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

We present a model-independent extraction of the φ ϕ – ⁴He 4 He scattering length from near-threshold φ ϕ photoproduction on helium-4, based on LEPS Collaboration data for the coherent process γ + ⁴He → φ + ⁴He γ + 4 He → ϕ + 4 He and the Vector Meson Dominance framework. Assuming an energy-independent differential cross section, we extract the absolute value of the φ -⁴\!He ϕ - 4 He scattering length |α _φ ⁴He| = (3.33 ± 0.06) × 10⁻⁴~fm | α ϕ 4 He | = ( 3.33 ± 0.06 ) × 10 - 4 fm from a fit at threshold tₜₕᵣ t thr . This value is orders of magnitude smaller than those for φ N ϕ N and φ d ϕ d scattering length, indicating an inverse dependence of |α VA| | α VA | on the target nucleus mass. Our results provide new insight into the φ ϕ –nucleus interaction, supporting the notion of weak φ ϕ –nucleus coupling. We further explore the dependence of |α VA| | α VA | on the vector meson mass, the target atom mass, and the threshold energy. An approximate exponential suppression of |α VA| | α 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.