 °C and the thermodynamic data available to describe the evolution of the speciation of U(VI) in solution in function of temperature. The enthalpy values associated with the surface complexes were fitted from the experimental data following a stepwise approach based on the van't Hoff equation