Search

We present results on the Central Exclusive Production of charged particle pairs $h^{+}h^{-}$ ($h = \pi, K, p$), $pp\to p^\prime+h^{+}h^{-}+p^\prime$, obtained with the STAR experiment at RHIC in proton-proton collisions at a center-of-mass energy of $\sqrt{s} = 200$ GeV. All final-state particles 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 model predictions based on the DPE. We also present preliminary results on the measurement of the same physics process at higher collision energy $\sqrt{s} = 510$ GeV. The data demonstrate features similar to those observed at $\sqrt{s} = 200$ GeV., Comment: Submission to SciPost Proceedings

The measurement of the central exclusive production of charged hadron pairs $h^{+}h^{-}$ ($h = \pi, K, p$) by the STAR experiment at RHIC is reported. The data from proton-proton collisions at $\sqrt{s} = 200$ GeV were used in this study. The pairs of charged hadrons produced in the reaction $pp\to p^\prime+h^{+}h^{-}+p^\prime$ were reconstructed from the tracks in the central detector, while the forward-scattered protons were measured in the Roman Pot system. Differential cross sections were measured in the fiducial region determined by the geometrical acceptance of the experimental setup. They were compared to phenomenological predictions based on the Double Pomeron Exchange model. The fiducial $\pi^+\pi^-$ cross section was extrapolated to the Lorentz-invariant region, which allowed decomposition of the invariant mass spectrum into continuum and resonant contributions., Comment: 6 pages, 6 figures, Proceedings of 40th International Conference on High Energy Physics - ICHEP 2020, July 28 - August 6, 2020, Prague, Czech Republic (virtual meeting)

We present preliminary differential fiducial cross sections on Central Exclusive Production (CEP, $pp\to pXp$) of two opposite-charge mesons ($X=\pi^{+}\pi^{-}$, $K^{+}K^{-}$) in midrapidity region with small squared four-momentum transferred from forward protons, $0.03<|t_{1}|,|t_{2}|<0.2~\textrm{GeV}^{2}$. The process was measured in the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) in proton-proton collisions at the center-of-mass energy $\sqrt{s}~=~200~\textrm{GeV}$., Comment: Presented at "Diffraction and Low-x 2018", to be published in Acta Physica Polonica B Proceeding Supplement

The STAR experiment at the Relativistic Heavy Ion Collider (RHIC) performs studies of diffractive processes with the focus on the exclusive production of particles in central range of rapidity. In 2015 STAR collected 18 pb$^{-1}$ of data in polarized proton+proton collisions at $\sqrt{s}$=200 GeV to measure Central Exclusive Production (CEP) process $pp\to pXp$ through Double Pomeron Exchange (DPE) mechanism. The intact protons moving inside the RHIC beampipe after the collision were measured in silicon strip detectors (SSD), which were placed in the Roman Pot vessels. This enables full control over interaction kinematics and verification of the exclusivity of the reaction by measuring the total (missing) transverse momenta of all final state particles: the central diffractive system in the Time Projection Chamber (TPC) and the forward protons in the Roman Pots. With the use of ionization energy loss in the TPC, d$E$/d$x$, it was possible to discriminate various production channels in $pp\to pXp$ reaction. This paper presents results on exclusive production of two charged particles ($\pi^{+}\pi^{-}$ and $K^{+}K^{-}$) in mid-rapidity region, $-1<\eta<1$, with small squared four-momentum transfer of forward protons, $0.03<-t<0.3~(\textrm{GeV}/c)^{2}$, obtained using 2.5% of full statistics.