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Browsing by Author "CMS collaboration (2129 authors)"

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  • Measurement of prompt $J/\psi$ pair production in pp collisions at $ \sqrt{s} $ = 7 Tev
    Publication . CMS collaboration (2129 authors); Hollar, Jonathan; Nayak, Aruna; Bargassa, Pedrame; Beirão Da Cruz E Silva, Cristóvão; Faccioli, Pietro; Ferreira Parracho, Pedro Guilherme; Gallinaro, Michele; Nguyen, Federico; Rodrigues Antunes, Joao; Seixas, Joao; Varela, Joao; Vischia, Pietro; Lloret Iglesias, Lara; David Tinoco Mendes, Andre; Musella, Pasquale; Silva, Pedro; Pela, Joao; Leonardo, Nuno
    Production of prompt J/ψ meson pairs in proton-proton collisions at $ \sqrt{s} $ = 7 TeV is measured with the CMS experiment at the LHC in a data sample corresponding to an integrated luminosity of about 4.7 fb$^{−1}$. The two J/ψ mesons are fully reconstructed via their decays into μ$^{+}$ μ$^{−}$ pairs. This observation provides for the first time access to the high-transverse-momentum region of J/ψ pair production where model predictions are not yet established. The total and differential cross sections are measured in a phase space defined by the individual J/ψ transverse momentum (p$_{T}^{J/}^{ψ}$) and rapidity (|y$^{J/}^{ψ}$ |): |y$^{J/}^{ψ}$ | < 1.2 for p$_{T}^{J/}^{ψ}$ > 6.5 GeV/c, 1.2 < |y$^{J/}^{ψ}$ | < 1.43 for a p$_{T}$ threshold that scales linearly with |y$^{J/}^{ψ}$ | from 6.5 to 4.5 GeV/c, and 1.43 < |y$^{J/}^{ψ}$ | < 2.2 for p$_{T}^{J/}^{ψ}$ > 4.5 GeV/c. The total cross section, assuming unpolarized prompt J/ψ pair production is 1.49 ± 0.07 (stat) ±0.13 (syst) nb. Different assumptions about the J/ψ polarization imply modifications to the cross section ranging from −31% to +27%.
    2014-09-17Journal article Open access Show more
  • Search for Supersymmetry Using Razor Variables in Events with $b$-Tagged Jets in $pp$ Collisions at $\sqrt{s} =$ 8 TeV
    Publication . CMS collaboration (2129 authors); Hollar, Jonathan; Nayak, Aruna; Bargassa, Pedrame; Beirão Da Cruz E Silva, Cristóvão; Faccioli, Pietro; Ferreira Parracho, Pedro Guilherme; Gallinaro, Michele; Lloret Iglesias, Lara; Nguyen, Federico; Rodrigues Antunes, Joao; Seixas, Joao; Varela, Joao; Vischia, Pietro; David Tinoco Mendes, Andre; Silva, Pedro; Musella, Pasquale; Pela, Joao; Leonardo, Nuno

    An inclusive search for supersymmetry in events with at least one b-tagged jet is performed using proton-proton collision data collected by the CMS experiment in 2012 at a center-of-mass energy of 8 TeV. The data set size corresponds to an integrated luminosity of 19.3  fb−1. The two-dimensional distribution of the razor variables R2 and MR is studied in events with and without leptons. The data are found to be consistent with the expected background, which is modeled with an empirical function. Exclusion limits on supersymmetric particle masses at a 95% confidence level are derived in several simplified supersymmetric scenarios for several choices of the branching fractions. By combining the likelihoods of a search in events without leptons and a search that requires a single lepton (electron or muon), an improved bound on the top-squark mass is obtained. Assuming the lightest supersymmetric particle to be stable and weakly interacting, and to have a mass of 100 GeV, the branching-fraction-dependent (-independent) production of gluinos is excluded for gluino masses up to 1310 (1175) GeV. The corresponding limit for top-squark pair production is 730 (645) GeV.

    2015-03-23Journal article Open access Show more