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Systematic study of flow vector decorrelation in TeV Pb-Pb collisions
No full textInternational audienceMeasurements of the -dependent flow vector fluctuations in Pb-Pb collisions at using azimuthal correlations with the ALICE experiment at the LHC are presented. A four-particle correlation approach [1] is used to quantify the effects of flow angle and magnitude fluctuations separately. This paper extends previous studies to additional centrality intervals and provides measurements of the -dependent flow vector fluctuations at with two-particle correlations. Significant -dependent fluctuations of the flow vector in Pb-Pb collisions are found across different centrality ranges, with the largest fluctuations of up to 15% being present in the 5% most central collisions. In parallel, no evidence of significant -dependent fluctuations of or is found. Additionally, evidence of flow angle and magnitude fluctuations is observed with more than significance in central collisions. These observations in Pb-Pb collisions indicate where the classical picture of hydrodynamic modeling with a common symmetry plane breaks down. This has implications for hard probes at high , which might be biased by -dependent flow angle fluctuations of at least 23% in central collisions. Given the presented results, existing theoretical models should be re-examined to improve our understanding of initial conditions, quark--gluon plasma (QGP) properties, and the dynamic evolution of the created system
Exposing the parton-hadron transition within jets with energy-energy correlators in pp collisions at TeV
No full textInternational audienceThis paper presents a fully-corrected measurement of the energy-energy correlator (EEC) within jets in pp collisions. The EEC traces the energy flow as a highly energetic parton undergoes a QCD shower followed by the confinement of partons into hadrons, probing the correlation function of the energy flow inside jets. The EEC observable is measured as a function of the charged particle pair angular distance, , for GeV/. In the perturbative region (large ), a good agreement between the data and a next-to-leading-log perturbative QCD calculation is observed. In the non-perturbative region (small ), the data exhibits a linear dependence. There is a transition region in between, characterized by a turnover in the EEC distribution, corresponding to the confinement process. The peak of this transition region is located at GeV/ for jets of various energies, indicating a common energy scale for the hadronization process. State-of-the-art Monte Carlo event generators are compared with the measurements, and can be used to constrain the parton shower and hadronization mechanisms
Quark saturation in the QCD phase diagram
No full textInternational audienceWe determine the onset of Quarkyonic Matter corresponding to values of temperature and baryon chemical potential at which the quark phase space density becomes one. At zero temperature for baryon chemical potentials below the mass of the Lambda baryon, only nucleons contribute to the quark density. This is different at finite temperature, where all baryons, mesons and their resonances can be excited and thus add quarks to the phase space. The probability density to find a quark inside a hadron is determined using the Yukawa ansatz of the IdylliQ model of Quarkyonic Matter. We estimate separately the magnitude of the various contributions of nucleons, Delta baryons, pions as well as further hadrons and resonances. The uncertainty in the parametrization of the probability density to find a quark inside a nucleon is spanned by assuming that at zero temperature the transition density to Quarkyonic Matter is between one and three times that of nuclear matter. Various predictions for a possible critical point associated with the chiral phase transition are found close to a triple point at which the line of the deconfinement transition and the curve associated with the transition to Quarkyonic Matter intersect. These considerations provide an estimate for the region in the QCD phase diagram where Quarkyonic Matter may be found
Physics case for quarkonium studies at the Electron Ion Collider
No full textInternational audienceThe physics case for quarkonium-production studies accessible at the US Electron Ion Collider is described
Multiplicity dependence of production at forward rapidity in pp collisions at = 13 TeV
No full textInternational audienceThe measurement of (1S), (2S), and (3S) yields as a function of the charged-particle multiplicity density, , using the ALICE experiment at the LHC, is reported in pp collisions at 13 TeV. The meson yields are measured at forward rapidity () in the dimuon decay channel, whereas the charged-particle multiplicity is defined at central rapidity (). Both quantities are divided by their average value in minimum bias events to compute the self-normalized quantities. The increase of the self-normalized (1S), (2S), and (3S) yields is found to be compatible with a linear scaling with the self-normalized , within the uncertainties. The self-normalized yield ratios of excited-to-ground states are compatible with unity within uncertainties. Similarly, the measured double ratio of the self-normalized (1S) to the self-normalized J/ yields, both measured at forward rapidity, is compatible with unity for self-normalized charged-particle multiplicities beyond one. The measurements are compared with theoretical predictions incorporating initial or final state effects
New results for thermal axion production in the early Universe
