Near threshold angular distributions of the $^2$H$(\gamma,\Lambda)$X reaction

TL;DR

This study measures the angular distribution of the $^2$H($,Lambda)$X reaction near threshold energies, comparing experimental data with theoretical models to evaluate their accuracy in describing the reaction mechanism.

Contribution

First detailed measurement of the near-threshold angular distribution of the $^2$H($,Lambda)$X reaction, providing data to test and refine theoretical models.

Findings

Slight peak in cross section at small angles.

SLA and RPR models fit data well, KM underpredicts at forward angles.

Data supports the validity of certain isobar and Regge-plus-resonance models.

Abstract

A study of the $^2$H$({\gamma},{\Lambda})$X reaction was performed using a tagged photon beam at the Research Center for Electron Photon Science (ELPH), Tohoku University. The photoproduced $\Lambda$ was measured in the $p{\pi^{-}}$ decay channel by the upgraded Neutral Kaon Spectrometer (NKS2+). The momentum integrated differential cross section was determined as a function of the scatting angle of ${\Lambda}$ in the laboratory frame for five energy bins. Our results indicated a peak in the cross section at angles smaller than cos$\theta^{LAB}_{\Lambda}$ = $0.96$. The experimentally obtained angular distributions were compared to isobar models, Kaon-Maid (KM) and Saclay-Lyon A (SLA), in addition to the composite Regge-plus-resonance (RPR) model. Both SLA(r$K_{1}K_{\gamma}$ = $-1.4$) and RPR describe the data quite well in contrast to the KM model, which substantially under predicted the cross section at the most forward angles. With the anticipated finalized data on ${\Lambda}$ integrated and momentum dependent differential cross sections of $^2$H$({\gamma},{\Lambda})$X~\cite{Kaneta_Beckford}, we present our findings on the angular distributions in this report.