The $\rho^0$ and Drell-S\"oding contributions to central exclusive   production of $\pi^+ \pi^-$ pairs in proton-proton collisions at high   energies
  We present a study of the central exclusive $\pi^{+} \pi^{-}$ production via the photoproduction mechanism in nucleon-nucleon collisions. The photon-pomeron/reggeon and pomeron/reggeon-photon exchanges both for the $\rho^{0}$ resonance contribution and the Drell-S\"oding contribution are considered. The amplitudes for the processes are formulated in terms of vertices respecting the standard crossing and charge-conjugation relations of Quantum Field Theory. The coupling parameters of tensor pomeron and reggeon exchanges are fixed based on the H1 and ZEUS experimental data for the $\gamma p \to \rho^{0} p$ reaction. We present first predictions of this mechanism for the $pp \to pp \pi^{+} \pi^{-}$ reaction being studied at COMPASS, RHIC, Tevatron, and LHC. We show the influence of the experimental cuts on the integrated cross section and on various differential distributions for outgoing particles. Distributions in rapidities and transverse momenta of outgoing protons and pions as well as correlations in azimuthal angle between them are presented. We compare the photoproduction contribution to $\pi^{+} \pi^{-}$ distributions with double pomeron/reggeon two-pion continuum. We discuss whether the high-energy central production of $\rho^{0}$ mesons could be selected experimentally. 
Piotr Lebiedowicz, Otto Nachtmann and Antoni Szczurek
hep-ph hep-ex