Exclusive production of large invariant mass pion pairs in ultraperipheral ultrarelativistic heavy ion collisions

Abstract

The cross section for exclusive production of ${\pi }^{+}{\pi }^{-}$ and ${\pi }^0{\pi }^0$ meson pairs in ultrarelativistic heavy ion collisions is calculated for LHC energy $\sqrt{s_{NN}}=$ 3.5 TeV taking into account photon-photon mechanism. We concentrate on the production of large two-pion invariant masses where the mechanism of the elementary $\gamma \gamma \to \pi \pi$ process is not fully understood. In order to include a size of nuclei we perform calculation in the impact-parameter equivalent photon approximation (EPA). Realistic charge densities are used to calculate charged form factor of ${}^{208}$Pb nucleus and to generate photon fluxes associated with ultrarelativistic heavy ions. Sizeable cross sections are obtained that can be measured at LHC. The cross section for elementary $\gamma \gamma \to \pi \pi$ is calculated in the framework of pQCD Brodsky-Lepage (BL) mechanism with the distribution amplitude used to descibe recent data of the BABAR collaboration on pion transition form factor, using hand-bag mechanism advocated to describe recent Belle data as well as $t$ and $u$-channel meson/reggeon exchanges. We present distributions in two-pion invariant mass as well as the pion pair rapidity for the nuclear process.

13 pages, 10 figures

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• Measurement of light-by-light scattering and search for axion-like particles with 2.2 nb${}^{-1}$ of Pb+Pb data with the ATLAS detector
• Constraints on the Light Pseudoscalar Meson Distribution Amplitudes from Their Meson-Photon Transition Form Factors
• Equivalent photons in proton-proton and ion-ion collisions at the LHC
• ${\pi }^{+}{\pi }^{-}$ and ${\pi }^0{\pi }^0$ pair production in photon-photon and in ultraperipheral ultrarelativistic heavy ion collisions
• The $\gamma \gamma \to J/\psi J/\psi$ reaction and the $J/\psi J/\psi$ pair production in exclusive ultraperipheral ultrarelativistic heavy ion collisions
• Electromagnetic excitation of nuclei and neutron evaporation in ultrarelativistic ultraperipheral heavy ion collisions
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