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Search for heavy long-lived charged particles with large ionization energy loss in proton-proton collisions at = 13 TeV
No full textInternational audienceA search for heavy, long-lived, charged particles with large ionization energy loss within the silicon tracker of the CMS experiment is presented. A data set of proton-proton collisions at a center of mass energy at = 13 TeV, collected in 2017 and 2018 at the CERN LHC, corresponding to an integrated luminosity of 101 fb, is used in this analysis. Two different approaches for the search are taken. A new method exploits the independence of the silicon pixel and strips measurements, while the second method improves on previous techniques using ionization to determine a mass selection. No significant excess of events above the background expectation is observed. The results are interpreted in the context of the pair production of supersymmetric particles, namely gluinos, top squarks, and tau sleptons, and of the Drell-Yan pair production of fourth generation (τ′) leptons with an electric charge equal to or twice the absolute value of the electron charge (e). An interpretation of a Z’ boson decaying to two τ′ leptons with an electric charge equal to 2e is presented for the first time. The 95% confidence upper limits on the production cross section are extracted for each of these hypothetical particles.[graphic not available: see fulltext
Search for pair production of heavy particles decaying to a top quark and a gluon in the lepton+jets final state in proton-proton collisions at = 13 TeV
No full textInternational audienceA search is presented for the pair production of new heavy resonances, each decaying into a top quark (t) or antiquark and a gluon (g). The analysis uses data recorded with the CMS detector from proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC, corresponding to an integrated luminosity of 138 fb. Events with one muon or electron, multiple jets, and missing transverse momentum are selected. After using a deep neural network to enrich the data sample with signal-like events, distributions in the scalar sum of the transverse momenta of all reconstructed objects are analyzed in the search for a signal. No significant deviations from the standard model prediction are found. Upper limits at 95% confidence level are set on the product of cross section and branching fraction squared for the pair production of excited top quarks in the tg decay channel. The upper limits range from 120 to 0.8 fb for a with spin-1/2 and from 15 to 1.0 fb for a with spin-3/2. These correspond to mass exclusion limits up to 1050 and 1700 GeV for spin-1/2 and spin-3/2 particles, respectively. These are the most stringent limits to date on the existence of tg resonances
Search for -channel scalar and vector leptoquark exchange in the high-mass dimuon and dielectron spectra in proton-proton collisions at = 13 TeV
No full textInternational audienceA search for -channel exchange of leptoquarks (LQs) is performed in dimuon and dielectron spectra using proton-proton collision data collected at = 13 TeV with the CMS detector at the CERN LHC. The data correspond to an integrated luminosity of 138 fb. Eight scenarios are considered, in which scalar or vector LQs couple up or down quarks to muons or electrons, for dilepton invariant masses above 500 GeV. The LQ masses are probed up to 5 TeV, beyond a regime probed by previous pair-production and single-production searches. The differential distributions of dilepton events are fit to templates that model the nonresonant LQ exchange and various standard model background processes. Limits are set on LQ-fermion coupling strengths for scalar and vector LQ masses in the 1-5 TeV range at 95% confidence level, establishing stringent limits on first- and second-generation LQs
Measurement of the inclusive cross section in final states with at least one lepton and additional jets with 302 pb of pp collisions at = 5.02 TeV
No full textInternational audienceA measurement of the top quark pair () production cross section in proton-proton collisions at a centre-of-mass energy of 5.02 TeV is presented. The data were collected at the LHC in autumn 2017, in dedicated runs with low-energy and low-intensity conditions with respect to the default configuration, and correspond to an integrated luminosity of 302 pb. The measurement is performed using events with one electron or muon, and multiple jets, at least one of them being identified as originating from a b quark (b tagged). Events are classified based on the number of all reconstructed jets and of b-tagged jets. Multivariate analysis techniques are used to enhance the separation between the signal and backgrounds. The measured cross section is pb. A combination with the result in the dilepton channel based on the same data set yields a value of 62.3 ± 1.5 (stat) ± 2.4 (syst) ± 1.2 (lumi) pb, to be compared with the standard model prediction of pb at next-to-next-to-leading order in perturbative quantum chromodynamics.[graphic not available: see fulltext
Optimal Liquidation with Signals: the General Propagator Case
