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Measurement of the top quark pair production cross section in proton-proton collisions at sqrt(s)=13 TeV
No full textSubmitted to Phys. Rev. Lett ; see paper for full list of authorsInternational audienceThe top quark pair production cross section is measured for the first time in proton-proton collisions at sqrt(s) = 13 TeV by the CMS experiment at the CERN LHC, using data corresponding to an integrated luminosity of 42 inverse picobarns. The measurement is performed by analyzing events with at least one electron and one muon of opposite charge, and at least two jets. The measured cross section is 769 +/- 60 (stat) +/- 55 (syst) +/- 92 (lum) pb, in agreement with the expectation from the standard model
Measurement of the ttbar production cross section in the all-jets final state in pp collisions at sqrt(s)=8 TeV
No full textSubmitted to Eur. Phys. J. C ; see paper for full list of authorsInternational audienceThe cross section for ttbar production in the all-jets final state is measured in pp collisions at a centre-of-mass energy of 8 TeV at the LHC with the CMS detector, in data corresponding to an integrated luminosity of 18.4 inverse femtobarns. The inclusive cross section is found to be 275.6 +/- 6.1 (stat) +/- 37.8 (syst) +/- 7.2 (lumi) pb. The normalized differential cross sections are measured as a function of the top quark transverse momenta, pt, and compared to predictions from quantum chromodynamics. The results are reported at detector, parton, and particle levels. In all cases, the measured top quark pt spectra are significantly softer than theoretical predictions
Search for exotic decays of a Higgs boson into undetectable particles and photons
No full textSubmitted to Phys. Lett. B ; see paper for full list of authorsInternational audienceA search is presented for exotic decays of a Higgs boson into undetectable particles and one or two isolated photons in pp collisions at a center-of-mass energy of 8 TeV. The data correspond to an integrated luminosity of up to 19.4 inverse femtobarns collected with the CMS detector at the LHC. Higgs bosons produced in gluon-gluon fusion and in association with a Z boson are investigated, using models in which the Higgs boson decays into a gravitino and a neutralino or a pair of neutralinos, followed by the decay of the neutralino to a gravitino and a photon. The selected events are consistent with the background-only hypothesis, and limits are placed on the product of cross sections and branching fractions. Assuming a standard model Higgs boson production cross-section, a 95% confidence level upper limit is set on the branching fraction of a 125 GeV Higgs boson decaying into undetectable particles and one or two isolated photons as a function of the neutralino mass. For neutralino masses from 1 to 120 GeV an upper limit in the range of 7 to 13% is obtained. Further results are given as a function of the neutralino lifetime, and also for a range of Higgs boson masses
Global trends and variability in integrated water vapour from ground-based GPS data and atmospheric models
No full textInternational audienceA high-quality, consistent, global, long-term dataset of integrated water vapour (IWV) was produced from Global Positioning System (GPS) measurements at more than 400 sites over the globe among which 120 sites have more than 15 years of data. The GPS delay data were converted to IWV using surface pressure and weighted mean temperature estimates from ERA-Interim reanalysis. A two-step screening method was developed to detect and remove outliers in the IWV data. It is based on: 1) GPS data processing information and delay formal errors, and 2) intercomparison with ERA-Interim reanalysis data. The GPS IWV data are also homogenized to correct for offsets due to instrumental changes and other unknown factors. The differential homogenization method uses ERA-Interim IWV as a reference. The resulting GPS data are used to document the mean distribution, the global trends and the variability of IWV over the period 1995-2010, and are analysed in coherence with precipitation and surface temperature data (from observations and ERA-Interim reanalysis). These data are also used to assess global climate model simulations extracted from the IPCC AR5 archive. Large coherent spatial patterns of moistening and drying are evidenced but significant discrepancies are also seen between GPS measurements, reanalysis and climate models in various regions. In terms of variability, the monthly mean anomalies are intercompared. The temporal correlation between GPS and the climate model simulations is overall quite small but the spatial variation of the magnitude of the anomalies is globally well simulated. GPS IWV data prove to be useful to validate global climate model simulations and highlight deficiencies in their representation of the water cycle
Reconstruction of flux and altitude of volcanic SO2 emissions from IASIsatellite observations: implications for volcanological and atmosphericalstudies.
