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

TL;DR

This paper reports the first model-independent measurement of the phi-4He scattering length from near-threshold phi photoproduction data, revealing very weak phi-nucleus interactions and an inverse relation with target mass.

Contribution

It provides the first extraction of the phi-4He scattering length using a model-independent approach based on experimental data and the Vector Meson Dominance framework.

Findings

The phi-4He scattering length is approximately 3.33 x 10^{-4} fm.

The phi-4He scattering length is much smaller than phi-N and phi-d scattering lengths.

Heavier vector mesons and nuclei show weaker coupling in vector meson-nucleus interactions.

Abstract

We present a model-independent extraction of the phi-4He scattering length from near-threshold phi photoproduction on helium-4, based on LEPS Collaboration data for the coherent process gamma + 4He -> phi + 4He and the Vector Meson Dominance framework. Assuming an energy-independent differential cross section, we extract the absolute value of the phi-4He scattering length |alpha_{phi4He}| = (3.33 +- 0.06) x 10^{-4} fm from a fit at threshold t_thr. This value is orders of magnitude smaller than those for phi-N and phi-d scattering lengths, indicating an inverse dependence of |alpha_VA| 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_VA| on the vector meson mass, the target atom mass, and the threshold energy. An approximate exponential suppression of |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.