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Production of leading charged particles and leading charged-particle jets at small transverse momenta in pp collisions at sqrt(s)=8 TeV
No full textsee paper for full list of authorsInternational audienceThe per-event yield of the highest transverse momentum charged particle and charged-particle jet, integrated above a given pt(min) threshold starting at pt(min)=0.8 and 1 GeV, respectively, is studied in pp collisions at sqrt(s)=8 TeV. The particles and the jets are measured in the pseudorapidity ranges abs(eta)<2.4 and 1.9, respectively. The data are sensitive to the momentum scale at which parton densities saturate in the proton, to multiple partonic interactions, and other key aspects of the transition between the soft and hard QCD regimes in hadronic collisions
Construction and commissioning of a technological prototype of a high-granularity semi-digital hadronic calorimeter
No full text49 pages, 41 figuresInternational audienceA large prototype of 1.3m3 was designed and built as a demonstrator of the semi-digital hadronic calorimeter (SDHCAL) concept proposed for the future ILC experiments. The prototype is a sampling hadronic calorimeter of 48 units. Each unit is built of an active layer made of 1m2 Glass Resistive Plate Chamber(GRPC) detector placed inside a cassette whose walls are made of stainless steel. The cassette contains also the electronics used to read out the GRPC detector. The lateral granularity of the active layer is provided by the electronics pick-up pads of 1cm2 each. The cassettes are inserted into a self-supporting mechanical structure built also of stainless steel plates which, with the cassettes walls, play the role of the absorber. The prototype was designed to be very compact and important efforts were made to minimize the number of services cables to optimize the efficiency of the Particle Flow Algorithm techniques to be used in the future ILC experiments. The different components of the SDHCAL prototype were studied individually and strict criteria were applied for the final selection of these components. Basic calibration procedures were performed after the prototype assembling. The prototype is the first of a series of new-generation detectors equipped with a power-pulsing mode intended to reduce the power consumption of this highly granular detector. A dedicated acquisition system was developed to deal with the output of more than 440000 electronics channels in both trigger and triggerless modes. After its completion in 2011, the prototype was commissioned using cosmic rays and particles beams at CERN
Measurement of electroweak production of two jets in association with a Z boson in proton-proton collisions at sqrt(s)= 8 TeV
No full textReplaced with published version. Added journal reference and DOI ; see paper for full list of authorsInternational audienceThe purely electroweak (EW) cross section for the production of two jets in association with a Z boson, in proton-proton collisions at sqrt(s) = 8 TeV, is measured using data recorded by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 19.7 inverse femtobarns. The electroweak cross section for the lljj final state (with l = e or mu and j representing the quarks produced in the hard interaction) in the kinematic region defined by M[ll] > 50 GeV, M[jj] > 120 GeV, transverse momentum pt[j] > 25 GeV, and pseudorapidity abs(eta[j]) < 5, is found to be sigma[EW](lljj) = 174 +/- 15 (stat) +/- 40 (syst) fb, in agreement with the standard model prediction. The associated jet activity of the selected events is studied, in particular in a signal-enriched region of phase space, and the measurements are found to be in agreement with QCD predictions
Cross section for bb¯ production via dielectrons in d + Au collisions at sNN−−−−√=200 GeV
No full textInternational audienceWe report a measurement of e+e− pairs from semileptonic heavy-flavor decays in d+Au collisions at sNN−−−√=200 GeV. By exploring the mass and transverse-momentum dependence of the yield, the bottom decay contribution can be isolated from charm, and quantified by comparison to pythia and mc@nlo simulations. The resulting bb¯-production cross section is σdAubb¯=1.37±0.28(stat)±0.46(syst) mb, which is equivalent to a nucleon-nucleon cross section of σNNbb=3.4±0.8(stat)±1.1(syst)μb
Fiscal Devaluations in a Monetary Union and the Extensive Margin of Trade
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West African Monsoon dynamics in idealized simulations: the competitive roles of SST warming and CO 2
No full textInternational audienceThe West African Monsoon (WAM) is affected by large climate variability at different timescales, from interannual to multidecadal, with strong environmental and socioeconomic impacts associated to climate-related rainfall variability, especially in the Sahelian belt. State-of-the-art coupled climate models still show poor ability in correctly simulating the WAM past variability and also a large spread is observed in future climate projections. In this work, the July-to-September (JAS) WAM variability in the period 1979-2008 is studied in AMIP-like simulations (SST-forced) from CMIP5. The individual roles of global SST warming and CO 2 concentration increasing are investigated through idealized experiments simulating a 4K warmer SST and a 4x CO 2 concentration , respectively. Results show a dry response in Sahel to SST warming, with dryer conditions over western Sahel. On the contrary, wet conditions are observed when CO 2 is increased, with the strongest response over central-eastern Sahel. The precipitation changes are associated to modifications in the regional atmospheric circulation: dry (wet) conditions are associated with reduced (increased) convergence in the lower troposphere, a southward (northward) shift of the African Easterly Jet, and a weaker (stronger) Tropical Easterly Jet. The co-variability between global SST and WAM precipitation is also investigated, highlighting a reorganization of the main co-variability modes. Namely, in the 4xCO 2 simulation the influence of Tropical Pacific is dominant, while it is reduced in the 4K simulation, which also shows an increased coupling with the eastern Pacific and the Indian Ocean. The above results suggest a competitive action of SST warming and CO 2 increasing on the WAM climate variability, with opposite effects on precipitation. The combination of the observed positive and negative response in precipitation, with wet conditions in central-eastern Sahel and dry conditions in western Sahel, is consistent with the future precipitation trends over West Africa resulting from CMIP5 coupled simulations. It is argued that the large spread in CMIP5 future projections may be related to the weight given to SST warming and direct CO 2 effect by individual models. The capability of climate models in reproducing the SST-precipitation relationship appears to be crucial in this respect
Geographic distribution of zonal wind and UV albedo at cloud top level from VMC camera on Venus Express: Influence of Venus topography through stationary gravity waves vertical propagation.
