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Measurement of the central exclusive production of charged particle pairs in proton-proton collisions at $\sqrt{s} = 200$ GeV with the STAR detector at RHIC

The STAR collaboration
2020.

Abstract (data abstract)
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 $pp \to p^{\prime}+h^{+}h^{-}+p^{\prime}$ 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 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 $0.04~\mathrm{GeV}^2 < -t_1 , -t_2 < 0.2~\mathrm{GeV}^2$, invariant masses of the charged particle pairs up to a few GeV and pseudorapidities of the centrally-produced hadrons in the range $|\eta|<0.7$.The measured cross sections are compared to phenomenological predictions based on the Double Pomeron Exchange (DPE) model. Structures observed in the mass spectra of $\pi^{+}\pi^{-}$ and $K^{+}K^{-}$ pairs are consistent with the DPE model, while angular distributions of pions suggest a dominant spin-0 contribution to $\pi^{+}\pi^{-}$ production.For $\pi^+\pi^-$ 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 by 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 $t_1$ and $t_2$ enable 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.

  • Figure 8

    Data from Figure 8

    10.17182/hepdata.94264.v1/t1

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the invariant mass of the pair. Systematic...

  • Figure 9 (left)

    Data from Figure 9 (left)

    10.17182/hepdata.94264.v1/t2

    Differential fiducial cross section for CEP of $K^+K^-$ pairs as a function of the invariant mass of the pair. Systematic...

  • Figure 9 (right)

    Data from Figure 9 (right)

    10.17182/hepdata.94264.v1/t3

    Differential fiducial cross section for CEP of $p\bar{p}$ pairs as a function of the invariant mass of the pair. Systematic...

  • Figure 10 (left)

    Data from Figure 10 (left)

    10.17182/hepdata.94264.v1/t4

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the rapidity of the pair. Systematic uncertainties...

  • Figure 10 (middle)

    Data from Figure 10 (middle)

    10.17182/hepdata.94264.v1/t5

    Differential fiducial cross section for CEP of $K^+K^-$ pairs as a function of the rapidity of the pair. Systematic uncertainties...

  • Figure 10 (right)

    Data from Figure 10 (right)

    10.17182/hepdata.94264.v1/t6

    Differential fiducial cross section for CEP of $p\bar{p}$ pairs as a function of the rapidity of the pair. Systematic uncertainties...

  • Figure 11 (top, left)

    Data from Figure 11 (top, left)

    10.17182/hepdata.94264.v1/t7

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the difference of azimuthal angles of the...

  • Figure 11 (top, middle)

    Data from Figure 11 (top, middle)

    10.17182/hepdata.94264.v1/t8

    Differential fiducial cross section for CEP of $K^+K^-$ pairs as a function of the difference of azimuthal angles of the...

  • Figure 11 (top, right)

    Data from Figure 11 (top, right)

    10.17182/hepdata.94264.v1/t9

    Differential fiducial cross section for CEP of $p\bar{p}$ pairs as a function of the difference of azimuthal angles of the...

  • Figure 11 (bottom, left)

    Data from Figure 11 (bottom, left)

    10.17182/hepdata.94264.v1/t10

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the sum of the squares of the...

  • Figure 11 (bottom, middle)

    Data from Figure 11 (bottom, middle)

    10.17182/hepdata.94264.v1/t11

    Differential fiducial cross section for CEP of $K^+K^-$ pairs as a function of the sum of the squares of the...

  • Figure 11 (bottom, right)

    Data from Figure 11 (bottom, right)

    10.17182/hepdata.94264.v1/t12

    Differential fiducial cross section for CEP of $p\bar{p}$ pairs as a function of the sum of the squares of the...

  • Figure 12 (top, left)

    Data from Figure 12 (top, left)

    10.17182/hepdata.94264.v1/t13

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the invariant mass of the pair, for...

  • Figure 12 (top, right)

    Data from Figure 12 (top, right)

    10.17182/hepdata.94264.v1/t14

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the invariant mass of the pair, for...

  • Figure 12 (middle, left)

    Data from Figure 12 (middle, left)

    10.17182/hepdata.94264.v1/t15

    Differential fiducial cross section for CEP of $K^+K^-$ pairs as a function of the invariant mass of the pair, for...

  • Figure 12 (middle, right)

    Data from Figure 12 (middle, right)

    10.17182/hepdata.94264.v1/t16

    Differential fiducial cross section for CEP of $K^+K^-$ pairs as a function of the invariant mass of the pair, for...

  • Figure 12 (bottom, left)

    Data from Figure 12 (bottom, left)

    10.17182/hepdata.94264.v1/t17

    Differential fiducial cross section for CEP of $p\bar{p}$ pairs as a function of the invariant mass of the pair, for...

  • Figure 12 (bottom, right)

    Data from Figure 12 (bottom, right)

    10.17182/hepdata.94264.v1/t18

    Differential fiducial cross section for CEP of $p\bar{p}$ pairs as a function of the invariant mass of the pair, for...

  • Figure 13 (left)

    Data from Figure 13 (left)

    10.17182/hepdata.94264.v1/t19

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the invariant mass of the pair, for...

  • Figure 13 (right)

    Data from Figure 13 (right)

    10.17182/hepdata.94264.v1/t20

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the invariant mass of the pair, for...

  • Figure 14 (top, left)

    Data from Figure 14 (top, left)

    10.17182/hepdata.94264.v1/t21

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the $\cos{\theta^{CS}}$ of the positive charge pion...

