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Register a new userExclusive Rho Rho Production in Tagged Gamma-Gamma Interactions at LEP
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I. Vorobiev
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Exclusive rho rho production in two-photon collisions between a quasi-real, gamma, and a virtual, gamma*, photons is studied at LEP at centre-of-mass energies 89 GeV < sqrt{s} < 209 GeV with a total integrated luminosity of 854.7 pb-1. The cross sections of the gamma gamma* -> rho rho processes are determined as a function of the photon virtuality, Q^2, and the two-photon centre-of-mass energy, Wgg, in the kinematic region: 0.2 GeV^2 < Q^2 < 30 GeV^2 and 1.1 GeV < Wgg < 3 GeV.
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We present a non-perturbative QCD calculation of high-energy diffractive photo- and leptoproduction of vector mesons $rho$, $rho$ and $rho$ on a nucleon. The initial photon splits up in a $qbar{q}$-dipole and transforms into a vector meson by scattering on the quark-diquark nucleon. The dipole-dipole scattering amplitude is provided by the non-perturbative model of the stochastic QCD vacuum, the wave functions result from considerations on the light-cone. We assume the physical $rho$- and $rho$-states to be mixed states of an active 2S-excitation and a rest whose coupling to the photon is suppressed. We obtain good agreement with the experimental data and get an understanding of the markedly different spectrum in the $pi^+pi^-$-invariant mass for photoproduction and $e^+e^-$-annihilation.
Particle production in two-photon interactions at hadronic collisions is becoming increasingly relevant in the LHC physics programme as a way to improve our understanding of the Standard Model and search for signals of New Physics. A key ingredient for the study of these interactions in $pp$ collisions is the description of the photon content of the proton, which allow us to derive predictions for the cross sections associated to events where occur the proton dissociation (non - exclusive processes) and for those where both incident protons remain intact (exclusive processes). In this paper, a detailed comparison of the different models for the elastic and inelastic photon distributions found in the literature is presented and the current theoretical uncertainty is estimated. The impact on the invariant mass distribution for the dimuon production is analyzed. Moreover, the relative contribution of non - exclusive events is estimated and its dependence on the invariant mass of the pair is presented. We demonstrate that the predictions for production of pairs with large invariant mass is strongly dependent on the model assumed to describe the elastic and inelastic photon distributions and that the ratio between non - exclusive and exclusive cross sections present a mild energy dependence. Finally, our results indicate that a future experimental analysis of the non - exclusive events will be useful to constrain the photon content of proton.
We present a study of the decays B+ -> rho+ gamma, B0 -> rho0 gamma, and B0 -> omega gamma. The analysis is based on data containing 347 million BBbar events recorded with the BaBar detector at the PEP-II asymmetric B factory. We measure the branching fractions BR(B+ -> rho+ gamma) = (1.10 +0.37/-0.33 +/- 0.09) x 10-6 and BR(B0 -> rho0 gamma) = (0.79 +0.22/-0.20 +/- 0.06) x 10-6, and set a 90% C.L. upper limit BR(B0 -> omega gamma) < 0.78 x 10-6. We also measure the isospin-averaged branching fraction BR(B->rho/omega gamma) = (1.25 +0.25/-0.24 +/- 0.09) x 10-6, from which we determine |Vtd/Vts| = 0.200 +0.021/-0.020 +/- 0.015, where the first uncertainty is experimental and the second is theoretical.
We have observed exclusive gammagamma production in proton-antiproton collisions at sqrt{s}=1.96 TeV, using data from 1.11 pm 0.07 fb^{-1} integrated luminosity taken by the Run II Collider Detector at Fermilab. We selected events with two electromagnetic showers, each with transverse energy E_T > 2.5 GeV and pseudorapidity |eta| < 1.0, with no other particles detected in -7.4 < eta < +7.4. The two showers have similar E_T and azimuthal angle separation Deltaphi sim pi; 34 events have two charged particle tracks, consistent with the QED process p bar{p} to p + e^+e^- + bar{p} by two-photon exchange, while 43 events have no charged tracks. The number of these events that are exclusive pi^0pi^0 is consistent with zero and is < 15 at 95% C.L. The cross section for pbar{p} to p+gammagamma+bar{p} with |eta(gamma)| < 1.0 and E_T(gamma) > 2.5$ GeV is 2.48^{+0.40}_{-0.35}(stat)^{+0.40}_{-0.51}(syst) pb.
We calculate cross sections for the exclusive diffractive leptoproduction of $rho$-mesons, $gamma^*~p~to~rho~p$, within the framework of high-energy factorization. Cross sections for longitudinally and transversally polarized mesons are shown. We employ a wide variety of unintegrated gluon distributions available in the literature and compare to HERA data. The resulting cross sections strongly depend on the choice of unintegrated gluon distribution. We also present predictions for the proton target in the kinematics of the Brookhaven EIC.
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