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Search for meson decays to and final states
No full textInternational audienceA search for meson decays to the and final states is reported using a sample of proton-proton collisions collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb. The decay is observed for the first time when requiring that the two electrons are consistent with coming from the decay of a or meson. The corresponding branching fractions are measured relative to the decay, where the two electrons are consistent with coming from the decay of a or meson. No evidence is found for the decay and world-best limits are set on its branching fraction. The results are compared to, and found to be consistent with, the branching fractions of the and decays recently measured by LHCb and confirm lepton universality at the current precision
Characterization of the optical model of the T2K 3D segmented plastic scintillator detector
No full textInternational audienceThe magnetised near detector (ND280) of the T2K long-baseline neutrino oscillation experiment has been recently upgraded aiming to satisfy the requirement of reducing the systematic uncertainty from measuring the neutrinonucleus interaction cross section, which is the largest systematic uncertainty in the search for leptonic charge-parity symmetry violation. A key component of the upgrade is SuperFGD, a 3D segmented plastic scintillator detector made of approximately 2,000,000 optically-isolated 1 cm3 cubes. It will provide a 3D image of GeV neutrino interactions by combining tracking and stopping power measurements of final state particles with sub-nanosecond time resolution. The performance of SuperFGD is characterized by the precision of its response to charged particles as well as the systematic effects that might affect the physics measurements. Hence, a detailed Geant4 based optical simulation of the SuperFGD building block, i.e. a plastic scintillating cube read out by three wavelength shifting fibers, has been developed and validated with the different datasets collected in various beam tests. In this manuscript the description of the optical model as well as the comparison with data are reported
Measurement of the CKM angle in decays
No full textInternational audienceMeasurements of observables and the CKM angle are performed in decays, where represents a superposition of and states, using the LHCb dataset collected during Run 1 (2011-2012) and Run 2 (2015-2018). A comprehensive study of this channel is presented with the meson reconstructed in two-body final states , and ; four-body final states and ; and three-body final states and . This analysis includes the first observation of the suppressed and decays. The combined result gives
Un problème de transport optimal extérieur
No full textInternational audienceThis paper deals with a variant of the optimal transportation problem. Given f ∈ L 1 (R d , [0, 1]) and a cost function c ∈ C(R d × R d) of the form c(x, y) = k(y − x), we minimise ∫ c dγ among transport plans γ whose first marginal is f and whose second marginal is not prescribed but constrained to be smaller than 1 − f. Denoting by Υ(f) the infimum of this problem, we then consider the maximisation problem sup{Υ(f) : ∫ f = m} where m > 0 is given. We prove that maximisers exist under general assumptions on k, and that for k radial, increasing and coercive these maximisers are the characteristic functions of the balls of volume m
Pseudorapidity distributions of charged hadrons in lead-lead collisions at = 5.36 TeV
No full textInternational audienceThe pseudorapidity () distributions of charged hadrons are measured using data collected at the highest ever nucleon-nucleon center-of-mass energy of = 5.36 TeV for collisions of lead-lead ions. The data were recorded by the CMS experiment at the LHC in 2022 and correspond to an integrated luminosity of 0.30 0.03 b. Using the CMS silicon pixel detector, the yields of primary charged hadrons produced in the range 2.6 are reported. The evolution of the midrapidity particle density as a function of collision centrality is also reported. In the 5% most central collisions, the charged-hadron density in the range 0.5 is found to be 2032 91 (syst), with negligible statistical uncertainty. This result is consistent with an extrapolation from nucleus-nucleus collision data at lower center-of-mass energies. Comparisons are made to various Monte Carlo event generators and to previous measurements of lead-lead and xenon-xenon collisions at similar collision energies. These new data detail the dependence of particle production on the collision energy, initial collision geometry, and the size of the colliding nuclei
Step-by-step verification of particle-in-cell Monte Carlo collision codes
No full textInternational audienceThe particle-in-cell (PIC) method with Monte Carlo collisions (MCC) is widely used in the simulation of non-equilibrium plasmas for electric propulsion and laboratory applications. Due to the simplicity of the basic PIC algorithm and the specific modeling needs of the different research groups, many codes have been independently developed. Verification of these codes, i.e., ensuring that the computational code correctly implements the intended mathematical models and algorithms, is of fundamental importance. Different benchmark cases, such as one from Turner et al. [Phys. Plasmas 20, 013507 (2013)], Charoy et al. [Plasma Sources Sci. Technol. 28, 105010 (2019)], and Villafana et al. [Plasma Sources Sci. Technol. 30, 075002 (2021)], have been published in recent years. These have consisted of a complex physical setup, in which many computation modules interact to yield the final result. Although this approach has the advantage of testing the code in a realistic case, it may hide some implementation errors. Moreover, in the case of disagreement, the previous works do not provide an easy way to identify the faulty code modules. In this work, we propose a step-by-step approach for the verification of PIC-MCC codes in a 2D-3V electrostatic setup. The criteria for the test cases are (i) they should highlight possible implementation errors by testing the modules separately, whenever possible (ii) they should be free from physical instabilities to avoid chaotic behavior, and (iii) the numerical result should be accompanied by analytical calculations, for confirmation purposes. The seven test cases identified all show excellent agreement between the authors' codes
On the need for better groundwater initial conditions estimation in seasonal forecasts: a data assimilation scheme for Aqui-FR hydrometeorological modelling platform. Example with the regional case study of the Somme basin (France)
