First measurement of helicity-dependent cross sections in pi0-eta photoproduction from quasi-free nucleons

Abstract

The helicity-dependent cross sections for the photoproduction of ${\pi }^0\eta$ pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the ${\sigma }_{1/2}$ (photon and target spin antiparallel) and ${\sigma }_{3/2}$ (parallel spins) components to be measured for quasi-free production of ${\pi }^0\eta$ pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant protons and neutrons. The absolute couplings for protons and neutrons are also identical. This means that nucleon resonances contributing to this reaction in the investigated energy range have almost equal electromagnetic helicity couplings, $A_{1/2}^{n,p}$ and $A_{3/2}^{n,p}$. Identical couplings for protons and neutrons are typical for $\Delta$ resonances and identical $A_{1/2}$ and $A_{3/2}$ components are only possible for $J\ge 3/2$ states, which constrains possible contributions of nucleon resonances.

arXiv commentaccepted for publication in Phys. Lett. B

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Cited by in corpus (7)

• Light Baryon Spectroscopy
• Photoproduction Reactions and Non-Strange Baryon Spectroscopy
• Observation of a structure in the M${}_{p\eta }$ invariant mass distribution near 1700 MeV/$c^2$ in the $\gamma \mathbf{p}\to \mathbf{p}{\pi }^0\eta$ reaction
• Helicity-dependent cross sections for the photoproduction of ${\pi }^0$ pairs from nucleons
• Coherent photoproduction of the neutral pion and eta meson on the deuteron at incident energies below 1.15 GeV
• Measurement of the beam-helicity asymmetry in photoproduction of ${\pi }^0\eta$ pairs on carbon, aluminum, and lead
• Helicity dependent cross sections for the photoproduction of ${\pi }^0{\pi }^{\pm }$ pairs from quasi-free nucleons