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Measurement of the integrated and differential t-tbar production cross sections for high-pt top quarks in pp collisions at sqrt(s) = 8 TeV
No full textSubmitted tp Phys. Rev. D. All figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/TOP-14-012/,see paper for full list of authorsInternational audienceThe cross section for pair pp collisions, collected with the CMS detector at the LHC with sqrt(s) = 8 TeV in data corresponding to an integrated luminosity of 19.7 inverse-femtobarns. The measurement is performed using lepton+jets events, where one top quark decays semileptonically, while the second top quark decays to a hadronic final state. The hadronic decay is reconstructed as a single, large-radius jet, and identified as a top quark candidate using jet substructure techniques. The integrated cross section and the differential cross sections as a function of top quark pt and rapidity are measured at particle level within a fiducial region related to the detector-level requirements and at parton level. The particle-level integrated cross section is found to be sigma[t-tbar] = 0.499 +/- 0.035 (stat+syst) +/- 0.095 (theory) +/- 0.013 (lumi) pb for top quark pt > 400 GeV. The parton-level measurement is sigma[t-tbar] = 1.44 +/- 0.10 (stat+syst) +/- 0.29 (theory) +/- 0.04 (lumi) pb. The integrated and differential cross section results are compared to predictions from several event generators
Analysis of the diurnal cycles for a better understanding of the mean annual cycle of forests greenness in Central Africa.
No full text14 pagesInternational audienceCentral Africa hosts the world's second largest tropical forest after the Amazonian basin. However, as compared to its Amazonian counterpart, the Central Africa forests receive much less rain (∼1500 mm/year in mean spread over two rainy seasons in March-May and September-November, and two dry seasons). They also experience a slower deforestation rate, so that the main threat for the next decades might come from climate variations. Nonetheless, their response to the annual cycle of solar radiation and rainfall/clouds is still poorly known. Analysing high resolution remote sensing data of Enhanced Vegetation Index, rainfall, cloudiness, and solar radiation for a target region located between 0 and 5°N and 12–19°E, we explore the climatic drivers of the forests greenness mean annual cycle. Three main points emerge; first, the diurnal cycle is a key-scale for understanding the mean annual cycles of rainfall and incoming solar radiation at surface, then how climate shapes the greenness mean annual evolution; second, neither the two dry seasons nor the two rainy seasons resemble each other in terms of cloud cover, solar radiation and rainfall, and their links with greenness levels; third, whereas the first rainy season (March-May) appears optimal for greenness especially because of favorable light conditions, water availability is the main controlling factor during the main dry season and at the start of the first vegetative season (February). Regarding the little dry season (mid-June-mid-August) and the second rainy season (September-October), light availability might be the main limiting factor. These findings pave the way for further studies of the climate interannual variability and change impacts on the Central Africa forests, taking into account time-scale interactions
Supplement: Localization and broadband follow-up of the gravitational-wave transient GW150914
No full text19 pages, 1 table, submitted to ApJS, see paper for full list of authors.International audienceThis Supplement provides supporting material for arXiv:1602.08492 . We briefly summarize past electromagnetic follow-up efforts as well as the organization and policy of the current electromagnetic follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the electromagnetic follow-up observations that were performed in the different bands
Characterization of Atmospheric Ekman Spirals at Dome C, Antarctica
No full textInternational audienceWe use wind speed and temperature measurements taken along a 45-m meteorological tower located at Dome C, Antarctica (75.06°S, 123.19)E) to highlight and characterize the Ekman spiral. Firstly, temperature records reveal that the atmospheric boundary layer at Dome C is stable during winter and summer nights (i.e., >85 % of the time). The wind vector, in both speed and direction, also shows a strong dependence with elevation. An Ekman model was then fitted to the measurements. Results show that the wind vector follows the Ekman spiral structure for more than 20 % of the year (2009). Most Ekman spirals have been detected during summer nights, that is, when the boundary layer is slightly stratified. During these episodes, the boundary-layer height ranged from 25 to 100 m, the eddy viscosity from 0.004 to 0.06 m2 s−1, and the Richardson number from zero to 1.6
Ammonia emissions in biomass burning regions: Estimation from satellitederivedmeasurements and comparison with bottom-up inventories
No full textInternational audienceVegetation fires emit large amounts of ammonia in the atmosphere (NH3). Excess NH3 can affect theenvironment in many ways: eutrophication of the ecosystem, soil acidification and loss of plantdiversity. Despite the numerous studies achieved in the past decades to better quantify NH3 emissionsfrom biomass burning (mainly from bottom-up approaches), the uncertainties remain still large. NH3satellite measurements are now available for a few years and offer the possibility to better assess theNH3 atmospheric budget, its spatial distribution and long-term trends.In this presentation we first analyze monthly NH3 total columns (molec cm-2) from IASI on MetOp-Asatellite over four large tropical regions known for their important seasonal fire activity. We nextderive for these regions the monthly NH3 emissions using a simplified box model and perform a topdownevaluation for NH3 of the most widely used fire emission inventories (GFEDv3.1 and theGFASv1.2).We then focus our attention on the NH3 emissions from the intense fires which were devastatingIndonesia in fall 2015. The region of Indonesia is characterized by peat soils, whose burning is thoughtto emit large amounts of NH3. To assess the importance of NH3 emissions from peat fires compared toother biomes, we derive NH3 enhancement ratios (ERs) relative to CO and we compare them to ERsderived from other biomes in tropical biomass burning regions. We also compare these results to theERs reported in the literature
