First measurement of the polarization observable $E$ and helicity-dependent cross sections in single ${\pi }^0$ photoproduction from quasi-free nucleons

Abstract

The double-polarization observable $E$ and the helicity-dependent cross sections ${\sigma }_{1/2}$ and ${\sigma }_{3/2}$ have been measured for the first time for single ${\pi }^0$ photoproduction from protons and neutrons bound in the deuteron at the electron accelerator facility MAMI in Mainz, Germany. The experiment used a circularly polarized photon beam and a longitudinally polarized deuterated butanol target. The reaction products, recoil nucleons and decay photons from the ${\pi }^0$ meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the ${\pi }^{0}N$ final state. A comparison to data measured with a free proton target showed that the absolute scale of the cross sections is significantly modified by nuclear final-state interaction (FSI) effects. However, there is no significant effect on the asymmetry $E$ since the ${\sigma }_{1/2}$ and ${\sigma }_{3/2}$ components appear to be influenced in a similar way. Thus, the best approximation of the two helicity-dependent cross sections for the free neutron is obtained by combining the asymmetry $E$ measured with quasi-free neutrons and the unpolarized cross section corrected for FSI effects under the assumption that the FSI effects are similar for neutrons and protons.

accepted for publication in Phys. Lett. B

References in corpus (11)

• Unitary Isobar Model - MAID2007
• Upgrade of the Glasgow photon tagging spectrometer for Mainz MAMI-C
• Evidence for a narrow structure at W~1.68 GeV in eta photoproduction on the neutron
• Quasi-free photoproduction of eta-mesons of the neutron
• Quasifree photoproduction of $\eta$ mesons off protons and neutrons
• Linearly polarised photon beams at ELSA and measurement of the beam asymmetry in pi^0-photoproduction off the proton
• Production of $\eta$ and ${\eta }^{\prime }$ Mesons on Nucleons and Nuclei
• Insight into the narrow structure in {\boldmath{$\eta$}}-photoproduction on the neutron from helicity dependent cross sections
• Photoproduction of pi0-mesons off neutrons in the nucleon resonance region
• Measurement of the beam-helicity asymmetry $I^{\odot }$ in the photoproduction of ${\pi }^0{\pi }^{\pm }$-pairs off protons and off neutrons
• Photoproduction ofeta-pi pairs off nucleons and deuterons

Cited by in corpus (7)

• Light Baryon Spectroscopy
• On the Photoproduction Reactions $\gamma d\to \pi NN$
• Helicity-dependent cross sections for the photoproduction of ${\pi }^0$ pairs from nucleons
• Single-pion contribution to the Gerasimov--Drell--Hearn sum rule and related integrals
• Single-energy partial wave analysis for pion photoproduction with fixed-t analyticity
• Helicity dependent cross sections for the photoproduction of ${\pi }^0{\pi }^{\pm }$ pairs from quasi-free nucleons
• New graphical criterion for the selection of complete sets of polarization observables and its application to single-meson photoproduction as well as electroproduction