Exclusive diffractive production of $\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ via   the intermediate $\sigma\sigma$ and $\rho\rho$ states in proton-proton   collisions within tensor pomeron approach
  We present first predictions of the cross sections and differential distributions for the central exclusive reaction $pp \to pp \pi^{+} \pi^{-} \pi^{+} \pi^{-}$ being studied at RHIC and LHC. The amplitudes for the processes are formulated in terms of the tensor pomeron and tensor $f_{2 R}$ reggeon exchanges with the vertices respecting the standard crossing and charge-conjugation relations of Quantum Field Theory. The $\sigma \sigma$ and $\rho \rho$ contributions to the $\pi^{+} \pi^{-} \pi^{+} \pi^{-}$ final state are considered focussing on their specificities. The correct inclusion of the pomeron spin structure seems crucial for the considered sequential mechanisms in particular for the $\rho\rho$ contribution which is treated here for the first time. The mechanism considered gives a significant contribution to the $pp \to pp \pi^{+} \pi^{-} \pi^{+} \pi^{-}$ reaction. We adjust parameters of our model to the CERN-ISR experimental data and present several predictions for the STAR, ALICE, ATLAS and CMS experiments. A measurable cross section of order of a few $\mu b$ is obtained including the experimental cuts relevant for the LHC experiments. We show the influence of the experimental cuts on the integrated cross section and on various differential distributions. 
Piotr Lebiedowicz, Otto Nachtmann, Antoni Szczurek
hep-ph