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Evidence for the rare decay
No full textInternational audienceA search for the rare decay is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of TeV, corresponding to an integrated luminosity of 5.4 fb. An excess of events is found with respect to the background-only expectation, with a signal significance of 3.5 standard deviations, in the low invariant-mass region of GeV/. The branching fraction is measured to be , where the last uncertainty is due to external inputs on . With no significant signal observed in the high region above 2.8 GeV/, an upper limit is set to be at the () confidence level
A Minrank-based Encryption Scheme à la Alekhnovich-Regev
No full textInternational audienceIntroduced in 2003 and 2005, Alekhnovich and Regev' schemes were the first public-key encryptions whose security is only based on the average hardness of decoding random linear codes and LWE, without other security assumptions. Such security guarantees made them very popular, being at the origin of the now standardized HQC or Kyber. We present an adaptation of Alekhnovich and Regev' encryption scheme whose security is only based on the hardness of a slight variation of MinRank, the so-called stationary-MinRank problem. We succeeded to reach this strong security guarantee by showing that stationary-MinRank benefits from a search-to-decision reduction. Our scheme therefore brings a partial answer to the long-standing open question of building an encryption scheme whose security relies solely on the hardness of MinRank. Finally, we show after a thoroughly security analysis that our scheme is practical and competitive with other encryption schemes admitting such strong security guarantees. Our scheme is slightly less efficient than FrodoKEM, but much more efficient than Alekhnovich and Regev' original schemes, with possibilities of improvements by considering more structure, in the same way as HQC and Kyber
Density dependence of measured line intensities for O2 transitions
No full textInternational audienceWe report predictions and measurements of O2 absorption spectra that exhibit line intensity depletion with increasing gas density. This effect, which is attributed to the finite duration of collisions, alters the line shape by redistributing a portion of the intensity from a relatively narrow spectrum that can be described by an impact-approximation-based profile to a broad pedestal with a width that is inversely related to the collision duration. Using classical molecular dynamics simulations (CMDS), we predicted details regarding this mechanism for O2 with four collision partners: O2, N2, Ar, and He at a temperature of 296 K. These simulations were validated by comparisons with experimental intensity depletion coefficients obtained from absorption spectra of the 1.27 μm band of O2 in air; Ar and He acquired over a wide pressure range up to 120 kPa. All experimental spectra were recorded using high-precision cavity ring-down spectroscopy (CRDS) apparatuses at NIST (United States of America) and LIPhy (France). For air-broadened O2, more specifically, a mean depletion value of ∼0.3% amagat−1 was observed, with almost no resolvable rotational dependence. The temperature dependence of the intensity depletion in this system was also investigated by CMDS at 250 and 296 K and by CRDS spectra of air at 250, 275, and 296 K. The theoretical results suggest a nearly 1/T2 temperature dependence of the intensity-weighted depletion coefficient, which over the limited temperature range considered, was only slightly greater than the measurement precision. Finally, simulations of atmospheric solar absorption spectra were implemented to quantify the impact of neglecting this depletion effect on the retrieved surface pressure, resulting in a negatively biased measurement of ∼0.14%, with a spread of ∼0.02% caused by seasonal variations in gas temperature
Search for a boosted Higgs boson decaying to bottom quark pairs in association with a W or Z boson in proton-proton collisions at = 13 TeV
No full textInternational audienceA search is conducted for standard model Higgs bosons with large transverse momentum () decaying to bottom quark pairs and produced in association with a hadronically decaying W or Z boson at the LHC. The result is based on a dataset of proton-proton collisions at a center-of-mass energy of 13 TeV collected with the CMS detector in 20162018, corresponding to an integrated luminosity of 138 fb. Boosted Higgs, W, and Z boson decays are reconstructed using large-radius jets with 450 GeV and identified with heavy-flavor classifiers based on a graph convolutional neural network. The observed signal strength relative to the standard model expectation is = 0.7 including statistical and systematic uncertainties
Nonlinear phase synchronization and the role of spacing in shell models
No full textInternational audienceA shell model can be considered as a self-similar chain of interacting triads, where each triad can be interpreted as a nonlinear oscillator that can be mapped to a spinning top. Investigating the relation between phase dynamics and intermittency in such a chain of nonlinear oscillators, it is found that synchronization is linked to increased energy transfer. In particular, our results indicate that the observed systematic increase of intermittency, as the shell spacing is decreased, is associated with strong phase alignment among consecutive triadic phases, facilitating the energy cascade. It is shown that while the overall level of synchronization can be quantied using a Kuramoto order parameter for the global phase coherence in the inertial range, a local, weighted Kuramoto parameter can be used for the detection of burst-like events propagating across shells in the inertial range. This novel analysis reveals how locally phase-locked states are associated with the passage of extreme events of energy ux. Applying this method to helical shell models ( i.e. for a class of helical interactions that couple the two helicities in a non separable topology) reveals that a reduction in phase coherence correlates with suppression of intermittency. When inverse cascade scenarios are considered using two dierent shell models including a non local helical shell model, and a local standard shell model with a modied conservation law, it was shown that a particular phase organization is needed in order to sustain the inverse energy cascade. It was also observed that the PDFs of the triadic phases were peaked in accordance with the basic considerations of the form of the ux, which suggests that a triadic phase of π/2 and -π/2 maximizes the forward and the inverse energy cascades respectively
