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Photoproduction and detection of ρ′→π+π−π+π− decays in ultraperipheral collisions and at an electron-ion collider

Neha Devi* and Janet Seger

Minjung Kim

Spencer R. Klein†

  • *Present address: Jaeger Corporation, P.O. Box 540364 Omaha, NE 68154.
  • †Contact author: srklein@lbl.gov
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Phys. Rev. C 113, 015207 – Published 26 January, 2026

DOI: https://doi.org/10.1103/wpbg-h511

Abstract

Vector meson photoproduction is an important probe of nuclear structure. Light vector mesons are most sensitive to low−x structure, as long as they are not too light for perturbative QCD calculations. The ρ′ is of interest as an intermediate mass state (between the ρ and J/ψ) that is easier to detect than the ϕ. Using HERA data on proton targets, we make projections for lead/gold targets in ultraperipheral collisions (UPCs) at the CERN Large Hadron Collider and the BNL Relativistic Heavy Ion Collider, and for ep and eA collisions at a future electron-ion collider (EIC). We compare the UPC projections with ALICE data, and constrain the branching ratio divided by the square of the photon-ρ′ coupling. The data prefer large couplings and small branching ratio, probably less than 25%. The photon-meson coupling predicted by generalized vector meson dominance does not fit the data. The HERA ep and ALICE UPC ePb data exhibit very similar 4π mass spectra, indicating that, if the system is composed of two resonances, the products of their photon couplings with their four-pion branching ratios are similar. The predicted rates are high for both UPCs and the EIC. The ρ′→π+π−π+π− decay can be observed at the EIC with high efficiency. In ep collisions at the highest energy, the forward B0 detector is needed to observe this channel down to the lowest achievable Bjorken−x values.

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Phys. Rev. C 113, 015207– Published 26 January, 2026
  • Received 1 May 2025
  • Revised 26 September 2025
  • Accepted 1 December 2025
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