# Diffractive interaction of protons at CDF

Project realized independently during my Master and PhD studies

In quantum chromodynamics (QCD), the theory of strong interactions between quarks and gluons, calculations of hadronic interactions are most reliable in the perturbative regime of high four-momentum transfer squared, i.e., for distance scales much smaller than the size of hadrons, typically 1 fm. Diffractive processes with low transverse-momentum hadrons involve nonperturbative physics. Elastic scattering and other diffractive interactions are described in the regime of Regge theory by the exchange of a pomeron, which is a strongly interacting color-singlet. At leading order it is a pair of gluons. Such processes are characterized by a region of large rapidity gaps, $\Delta y$, with no hadron production. With the requirements of two large forward rapidity gaps and central hadrons production, it is expected that the observed processes are dominated by the so-called double pomeron exchange.

The exclusive central hadronic systems resulting primarily from double pomeron exchange have very restrictive quantum numbers: $I^GJ^{PC} = 0^+(\mathrm{even})^{++}$. This “quantum number filter” is a powerful tool for meson spectroscopy favoring states having valence gluons, such as glueballs, i.e., hadrons with no valence quarks. Such states are expected in QCD, but 40 years after being proposed their existence is not established. More measurements in different production modes and decay channels should provide insight on the issue. In addition to its role in meson spectroscopy, double pomeron exchange studies shed light on the nature of the pomeron.

In the analysis performed with the CDF experiment, we investigated the central exclusive $\pi^+\pi^-$ production in $p\bar{p}$ collisions at two center-of-mass energies $\sqrt{s}$ = 0.9 and 1.96 TeV. The data extend up to dipion mass $M(\pi^+\pi^-)$ = 5 GeV/c2, and show resonance structures attributed to $\mathrm{f}_0$ and $\mathrm{f}_2 (1270)$ mesons.

. Measurement of central exclusive $\pi^+ \pi^-$ production in $p\bar{p}$ collisions at $\sqrt{s} = 0.9$ and 1.96 TeV at CDF. In: Phys. Rev. D (Rapid Communications) 91, 2015.