163 research outputs found

    Effective Lagrangian Approach to the Theory of Eta Photoproduction in the N∗(1535)N^{*}(1535) Region

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    We investigate eta photoproduction in the N∗(1535)N^{*}(1535) resonance region within the effective Lagrangian approach (ELA), wherein leading contributions to the amplitude at the tree level are taken into account. These include the nucleon Born terms and the leading tt-channel vector meson exchanges as the non-resonant pieces. In addition, we consider five resonance contributions in the ss- and uu- channel; besides the dominant N∗(1535)N^{*}(1535), these are: N∗(1440),N∗(1520),N∗(1650)N^{*}(1440),N^{*}(1520),N^{*}(1650) and N∗(1710)N^{*}(1710). The amplitudes for the π∘\pi^\circ and the η\eta photoproduction near threshold have significant differences, even as they share common contributions, such as those of the nucleon Born terms. Among these differences, the contribution to the η\eta photoproduction of the ss-channel excitation of the N∗(1535)N^{*}(1535) is the most significant. We find the off-shell properties of the spin-3/2 resonances to be important in determining the background contributions. Fitting our effective amplitude to the available data base allows us to extract the quantity χΓηA1/2/ΓT\sqrt{\chi \Gamma_\eta} A_{1/2}/\Gamma_T, characteristic of the photoexcitation of the N∗(1535)N^{*}(1535) resonance and its decay into the η\eta-nucleon channel, of interest to precise tests of hadron models. At the photon point, we determine it to be (2.2±0.2)×10−1GeV−1(2.2\pm 0.2)\times 10^{-1} GeV^{-1} from the old data base, and (2.2±0.1)×10−1GeV−1(2.2\pm 0.1) \times 10^{-1} GeV^{-1} from a combination of old data base and new Bates data. We obtain the helicity amplitude for N∗(1535)→γpN^{*}(1535)\rightarrow \gamma p to be A1/2=(97±7)×10−3GeV−1/2A_{1/2}=(97\pm 7)\times 10^{-3} GeV^{-1/2} from the old data base, and A1/2=(97±6)×10−3GeV−1/2A_{1/2}=(97\pm 6)\times 10^{-3} GeV^{-1/2} from the combination of the old data base and new Bates data, compared with the results of the analysis of pion photoproduction yielding 74±1174\pm 11, in the same units.Comment: 43 pages, RevTeX, 9 figures available upon request, to appear in Phys. Rev.

    The Earth: Plasma Sources, Losses, and Transport Processes

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    This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed

    Search for leptophobic Z ' bosons decaying into four-lepton final states in proton-proton collisions at root s=8 TeV

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    Search for black holes and other new phenomena in high-multiplicity final states in proton-proton collisions at root s=13 TeV

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    Search for heavy resonances decaying into a vector boson and a Higgs boson in final states with charged leptons, neutrinos, and b quarks

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    Search for high-mass diphoton resonances in proton-proton collisions at 13 TeV and combination with 8 TeV search

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    Measurements of differential production cross sections for a Z boson in association with jets in pp collisions at root s=8 TeV

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    Phenomenological MSSM interpretation of CMS searches in pp collisions at √s=7 and 8 TeV

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    Searches for new physics by the CMS collaboration are interpreted in the framework of the phenomenological minimal supersymmetric standard model (pMSSM). The data samples used in this study were collected at root s = 7 and 8 TeV and have integrated luminosities of 5.0 fb(-1) and 19.5 fb(-1), respectively. A global Bayesian analysis is performed, incorporating results from a broad range of CMS supersymmetry searches, as well as constraints from other experiments. Because the pMSSM incorporates several well-motivated assumptions that reduce the 120 parameters of the MSSM to just 19 parameters defined at the electroweak scale, it is possible to assess the results of the study in a relatively straightforward way. Approximately half of the model points in a potentially accessible subspace of the pMSSM are excluded, including all pMSSM model points with a gluino mass below 500 GeV, as well as models with a squark mass less than 300 GeV. Models with chargino and neutralino masses below 200 GeV are disfavored, but no mass range of model points can be ruled out based on the analyses considered. The nonexcluded regions in the pMSSM parameter space are characterized in terms of physical processes and key observables, and implications for future searches are discussed

    Measurement of the azimuthal anisotropy of Y(1S) and Y(2S) mesons in PbPb collisions at √S^{S}NN = 5.02 TeV

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    The second-order Fourier coefficients (υ2_{2}) characterizing the azimuthal distributions of ΄(1S) and ΄(2S) mesons produced in PbPb collisions at sNN\sqrt{s_{NN}} = 5.02 TeV are studied. The ΄mesons are reconstructed in their dimuon decay channel, as measured by the CMS detector. The collected data set corresponds to an integrated luminosity of 1.7 nb−1^{-1}. The scalar product method is used to extract the υ2_{2} coefficients of the azimuthal distributions. Results are reported for the rapidity range |y| < 2.4, in the transverse momentum interval 0 < pT_{T} < 50 GeV/c, and in three centrality ranges of 10–30%, 30–50% and 50–90%. In contrast to the J/ψ mesons, the measured υ2_{2} values for the ΄ mesons are found to be consistent with zero
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