No full textInternational audienceWe consider a class of optimal liquidation problems where the agent's transactions create transient price impact driven by a Volterra-type propagator along with temporary price impact. We formulate these problems as minimization of a revenue-risk functionals, where the agent also exploits available information on a progressively measurable price predicting signal. By using an infinite dimensional stochastic control approach, we characterize the value function in terms of a solution to a free-boundary -valued backward stochastic differential equation and an operator-valued Riccati equation. We then derive analytic solutions to these equations which yields an explicit expression for the optimal trading strategy.We show that our formulas can be implemented in a straightforward and efficient way for a large class of price impact kernels with possible singularities such as the power-law kernel
Observation of nuclear modification of energy-energy correlators inside jets in heavy ion collisions
No full textInternational audienceEnergy-energy correlators are constructed by averaging the number of charged particle pairs within jets, weighted by the product of their transverse momenta, as a function of the angular separation of the particles within a pair. They are sensitive to a multitude of perturbative and nonperturbative quantum chromodynamics phenomena in high-energy particle collisions. Using lead-lead data recorded with the CMS detector, energy-energy correlators inside high transverse momentum jets are measured in heavy ion collisions for the first time. The data are obtained at a nucleon-nucleon center-of-mass energy of 5.02 TeV and correspond to an integrated luminosity of 1.70 nb. A similar analysis is done for proton-proton collisions at the same center-of-mass energy to establish a reference. The ratio of lead-lead to proton-proton energy-energy correlators reveals significant jet substructure modifications in the quark-gluon plasma. The results are compared to different models that incorporate either color coherence or medium response effects, where the two effects predict similar substructure modifications
(1+1) Genetic Programming with Functionally Complete Instruction Sets Can Evolve Boolean Conjunctions and Disjunctions with Arbitrarily Small Error
No full textInternational audienceRecently it has been proven that simple GP systems can efficiently evolve a conjunction of n variables if they are equipped with the minimal required components. In this paper, we make a considerable step forward by analysing the behaviour and performance of a GP system for evolving a Boolean conjunction or disjunction of n variables using a complete function set that allows the expression of any Boolean function of up to n variables. First we rigorously prove that a GP system using the complete truth table to evaluate the program quality, and equipped with both the AND and OR operators and positive literals, evolves the exact target function in O(\ell n log^2 n) iterations in expectation, where\ell ≥ n is a limit on the size of any accepted tree. Additionally, we show that when a polynomial sample of possible inputs is used to evaluate the solution quality, conjunctions or disjunctions with any polynomially small generalisation error can be evolved with probability 1 − O(log^2(n)/n). The latter result also holds if GP uses AND, OR and positive and negated literals, thus has the power to express any Boolean function of n distinct variables. To prove our results we introduce a super-multiplicative drift theorem that gives significantly stronger runtime bounds when the expected progress is only slightly superlinear in the distance from the optimum
The New Titan Planetary Climate Model. I. Seasonal Variations of the Thermal Structure and Circulation in the Stratosphere
No full textInternational audienceObservations of Titan through Cassini’s mission allowed Saturn’s moon’s stratospheric thermal structure and composition to be mapped over half a Titan year. Seasonal variations revealed various unexplained phenomena, such as mechanisms within the polar vortex, thermal structure evolution at high latitudes, and the impact of the enrichment in trace compounds during winter polar nights. We have developed the Titan Planetary Climate Model (Titan PCM)—an improved version of the IPSL Titan Global Climate Model (GCM)—including upgraded radiative transfer, now based on a flexible correlated- k method, updated spectroscopic data on gases, and integration of a new microphysics model for haze and clouds. Our photochemical solver extends computation of the composition above the top of the model up to 1300 km. The radiative transfer is now coupled with microphysics, consisting of the first full radiative coupling of microphysics within a Titan GCM. The model is presented along with its dynamics, thermal structure, and seasonal variations. Despite biases above 10 Pa due to upper boundary limitations, the Titan PCM leads to better modeling of the temperature profiles in the middle atmosphere. Consequently, it is now possible to address some scientific issues about thermal structure in polar regions. Investigations into fall and winter polar phenomena, particularly focusing on thermal structure control and equinoctial circulation reversal, were conducted. This study is linked to the radiative destabilization of the lower polar stratosphere, observed at the end of winter by Cassini radio-occultations. The results confirm a dynamic interplay between haze and gas distributions, which influence the thermal structure
