Measurement of the central exclusive production of charged particle pairs in proton-proton collisions at s $$ \sqrt{s}
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Received: April 24, Revised: June 19, Accepted: July 6, Published: July 24,
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STAR The STAR collaboration E-mail: [email protected] Abstract: We report on the measurement of the Central Exclusive Production of charged particle pairs h+ h− (h = π, K, p) with the STAR detector at RHIC in proton-proton √ collisions at s = 200 GeV. The charged particle pairs produced in the reaction pp → p0 + h+ h− + p0 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 in the Roman Pot system. Exclusivity of the event is guaranteed by requiring the transverse momentum balance of all four final-state particles. Differential cross sections are measured as functions of observables related to the central 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 momenta and pseudorapidities as well as by the forward-scattered protons’ momenta. This fiducial region roughly corresponds to the square of the four-momentum transfers at the proton vertices in the range 0.04 GeV2 < −t1 , −t2 < 0.2 GeV2 , invariant masses of the charged particle pairs up to a few GeV and pseudorapidities of the centrallyproduced hadrons in the range |η| < 0.7. The measured cross sections are compared to phenomenological predictions based on the Double Pomeron Exchange (DPE) model. Structures observed in the mass spectra of π + π − and K + K − pairs are consistent with the DPE model, while angular distributions of pions suggest a dominant spin-0 contribution to π + π − production. For π + π − production, the fiducial cross section is extrapolated to the Lorentz-invariant region, which allows decomposition of the invariant mass spectrum into continuum and resonant contributions. The extrapolated cross section is well described
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP07(2020)178
JHEP07(2020)178
Measurement of the central exclusive production of charged particle pairs in proton-proton collisions at √ s = 200 GeV with the STAR detector at RHIC
by the continuum production and at least three resonances, the f0 (980), f2 (1270) and f0 (1500), with a possible small contribution from the f0 (1370). Fits to the extrapolated differential cross section as a function of t1 and t2 enable extraction of the exponential slope parameters in several bins of the invariant mass of π + π − pairs. These parameters are sensitive to the size of the interaction region. Keywords: Diffraction, Forward physics, Hadron-Hadron scattering (experiments) ArXiv ePrint: 2004.11078
JHEP07(2020)178
Contents 1
2 Theoretical framework and current experimental situation
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3 Experimental setup
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4 Event reconstruction
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5 Monte Carlo simulation
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6 Data sample and event selection
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7 Kinematic variables and fiducial region
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8 Bac
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