Speaker
Description
We present results on the Central Exclusive Production of charged particle pairs $h^{+}h^{-}$ ($h = \pi, K, p$) obtained in the STAR experiment at RHIC in proton-proton collisions at center-of-mass energy of $\sqrt{s} = 200$ GeV. All final-state particles of the process $pp\to p^\prime+h^{+}h^{-}+p^\prime$ were reconstructed, including forward-scattered protons detected in the Roman Pot system. As a result, the Double Pomeron Exchange (DPE) events were selected and the non-exclusive backgrounds were efficiently rejected.
Differential fiducial cross sections were measured as functions of observables related to the central hadronic final state and to the forward-scattered protons. The measured cross sections were compared to phenomenological predictions based on the DPE model. Structures observed in the mass spectra of $\pi^{+}\pi^{-}$ and $K^{+}K^{-}$ pairs were found consistent with the DPE model, while angular distributions of pions suggested a dominant spin-0 contribution to $\pi^{+}\pi^{-}$ production.
For $\pi^+\pi^-$ production, the fiducial cross section was extrapolated to the Lorentz-invariant region and was successfully modeled assuming the continuum production and at least three resonances, the $f_0(980)$, $f_2(1270)$, and $f_0(1500)$, with a possible small contribution from the $f_0(1370)$.
Fits to the extrapolated differential cross section as a function of squared four-momentum transfers in proton vertices enabled extraction of the exponential slope parameters in several bins of the invariant mass of $\pi^+\pi^-$ pairs. These parameters are sensitive to the size of the interaction region.
We also present preliminary results on the measurement of the same physics process at higher $\sqrt{s} = 510$ GeV. The data demonstrate features similar to those observed at $\sqrt{s} = 200$ GeV.
