863 research outputs found

    Exclusive J/ψJ/\psi and Υ\Upsilon photoproduction and the low xx gluon

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    We study exclusive vector meson photoproduction, γpV+p\gamma p \to V + p with V=J/ψV=J/\psi or Υ\Upsilon, at NLO in collinear factorisation, in order to examine what may be learnt about the gluon distribution at very low xx. We examine the factorisation scale dependence of the predictions. We argue that, using knowledge of the NLO corrections, terms enhanced by a large ln(1/ξ)\ln(1/\xi) can be reabsorbed in the LO part by a choice of the factorisation scale. (In these exclusive processes ξ\xi takes the role of Bjorken-xx.) Then, the scale dependence coming from the remaining NLO contributions has no ln(1/ξ)\ln(1/\xi) enhancements. As a result, we find that predictions for the amplitude of Υ\Upsilon production are stable to within about ±15%\pm 15\%. This will allow data for the exclusive process pppΥpp p \to p\Upsilon p at the LHC, particularly from LHCb, to be included in global parton analyses to constrain the gluon PDF down to x105x\sim 10^{-5}. Moreover, the study of exclusive J/ψJ/\psi photoproduction indicates that the gluon density found in the recent global PDF analyses is too small at low xx and low scales.Comment: 21 pages, 6 figures. Text significantly improved, references added, version to be published in J.Phys.

    A note on frictional effects in Taylor\u27s problem

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    Taylor\u27s tidal problem of the reflection of a Kelvin wave in a semi-infinite rotating channel is modified here by considering the effect of the inclusion of fri ction in the analysis. Results are obtained using Galerkin and Collocation methods to satisfy the end boundary condition, and these are compared with results given by other authors for the nonfriction case

    The QCD description of diffractive rho meson electroproduction

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    We critically review the QCD predictions for the cross sections sigma_L and sigma_T for diffractive rho meson electroproduction in longitudinally and transversely polarised states in the HERA energy region. We show that both perturbative and non-perturbative approaches which involve convolution with the rho meson wave function predict values of sigma_T which fall-off too quickly with increasing Q^2, in comparison with the data. We present a perturbative QCD model based on the open production of light qqbar pairs and parton-hadron duality, which describes all features of the data for rho electroproduction at high Q^2 and, in particular, predicts a satisfactory Q^2 behaviour of sigma_L/sigma_T. We find that precise measurements of the latter can give valuable information on the Q^2 behaviour of the gluon distribution at small x.Comment: 19 pages, LaTeX, 6 Postscript figures. The complete paper, including figures, is also available via anonymous ftp at ftp://cpt1.dur.ac.uk/pub/preprints/dtp96/dtp9664

    Relativistic Doppler effect: universal spectra and zeptosecond pulses

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    We report on a numerical observation of the train of zeptosecond pulses produced by reflection of a relativistically intense femtosecond laser pulse from the oscillating boundary of an overdense plasma because of the Doppler effect. These pulses promise to become a unique experimental and technological tool since their length is of the order of the Bohr radius and the intensity is extremely high 1019\propto 10^{19} W/cm2^2. We present the physical mechanism, analytical theory, and direct particle-in-cell simulations. We show that the harmonic spectrum is universal: the intensity of nnth harmonic scales as 1/np1/n^{p} for n<4γ2n < 4\gamma^2, where γ\gamma is the largest γ\gamma--factor of the electron fluid boundary, p=3p=3 and p=5/2p=5/2 for the broadband and quasimonochromatic laser pulses respectively.Comment: 4 figure

    Implications of exclusive J/ψJ/\psi photoproduction in a tamed collinear factorisation approach to NLO

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    We discuss exclusive J/ψJ/\psi photoproduction, initially in conventional collinear factorisation at NLO and then subsequently in a refined approach with a programme of low xx resummation and implementation of a crucial low Q0Q_0 subtraction included. We compare and contrast predictions in both frameworks and remark about the possibility to constrain and ultimately determine the low xx and low scale gluon PDF, emphasising the significance of this for future global PDF analyses.Comment: 6 pages, 4 figures. Presented by C. Flett at the 51st International Symposium on Multiparticle Dynamics (ISMD2022) Pitlochry, Scottish Highlands, 1-5 August 202

    Low scale B-L extension of the Standard Model at the LHC

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    The fact that neutrinos are massive indicates that the Standard Model (SM) requires extension. We propose a low energy (<TeV) B-L extension of the SM, which is based on the gauge group SU(3)_C x SU(2)_L x U(1)_Y x U(1)_{B-L}. We show that this model provides a natural explanation for the presence of three right-handed neutrinos in addition to an extra gauge boson and a new scalar Higgs. Therefore, it can lead to very interesting phenomenological implications different from the SM results which can be tested at the LHC. Also we analyze the muon anomalous magnetic moment in this class of models. We show that one-loop with exchange Z' may give dominant new contribution ~ few x 10^{-11}.Comment: 12 page
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