Study of Central Exclusive Production of $\pi^+\pi^-$, $K^+K^-$ and $p \bar{p}$ Pairs in Proton-Proton Collisions at $\sqrt{s} = 510$ GeV

PAs:    Tomas Truhlar, Wlodek Guryn, Michal Vranovsky, Jaroslav Bielcik
   Tomas.Truhlar@fjfi.cvut.cz, guryn@bnl.gov, vranomic@fjfi.cvut.cz, jaroslav.bielcik@fjfi.cvut.cz

Target journal: Journal of High Energy Physics (JHEP)

Abstract

We report on the measurement of the $pp \ \rightarrow \ p h^+ h^- p$ ($h = \pi, K, p$) central exclusive production process in proton-proton collisions at the center-of-mass energy $\sqrt{\mathrm{s}} = 510$ GeV with the STAR detector at RHIC. At this energy, the process is dominated by a double I$\!$Pomeron exchange mechanism. The oppositely charged hadron pairs are measured within the central detector of STAR, the Time Projection Chamber, and the Time of Flight detector. The hadron pairs are identified using the ionization energy loss and the time of flight method. The forward scattered protons, which remain intact inside the RHIC beam pipe after the collision, are measured in the Roman Pot system allowing the verification of event's exclusivity. Differential fiducial cross sections within the STAR acceptance are presented as function of the difference in the azimuthal angle between the outgoing protons, hadron pair invariant mass and rapidity of the central system. The STAR detector’s acceptance is determined by pseudorapidity $\eta$ of the centrally-produced hadrons in the range $|\eta| < 0.9$. The invariant masses of the charged hadrons pairs are measured up to about 3 GeV and the square of the four-momentum transfer $t$ of the forward protons is in the range $0.3 \text{ GeV}^2 < -t_1, -t_2 < 1.6 \text{ GeV}^2$. The differential fiducial cross sections of the forward protons as a function of the $|t_1 + t_2|$ are also presented. All results for the $\pi^+\pi^-$ pair are presented in three mass ranges. A comparison with GRANIITTI Monte Carlo predictions are also presented, where the spectra include continuum and resonant contributions.