No full textInternational audienceGeographic distribution of zonal wind and UV albedo at cloud top level from VMC camera on Venus Express: Influence of Venus topography through stationary gravity waves vertical propagation. UV images (at 365 nm) of Venus cloud top collected with VMC camera on board Venus Express allowed to derive a large number of wind measurements at altitude 67±2 km from tracking of cloud features in the period 2006-2012. Both manual (45,600) and digital (391,600) individual wind measurements over 127 orbits were analyzed showing various patterns with latitude and local time. A new longitude-latitude geographic map of the zonal wind shows a conspicuous region of strongly decreased zonal wind, a remarkable feature that was unknown up to now. While the average zonal wind near equator (from 5 • S to 15 • s) is-100.9 m/s in the longitude range 200-330 • , it reaches-83.4 m/s in the range 60-100 • , a difference of 17.5 m/s. When compared to the altimetry map of Venus, it is found that the zonal wind pattern is well correlated with the underlying relief in the region of Aphrodite Terra, with a downstream shift of about 30 • (∼3,200 km). We interpret this pattern as the result of stationary gravity waves produced at ground level by the up lift of air when the horizontal wind encounters a mountain slope. These waves can propagate up to cloud top level, break there and transfer their momentum to the zonal flow. A similar phenomenon is known to operate on Earth with an influence on mesospheric winds. The LMD-GCM for Venus was run with or without topography, with and without a parameterization of gravity waves and does not display such an observed change of velocity near equator. The cloud albedo map at 365 nm varies also in longitude and latitude. We speculate that it might be the result of increased vertical mixing associated to wave breaking, and decreased abundance of the UV absorber which makes the contrast in images. The impact of these new findings on current super rotation theories remains to be assessed. This work was triggered by the presence of a conspicuous peak at 117 days in a time series of wind measurements. This is the length of the solar day as seen at the ground of Venus. Since VMC measurements are done preferably in a local time window centred on the sub-solar point, any parameter having a geographic longitude dependence will show a peak at 117 days
Observation of the baryonic decay
No full textInternational audienceWe report the observation of the baryonic decay using a data sample of pairs produced in annihilations at . This data sample was recorded with the detector at the PEP-II storage ring at SLAC. We find , where the uncertainties are statistical, systematic, and due to the uncertainty of the branching fraction, respectively. The result has a significance corresponding to 5.0 standard deviations, including all uncertainties. For the resonant decay , we determine the upper limit at confidence level
Measurement of the Z boson differential cross section in transverse momentum and rapidity in proton-proton collisions at 8 TeV
No full textsee paper for full list of authorsInternational audienceWe present a measurement of the Z boson differential cross section in rapidity and transverse momentum using a data sample of pp collision events at a centre-of-mass energy sqrt(s)=8 TeV, corresponding to an integrated luminosity of 19.7 inverse femtobarns. The Z boson is identified via its decay to a pair of muons. The measurement provides a precision test of quantum chromodynamics over a large region of phase space. In addition, due to the small experimental uncertainties in the measurement the data has the potential to constrain the gluon parton distribution function in the kinematic regime important for Higgs boson production via gluon fusion. The results agree with the next-to-next-to-leading-order predictions computed with the FEWZ program. The results are also compared to the commonly used leading-order MADGRAPH and next-to-leading-order POWHEG generators