3,909 research outputs found

    Whistler oscillitons revisited: the role of charge neutrality?

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    International audienceWhen studying transverse modes propagating parallel to a static magnetic field, an apparent contradiction arises between the weakly nonlinear results obtained from the derivative nonlinear Schrödinger equation, predicting envelope solitons (where the amplitude is stationary in the wave frame, but the phase is not), and recent results for whistler oscillitons, indicating that really stationary structures of large amplitude are possible. Revisiting this problem in the fluid dynamic approach, care has been taken not to introduce charge neutrality from the outset, because this not only neglects electric stresses compared to magnetic stresses, which is reasonable, but could also imply from Poisson's equation a vanishing of the wave electric field. Nevertheless, the fixed points of the remaining equations are the same, whether charge neutrality is assumed from the outset or not, so that the solitary wave solutions at not too large amplitudes will be very similar. This is borne out by numerical simulations of the solutions under the two hypotheses, showing that the lack of correspondence with the DNLS envelope solitons indicates the limitations of the reductive perturbation approach, and is not a consequence of assuming charge neutrality

    Suppression of non-prompt J/ψ, prompt J/ψ, and Y(1S) in PbPb collisions at √s_(NN) = 2.76 TeV

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    Yields of prompt and non-prompt J/ψ, as well as ^Y(1S) mesons, are measured by the CMS experiment via their μ^+μ^− decays in PbPb and pp collisions at √s_(NN)=276 TeV for quarkonium rapidity |y| < 2.4. Differential cross sections and nuclear modification factors are reported as functions of y and transverse momentum p_T, as well as collision centrality. For prompt J/ψ with relatively high p_T (6.5 < p_T < 30 GeV/c), a strong, centrality-dependent suppression is observed in PbPb collisions, compared to the yield in pp collisions scaled by the number of inelastic nucleon-nucleon collisions. In the same kinematic range, a suppression of non-prompt J/ψ, which is sensitive to the in-medium b-quark energy loss, is measured for the first time. Also the low-p_T ^Y(1S) mesons are suppressed in PbPb collisions

    Search for heavy bottom-like quarks in 4.9 fb^(-1) of pp collisions at √s = 7 TeV

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    Results are presented from a search for heavy bottom-like quarks, pair-produced in pp collisions at √s=7 TeV, undertaken with the CMS experiment at the LHC. The b′ quarks are assumed to decay exclusively to tW. The b'b' → tW^−tW^+ process can be identified by its distinctive signatures of three leptons or two leptons of same charge, and at least one b-quark jet. Using a data sample corresponding to an integrated luminosity of 4.9 fb^(−1), observed events are compared to the standard model background predictions, and the existence of b′ quarks having masses below 611 GeV/c^2 is excluded at 95% confidence level

    Observation of a New Ξ_b Baryon

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    The observation of a new b baryon via its strong decay into Ξ_b^-π^+ (plus charge conjugates) is reported. The measurement uses a data sample of pp collisions at √s=7  TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 5.3  fb^(-1). The known Ξb- baryon is reconstructed via the decay chain Ξ_b^-→J/ψΞ^-→μ^+μ^-Λ^0π^-, with Λ^0→pπ^-. A peak is observed in the distribution of the difference between the mass of the Ξ^b^-π^+ system and the sum of the masses of the Ξ_b^- and π^+, with a significance exceeding 5 standard deviations. The mass difference of the peak is 14.84±0.74(stat)±0.28(syst)  MeV. The new state most likely corresponds to the J^P=3/2^+ companion of the Ξ_b
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