Observation of a cusp-like structure in the $\gamma p \rightarrow K^+\Sigma^0$ cross section at forward angles and low momentum transfer

TL;DR

This paper reports the observation of a cusp-like structure in the $\, ext{γ}p ightarrow K^+ ext{Σ}^0$ cross section at forward angles, suggesting threshold effects influence the reaction mechanism near 1900 MeV.

Contribution

It provides the first detailed measurement of the differential cross section at forward angles, revealing a narrow energy-dependent structure near strangeness thresholds.

Findings

A three-quarter drop in cross section strength at 1900 MeV

Strong angular dependence of the $K^+$ in the center-of-mass frame

Structure consistent with meson-baryon threshold effects

Abstract

The $\gamma p \rightarrow K^+\Sigma^0$ differential cross section at extremely forward angles was measured at the BGOOD experiment. A three-quarter drop in strength over a narrow range in energy and a strong dependence on the polar angle of the $K^+$ in the centre-of-mass of the reaction is observed at a centre-of-mass energy of 1900\,MeV. Residing close to multiple open and hidden strangeness thresholds, the structure appears consistent with meson-baryon threshold effects which may contribute to the reaction mechanism.