Inter-hourly variability of total electron content during the quiet condition over Nigeria, within the equatorial ionization anomaly region
No full textInternational audienceThe inter-hourly variability (IHV) of the Total Electron Content (TEC) over Nigeria during the quiet days (Ap<4) of the year 2013 was examined using ground-based GPS receivers installed at seven (7) different locations across Nigeria by the Nigerian Global Navigation Satellite Systems (GNSS) Reference Network (NIGNET) operated by the office of the surveyor general of Nigeria. Nigeria is a country that lies within equatorial ionospheric anomaly (EIA) region. The IHV was calculated by converting the observed hourly slant TEC (STEC) value into the hourly vertical TEC (VTEC) and the differencing (∆TEC) with its corresponding hourly value from the previous day. There is a clear variation which depicts the expected temporal variability. The IHV in TEC in all the stations ranges between 0-20 TECU (TEC Units). The seasonal variation of the IHV of TEC over Nigeria maximizes (5-20 TECU) during Equinoctial months and minimizes (1-10 TECU) during the Solstice months. The IHV of TEC in September equinox period is higher than that of March equinox. Minimum value of IHV (~7 TECU at equinoxes and ~5 TECU at Solstice) was recorded at the Office of Surveyor General of the Federation (OSGF) station and the maximum value (~12 TECU at equinoxes and ~16 TECU at Solstice) was recorded at the Birni Kebbi Federal Polytechnic (BKFP) station which may be due to the fact that BKFP at 0.72° dip latitude is closer to the dip equator
Search for dark matter particles in proton-proton collisions at sqrt(s) = 8 TeV using the razor variables
No full textSubmitted to JHEP ; see paper for full list of authorsInternational audienceA search for dark matter particles directly produced in proton-proton collisions recorded by the CMS experiment at the LHC is presented. The data correspond to an integrated luminosity of 18.8 inverse femtobarns, at a center-of-mass energy of 8 TeV. The event selection requires at least two jets and no isolated leptons. The razor variables are used to quantify the transverse momentum balance in the jet momenta. The study is performed separately for events with and without jets originating from b quarks. The observed yields are consistent with the expected backgrounds and, depending on the nature of the production mechanism, dark matter production at the LHC is excluded at 90% confidence level for a mediator mass scale Lambda below 1 TeV. The use of razor variables yields results that complement those previously published
Search for neutral resonances decaying into a Z boson and a pair of b jets or tau leptons
No full textSubmitted to Phys. Lett. B ; see paper for full list of authorsInternational audienceA search is performed for a new resonance decaying into a lighter resonance and a Z boson. Two channels are studied, targeting the decay of the lighter resonance into either a pair of oppositely charged tau leptons or a b-bbar pair. The Z boson is identified via its decays to electrons or muons. The search exploits data collected by the CMS experiment at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.8 inverse femtobarns. No significant deviations are observed from the standard model expectation and limits are set on production cross sections and parameters of two-Higgs-doublet models
Nanoscale mechanisms for the reduction of heat transport in bismuth
No full textInternational audienceHand-on routes to reduce lattice thermal conductivity (LTC) in bismuth have been explored by employing a combination of Boltzmann's transport equation and ab initio calculations of phonon-phonon interaction within the density functional perturbation theory. We have first obtained the temperature dependence of the bulk LTC in excellent agreement with available experiments. A very accurate microscopic description of heat transport has been achieved and the electronic contribution to thermal conductivity has been determined. By controlling the interplay between phonon-phonon interaction and phonon scattering by sample boundaries, we predict the effect of size reduction for various temperatures and nanostructure shapes. The largest heat transport reduction is obtained in polycrystals with grain sizes smaller than 100 nm
Search for a Higgs boson decaying into gamma* gamma to ll gamma with low dilepton mass in pp collisions at sqrt(s) = 8 TeV
No full textReplaced with published version. Added journal reference. See paper for full list of authorsInternational audienceA search is described for a Higgs boson decaying into two photons, one of which has an internal conversion to a muon or an electron pair (ll gamma). The analysis is performed using proton-proton collision data recorded with the CMS detector at the LHC at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 inverse femtobarns. The events selected have an opposite-sign muon or electron pair and a high transverse momentum photon. No excess above background has been found in the three-body invariant mass range 120 < m[ll gamma] < 150 GeV, and limits have been derived for the Higgs boson production cross section times branching fraction for the decay H to gamma* gamma to ll gamma, where the dilepton invariant mass is less than 20 GeV. For a Higgs boson with m[H] = 125 GeV, a 95% confidence level (CL) exclusion observed (expected) limit is 6.7 (5.9 +2.8/-1.8) times the standard model prediction. Additionally, an upper limit at 95% CL on the branching fraction of H to J/Psi gamma for the 125 GeV Higgs boson is set at 1.5E-3