Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                

Photoproduction of η mesons off the proton for 1.2<Eγ<4.7GeV using CLAS at Jefferson Laboratory

T. Hu et al. (CLAS Collaboration)
Phys. Rev. C 102, 065203 – Published 14 December 2020
PDFHTMLExport Citation
Abstract
Authors
Article Text
  • INTRODUCTION
  • PREVIOUS MEASUREMENTS
  • EXPERIMENTAL SETUP
  • CALIBRATION AND EVENT RECONSTRUCTION
  • EXTRACTION OF CROSS SECTIONS
  • EXPERIMENTAL RESULTS
  • PHYSICS DISCUSSION
  • SUMMARY AND OUTLOOK
  • ACKNOWLEDGMENTS
    • References

    Abstract

    Photoproduction cross sections are reported for the reaction γp→pη using energy-tagged photons and the CLAS spectrometer at Jefferson Laboratory. The η mesons are detected in their dominant charged decay mode, η→π+π−π0, and results on differential cross sections are presented for incident photon energies between 1.2 and 4.7 GeV. These new η photoproduction data are consistent with earlier CLAS results but extend the energy range beyond the nucleon resonance region into the Regge regime. The normalized angular distributions are also compared with the experimental results from several other experiments, and with predictions of η-MAID 2018 and the latest solution of the Bonn-Gatchina coupled-channel analysis. Differential cross sections dσ/dt are presented for incident photon energies Eγ>2.9GeV (W>2.5GeV), and compared with predictions which are based on Regge trajectories exchange in the t-channel (Regge models). The data confirm the expected dominance of ρ, ω vector-meson exchange in an analysis by the Joint Physics Analysis Center.

    • Figure
    • Figure
    • Figure
    • Figure
    • Figure
    • Figure
    • Figure
    15 More
    • Received 15 June 2020
    • Revised 5 October 2020
    • Accepted 24 November 2020

    DOI:https://doi.org/10.1103/PhysRevC.102.065203

    ©2020 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Photonuclear reactionsQCD in nuclear reactionsResonance reactions
    1. Physical Systems
    Light mesonsProtons
    Nuclear Physics

    Authors & Affiliations

    Click to Expand

    Article Text (Subscription Required)

    Click to Expand

    References (Subscription Required)

    Click to Expand
    Issue

    Vol. 102, Iss. 6 — December 2020

    Reuse & Permissions
    Access Options
    Author publication services for translation and copyediting assistance advertisement

    Authorization Required

    Log In
    Other Options
    ×

    Images

    • Figure 1
      Figure 1

      Dominant contributions to η photoproduction off the nucleon: s-channel intermediate nucleon resonance excitation (left) and t-channel exchange of Reggeons (right).

      Reuse & Permissions
    • Figure 2
      Figure 2

      Side view of the CLAS detector in Hall B at Jefferson Lab including the photon tagging facility upstream of CLAS. Reproduced figure with permission from Ref. [7]. Copyright 2003 by Elsevier.

      Reuse & Permissions
    • Figure 3
      Figure 3

      Distribution of the tagger-start counter coincidence times. The 2-ns bunch structure is visible. Events were considered for further analysis only if a single photon candidate remained after a timing cut of |ΔtTGPB|<1 ns.

      Reuse & Permissions
    • Figure 4
      Figure 4

      The z-vertex distribution of γp→pη Monte Carlo (black) and data events (blue). The target length of 40 cm is clearly visible. In this experiment, the target cell was moved upstream from the CLAS center by 90 cm. The vertical lines define the range of the z-vertex cut.

      Reuse & Permissions
    • Figure 5
      Figure 5

      Left and middle: Δβ=|βc−βm| distributions for protons and positively charged pions, respectively. The blue area indicates the 3σ cut according to Eq. (3). Right: The distribution of βm vs. particle momentum before and after (inset) the 3σ cut. Note that the momentum range in the inset is limited to p<3.1GeV to better illustrate the separation of the two bands at low momenta.

