395 research outputs found

    Search for exotic particles decaying into WZ boson pairs at the CMS experiment

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    The Standard Model (SM) is the theoretical framework that describes the state of the art in particle physics. It has been extremely successful at describing the particles and forces observed in nature. However, the theory is known to be incomplete. Among other things, it cannot explain dark matter, the dynamics of electroweak symmetry breaking, neutrino masses, nor how gravity is to be incorporated into its framework. A popular extension of the SM introduces a new particle similar to a W boson, typically called a W' boson. Other classes of theories, such as technicolor, offer alternatives to the SM's implementation of electroweak symmetry breaking and predict, among others, a new particle called technirho. The new particles introduced by these extensions are expected to decay into WZ boson pairs. This final state provides a distinctive search signal. This dissertation describes a search for these exotic new particles decaying via WZ pairs to a leptonic ( l+l-l'v, with l, l' = e, u) final state. The data was collected with the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider at CERN (European Organization for Nuclear Research). Data from 5 /fb of proton-proton collisions taken at a center of mass energy of 7 TeV in 2011 and 20 /fb taken at a center of mass energy of 8 TeV in 2012 were analyzed. No significant excess over the expected Standard Model background was observed and 95% confidence level upper exclusion limits were placed on the production cross section. These were interpreted as mass exclusion limits in the common benchmark of the Sequential Standard Model (SSM) and low-scale technicolor. Assuming the SSM, W' masses between 170 and 1450 GeV were excluded. Limits were also set on the mass of the technirho under a range of scenarios. These are the strongest limits to date in this channel

    Differential cross section measurements for the production of a W boson in association with jets in proton‚Äďproton collisions at ‚ąös = 7 TeV

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    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 ‚ąí1]. 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

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