3,453 research outputs found

    Identification of Long-lived Charged Particles using Time-Of-Flight Systems at the Upgraded LHC detectors

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    We study the impact of picosecond precision timing detection systems on the LHC experiments' long-lived particle search program during the HL-LHC era. We develop algorithms that allow us to reconstruct the mass of such charged particles and perform particle identification using the time-of-flight measurement. We investigate the reach for benchmark scenarios as a function of the timing resolution, and find sensitivity improvement of up to a factor of ten, depending on the new heavy particle mass.Comment: 20 pages, 13 figure

    Adversarially Learned Anomaly Detection on CMS open data: re-discovering the top quark

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    We apply an Adversarially Learned Anomaly Detection (ALAD) algorithm to the problem of detecting new physics processes in proton–proton collisions at the Large Hadron Collider. Anomaly detection based on ALAD matches performances reached by Variational Autoencoders, with a substantial improvement in some cases. Training the ALAD algorithm on 4.4 fb⁻Âč of 8 TeV CMS Open Data, we show how a data-driven anomaly detection and characterization would work in real life, re-discovering the top quark by identifying the main features of the tt̄ experimental signature at the LHC

    Nonlinear evolution of the magnetized Kelvin-Helmholtz instability: from fluid to kinetic modeling

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    The nonlinear evolution of collisionless plasmas is typically a multi-scale process where the energy is injected at large, fluid scales and dissipated at small, kinetic scales. Accurately modelling the global evolution requires to take into account the main micro-scale physical processes of interest. This is why comparison of different plasma models is today an imperative task aiming at understanding cross-scale processes in plasmas. We report here the first comparative study of the evolution of a magnetized shear flow, through a variety of different plasma models by using magnetohydrodynamic, Hall-MHD, two-fluid, hybrid kinetic and full kinetic codes. Kinetic relaxation effects are discussed to emphasize the need for kinetic equilibriums to study the dynamics of collisionless plasmas in non trivial configurations. Discrepancies between models are studied both in the linear and in the nonlinear regime of the magnetized Kelvin-Helmholtz instability, to highlight the effects of small scale processes on the nonlinear evolution of collisionless plasmas. We illustrate how the evolution of a magnetized shear flow depends on the relative orientation of the fluid vorticity with respect to the magnetic field direction during the linear evolution when kinetic effects are taken into account. Even if we found that small scale processes differ between the different models, we show that the feedback from small, kinetic scales to large, fluid scales is negligable in the nonlinear regime. This study show that the kinetic modeling validates the use of a fluid approach at large scales, which encourages the development and use of fluid codes to study the nonlinear evolution of magnetized fluid flows, even in the colisionless regime

    Modeling Hot Tearing during Solidification of Steels: Assessment and Improvement of Macroscopic Criteria through the Analysis of Two Experimental Tests

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    International audienceHot tearing is an unacceptable defect found in products and parts obtained by solidification processes such as ingot and continuous casting. It consists of the development of cracks during solidification, in regions that are not completely solidified, more precisely, in areas of mushy zones with a high fraction of solid (typically 0.9 and beyond), when the material undergoes deformations associated with tensile stress. In this study, two hot tearing tests have been studied in order to evaluate the predictive capability of several macroscopic criteria published in the literature. The first test is a new test specifically designed for constrained shrinkage by the present authors, while the second test is an ingot bending test developed in the 1980s. For both tests, a thermal-mechanical analysis is performed, in order to provide the key variables for the different selected criteria. A comparison with experimental results allows us to make a critical assessment of those criteria regarding their ability to predict crack occurrence. The criterion initially proposed by Won et al.[7] has been found to be the best suited for the prediction of solidification cracking. Because this criterion is essentially based on the "brittle temperature range," (BTR) critical considerations regarding nonequilibrium solidification have led to suggest an extension of this criterion. This new macroscopic criterion improves the prediction capacity