Bubbling wormholes and matrix models
No full textInternational audienceThe thermofield double state entangles two copies of a CFT via a sum over energy eigenstates and is dual to the two-sided eternal black hole. We explore an analogous construction using sums over gauge group representations of half-BPS Wilson loops in multiple copies of super Yang-Mills. These sums act as delta function-like operators that correlate the eigenvalues of the corresponding half-BPS matrix models. We suggest that the holographic duals are ''bubbling wormhole'' geometries: multi-covers of AdS whose conformal boundary consists of multiple four-spheres intersecting on a common circle. We analyze the matrix model free energy, discuss its bulk interpretation, and study probe loops in these backgrounds
Combination of searches for nonresonant Higgs boson pair production in proton-proton collisions at = 13 TeV
No full textInternational audienceThis paper presents a combination of searches for the nonresonant production of Higgs boson pairs (HH) in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data set was collected by the CMS experiment at the LHC from 2016 to 2018 and corresponds to a total integrated luminosity of 138 fb. The observed (expected) upper limit on the inclusive HH production cross section relative to the standard model (SM) prediction is found to be 3.5 (2.5). Assuming all other Higgs boson couplings are equal to their SM values, the Higgs boson trilinear self-coupling modifier is constrained in the range 1.35 6.37 at 95% confidence level. Similarly, for the coupling modifier , which governs the interaction between two vector bosons and two Higgs bosons, we have excluded = 0 at more than 5 standard deviations for all values of . At 95% confidence level assuming other couplings are equal to their SM values, is constrained in the range 0.64 1.40. This work also studies HH production in several new physics scenarios, using the Higgs effective field theory (HEFT) framework. The HEFT framework is further exploited to study various ultraviolet complete models with an extended Higgs sector and set constraints on specific parameters. An extrapolation of the results to the integrated luminosity expected after the high-luminosity upgrade of the LHC is reported as well
Impact of MAPbI3 Phase Transitions on Solar Cell Performance: Everything you need to know about ab-initio methods in device performance
No full textThis paper presents a first step toward a pragmatic phenomenological multiscale approach to evaluate perovskite solar cell performance which determines material properties at the atomistic scale with first-principles calculations, and applies them in macro-scale device models. This work focuses on the MAPbI3 (MA = CH3NH3) perovskite and how its phase transitions impact on its optical, electronic, and structural properties which are investigated at the first-principles level. The obtained data are coupled to a numerical drift-diffusion device model enabling evaluation of the performance of corresponding single junction devices. The first-principles simulation applies a hybrid exchange-correlation functional adapted to the studied family of compounds. Validation by available experimental data is presented from materials properties to device performance, justifying the use of the approach for predictive evaluation of existing and novel perovskites. The coupling between atomistic and device models is described in terms of a framework for exchange of optical and electronic parameters between the two scales. The obtained results are systematically discussed in terms of first-principles levels of approximation performances
First evidence of violation in beauty baryon to charmonium decays
No full textInternational audienceA study of the difference in the asymmetries between and decays, , is performed using proton-proton collision data collected by the LHCb experiment in the years 2015--2018, corresponding to an integrated luminosity of . This quantity is measured to be , where the first uncertainty is statistical and the second is systematic. When combined with the previous LHCb result, a value of is obtained, corresponding to a significance of against the symmetry hypothesis. Studies of triple-product asymmetries, which provide an additional probe of violation, show no significant deviation from symmetry
Robust a posteriori estimation of probit-lognormal seismic fragility curves via sequential design of experiments and constrained reference prior
No full textInternational audienceA seismic fragility curve expresses the probability of failure of a structure conditional to an intensity measure (IM) derived from seismic signals. When only limited data is available, the practitioner often refers to the probit-lognormal model coupled with maximum likelihood estimation (MLE) to obtain estimates of these curves. This means that only a binary indicator of the state (BIS) of the structure is known, namely a failure or non-failure state indicator, when it is subjected to a seismic signal with an intensity measure IM. In this context, the objective of this work is to propose a method for optimally estimating such curves by obtaining the most precise estimate possible with the minimum of data. The novelty of our work is twofold. First, we present and show how to mitigate the likelihood degeneracy problem which is ubiquitous with small data sets and hampers frequentist approaches such as MLE. Second, we propose a novel strategy for sequential design of experiments (DoE) that selects seismic signals from a large database of synthetic or real signals via their IM values, to be applied to structures to evaluate the corresponding BISs. This strategy relies on a criterion based on information theory in a Bayesian framework. It therefore aims to sequentially designate the IM value such that the pair (IM, BIS) has on average, with respect to the BIS of the structure, the greatest impact on the posterior distribution of the fragility curve. The methodology is applied to a case study from the nuclear industry. The results demonstrate its ability to efficiently and robustly estimate the fragility curve, and to avoid degeneracy even with a limited amount of data, i.e., less than 100. Furthermore, we demonstrate that the estimates quickly reach the model bias induced by the probit-lognormal modeling. Eventually, two criteria are suggested to help the user stop the DoE algorithm