A search for supersymmetry with R-parity conservation in proton-proton collisions at a centre-of-mass energy of 7 TeV is presented. The data correspond to an integrated luminosity of 35 inverse picobarns collected by the CMS experiment at the LHC. The search is performed in events with jets and significant missing transverse energy, characteristic of the decays of heavy, pair-produced squarks and gluinos. The primary background, from standard model multijet production, is reduced by several orders of magnitude to a negligible level by the application of a set of robust kinematic requirements. With this selection, the data are consistent with the standard model backgrounds, namely t t-bar, W + jet and Z + jet production, which are estimated from data control samples. Limits are set on the parameters of the constrained minimal supersymmetric extension of the standard model. These limits extend those set previously by experiments at the Tevatron and LEP colliders
The results of comprehensive studies of missing transverse energy as measured by the CMS detector in pp collisions at a centre-of-mass energy of 7 TeV are presented. Three missing transverse energy reconstruction algorithms are deployed for various physics analyses. The scale and resolution for missing transverse energy are validated using vector boson and dijet events, and severe mismeasurements due to the detector are studied. We also parametrize the effects of multiple pp interactions within the same bunch crossings on the scale and resolution. A tool, called missing transverse energy significance, based on particle resolutions in each event is also presented.
A measurement is presented of the charged hadron multiplicity in hadronic PbPb collisions, as a function of pseudorapidity and centrality, at a collision energy of 2.76 TeV per nucleon pair. The data sample is collected using the CMS detector and a minimum-bias trigger, with the CMS solenoid off. The number of charged hadrons is measured both by counting the number of reconstructed particle hits and by forming hit doublets of pairs of layers in the pixel detector. The two methods give consistent results. The charged hadron multiplicity density, dN ch /dη| η=0 , for head-on collisions is found to be 1612 ± 55, where the uncertainty is dominated by systematic effects. Comparisons of these results to previous measurements and to various models are also presented. Keywords: Hadron-Hadron ScatteringOpen Access, Copyright CERN, for the benefit of the CMS collaboration doi:10.1007/JHEP08(2011)141 The CMS collaboration 21 JHEP08(2011)141 IntroductionQuantum chromodynamics (QCD), the theory of strong interactions, predicts a phase transition at high temperature between hadronic and deconfined matter [1]. Strongly interacting matter under extreme conditions can be studied experimentally using ultrarelativistic collisions of heavy nuclei. The field entered a new era in November 2010 when the Large Hadron Collider (LHC) produced the first PbPb collisions at a centre-of-mass energy per nucleon pair of 2.76 TeV. This represents an increase of more than one order of magnitude over the highest-energy nuclear collisions previously achieved in the laboratory. The multiplicity of charged particles produced in the central-rapidity region is a key observable characterising the properties of the quark-gluon matter created in these collisions [2]. Nuclei are extended objects, and their collisions occur at various impact parameters, referred to as "centralities". The studies of the dependence of the charged particle density on the type of colliding nuclei, on the centre-of-mass energy, and on the collision geometry are important for understanding the relative contributions of hard scattering and soft processes to particle production and provide insight into the partonic structure of the nuclei.-1 - JHEP08(2011)141In this paper we report measurements of the multiplicity density dN ch /dη of primary charged hadrons. The analysis is based on the 2.76 TeV-per-nucleon PbPb collision data recorded by the Compact Muon Solenoid (CMS) detector in December 2010, in runs without magnetic field. The pseudorapidity is defined as η = − ln[tan(θ/2)] with θ the polar angle with respect to the counterclockwise beam direction (the z axis). The number of primary charged hadrons N ch is defined as all charged hadrons produced in an event including decay products of particles with proper lifetimes less than 1 cm.A detailed description of the CMS experiment can be found in ref. [3]. The pixel tracker used for the analysis covers the region |η| < 2.5 and a full 2π in azimuth, with 66M detector channels out of which 97.5% were functional during data...
Cotton fiber is an extremely long plant cell. Fiber elongation is a complex process and the genes that are crucial for elongation are largely unknown. We previously cloned a cDNA encoding an isoform of cotton profilin and found that the gene (designated GhPFN1) was preferentially expressed in cotton fibers. In the present study, we have further analyzed the expression pattern of GhPFN1 during fiber development and studied its cellular function using tobacco suspension cells as an experimental system. We report that expression of GhPFN1 is tightly associated with fast elongation of cotton fibers whose growth requires an intact actin cytoskeleton. Overexpression of GhPFN1 in the transgenic tobacco cells was correlated with the formation of elongated cells that contained thicker and longer microfilament cables. Quantitative analyses revealed a 2.5-3.6 fold increase in total profilin levels and a 1.6-2.6 fold increase in the F-actin levels in six independent transgenic lines. In addition to the effect on cell elongation, we also observed delayed cell cycle progression and a slightly lower mitotic index in the transgenic cells. Based on these data, we propose that GhPFN1 may play a critical role in the rapid elongation of cotton fibers by promoting actin polymerization.
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