Contact interactions in the four-fermion processes at LEP2 and HERA

We consider the possibility of experimental observation of flavor-diagonal and helicity conserving contact terms in the four fermion reactions e^+ e^- -> e^+ e^- \mu^+ \mu^- and e^- q -> e^- \mu^+ \mu^- q at LEP2 and HERA.Comment: LaTeX, 7 pages, 12 figures in LaTeX format, uses axodraw.sty. To appear in the Proc. of XI Workshop on Quantum Field Theory and High Energy Physics (QFTHEP'96, St.Petersburg, Russia, September 1996

Comment on "Obliquely propagating large amplitude solitary waves in charge neutral plasmas" by F. Verheest, Nonlin. Processes Geophys., 14, 49?57, 2007

International audienceNo abstract available

Whistler oscillitons revisited: the role of charge neutrality?

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

Hamiltonian formulation of nonlinear travelling Whistler waves

International audienceA Hamiltonian formulation of nonlinear, parallel propagating, travelling whistler waves is developed. The complete system of equations reduces to two coupled differential equations for the transverse electron speed $u$ and a phase variable $\phi{=}\phi_p-\phi_e$ representing the difference in the phases of the transverse complex velocities of the protons and the electrons. Two integrals of the equations are obtained. The Hamiltonian integral H, is used to classify the trajectories in the $(phi,w)$ phase plane, where $phi$ and w=u2 are the canonical coordinates. Periodic, oscilliton solitary wave and compacton solutions are obtained, depending on the value of the Hamiltonian integral H and the Alfvén Mach number M of the travelling wave. The second integral of the equations of motion gives the position x in the travelling wave frame as an elliptic integral. The dependence of the spatial period, L, of the compacton and periodic solutions on the Hamiltonian integral H and the Alfvén Mach number M is given in terms of complete elliptic integrals of the first and second kind. A solitary wave solution, with an embedded rotational discontinuity is obtained in which the transverse Reynolds stresses of the electrons are balanced by equal and opposite transverse stresses due to the protons. The individual electron and proton phase variables $phi_e$ and $phi_p$ are determined in terms of $phi$ and $w$. An alternative Hamiltonian formulation in which ${\tilde\phi}{=}\phi_p+\phi_e$ is the new independent variable replacing x is used to write the travelling wave solutions parametrically in terms of ${\tilde\phi}$

Dependence on pseudorapidity and on centrality of charged hadron production in PbPb collisions at √s_(NN)=2.76 TeV

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 2.76TeV 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)/d_η|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

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

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

Inclusive b-jet production in pp collisions at √s = 7 TeV

The inclusive b-jet production cross section in pp collisions at a center-of mass energy of 7 TeV is measured using data collected by the CMS experiment at the LHC. The cross section is presented as a function of the jet transverse momentum in the range 18 < p_T  < 200 GeV for several rapidity intervals. The results are also given as the ratio of the b-jet production cross section to the inclusive jet production cross section. The measurement is performed with two different analyses, which differ in their trigger selection and b-jet identification: a jet analysis that selects events with a b jet using a sample corresponding to an integrated luminosity of 34 pb^(−1), and a muon analysis requiring a b jet with a muon based on an integrated luminosity of 3 pb^(−1). In both approaches the b jets are identified by requiring a secondary vertex. The results from the two methods are in agreement with each other and with next-to-leading order calculations, as well as with predictions based on the pythia event generator