Polarization of Hyperons in Elementary Photoproduction

TL;DR

This paper reports the first measurements of spin transfer coefficients in hyperon photoproduction, revealing unexpected full polarization of Lambda hyperons and suggesting a spin-orbit interaction mechanism during hadronization.

Contribution

It provides new experimental data on hyperon polarization transfer and proposes a novel hypothesis involving spin-orbit interactions to explain the observations.

Findings

Lambda hyperons are produced 100% polarized.

C_x and C_z are linearly related.

Spin-orbit interaction may preserve polarization during hadronization.

Abstract

Recent measurements using the CLAS detector at Jefferson Lab of the reactions $\vec\gamma + p \to K^+ + \vec\Lambda$ and $\vec\gamma + p \to K^+ + \vec\Sigma^0$ have been used to extract the spin transfer coefficients $C_x$ and $C_z$ for the first time. These observables quantify the degree of the photon circular polarization that is transferred to the recoiling hyperons in the scattering plane. The unexpected result is that $\Lambda$ hyperons are produced ``100% polarized'' as seen when combining $C_x$ and $C_z$ with the induced transverse polarization, $P$. Furthermore, $C_x$ and $C_z$ seem to be linearly related. This paper discusses the experimental results and offers a hypothesis which can explain these observations. We show how the produced strange quark can be subject to a pure spin-orbit type of interaction which preserves its state of polarization throughout the hadronization process.