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Search for ttbar resonances in final states with exactly one or two leptons using 140 fb of pp collision data at TeV with the ATLAS experiment
No full textInternational audienceA search for heavy spin-1 and spin-2 resonances decaying into a top-antitop-quark pair has been performed with 140 fb of proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a centre-of-mass energy of TeV. Final states with either exactly one electron or muon, or exactly two leptons (, or ), large missing transverse momentum, and two jets, at least one of which must be identified as likely containing a b-hadron decay, are considered. The search targets resonances with both narrow and broad widths relative to the detector resolution, and with masses in the range of 0.4-5.0 TeV. No significant deviation from the Standard Model prediction is observed. Exclusion limits are set on the production cross-section times branching ratio for hypothetical bosons, Kaluza-Klein gravitons, and Kaluza-Klein gluons that decay into top-quark pairs
A comprehensive analysis of the decay
No full textInternational audienceAn analysis of the decay is presented using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 8.4 fb. The full set of -averaged and -asymmetric angular observables is determined in bins of the invariant mass squared of the dimuon system, as well as the branching fraction relative to the decay. For the first time, the full set of observables pertaining to the S-wave contribution to the final state are presented and consideration is given to effects arising from the mass of the muons. The measurements of the -averaged observables and the branching fractions continue to exhibit the pattern of tensions with the Standard Model predictions that have been seen in previous analyses that use part of the dataset considered in this study. The extracted -asymmetry observables show no significant deviations from zero
A universal scaling law for gravitational waves induced during inflation
No full textInternational audienceWe consider the stochastic gravitational wave background induced by arbitrary source fields that are amplified during cosmological inflation. The associated tensor spectral index is shown to be given, under minimal assumptions, by a simple formula easy to use in most situations of accelerated expansion. For slow-roll inflation, the induced spectrum is nearly scale-invariant, with an index that slightly deviates from the standard outcome of vacuum generated gravitational waves. Remarkably, we demonstrate that scale invariance remains true regardless of the original spectrum of the source
Global fits and the search for new physics: past, present and future
No full textInternational audienceIn this work, we review the history and current role of global fits in the search for physics beyond the Standard Model~(BSM), including precision tests of the Standard Model (SM). Although BSM global fits were initially focused on minimal supersymmetric models, we describe how fits have evolved in response to new data from the Large Hadron Collider (LHC) and elsewhere, expanding to encompass a broad spectrum of BSM scenarios including non-minimal supersymmetry, axion-like particles, extended Higgs sectors, dark matter models, and effective field theories such as SMEFT. We discuss how the role of global fits has shifted from forecasting possible signals of new physics at the LHC to understanding the impact of null results from LHC run-I and II and the discovery of the Higgs boson, and how interest has shifted from global fits for parameter estimation to comprehensive model comparison. We close by discussing potential trends and future applications, emphasizing the potential for machine learning and artificial intelligence to enhance the efficiency of sampling algorithms and comparison between theory and experiment, as well as collaboration and software development
Probing hard/soft factorization via beam-spin asymmetry in exclusive pion electroproduction from the proton
No full textInternational audienceDeep exclusive meson production (DEMP) reactions, such as , provide opportunities to study the three-dimensional structure of the nucleon through differential cross section and beam- and target-spin asymmetry measurements. This work aims to probe the onset of the hard/soft factorization regime through the exclusive reaction, as measured in the KaonLT experiment at Jefferson Lab Hall C. A 10.6 GeV longitudinally polarized electron beam was incident on an unpolarized liquid hydrogen target, and the scattered electron and produced meson were detected in two magnetic focusing spectrometers, enabling precision cross section measurements. The cross section ratio was extracted from the beam-spin asymmetry . The -dependence of was determined at fixed and over a range of kinematics from GeV). Furthermore, these data are combined with recent results from CLAS/CLAS12 to determine the -dependence of at two (, ) settings. This was fairly flat, with not having a measurable effect on the value of in the range explored. Results are compared to predictions from the generalized parton distribution (GPD) formalism, which relies explicitly on hard/soft factorization, and Regge formalism. The Regge models better predict , which suggests that the factorization regime is not yet reached
Performance of the front-end electronics of the CMS electromagnetic calorimeter barrel for the High-Luminosity LHC