      Reuse & Permissions
    • Figure 6
      Figure 6

      Confidence-level distribution for the missing-π0 hypothesis after all corrections for Monte Carlo (MC) events (left) and CLAS-g12 data (center). The covariance matrix for both data and MC events was initially tuned using fully exclusive γp→pπ+π− events. Right: Distribution of normalized slopes for data events, see text for more details.

      Reuse & Permissions
    • Figure 7
      Figure 7

      Missing mass X in the reaction γp→pη→pπ+π−(X) after all cuts and the final η background subtraction. A clean π0 peak is visible.

      Reuse & Permissions
    • Figure 8
      Figure 8

      Typical example of a normalized λ=|p⃗π+×p⃗π−|2 distribution for the center-of-mass energy bin W∈[2360,2400] MeV.

      Reuse & Permissions
    • Figure 9
      Figure 9

      Examples of π+π−π0 mass distributions for the center-of-mass energy range W∈[1.90,1.92]GeV for events that were subject to the Q-factor fitting (background subtraction). These events survived all kinematic cuts. The invariant 3π mass of each event weighted by 1−Q gives the blue area (background), whereas the signal peak comes from the invariant mass weighted by Q.

      Reuse & Permissions
    • Figure 10
      Figure 10

      Total invariant π+π−π0 mass distribution for the center-of-mass energy W∈[1.76,2.36]GeV corresponding to the combined γp→pη event statistics of Figs. 11, 12, 13, 14, 15.

      Reuse & Permissions
    • Figure 11
      Figure 11

      The differential cross sections dσ/dΩ for three 40-MeV-wide center-of-mass energy W bins. The new CLAS data are shown as the black solid circles (•) and the uncertainties associated with each point comprise the statistical uncertainty and contributions from the Q-value correlation uncertainty added in quadrature. Also shown for comparison are data from CLAS-g11a [30] ( ▪), the A2 Collaboration at MAMI [33] ( ▾) using their published center-of-bin energies of W=1.78GeV (left), 1.82 GeV (center), 1.86 GeV (right), and the CBELSA/TAPS Collaboration at ELSA [31] (▴). The blue solid and purple dashed curves denote the η-MAID 2018 [4] and the BnGa 2019 [21] description of the γp→pη cross section, respectively.

      Reuse & Permissions
    • Figure 12
      Figure 12

      The differential cross sections dσ/dΩ for the energy bin 1.84<W<1.88GeV. The new CLAS data are shown as the black solid circles (•) and the uncertainties associated with each point comprise the statistical uncertainty and contributions from the Q-value correlation uncertainty added in quadrature. Also shown for comparison are data from the GRAAL Collaboration [16] ( ▪).

      Reuse & Permissions
    • Figure 13
      Figure 13

      The differential cross sections dσ/dΩ for the backward angle bins −0.8<cosθ<−0.7 (top) and −0.7<cosθ<−0.6 (bottom). The new CLAS data are shown as the black solid circles (•) and the uncertainties associated with each point comprise the statistical uncertainty and contributions from the Q-value correlation uncertainty added in quadrature. Also shown for comparison are data from CLAS-g11a [30] ( ▪) and from the LEPS Collaboration [27] (▴).

      Reuse & Permissions
    • Figure 14
      Figure 14

      The differential cross sections dσ/dΩ in 20-MeV-wide center-of-mass bins for W∈[1.88,2.12]GeV. The new CLAS data are shown as the black solid circles (•) and the uncertainties associated with each point comprise the statistical uncertainty and contributions from the Q-value correlation uncertainty added in quadrature. Also shown for comparison are data from CLAS-g11a [30] (▪) and from the CBELSA/TAPS Collaboration at ELSA [31] (▴). The blue solid and purple dashed curves denote the η-MAID 2018 [4] and the BnGa 2019 [21] description of the γp→pη cross section, respectively.

