Abstract

The BGO-OD experiment at the ELSA accelerator facility uses an energy tagged bremsstrahlung photon beam to investigate the excitation structure of the nucleon. The setup consists of a highly segmented BGO calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles.BGO-OD is ideal for investigating low momentum transfer processes due to the acceptance and high momentum resolution at forward angles. In particular, this enables the investigation of strangeness photoproduction where t-channel exchange mechanisms play an important role. This also allows access to low momentum exchange kinematics where extended, molecular structure may manifest in reaction mechanisms.First key results at lowtindicate a cusp-like structure inK+Σ0photoproduction atW =1900 MeV, line shapes and differential cross sections for K+Λ(1405)→K+Σ0π0, and a peak structure inK0SΣ0photoproduction. The peak in theK0SΣ0channel appears consistent with meson-baryon generated states, where equivalent models have been used to describe thePCpentaquark candidates in the heavy charmed quark sector.

Highlights

  • Hadron spectroscopy has been used for many years to understand the interactions of the constituents and the relevant degrees of freedom

  • First key results at low t indicate a cusp-like structure in K+Σ0 photoproduction at W = 1900 MeV, line shapes and differential cross sections for K+Λ(1405)→ K+Σ0π0, and a peak structure in KS0 Σ0 photoproduction

  • Despite the wealth of data available using both pion and photon beams and a multitude of final states, there are still many resonances predicted by constituent quark models (CQMs) that have not been observed experimentally

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Summary

Introduction

Hadron spectroscopy has been used for many years to understand the interactions of the constituents and the relevant degrees of freedom. Since the conception of the quark model, there have been descriptions of hadrons with more than three constituent quarks [3,4,5], and models explicitly including light mesons interacting as elementary objects have had markedly improved success in describing nucleon excitation spectra [6,7,8] Such interactions may give rise to meson rescattering effects near production thresholds, and molecular like systems. The BGO-OD experiment at the ELSA facility, Bonn, Germany, is a unique setup that is ideal to study molecular like interactions in strangeness photoproduction which may manifest in the reaction mechanisms.

Exotic hadron structure - parallels in strange and charmed quark sectors?
The BGO-OD experiment at ELSA
BGO-OD performance
Preliminary results in strangeness photoproduction
Neutral kaon photoproduction
Findings
Conclusions
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