Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at √s = 7 TeV

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb[superscript −1]. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

Search for stop and higgsino production using diphoton Higgs boson decays

Results are presented of a search for a "natural" supersymmetry scenario with gauge mediated symmetry breaking. It is assumed that only the supersymmetric partners of the top-quark (stop) and the Higgs boson (higgsino) are accessible. Events are examined in which there are two photons forming a Higgs boson candidate, and at least two b-quark jets. In 19.7 inverse femtobarns of proton-proton collision data at sqrt(s) = 8 TeV, recorded in the CMS experiment, no evidence of a signal is found and lower limits at the 95% confidence level are set, excluding the stop mass below 360 to 410 GeV, depending on the higgsino mass

Impacts of the Tropical Pacific/Indian Oceans on the Seasonal Cycle of the West African Monsoon

The current consensus is that drought has developed in the Sahel during the second half of the twentieth century as a result of remote effects of oceanic anomalies amplified by local land–atmosphere interactions. This paper focuses on the impacts of oceanic anomalies upon West African climate and specifically aims to identify those from SST anomalies in the Pacific/Indian Oceans during spring and summer seasons, when they were significant. Idealized sensitivity experiments are performed with four atmospheric general circulation models (AGCMs). The prescribed SST patterns used in the AGCMs are based on the leading mode of covariability between SST anomalies over the Pacific/Indian Oceans and summer rainfall over West Africa. The results show that such oceanic anomalies in the Pacific/Indian Ocean lead to a northward shift of an anomalous dry belt from the Gulf of Guinea to the Sahel as the season advances. In the Sahel, the magnitude of rainfall anomalies is comparable to that obtained by other authors using SST anomalies confined to the proximity of the Atlantic Ocean. The mechanism connecting the Pacific/Indian SST anomalies with West African rainfall has a strong seasonal cycle. In spring (May and June), anomalous subsidence develops over both the Maritime Continent and the equatorial Atlantic in response to the enhanced equatorial heating. Precipitation increases over continental West Africa in association with stronger zonal convergence of moisture. In addition, precipitation decreases over the Gulf of Guinea. During the monsoon peak (July and August), the SST anomalies move westward over the equatorial Pacific and the two regions where subsidence occurred earlier in the seasons merge over West Africa. The monsoon weakens and rainfall decreases over the Sahel, especially in August.Peer reviewe

Search for anomalous production of events with three or more leptons in pp collisions at √s = 8TeV

Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published articles title, journal citation, and DOI.A search for physics beyond the standard model in events with at least three leptons is presented. The data sample, corresponding to an integrated luminosity of 19.5fb-1 of proton-proton collisions with center-of-mass energy s=8TeV, was collected by the CMS experiment at the LHC during 2012. The data are divided into exclusive categories based on the number of leptons and their flavor, the presence or absence of an opposite-sign, same-flavor lepton pair (OSSF), the invariant mass of the OSSF pair, the presence or absence of a tagged bottom-quark jet, the number of identified hadronically decaying τ leptons, and the magnitude of the missing transverse energy and of the scalar sum of jet transverse momenta. The numbers of observed events are found to be consistent with the expected numbers from standard model processes, and limits are placed on new-physics scenarios that yield multilepton final states. In particular, scenarios that predict Higgs boson production in the context of supersymmetric decay chains are examined. We also place a 95% confidence level upper limit of 1.3% on the branching fraction for the decay of a top quark to a charm quark and a Higgs boson (t→cH), which translates to a bound on the left- and right-handed top-charm flavor-violating Higgs Yukawa couplings, λtcH and λctH, respectively, of |λtcH|2+|λctH|2<0.21

Study of W boson production in pPb collisions at vsNN = 5.02 TeV

The first study of W boson production in pPb collisions is presented, for bosons decaying to a muon or electron, and a neutrino. The measurements are based on a data sample corresponding to an integrated luminosity of 34.6 nb-1 at a nucleon–nucleon centre-of-mass energy of vsNN = 5.02 TeV, collected by the CMS experiment. The W boson differential cross sections, lepton charge asymmetry, and forward–backward asymmetries are measured for leptons of transverse momentum exceeding 25 GeV/c, and as a function of the lepton pseudorapidity in the |?lab| < 2.4range. Deviations from the expectations based on currently available parton distribution functions are observed, showing the need for including W boson data in nuclear parton distribution global fits

