First extraction of the - scattering length from near-threshold photoproduction on helium-4

Chengdong Han; Wei Kou; Rong Wang; Xurong Chen

doi:10.1140/epjc/s10052-025-14877-5

2024 Impact factor 4.8

Particles and Fields

Open Access

Eur. Phys. J. C (2025) 85: 1148
https://doi.org/10.1140/epjc/s10052-025-14877-5

Regular Article - Theoretical Physics

First extraction of the $ϕ$ $\phi$ - $^{4} He$ $^{4}\textrm{He}$ scattering length from near-threshold $ϕ$ $\phi$ photoproduction on helium-4

Chengdong Han¹^,2^,3^a, Wei Kou¹^,2, Rong Wang¹^,2^,3 and Xurong Chen¹^,2^,3^,4^b

¹ Institute of Modern Physics, Chinese Academy of Sciences, 730000, Lanzhou, China
² School of Nuclear Science and Technology, University of Chinese Academy of Sciences, 100049, Beijing, China
³ State Key Laboratory of Heavy Ion Science and Technology, Institute of Modern Physics, Chinese Academy of Sciences, 730000, Lanzhou, China
⁴ Southern Center for Nuclear Science Theory, Institute of Modern Physics, Chinese Academy of Sciences, 516000, Huizhou, China

^a This email address is being protected from spambots. You need JavaScript enabled to view it.
^b This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 31 July 2025
Accepted: 1 October 2025
Published online: 13 October 2025

Abstract

We present a model-independent extraction of the $ϕ$ $\phi$ – $^{4} He$ $^{4}\textrm{He}$ scattering length from near-threshold $ϕ$ $\phi$ photoproduction on helium-4, based on LEPS Collaboration data for the coherent process $γ +^{4} He \to ϕ +^{4} He$ $\gamma + {}^{4}\textrm{He} \rightarrow \phi + {}^{4}\textrm{He}$ and the Vector Meson Dominance framework. Assuming an energy-independent differential cross section, we extract the absolute value of the $ϕ -^{4} He$ $\phi -^4\!\textrm{He}$ scattering length $| α_{ϕ^{4} He} | = (3.33 \pm 0.06) \times 10^{- 4} fm$ $|\alpha _{\phi ^{4}\textrm{He}}| = (3.33 \pm 0.06) \times 10^{-4}~\textrm{fm}$ from a fit at threshold $t_{thr}$ $t_{\text {thr}}$ . This value is orders of magnitude smaller than those for $ϕ N$ $\phi N$ and $ϕ d$ $\phi d$ scattering length, indicating an inverse dependence of $| α_{VA} |$ $|\alpha _{VA}|$ on the target nucleus mass. Our results provide new insight into the $ϕ$ $\phi$ –nucleus interaction, supporting the notion of weak $ϕ$ $\phi$ –nucleus coupling. We further explore the dependence of $| α_{VA} |$ $|\alpha _{VA}|$ on the vector meson mass, the target atom mass, and the threshold energy. An approximate exponential suppression of $| α_{VA} |$ $|\alpha _{VA}|$ is observed with increasing vector meson mass or target atom mass, indicating that heavier vector mesons or heavier target nuclei exhibit weaker couplings in vector meson–nucleus interactions.

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First extraction of the $ϕ$ $\phi$ - $^{4} He$ $^{4}\textrm{He}$ scattering length from near-threshold $ϕ$ $\phi$ photoproduction on helium-4