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

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 root 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 -> 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 Pb-208 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 -> pi pi process is calculated in the framework of pQCD Brodsky-Lepage (BL) mechanism with the distribution amplitude used to describe 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. (C) 2011 Published by Elsevier B.V.