Anomaly in the K^0_S Sigma^+ photoproduction cross section off the proton at the K* threshold

TL;DR

This paper investigates the photoproduction of K^0 and Sigma^+ off protons, revealing an anomaly at the K* threshold that suggests a change in the underlying reaction mechanism.

Contribution

It provides the first detailed measurement of the differential and total cross sections around the K* threshold, highlighting a possible transition from t-channel to s-channel processes.

Findings

Forward-peaking cross section increases with energy up to the K* threshold.

A sudden drop in forward cross section beyond the K* threshold.

Pronounced structure in total cross section indicating a reaction mechanism change.

Abstract

The $\gamma + p \rightarrow K^0 + \Sigma^+$ photoproduction reaction is investigated in the energy region from threshold to $E_\gamma = 2250$\,MeV. The differential cross section exhibits increasing forward-peaking with energy, but only up to the $K^*$ threshold. Beyond, it suddenly returns to a flat distribution with the forward cross section dropping by a factor of four. In the total cross section a pronounced structure is observed between the $K^*\Lambda$ and $K^*\Sigma$ thresholds. It is speculated whether this signals the turnover of the reaction mechanism from t-channel exchange below the $K^*$ production threshold to an s-channel mechanism associated with the formation of a dynamically generated $K^*$-hyperon intermediate state.