Measurement of the tt¯ production cross section in the dilepton channel in pp collisions at s√ = 8 TeV

The top-antitop quark ( tt¯ ) production cross section is measured in proton-proton collisions at s√ = 8 TeV with the CMS experiment at the LHC, using a data sample corresponding to an integrated luminosity of 5.3 fb−1. The measurement is performed by analysing events with a pair of electrons or muons, or one electron and one muon, and at least two jets, one of which is identified as originating from hadronisation of a bottom quark. The measured cross section is 239 ± 2 (stat.) ± 11 (syst.) ± 6 (lum.) pb, for an assumed top-quark mass of 172.5 GeV, in agreement with the prediction of the standard model

Impacts of Mowing on Bird Abundance, Distribution, and Hazards to Aircraft at Westover Air Reserve Base, Massachusetts

Few studies have measured the impacts of mowing on bird use of habitat and the risk of bird collisions with aircraft on North American airfields. The need for this research has increased as airfields become some of the only large contiguous grasslands available to rare migratory birds in some areas. I studied bird abundance, distribution and behaviors at Westover Air Reserve Base, Massachusetts, USA in June and July 2004. I compared my data with bird strike records to discern any patterns associated with mowing of airfield vegetation. There was no difference in total number of birds or species between mowed and unmowed plots adjacent to runways and taxiways. There were more Upland Sandpipers and Eastern Meadowlarks in mowed vegetation and more sparrows (Grasshopper and Savannah) in unmowed vegetation. From 1997 to 2005, swallows were the birds most often struck by aircraft in June and July at Westover, and were also the second most numerous birds in both mowed and unmowed plots. Bird species that pose high Bird/Wildlife Aircraft Strike Hazard (BASH) risk at Westover included Turkey Vulture, Red-tailed Hawk, Great Blue Heron, and Canada Goose. I did not observe those species in paired plots of mowed or unmowed airfield vegetation adjacent to runways and taxiways at Westover. I opportunistically observed 64 incidents where species that pose high BASH risk were in or adjacent to areas where aircraft operate. Birds struck most frequently at Westover between April 1997 and January 2005 were “swallows”, American Kestrel, Killdeer, Horned Lark, Eastern Meadowlark, and Mourning Dove. Current mowing practices at Westover may have adverse effects on Upland Sandpiper and Grasshopper Sparrow, both state-listed, rare, grassland birds, but may not measurably reduce overall risk to aircraft, given the continued presence of large, high BASH risk species. I recommend methods to reduce threats posed by high-risk species at Westover, and further research to seek ways to reduce adverse effects of mowing on state-listed, rare, migratory species of birds

Measurement of prompt ψ (2S) to J /ψ yield ratios in Pb-Pb and p - p collisions at sNN =2.76 TeV

The ratio between the prompt ψ(2S) and J/ψ yields, reconstructed via their decays into μ+μ-, is measured in Pb-Pb and p-p collisions at sNN=2.76 TeV. The analysis is based on Pb-Pb and p-p data samples collected by CMS at the Large Hadron Collider, corresponding to integrated luminosities of 150 μb-1 and 5.4 pb-1, respectively. The double ratio of measured yields (Nψ(2S)/NJ/ψ)Pb-Pb/(Nψ(2S)/NJ/ψ)p-p is computed in three Pb-Pb collision centrality bins and two kinematic ranges: one at midrapidity, |y|&lt;1.6, covering the transverse momentum range 6.5&lt;30 GeV/c, and the other at forward rapidity, 1.6&lt;|y|&lt;2.4, extending to lower pT values, 3&lt;30 GeV/c. The centrality-integrated double ratio changes from 0.45±0.13(stat)±0.07(syst) in the first range to 1.67±0.34(stat)±0.27(syst) in the second. This difference is most pronounced in the most central collisions