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Measurements of inclusive and differential cross sections for top quark production in association with a Z boson in proton-proton collisions at = 13 TeV
No full textInternational audienceMeasurements are presented of inclusive and differential cross sections for Z boson associated production of top quark pairs (Z) and single top quarks (tZq or tWZ). The data were recorded in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb. Events with three or more leptons, electrons or muons, are selected and a multiclass deep neural network is used to separate three event categories, the Z and tWZ processes, the tZq process, and the backgrounds. A profile likelihood approach is used to unfold the differential cross sections, to account for systematic uncertainties, and to determine the correlations between the two signal categories in one global fit. The inclusive cross sections for a dilepton invariant mass between 70 and 110 GeV are measured to be 1.14 0.07 pb for the sum of Z and tWZ, and 0.81 0.10 pb for tZq, in good agreement with theoretical predictions
Measurements of and production within fully reconstructed jets
No full textInternational audienceThis paper presents the first measurement of and meson production within fully reconstructed jets. Each quarkonium state (tag) is reconstructed via its decay to the () final state in the forward region using proton-proton collision data collected by the LHCb experiment at the center-of-mass-energy of in 2016, corresponding to an integrated luminosity of . The fragmentation function, presented as the ratio of the quarkonium-tag transverse momentum to the full jet transverse momentum (), is measured differentially in and bins. The distributions are separated into promptly produced quarkonia from proton-proton collisions and quarkonia produced from displaced -hadron decays. While the displaced quarkonia fragmentation functions are in general well described by parton-shower predictions, the prompt quarkonium distributions differ significantly from fixed-order non-relativistic QCD (NRQCD) predictions followed by a QCD parton shower
An end-to-end calibration of the Mini-EUSO detector in space
No full textInternational audienceMini-EUSO is a wide Field-of-View (44∘×44∘) telescope currently in operation from a nadir-facing Ultra-Violet (UV) transparent window in the Russian Zvezda module on the International Space Station (ISS). Mini-EUSO has been designed as a scaled-down version of the original JEM-EUSO telescope to raise its instrumentation’s technological readiness level and demonstrate its observational principle, while performing multidisciplinary studies on different fields such as atmospheric science and planetology. One of Mini-EUSO main goals is the study of the UV background for future space missions employing the same concept as the original JEM-EUSO telescope, which requires an absolute calibration of the Mini-EUSO instrument. During the past years, a few observational campaigns have been completed, employing a ground-based UV flasher to perform an end-to-end calibration of the instrument. In this paper, we present the assembled UV flasher system, the operation of the field campaign and the analysis of the obtained data. The results are interpreted by the means of a parametrization of the Mini-EUSO photon counts. The end-to-end efficiency of several pixels has been obtained, taking into account different parameters such as the atmospheric attenuation, the optics efficiency and the multi-anode photomultiplier detection efficiency
Basis restricted elastic shape analysis on the space of unregistered surfaces
No full textInternational audienceThis paper introduces a new framework for surface analysis derived from the general setting of elastic Riemannian metrics on shape spaces. Traditionally, those metrics are defined over the infinite dimensional manifold of immersed surfaces and satisfy specific invariance properties enabling the comparison of surfaces modulo shape preserving transformations such as reparametrizations. The specificity of our approach is to restrict the space of allowable transformations to predefined finite dimensional bases of deformation fields. These are estimated in a data-driven way so as to emulate specific types of surface transformations. This allows us to simplify the representation of the corresponding shape space to a finite dimensional latent space. However, in sharp contrast with methods involving e.g. mesh autoencoders, the latent space is equipped with a non-Euclidean Riemannian metric inherited from the family of elastic metrics. We demonstrate how this model can be effectively implemented to perform a variety of tasks on surface meshes which, importantly, does not assume these to be pre-registered or to even have a consistent mesh structure. We specifically validate our approach on human body shape and pose data as well as human face and hand scans for problems such as shape registration, interpolation, motion transfer or random pose generation.</div
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
Magnetic phase diagram of the three-dimensional doped Hubbard model
No full textInternational audienceWe establish the phase diagram of the Hubbard model on a cubic lattice for a wide range of temperatures, dopings and interaction strengths, considering both commensurate and incommensurate magnetic orders. We use the dynamical mean-field theory together with an efficient method to compute the free energy which enable the determination of the correct ordering vectors. Besides an antiferromagnetic state close to half-filling, we identify a number of different magnetic spiral phases with ordering vectors , and as well as a region with close competition between them, hinting at spatial phase separation or at the onset of a stripe phase. Additionally, we extensively study several thermodynamic properties with direct relevance to cold-atom experiments: the entropy, energy and double-occupancy
Measurement of mixing and search for violation with decays
No full textInternational audienceA measurement of the time-dependent ratio of the to decay rates is reported. The analysis uses a sample of proton-proton collisions corresponding to an integrated luminosity of 6 fb recorded by the LHCb experiment from 2015 through 2018 at a center-of-mass energy of 13 TeV. The meson is required to originate from a decay, such that its flavor at production is inferred from the charge of the accompanying pion. The measurement is performed simultaneously for the and final states, allowing both mixing and -violation parameters to be determined. The value of the ratio of the decay rates at production is determined to be . The mixing parameters are measured to be and , where is the linear coefficient of the expansion of the ratio as a function of decay time in units of the lifetime, and is the quadratic coefficient, both averaged between the and final states. The precision is improved relative to the previous best measurement by approximately 60%. No evidence for violation is found
Hydrodynamics of Relativistic Superheated Bubbles
No full textInternational audienceRelativistic, charged, superheated bubbles may play an important role in neutron star mergers if first-order phase transitions are present in the phase diagram of Quantum Chromodynamics. We describe the properties of these bubbles in the hydrodynamic regime. We find two qualitative differences with supercooled bubbles. First, the pressure inside an expanding superheated bubble can be higher or lower than the pressure outside the bubble. Second, some fluid flows develop metastable regions behind the bubble wall. We consider the possible role of a conserved charge akin to baryon number. The fluid flow profiles are unaffected by this charge if the speed of sound is constant in each phase, but they are modified for more general equations of state. We compute the efficiency factor relevant for gravitational wave production
Uniform attachment with freezing
No full textInternational audienceIn the classical model of random recursive trees, trees are recursively built by attaching new vertices to old ones. What happens if vertices are allowed to freeze, in the sense that new vertices cannot be attached to already frozen ones? We are interested in the impact of freezing on the height of such trees
Short-range excitonic phenomena in low-density metals
No full textInternational audienceExcitonic effects in metals are commonly supposed to be weak, because the Coulomb interaction is strongly screened. We investigate the low-density regime of the homogeneous electron gas, where low-energy collective excitations and ghost modes were anticipated. Using the Bethe-Salpeter equation (BSE), we show that both phenomena exist thanks to reduced screening at short distances. This is not captured by common approximations used in ab initio BSE calculations, but requires vertex corrections that take the fermionic nature of charges into account. The electron-hole wavefunction of the low-energy modes shows strong and very anisotropic electron-hole correlation, which speaks for an excitonic character of these modes. The fact that short-range physics is at the origin of these phenomena explains why, on the other hand, also the simple adiabatic local density approximation to time-dependent density functional theory can capture these effects