Speaker
Description
We report on the measurement of the Central Exclusive
Production of charged particle pairs $h^{+}h^{-}$ ($h = \pi, K, p$)
with the STAR detector at RHIC in proton-proton collisions at
$\sqrt{s} = 200$ GeV. The charged particle pairs produced in the
reaction $p+p \rightarrow p^\prime+h^{+}h^{-}+p^\prime$ are reconstructed from
the tracks in the central detector and identified using the specific
energy loss and the time of flight method, while the forward
scattered protons are measured by the Roman Pot detectors.
Exclusivity of the event is guaranteed by requiring transverse
momentum balance of all four final state particles. Differential
cross sections are measured as functions of observables related to
the hadronic final state and to the forward scattered protons. They
are measured in a fiducial region corresponding to the acceptance of
the STAR detector and determined by the central particles'
transverse momentum and pseudorapidity as well as by the forward
scattered protons mome
nta. This fiducial region roughly corresponds to the square of the
four-momenta transfers at the proton vertices in the range $0.04 <
-t_1 , -t_2 < 0.2$ GeV$^2$ and invariant masses of the charged
particle pairs up to a few GeV.
The measured cross sections are compared to phenomenological
predictions based on the Double Pomeron Exchange (DPE) model.
Structures observed in the mass spectra of $\pi^{+}\pi^{-}$ and
$K^{+}K^{-}$ pairs are consistent with DPE model while angular
distributions of pions suggest dominant spin-0 contribution to
$\pi^{+}\pi^{-}$ production. For $\pi^+\pi^-$ production fiducial cross
section is extrapolated to Lorentz invariant region which allows
decomposition of the invariant mass spectrum into continuum and
resonant contributions. Extrapolated cross section is well described
by the continuum production and at least three resonances,
$f_0(980)$, $f_2(1270)$ and $f_0(1500)$, with a possible small
contribution of $f_0(1370)$. Fits to extrapolated differential cross
section as a function of $t_1$ and $t_2$ enabled the extraction of
the exponential slope parameters in several bins of invariant masses
of $\pi^+\pi^-$ pairs.