No full textInternational audienceIn France, groundwater is one of the main resource for industry, agriculture, and drinking water. While severe droughts affecting groundwater tend to be more frequent, forecast development have become essential for stakeholders. The Aqui-FR hydro-meteorological platform (Vergnes et al., 2020), which gather different regional groundwater models, is coupled with atmospheric reanalysis and downscaled seasonal forecasts (Willemet et al., 2022) to achieve this goal. Never theless, bias and error still presents in the models used impact the estimation of forecast initial conditions (IC), limiting the potential for operational uses. In order to overcome these issues, a data assimilation (DA) scheme has been developed within the Aqui-FR workflow. The analysis step focuses on state estimation, and more precisely on piezometric (groundwater) levels during a reanalysis run. An Ensemble Kalman Filter (EnKF ; Evensen, 1994; Burgers et al., 1998) has been implemented in a python library (aquida) to set up a sequential DA. Two inflation methods (additive and multiplicative) and two localisation methods (quasi gaussian distance-based [Gaspari and Cohn, 1999] and spatial autocorrelation based [Revel et al., 2019]) are used. To analyse the efficiency of the DA scheme, this first study focus on one of the regional model of the Aqui-FR platform, the Somme basin model which use the MARTHE hydrogeological computer code (Thiéry et al., 2020) to simulate both piezometric levels and rivers discharge. In situ piezometric data from monitored wells are assimilated. Preliminary results obtained from our numerical experiments show the benefit of DA on ground water state estimation with a regional model (mean RMSE reduced from 4.26 to 0.32), even with spatially sparse data. When assimilation is stopped, the analysis shows an impact on state estimation up to a seasonal time step (mean RMSE about 2.9 after 180 days without assimi lation), encouraging for forecast improvements. Nevertheless, in regions of the model domain where initial calibration is too poor, the correction show less persistence and the dynamic of the model seems more governed by parameters than forcings. In order to improve the piezometric estimation in these areas, we plan to implement a two step DA with parameter estimation before state estimation
Ionospheric Conductances at the Giant Planets of the Solar System: A Comparative Study of Ionization Sources and the Impact of Meteoric Ions
No full textInternational audienceThe dynamics of giant planet magnetospheres is controlled by a complex interplay between their fast rotation, their interaction with the solar wind, and their diverse internal plasma and momentum sources. In the ionosphere, the Hall and Pedersen conductances are two key parameters that regulate the intensity of currents coupling the magnetosphere and the ionosphere, and the rate of angular momentum transfer and power carried by these currents. We perform a comparative study of Hall and Pedersen conductivities and conductances in the four giant planets of our Solar System -Jupiter, Saturn, Uranus and Neptune. We use a generic ionospheric model (restraining the studied ions to H + 3 , CH + 5 , and meteoric ions) to study the dependence of conductances on the structure and composition of these planets' upper atmospheres and on the main ionization sources (photoionization, ionization by precipitating electrons, and meteoroid ablation). After checking that our model reproduces the conclusions of Nakamura et al. ( 2022), https://doi.org/10.1029/2022ja030312 at Jupiter, that is, the contribution of meteoric ions to the height-integrated conductances is non-negligible, we show that this contribution could also be non-negligible at Saturn, Uranus and Neptune, compared with ionization processes caused by precipitating electrons of energies lower than a few keV (typical energies on these planets). However, because of their weaker magnetic field, the conductive layer of these planets is higher than the layer where meteoric ions are mainly produced, limiting their role in magnetosphere-ionosphere coupling
Small-scale interface dynamic modelling based on the geometric method of moments for a two-scale two-phase flow model with a disperse small scale
No full textInternational audienceIn this contribution, we develop a versatile formalism to derive unified two-phase models describing both the separated and disperse regimes as introduced by Loison et al. (2024). It relies on the stationary action principle and interface geometric variables.This contribution provides a novel method to derive small-scale models for the dynamics of the interface geometry.They are introduced here on a simplified case where all the scales and phases have the same velocity and that does not take into account large-scale capillary forces.The derivation tools yield a proper mathematical framework through hyperbolicity and signed entropy evolution.The formalism encompasses a hierarchy of small-scale reduced-order models based on a statistical description at a mesoscopic kinetic level and is naturally able to include the description of a disperse phase with polydispersity in size. This hierarchy includes both a cloud of spherical droplets and non-spherical droplets experiencing a dynamical behaviour through incompressible oscillations. The associated small-scale variables are moments of a number density function resulting from the geometric method of moments (GeoMOM).This method selects moments as small-scale geometric variables compatible with the structure and dynamics of the interface; they are defined independently of the flow topology and, therefore, this model allows the coupling of the two-scale flow with an inter-scale transfer.It is shown in particular that the resulting dynamics provides partial closures for the interface area density equation obtained from the averaging approach
Universal complexity bounds based on value iteration for stochastic mean payoff games and entropy games
No full textInternational audienceWe develop value iteration-based algorithms to solve in a unified manner different classes of combinatorial zero-sum games with mean-payoff type rewards. These algorithms rely on an oracle, evaluating the dynamic programming operator up to a given precision. We show that the number of calls to the oracle needed to determine exact optimal (positional) strategies is, up to a factor polynomial in the dimension, of order R/sep, where the “separation” sep is defined as the minimal difference between distinct values arising from strategies, and R is a metric estimate, involving the norm of approximate sub and super-eigenvectors of the dynamic programming operator. We illustrate this method by two applications. The first one is a new proof, leading to improved complexity estimates, of a theorem of Boros, Elbassioni, Gurvich and Makino, showing that turn-based mean-payoff games with a fixed number of random positions can be solved in pseudo-polynomial time. The second one concerns entropy games, a model introduced by Asarin, Cervelle, Degorre, Dima, Horn and Kozyakin. The rank of an entropy game is defined as the maximal rank among all the ambiguity matrices determined by strategies of the two players. We show that entropy games with a fixed rank, in their original formulation, can be solved in polynomial time, and that an extension of entropy games incorporating weights can be solved in pseudo-polynomial time under the same fixed rank condition