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Register a new userHadron production in electron-positron annihilation computed from the gauge gravity correspondence
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We provide a non-perturbative expression for the hadron production in electron-positron annihilation at zero temperature in a strongly coupled, large-Nc SU(Nc) field theory with Nf << Nc quark flavors. The resulting expressions are valid to leading order in the electromagnetic coupling constant but non-perturbatively in the SU(Nc) interactions and the mass of the quark. We obtain this quantity by computing the imaginary part of the hadronic vacuum polarization function Pi_q using holographic techniques, providing an alternative to the known method that uses the spectrum of infinitely stable mesons determined by the normalizable modes of the appropriated fields in the bulk. Our result exhibits a structure of poles localized at specific real values of q^2, which coincide with the ones found using the normalizable modes, and extends it offering the unique analytic continuation of this distribution to a function defined for values of q^2 over the complex plane. This analytic continuation permits to include a finite decay width for the mesons. By comparison with experimental data we find qualitatively good agreement on the shape of the first pole, when using the rho meson parameters and choosing a proper normalization factor. We then estimate the contribution to the anomalous magnetic moment of the muon finding an agreement within 25%, for this choice of parameters.
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The reactions of electron-positron to nucleon-antinucleon pairs are studied in a non-perturbative quark model. The work suggests that the two-step process, in which the primary quark-antiquark pair forms first a vector meson which in turn decays into a hadron pair, is dominant over the one-step process in which the primary quark-antiquark pair is directly dressed by additional quark-antiquark pairs to form a hadron pair. To reproduce the experimental data of the reactions of electron-positron to proton-antiproton and electron-positron to neutron-antineutron a D-wave omega-like vector meson with a mass of around 2 GeV has to be introduced.
In this work we study the e^{+}e^{-}tophi K^{+}K^{-} reaction. The leading order electromagnetic contributions to this process involve the gamma*phi K^{+}K^{-} vertex function with a highly virtual photon. We calculate this function at low energies using Rchi PT supplemented with the anomalous term for the VVP interactions. Tree level contributions involve the kaon form factors and the K*K transition form factors. We improve this result, valid for low photon virtualities, replacing the lowest order terms in the kaon form factors and K*K transition form factors by the form factors as obtained in Uchi PT in the former case and the ones extracted from recent data on e^{+}e^{-}to KK* in the latter case. We calculate rescattering effects which involve meson-meson amplitudes. The corresponding result is improved using the unitarized meson-meson amplitudes containing the scalar poles instead of the lowest order terms. Using the BABAR value for BR(Xto phi f_{0})Gamma (Xto e^{+} e^{-}), we calculate the contribution from intermediate X(2175). A good description of data is obtained in the case of destructive interference between this contribution and the previous ones, but more accurate data on the isovector K*K transition form factor is required in order to exclude contributions from an intermediate isovector resonance to e^{+}e^{-}to phi K^{+}K^{-} around 2.2 GeV.
According to the concept of universality in hadron production, the basic mechanisms of hadron formation are the same in all high-energy e+e-, lh and hh reactions, with differences in the composition of final-state particle types being due only to differences in initial parton flavours and configurations. This concept is discussed in the light of recent data and phenomenology.
In this work we evaluate the cross section of the process $e^+e^-to J/psi eta_c$ at energy $sqrt{s}approx 10.6$ GeV in the Bethe-Salpeter formalism. To simplify our calculation, the heavy quark limit is employed. Without taking the beyond-leading-order contribution(s) into account, the cross section calculated in this scenario is comparable with the experimental data. We also present our prediction for the cross section of double bottomonium production $e^+e^-to Upsilon(1S)eta_b$ for the energy range of $sqrt{s}approx (25 hbox{-} 30)$ GeV which may be experimentally tested, even though there is no facility of this range available at present yet.
High energy positron annihilation is a viable mechanism to produce dark photons ($A^prime$). This reaction plays a significant role in beam-dump experiments using experiments using multi-GeV electron-beams on thick targets by enhancing the sensitivity to $A^prime$ production. The positrons produced by the electromagnetic shower can produce an $A^prime$ via non-resonant ($e^+ + e^- to gamma + A^prime$) and resonant ($e^+ + e^- to A^prime$) annihilation on atomic electrons. For visible decays, the contribution of resonant annihilation results in a larger sensitivity with respect to limits derived by the commonly used $A^prime$-strahlung in certain kinematic regions. When included in the evaluation of the E137 beam-dump experiment reach, positron annihilation pushes the current limit on $varepsilon$ downwards by a factor of two in the range 33 MeV/c$^2<m_{A^prime}<120$ MeV/c$^2$.
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