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

Abstract: We present a model-independent extraction of the phi-helium-4 scattering length from near-threshold phi photoproduction on helium-4, based on LEPS Collaboration data for the coherent process gamma plus helium-4 to phi plus helium-4, and the Vector Meson Dominance framework. Assuming an energy-independent differential cross section, we extract the absolute value of the phi-helium-4 scattering length, |alpha_phiHe4| = (4.19 +/- 0.07) x 10^-4 fm, from a fit at the threshold t_thr. This value is orders of magnitude smaller than those for phi-nucleon and phi-deuteron scattering lengths, indicating an inverse dependence of |alpha_VN| on the target nucleus mass. Our results provide new insight into the phi-nucleus interaction, supporting the notion of weak phi-nucleus coupling. We further explore the dependence of |alpha_VN| on the vector meson mass, the target atom mass, and the threshold energy. An approximate exponential suppression of |alpha_VN| 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.