      Reuse & Permissions
    • Figure 15
      Figure 15

      The differential cross sections dσ/dΩ in 20-MeV-wide center-of-mass bins for W∈[2.12,2.36]GeV. The new CLAS data are shown as the black solid circles (•) and the uncertainties associated with each point comprise the statistical uncertainty and contributions from the Q-value correlation uncertainty added in quadrature. Also shown for comparison are data from CLAS-g11a [30] ( ▪) and from the CBELSA/TAPS Collaboration at ELSA [31] (▴). The blue solid and purple dashed curves denote the η-MAID 2018 [4] and the BnGa 2019 [21] description of the γp→pη cross section, respectively.

      Reuse & Permissions
    • Figure 16
      Figure 16

      The differential cross sections dσ/dΩ in 40-MeV-wide center-of-mass bins for W∈[2.36,3.12]GeV. The new CLAS data are shown as black solid circles (•) and the uncertainties associated with each point comprise the statistical uncertainty and contributions from the Q-value correlation uncertainty added in quadrature. Also shown for comparison are data from CLAS-g11a [30] ( ▪). The blue solid curve denotes the η-MAID 2018 [4] description of the γp→pη cross section.

      Reuse & Permissions
    • Figure 17
      Figure 17

      The differential cross sections dσ/dΩ in 40-MeV-wide center-of-mass bins for W∈[2.36,3.12]GeV and just the forward direction cos θc.m.η>0.5. The new CLAS data are shown as the black solid circles (•) and the uncertainties associated with each point are comprised of the statistical uncertainty and contributions from the Q-value correlation uncertainty added in quadrature. The blue solid curve denotes the η-MAID 2018 description [4] of the γp→pη cross section, whereas the red long-dashed curve represents the Regge model discussed in Ref. [3].

      Reuse & Permissions
    • Figure 18
      Figure 18

      The differential cross sections dσ/dt in 40-MeV-wide center-of-mass bins for W∈[2.52,3.12]GeV and for the −t range [0,2]GeV2. The new CLAS data are shown as the black solid circles (•) and the uncertainties associated with each point are comprised of the statistical uncertainty and contributions from the Q-value correlation uncertainty added in quadrature. In the energy range 2.52<W<2.56GeV, data from NINA at the Daresbury Laboratory [35] ( ▪) are given for comparison. And in the energy range 2.88<W<2.92GeV, also shown are data from DESY [36] (▴), MIT [38] (▪), and Cornell [39] (▾). The red long-dashed curve represents the Regge model discussed in Ref. [3] and the blue solid curve denotes the η-MAID 2018 description [4].

      Reuse & Permissions
    • Figure 19
      Figure 19

      The differential cross section dσ/dt for W∈[2.88,2.92]GeV and for the −t range [0,2]GeV2 using a linear scale. For the color code and an explanation of the curves, see the caption of Fig. 18.

      Reuse & Permissions
    • Figure 20
      Figure 20

      The differential cross sections dσ/dt in 40-MeV-wide center-of-mass bins for W∈[2.52,3.12]GeV and for the full range −t∈[0,4]GeV2. The new CLAS data are shown as the black solid circles (•) and the uncertainties associated with each point are comprised of the statistical uncertainty and contributions from the Q-value correlation uncertainty added in quadrature.

      Reuse & Permissions
    • Figure 21
      Figure 21

      Comparison between the new and the published [30] CLAS data in form of a difference distribution normalized to their uncertainties. See text for more details.

      Reuse & Permissions
    • Figure 22
      Figure 22

      Unweighted ratio distribution of the new and the published [30] CLAS data.

      Reuse & Permissions
    ×

    Sign up to receive regular email alerts from Physical Review C

    Log In

    Cancel
    ×

    Search

    Article Lookup

    Paste a citation or DOI
    Enter a citation
    ×