  • Figure 14 (top, middle)

    Data from Figure 14 (top, middle)

    10.17182/hepdata.94264.v1/t22

    Differential fiducial cross section for CEP of $K^+K^-$ pairs as a function of the $\cos{\theta^{CS}}$ of the positive charge kaon...

  • Figure 14 (top, right)

    Data from Figure 14 (top, right)

    10.17182/hepdata.94264.v1/t23

    Differential fiducial cross section for CEP of $p\bar{p}$ pairs as a function of the $\cos{\theta^{CS}}$ of the central state proton...

  • Figure 14 (bottom, left)

    Data from Figure 14 (bottom, left)

    10.17182/hepdata.94264.v1/t24

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the $\phi^{CS}$ of the positive charge pion...

  • Figure 14 (bottom, middle)

    Data from Figure 14 (bottom, middle)

    10.17182/hepdata.94264.v1/t25

    Differential fiducial cross section for CEP of $K^+K^-$ pairs as a function of the $\phi^{CS}$ of the positive charge kaon...

  • Figure 14 (bottom, right)

    Data from Figure 14 (bottom, right)

    10.17182/hepdata.94264.v1/t26

    Differential fiducial cross section for CEP of $p\bar{p}$ pairs as a function of the $\phi^{CS}$ of the central state proton...

  • Figure 15 (top, left)

    Data from Figure 15 (top, left)

    10.17182/hepdata.94264.v1/t27

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the rapidity of the pair, for invariant...

  • Figure 15 (top, middle)

    Data from Figure 15 (top, middle)

    10.17182/hepdata.94264.v1/t28

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the difference of azimuthal angles of the...

  • Figure 15 (top, right)

    Data from Figure 15 (top, right)

    10.17182/hepdata.94264.v1/t29

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the sum of the squares of the...

  • Figure 15 (middle, left)

    Data from Figure 15 (middle, left)

    10.17182/hepdata.94264.v1/t30

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the rapidity of the pair, for invariant...

  • Figure 15 (middle, middle)

    Data from Figure 15 (middle, middle)

    10.17182/hepdata.94264.v1/t31

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the difference of azimuthal angles of the...

  • Figure 15 (middle, right)

    Data from Figure 15 (middle, right)

    10.17182/hepdata.94264.v1/t32

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the sum of the squares of the...

  • Figure 15 (bottom, left)

    Data from Figure 15 (bottom, left)

    10.17182/hepdata.94264.v1/t33

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the rapidity of the pair, for invariant...

  • Figure 15 (bottom, middle)

    Data from Figure 15 (bottom, middle)

    10.17182/hepdata.94264.v1/t34

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the difference of azimuthal angles of the...

  • Figure 15 (bottom, right)

    Data from Figure 15 (bottom, right)

    10.17182/hepdata.94264.v1/t35

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the sum of the squares of the...

  • Figure 16 (top, left)

    Data from Figure 16 (top, left)

    10.17182/hepdata.94264.v1/t36

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the $\cos{\theta^{CS}}$ of the positive charge pion...

  • Figure 16 (top, middle)

    Data from Figure 16 (top, middle)

    10.17182/hepdata.94264.v1/t37

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the $\cos{\theta^{CS}}$ of the positive charge pion...

  • Figure 16 (top, right)

    Data from Figure 16 (top, right)

    10.17182/hepdata.94264.v1/t38

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the $\cos{\theta^{CS}}$ of the positive charge pion...

  • Figure 16 (bottom, left)

    Data from Figure 16 (bottom, left)

    10.17182/hepdata.94264.v1/t39

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the $\phi^{CS}$ of the positive charge pion...

  • Figure 16 (bottom, middle)

    Data from Figure 16 (bottom, middle)

    10.17182/hepdata.94264.v1/t40

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the $\phi^{CS}$ of the positive charge pion...

  • Figure 16 (bottom, right)

    Data from Figure 16 (bottom, right)

    10.17182/hepdata.94264.v1/t41

    Differential fiducial cross section for CEP of $\pi^+\pi^-$ pairs as a function of the $\phi^{CS}$ of the positive charge pion...

  • Table 2

    Data from Table 2

    10.17182/hepdata.94264.v1/t42

    Integrated fiducial cross sections with statistical and systematic uncertainties for CEP of $\pi^+\pi^-$, $K^+K^-$ and $p\bar{p}$ pairs in two ranges...

  • Table 3 (A)

    Data from Table 3 (A)

    10.17182/hepdata.94264.v1/t43

    Results of the fit to extrapolated $d\sigma/dm(\pi^+\pi^-)$ in two ranges of azimuthal angle difference $\Delta\varphi$ between forward-scattered protons. The fit...

  • Table 3 (B)

    Data from Table 3 (B)

    10.17182/hepdata.94264.v1/t44

    Results of the fit to extrapolated $d\sigma/dm(\pi^+\pi^-)$ in two ranges of azimuthal angle difference $\Delta\varphi$ between forward-scattered protons. The fit...

  • Table 4 (A)

    Data from Table 4 (A)

    10.17182/hepdata.94264.v1/t45

    Ratios of integrated cross sections of resonance production to cross sections for f2(1270) production, in the pi+pi- channel. The results...

  • Table 4 (B)

    Data from Table 4 (B)

    10.17182/hepdata.94264.v1/t46

    Ratios of integrated cross sections of resonance production in two ranges of $\Delta\varphi$, in the pi+pi- channel. The results are...

  • Table 5

    Data from Table 5

    10.17182/hepdata.94264.v1/t47

    Exponential slope of the $t$-distribution in three ranges of $m(\pi^+\pi^-)$ and two ranges of $\Delta\varphi$. The results are obtained for...

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