No full textInternational audienceThe performance of the CMS electromagnetic calorimeter upgraded readout electronics, developed for the High-Luminosity phase of the LHC, is discussed. Data collected in two beam test campaigns conducted in 2018 and 2021 at the H4 and H2 beam lines of the CERN SPS are analyzed. Time and energy resolutions are measured on a matrix of lead tungstate crystals equipped with prototypes of the new front end readout electronics, using electron and pion beams of energies spanning from 25 to 250 GeV. In both campaigns the constant term of the energy resolution is measured to be better than 0.6% and the time resolution for electrons with energies above 50 GeV is measured to be better than 30 ps, fulfilling the design requirements
Euclid preparation. Galaxy 2-point correlation function modelling in redshift space
No full textInternational audienceThe Euclid satellite will measure spectroscopic redshifts for tens of millions of emission-line galaxies. In the context of Stage-IV surveys, the 3-dimensional clustering of galaxies plays a key role in providing cosmological constraints. In this paper, we conduct a model comparison for the multipole moments of the galaxy 2-point correlation function (2PCF) in redshift space. We test state-of-the-art models, in particular the effective field theory of large-scale structure (EFT), one based on the velocity difference generating function (VDG), and different variants of Lagrangian perturbation theory (LPT) models, such as convolutional LPT (CLPT) and its effective-field-theory extension (CLEFT). We analyse the first three even multipoles of the 2PCF in the Flagship 1 simulation, which consists of four snapshots at . We study both template-fitting and full-shape approaches and find that with the template-fitting approach, only the VDG model is able to reach a minimum fitting scale of at without biasing the recovered parameters. Indeed, the EFT model becomes inaccurate already at . Conversely, in the full-shape analysis, the CLEFT and VDG models perform similarly well, but only the CLEFT model can reach while the VDG model is unbiased down to at the lowest redshift. Overall, in order to achieve the accuracy required by Euclid, non-perturbative modelling such as in the VDG or CLEFT models should be considered. At , the CLPT model is sufficient to describe the data with high figure of merit. This comparison selects baseline models that perform best in ideal conditions and sets the stage for an optimal analysis of Euclid data in configuration space
Black holes in a dense infinite medium: a toy-model regularizing the Schwarzschild metric
No full textInternational audienceWe revisit the dynamics of a black hole accreting energy from a surrounding homogeneous and infinite space. We argue for a simple heuristic modification of the Schwarzschild approximation when the density of the medium is not negligible anymore. The resulting behavior is drastically modified: the mass divergence at finite time is cured and the thermodynamical properties are deeply changed. Some potential consequences for quantum gravity and bouncing models are also pointed out. Those conclusions being mostly obtained from a Newtonian approach, they only aim at guiding toward a more rigorous treatment. Still, interestingly, the behavior is far more convincing that the one usually obtained
Ultra-sensitive radon assay using an electrostatic chamber in a recirculating system
No full textInternational audienceRare event searches such as neutrinoless double beta decay and Weakly Interacting Massive Particle detection require ultra-low background detectors. Radon contamination is a significant challenge for these experiments, which employ highly sensitive radon assay techniques to identify and select low-emission materials. This work presents the development of ultra-sensitive electrostatic chamber (ESC) instruments designed to measure radon emanation in a recirculating gas loop, for future lower background experiments. Unlike traditional methods that separate emanation and detection steps, this system allows continuous radon transport and detection. This is made possible with a custom-built recirculation pump. A Python-based analysis framework, PyDAn, was developed to process and fit time-dependent radon decay data. Radon emanation rates are given for various materials measured with this instrument. A radon source of known activity provides an absolute calibration, enabling statistically-limited minimal detectable activities of 20 Bq. These devices are powerful tools for screening materials in the development of low-background particle physics experiments
Exclusive four pion photoproduction in ultraperipheral Pb-Pb collisions at TeV
No full textInternational audienceThe intense photon fluxes from relativistic nuclei provide an opportunity to study photonuclear interactions in ultraperipheral collisions. The measurement of coherently photoproduced final states in ultraperipheral Pb-Pb collisions at TeV is presented for the first time. The cross section, d/d, times the branching ratio () is found to be mb in the rapidity interval . The invariant mass distribution is not well described with a single Breit-Wigner resonance. The production of two interfering resonances, and , provides a good description of the data. The values of the masses () and widths () of the resonances extracted from the fit are MeV/, MeV/, MeV/ and MeV/, respectively. The measured cross sections times the branching ratios are compared to recent theoretical predictions