CDF

Exclusive central hadronic systems from hadron collisions result primarily from double pomeron exchange, and these have very restrictive quantum numbers: $I^{G}J^{PC}$ = $0^+ (\text{even})^{++}$. This "quantum number filter" is a powerful tool for meson spectroscopy in the isoscalar sector, especially for glue-rich states. In addition it provides information on the nature of the pomeron. We have measured exclusive $\pi^{+}\pi^{-}$ production in proton-antiproton collisions at $\sqrt{s} = 0.9$ and 1.96 TeV in the Collider Detector at Fermilab. We selected events with exactly two oppositely charged particles, assumed to be pions, in $|\eta|<1.3$ with no other particles detected in $|\eta| < 5.9$. The central $\pi^{+}\pi^{-}$ was required to have rapidity $|y|<1$. By requiring no other charged particles, these events are dominated by double pomeron exchange, which constrains the quantum numbers of the central state. The data extend up to $M(\pi^{+}\pi^{-}) = 5$ GeV$/c^{2}$, and show resonance structures attributed to the $f_0$ and $f_2$ mesons. We place upper limits on exclusive $\chi_{c0} \rightarrow \pi^{+}\pi^{-}$ and $\chi_{c0} \rightarrow K^{+}K^{-}$. The data is valuable for light hadron spectroscopy, and understanding the pomeron in a region of transition between non-perturbative and perturbative QCD.