No full textInternational audienceThe axion is a hypothetical particle that was proposed by Peccei, Quinn, Weinberg and Wilczek to solve the strong CP problem.In the simplest model it couples only to gluons, but its interactions can be extended to include the electro-weak sector.It can be produced thermally in the early Universe via interactions with the Standard Model (SM) plasma and as it is almost massless, it makes a good candidate for dark radiation.Axions produced in such a way would manifest as an extra contribution to the so-called "effective number of neutrinos". It is this quantity that we would like to compute to compare it with observations and constrain the theoretical parameters.For this purpose, we require the thermal axion production rate.In this talk I present some newly obtained results in the Kim-Shifman-Vainshtein-Zakharov (KSVZ) model where the axion couples only to gluons.An important point to take into account while computing the production rate is the implementation of collective effects in the SM plasma to cure divergences due to soft gauge boson exchange.I introduce two new computation schemes and compare them to one in the literature, so as to get a better grasp on the theoretical uncertainties of the computation, and also point out potential issues with some of them.Lastly, I present new results for the axion contribution to the effective number of neutrinos.As an outlook, the methods used in this research rely on automated techniques and could be applied straightforwardly to other models of dark radiation as well
Anoxic corrosion of carbon steel in high pH cementitious media and high temperature conditions: New insights on the formation of (Fe,Al)Si-hydrogarnet corrosion product
No full textInternational audienceThe corrosion of carbon steel in alkaline anaerobic conditions and high temperature (80◦C) was studied throughmock-up tests representative of imperfect contact between steel and cementitious material. The evolution of thewhole system, including cement mineralogy, reservoir solution chemistry, corrosion product and rate, was fol-lowed over one year. SEM-EDX and XRD analyses indicated that the corrosion product layer was mostlyconstituted of (Fe,Al)Si-Hydrogarnet ((Fe,Al)Si-HG) and that its densification progressively inhibited corrosion.Thermodynamic and reactive transport modelling helped to better constrain the chemical and temperatureconditions of (Fe,Al)Si-HG formation
Particle production as a function of charged-particle flattenicity in pp collisions at = 13 TeV
No full textInternational audienceThis paper reports the first measurement of the transverse momentum () spectra of primary charged pions, kaons, (anti)protons, and unidentified particles as a function of the charged-particle flattenicity in pp collisions at TeV. Flattenicity is a novel event shape observable that is measured in the pseudorapidity intervals covered by the V0 detector, and . According to QCD-inspired phenomenological models, it shows sensitivity to multiparton interactions and is less affected by biases towards larger due to local multiplicity fluctuations in the V0 acceptance than multiplicity. The analysis is performed in minimum-bias (MB) as well as in high-multiplicity events up to GeV/. The event selection requires at least one charged particle produced in the pseudorapidity interval . The measured distributions, average , kaon-to-pion and proton-to-pion particle ratios, presented in this paper, are compared to model calculations using PYTHIA 8 based on color strings and EPOS LHC. The modification of the -spectral shapes in low-flattenicity events that have large event activity with respect to those measured in MB events develops a pronounced peak at intermediate ( GeV/), and approaches the vicinity of unity at higher . The results are qualitatively described by PYTHIA, and they show different behavior than those measured as a function of charged-particle multiplicity based on the V0M estimator
Monte Carlo simulations of microdosimetry and radiolytic species production at long time post proton irradiation using GATE and Geant4‐DNA
No full textInternational audienceBackground: Radiobiological effectiveness of radiation in cancer treatment can be studied at different scales (molecular till organ scale) and different time post irradiation. The production of free radicals and reactive oxygen species during water radiolysis is particularly relevant to understand the fundamental mechanisms playing a role in observed biological outcomes. The development and validation of Monte Carlo tools integrating the simulation of physical, physico-chemical and chemical stages after radiation is very important to maintain with experiments.Purpose: Therefore, in this study, we propose to validate a new Geant4-DNA chemistry module through the simulation of water radiolysis and Fricke dosimetry experiments on a proton preclinical beam line.Material and methods: In this study, we used the GATE Monte Carlo simulation platform (version 9.3) to simulate a 67.5 MeV proton beam produced with the ARRONAX isochronous cyclotron (IBA Cyclone 70XP) at conventional dose rate (0.2 Gy/s) to simulate the irradiation of ultra-pure liquid water samples and Fricke dosimeter. We compared the depth dose profile with measurements performed with a plane parallel Advanced PTW 34045 Markus ionization chamber. Then, a new Geant4-DNA chemistry application proposed from Geant4 version 11.2 has been used to assess the evolution of HO•, e-aq, H3O+, H2O2, H2, HO2•, HO2−, O2•− and HO− reactive species along time until 1-h post-irradiation. In particular, the effect of oxygen and pH has been investigated through comparisons with experimental measurements of radiolytic yields for H2O2 and Fe3+.Results: GATE simulations reproduced, within 4%, the depth dose profile in liquid water. With Geant4-DNA, we were able to reproduce experimental H2O2 radiolytic yields 1-h post-irradiation in aerated and deaerated conditions, showing the impact of small changes in oxygen concentrations on species evolution along time. For the Fricke dosimeter, simulated G(Fe3+) is 15.97 ± 0.2 molecules/100 eV which is 11% higher than the measured value (14.4 ± 04 molecules/100 eV).Conclusions: These results aim to be consolidated by new comparisons involving other radiolytic species, such as e−aq or, O2∙− to further study the mechanisms underlying the FLASH effect observed at ultra-high dose rates (UHDR)