No full textInternational audienceVolcanic SO2 degassing is a crucial indicator of the sub-surface volcanic activity, which is widelyused today for volcano monitoring and hazard assessment purposes. Volcanic SO2 is also importantregarding atmospherical studies. More easily detectable from space, SO2 can be used as a proxy ofthe presence of ash to anticipate air traffic issues caused by explosive eruptions. Moreover, volcanicSO2 strongly impacts air quality but also climate following its conversion to radiatively-activesulphate aerosols. However, the accurate assessment of these various impacts is currently hamperedby the poor knowledge of volcanic SO2 emissions, which can substantially vary with time, in termsof flux and altitude.To fulfil this need, we propose a strategy relying on satellite observations, which consequently allowsfor monitoring the eruptive activity of any remote volcano. The method consists in assimilatingsnapshots of the SO2 load, provided every ~12 hours by IASI, in an inversion scheme that involvesthe use of a chemistry-transport model to describe the dispersion of SO2 released in the atmosphere.Applied on Eyjafjallajökull (Iceland) and Etna (Italy) eruption case-studies, this procedure allows forretrospectively reconstructing both the flux and altitude of the SO2 emissions with an hourlyresolution. We show the improvement gained in the simulations and forecasts of the location andmass load of volcanic SO2 clouds using such a detailed reconstruction of emissions.For calibration-validation purpose, we compared our satellite-derived time-series of the SO2 fluxwith ground-based observations available on Etna. This comparison indicates a good agreementduring ash-poor phases of the eruption. However, large discrepancies are observed during the ashrichparoxysmal phase as a result of enhanced plume opacity affecting ground-based ultravioletspectroscopic retrievals. Therefore, the SO2 emission rate derived from the ground is underestimatedby almost one order of magnitude. This result calls for the necessity to revisit currently availableinventories of the global budget of sulfur released by volcanoes, because they heavily rely on groundbasedobservations. It also shows that volcano observatories cannot rely solely on ground-basedspectroscopical observations for the monitoring of ash-rich explosive eruptions.Moreover, we will discuss the assimilation procedure of recently-developed IASI products whichdeliver snapshots of the volcanic SO2 cloud altitude. Such improvement renders the inversionprocedure, used for the reconstruction of the altitude of emissions, independent of the wind shearprerequisite.Eventually, building on our accurate source of precursory SO2 gas emissions, we can explore theformation and lifecycle of sulphate aerosols in volcanic plumes. Remote sensing of troposphericsulphate aerosols from moderate eruptions is not straightforward. However, we will show how acombination of chemistry-transport modelling and space-borne CALIOP lidar observations allowsfor tracking these aerosols despite their small concentration. The latest promising developments fromhigh-resolution infrared sounders will bring further constraints on sulphate aerosol load andcharacteristics in dispersed volcanic clouds
Role of the magnetosheath in the interaction of magnetic clouds with the Earth’s magnetosphere
No full textInternational audienceMagnetic clouds are among the most geoeffective solar events capable to trigger strong magnetic storms in the terrestrial magnetosphere. However, their characteristics and those of the surrounding media are not always capable to explain their high level of geoeffectivity. From observations and simulations, we investigate here the role of the bow shock and of the magnetosheath. Conjugated observations upstream (ACE) and downstream (CLUSTER) of the bow shock show that the magnetic clouds’ magnetic structure in the magnetosheath can strongly depart from their pristine structure upstream of the bow shock. This modification depends on the shock configuration (quasi-perpendicular, quasi-parallel). We also discuss this question from hybrid simulations of the interaction of magnetic clouds with the bow shock. We show that this interaction may produce unexpected characteristics in the magnetosheath, such as asymmetric distributions of magnetic field, density, temperature, velocity. They thus lead to interactions with the magnetosphere which were not expected from the pristine characteristics of the magnetic clouds in the solar wind upstream of bow shock. We here discuss the effects of such an asymmetric magnetosheath on key parameters for the interaction with the magnetopause (reconnection, instabilities), responsible in turn for the development of geomagnetic activity inside the magnetosphere
Accurate prediction of the statistics of repetitions in random sequences: a case study in Archaea genomes
No full textInternational audienc
Search for direct pair production of supersymmetric top quarks decaying to all-hadronic final states in pp collisions at sqrt(s) = 8 TeV
No full textSubmitted to EPJC ; see paper for full list of authorsInternational audienceResults are reported from a search for the pair production of top squarks, the supersymmetric partners of top quarks, in final states with jets and missing transverse momentum. The data sample used in this search was collected by the CMS detector and corresponds to an integrated luminosity of 18.9 inverse femtobarns of proton-proton collisions at a centre-of-mass energy of 8 TeV produced by the LHC. The search features novel background suppression and prediction methods, including a dedicated top quark pair reconstruction algorithm. The data are found to be in agreement with the predicted backgrounds. Exclusion limits are set in simplified supersymmetry models with the top squark decaying to jets and an undetected neutralino, either through an on-shell top quark or through a bottom quark and chargino. Models with the top squark decaying via an on-shell top quark are excluded for top squark masses up to 755 GeV in the case of neutralino masses below 200 GeV. For decays via a chargino, top squark masses up to 620 GeV are excluded, depending on the masses of the chargino and neutralino
Measurement of the Z gamma to nu nu-bar gamma production cross section in pp collisions at sqrt(s) = 8 TeV and limits on anomalous Z-Z-gamma and Z-gamma-gamma trilinear gauge boson couplings
No full textSubmitted to Phys. Lett. B ; see paper for full list of authorsInternational audienceA measurement of the Z gamma to nu nu-bar gamma production cross section in pp collisions at sqrt(s) = 8 TeV is presented, using data corresponding to an integrated luminosity of 19.6 inverse-femtobarns collected with the CMS detector at the LHC. This measurement is based on the observation of events with large missing energy and with a single photon with transverse momentum above 145 GeV and absolute pseudorapidity in the range |eta| < 1.44. The measured Z gamma to nu nu-bar gamma production cross section, 52.7 +/- 2.1(stat) +/- 6.4 (syst) +/- 1.4 (lumi) fb, agrees well with the standard model prediction of 50.0+2.4-2.2 fb. A study of the photon transverse momentum spectrum yields the most stringent limits to date on the anomalous Z-Z-gamma and Z-gamma-gamma trilinear gauge boson couplings
Social, Structured and Semantic Search
No full textInternational audienceSocial content such as blogs, tweets, news etc. is a rich source of interconnected information. We identify a set of requirements for the meaningful exploitation of such rich content, and present a new data model, called S3, which is the first to satisfy them. S3 captures social relationships between users, and between users and content, but also the structure present in rich social content, as well as its semantics. We provide the first top-k keyword search algorithm taking into account the social, structured, and semantic dimensions and formally establish its termination and correctness. Experiments on real social networks demonstrate the efficiency and qualitative advantage of our algorithm through the joint exploitation of the social, structured, and semantic dimensions of S3