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Backward-angle electroproduction of $η'$ mesons off protons at $W=2.13~\text{GeV}$ and $Q^{2}=0.46~\left(\text{GeV}/c\right)^{2}$

T. Akiyama, P. Bydžovský, T. Gogami, K. Itabashi, S. Nagao, S. N. Nakamura, K. Okuyama, B. Pandey, D. Skoupil, K. N. Suzuki, L. Tang, D. Abrams, D. Androic, K. Aniol, C. Ayerbe Gayoso, J. Bane, S. Barcus, J. Barrow, V. Bellini, H. Bhatt, D. Bhetuwal, D. Biswas, A. Camsonne, J. Castellanos, J-P. Chen, J. Chen, S. Covrig, D. Chrisman, R. Cruz-Torres, R. Das, E. Fuchey, K. Gnanvo, F. Garibaldi, T. Gautam, J. Gomez, P. Gueye, T. J. Hague, O. Hansen, W. Henry, F. Hauenstein, D. W. Higinbotham, C. E. Hyde, M. Kaneta, C. Keppel, T. Kutz, N. Lashley-Colthirst, S. Li, H. Liu, J. Mammei, P. Markowitz, R. E. McClellan, F. Meddi, D. Meekins, R. Michaels, M. Mihovilovič, A. Moyer, D. Nguyen, M. Nycz, V. Owen, C. Palatchi, S. Park, T. Petkovic, S. Premathilake, P. E. Reimer, J. Reinhold, S. Riordan, V. Rodriguez, C. Samanta, S. N. Santiesteban, B. Sawatzky, S. Širca, K. Slifer, T. Su, Y. Tian, Y. Toyama, D. Trnková, K. Uehara, G. M. Urciuoli, D. Votaw, J. Williamson, B. Wojtsekhowski, S. A. Wood, B. Yale, Z. Ye, J. Zhang, X. Zheng

TL;DR

The study measures backward-angle electroproduction of $\eta'$ mesons off protons at $W=2.13~\mathrm{GeV}$ and $Q^{2}=0.46~(\mathrm{GeV}/c)^{2}$, extracting a differential cross section of $4.4\pm0.8\,\mathrm{(stat)}\pm0.4\,\mathrm{(sys)}\,\mathrm{nb/sr}$ in the One-Photon-Exchange framework. The analysis combines precise calibration, event selection, and SIMC-based simulations to model the missing-mass spectrum and backgrounds, enabling cross-section extraction and $Q^{2}$, $W$ dependence studies. An extended isobar model (BS12/BS3) with four resonance sets describes both photoproduction data and the current electroproduction results, highlighting the critical role of electromagnetic form factors in the $Q^{2}$ evolution and suggesting resonance contributions near $W\sim 2100$ MeV that couple to the $\eta'p$ final state. These findings provide new constraints on high-mass nucleon resonances and advance understanding of $\eta'$ production mechanisms in the nucleon resonance region.

Abstract

The electroproduction of $η'$ mesons from a $\mathrm{^{1}H}$ target at $W=2.13~\text{GeV}$, $Q^{2} = 0.46~\left( \text{GeV}/c\right)^{2}$ and $\cos θ^{\text{CM}}_{γ^{*}η'} \approx -1$ has been experimentally measured. The differential cross section of virtual-photoproduction has been obtained as $4.4 \pm 0.8 ~\left( \text{stat.} \right) \pm 0.4 ~\left( \text{sys.} \right)~ \text{nb/sr}$ in the One-Photon-Exchange Approximation. This value is one-sixth of that of real-photoproduction at backward angles. A comparison with newly-developed isobar model calculations not only shows validity of the theoretical framewark employed, but also imposes new constrains on coupling strength between the $η'p$ final state and nucleon resonances.

Backward-angle electroproduction of $η'$ mesons off protons at $W=2.13~\text{GeV}$ and $Q^{2}=0.46~\left(\text{GeV}/c\right)^{2}$

TL;DR

The study measures backward-angle electroproduction of mesons off protons at and , extracting a differential cross section of in the One-Photon-Exchange framework. The analysis combines precise calibration, event selection, and SIMC-based simulations to model the missing-mass spectrum and backgrounds, enabling cross-section extraction and , dependence studies. An extended isobar model (BS12/BS3) with four resonance sets describes both photoproduction data and the current electroproduction results, highlighting the critical role of electromagnetic form factors in the evolution and suggesting resonance contributions near MeV that couple to the final state. These findings provide new constraints on high-mass nucleon resonances and advance understanding of production mechanisms in the nucleon resonance region.

Abstract

The electroproduction of mesons from a target at , and has been experimentally measured. The differential cross section of virtual-photoproduction has been obtained as in the One-Photon-Exchange Approximation. This value is one-sixth of that of real-photoproduction at backward angles. A comparison with newly-developed isobar model calculations not only shows validity of the theoretical framewark employed, but also imposes new constrains on coupling strength between the final state and nucleon resonances.

Paper Structure

This paper contains 16 sections, 20 equations, 9 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Experiment
  3. Principle
  4. Apparatus and setup
  5. Analysis
  6. Calibration
  7. Event selection
  8. Simulation
  9. Missing mass
  10. Result and discussion
  11. Result of the present measurement
  12. Decomposition of the differential cross section
  13. Isobar model to the $\eta'$ electroproduction
  14. Discussion for $Q^{2}$-dependence
  15. Discussion for $W$-dependence
  16. ...and 1 more sections

Figures (9)

  • Figure 1: A schematic diagram based on OPEA of the $e+p \rightarrow e+p+\eta '$ reaction.
  • Figure 2: two-dimensional distribution of the $Z$-vertex reconstructed with both HRS-L and HRS-R. The regions of hydrogen gas and aluminum cells are clearly seen among the accidental background event. The violet dashed lines represent the gate of the target position selection for analysis.
  • Figure 3: Coincidence time distribution. The peaks located at $\mathrm{0~ns}$, $\mathrm{\sim 7.8~ns}$, $\mathrm{\sim 11.1~ns}$ correspond to proton, kaon, and pion, respectively. Accidental coincidence events are distributed uniformly beneath the three peaks. The two blue dashed-lines represent the timing gate for proton selection.
  • Figure 4: The two-dimensional dependence of the solid angle on momentum and $Z$-vertex for HRS-L and HRS-R. The Z-axis represents the solid angle, with units of msr.
  • Figure 5: $p_{e'}$ v.s $p_{p_{\mathrm{scat}}}$ distribution for data and multi-pi simulation.
  • ...and 4 more figures