A holographic global uniqueness in passive imaging
No full textInternational audienceWe consider a radiation solution for the Helmholtz equation in an exterior region in . We show that the restriction of to any ray in the exterior region is uniquely determinedby its imaginary part Im on an interval of this ray.As a corollary, the restriction of to any plane in the exterior region is uniquely determined by Im on an open domain in this plane.These results have holographic prototypes in the recent work Novikov (2024, Proc. Steklov Inst. Math. 325, 218-223).In particular, these and known results imply a holographic type global uniqueness in passive imaging and for the Gelfand-Krein-Levitan inverse problem (from boundary values of the spectral measure in the whole space) in the monochromatic case.Some other surfaces for measurements instead of the planes are also considered
modélisation mécanique et numérique de l'élastographie par ondes de cisaillement transitoires appliquée à la cornée
No full textRecent advances in dynamic elastography have enabled rapid, localized, and non-invasive acquisition of corneal mechanical data, making these techniques promising for in-vivo applications. The primary aim of this thesis is the development of a computational model that could reproduce transient elastographic measurements and give access to mechanical properties of the cornea as a diagnostic tool. As a first step, we derive a variational formulation for linear wave propagation in hyperelastic, nearly incompressible and preloaded solids. The numerical approximation of wave propagation problems in nearly or pure incompressible solids faces several challenges such as locking and stability constraints. In this work we propose a stabilized Leapfrog scheme based on the use of Chebyshev polynomials to relax the stability condition. A 3D nonlinear static model of the cornea is developed to simulate the tissue's preloaded state under intraocular pressure. The anisotropic behavior, given by the presence of a complex collagen network within the cornea, is described with a microsphere model. By linearization, the constitutive behavior of the tissue is derived for the wave propagation problem, which is then solved using the previously described numerical method. Furthermore, we address the case where the assumption of linear wave propagation may not be sufficient. We propose the application of a novel numerical method for solving nonlinear elastodynamic problems. This fully explicit, three-step method ensures stability through a posteriori energy criterion. The nonlinear static model of the cornea is then coupled with the nonlinear wave propagation model. Finally, the impact of fluid interaction on elastic waves is studied using guided wave theory, modeling the cornea as an incompressible waveguide and solving the problem as a generalized eigenvalue problem with boundary conditions for fluid interaction.Les progrès récents de l'élastographie dynamique ont permis une acquisition rapide, localisée et non invasive des données mécaniques de la cornée, ce qui rend ces techniques prometteuses pour les applications in vivo. L'objectif principal de cette thèse est le développement d'un modèle computationnel qui pourrait reproduire les mesures élastographiques transitoires et donner accès aux propriétés mécaniques de la cornée en tant qu'outil de diagnostic. Dans un premier temps, nous dérivons une formulation variationnelle pour la propagation d'ondes linéaires dans des solides hyperélastiques, presque incompressibles et préchargés. L'approximation numérique des problèmes de propagation d'ondes dans des solides presque ou purement incompressibles est confrontée à plusieurs défis comme le verrouillage et les contraintes de stabilité. Dans ce travail, nous proposons un schéma de Leapfrog stabilisé, basé sur l'utilisation de polynômes de Chebyshev pour relaxer la condition de stabilité. Un modèle statique non linéaire 3D de la cornée est développé pour simuler l'état de précharge du tissu sous pression intraoculaire. Le comportement anisotrope, dû à la présence d'un réseau complexe de collagène dans la cornée, est décrit par un modèle microsphere. Par linéarisation, le comportement constitutif du tissu est dérivé pour le problème de propagation des ondes, qui est ensuite résolu à l'aide de la méthode numérique décrite précédemment. En outre, nous abordons le cas où l'hypothèse de la propagation linéaire des ondes peut ne pas être suffisante. Nous proposons l'application d'une nouvelle méthode numérique pour résoudre les problèmes élastodynamiques non linéaires. Cette méthode entièrement explicite, en trois pas de temps, garantit la stabilité grâce à un critère d'énergie a posteriori. Le modèle statique non linéaire de la cornée est ensuite couplé au modèle non linéaire de propagation des ondes. Enfin, l'impact de l'interaction des fluides sur les ondes élastiques est étudié à l'aide de la théorie des ondes guidées, en modélisant la cornée comme un guide d'ondes incompressible et en résolvant le problème comme un problème de valeurs propres avec des conditions aux limites pour l'interaction des fluides