Photoproduction of {\boldmath{${\pi }^0$}} Mesons off Protons and Neutrons in the Second and Third Nucleon Resonance Region

Abstract

Photoproduction of mesons off quasi-free nucleons bound in the deuteron allows to study the electromagnetic excitation spectrum of the neutron and the isospin structure of the excitation of nucleon resonances. The database for such reactions is much more sparse than for free proton targets. Single ${\pi }^0$ photoproduction off quasi-free nucleons from the deuteron was experimentally studied. Nuclear effects were investigated by a comparison of the results for free protons and quasi-free protons and used as a correction for the quasi-free neutron data. The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator for photon energies between 0.45~GeV and 1.4~GeV, using an almost $4\pi$ electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. A complete kinematic reconstruction of the final state removed the effects of Fermi motion. Reaction model predictions and PWA for $\gamma n\to n{\pi }^0$, based on fits to data for the other isospin channels, disagreed between themselves and no model provided a good description of the new data. The results demonstrate clearly the importance of a measurement of the fully neutral final state for the isospin decomposition of the cross section. Model refits, for example from the Bonn-Gatchina analysis, show that the new and the previous data for the other three isospin channels can be simultaneously described when the contributions of several partial waves are modified. The results are also relevant for the suppression of the higher resonance bumps in total photoabsorption on nuclei, which are not well understood.

arXiv commentexcepted for publication in Phys. Rev. C

References in corpus (53)

• A unitary isobar model for pion photo- and electroproduction on the proton up to 1 GeV
• Unitary Isobar Model - MAID2007
• Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction
• Coupled-channel dynamics in the reactions piN --> piN, etaN, KLambda, KSigma
• Analysis of Pion Photoproduction Data
• Photon- and meson-induced reactions on the nucleon
• Completeness Rules for Spin Observables in Pseudoscalar Meson Photoproduction
• Study of Non-Strange Baryon Resonances with Meson Photoproduction
• Upgrade of the Glasgow photon tagging spectrometer for Mainz MAMI-C
• gamma* N -> Delta transition form factors: a new analysis of the JLab data on p(e,e'p)pi0 at Q^2=2.8 and 4.0 (GeV/c)^2
• Unified Chew-Mandelstam SAID analysis of pion photoproduction data
• ${\pi }^0$ photoproduction on the proton for photon energies from 0.675 to 2.875 GeV
• Multichannel parametrization of πN scattering amplitudes and extraction of resonance parameters
• Neutral pion photoproduction off protons in the energy range 0.3 GeV < E(gamma) < 3 GeV
• Quasi-free photoproduction of eta-mesons off the deuteron
• Well-established nucleon resonances revisited by double-polarization measurements
• 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
• Influence of final state interaction on incoherent pion photoproduction on the deuteron in the region of the Delta-resonance
• Photoproduction of pi0-mesons off protons from the Delta(1232) region to E(gamma) = 3 GeV
• First measurement of the helicity asymmetry for $\gamma p\to p{\pi }^0$ in the resonance region
• Effective Lagrangian Approach to pion photoproduction from the nucleon
• Photoproduction of pions and properties of baryon resonances from a Bonn-Gatchina partial wave analysis
• Photoproduction of mesons off nuclei
• Measurement of pi^0 photoproduction on the proton at MAMI C
• A narrow structure in the excitation function of eta-photoproduction off the neutron
• Extracting the photoproduction cross section off the neutron gn-->pi-p from deuteron data with FSI effects
• Photoproduction of pi0pi0 and pi0pi+-pairs off the proton from threshold to the second resonance region
• Radiative pi0 photoproduction on protons in the Delta+(1232) region
• Helicity amplitudes for photoexcitation of nucleon resonances off neutrons
• Photoproduction of ${\eta }^{\prime }$-mesons off the deuteron
• Amplitude analysis of gamma n --> pi- p data above 1 GeV
• Insight into the narrow structure in {\boldmath{$\eta$}}-photoproduction on the neutron from helicity dependent cross sections
• Electromagnetic Couplings of Nucleon Resonances
• Measurement of the beam-helicity asymmetry $I^{\odot }$ in the photoproduction of ${\pi }^0$-pairs off the proton and off the neutron
• Measurement of the Beam Asymmetry $\Sigma$ in the Forward Direction for pi0 Photoproduction
• The polarization observables T, P, and H and their impact on $\gamma p\to p{\pi }^0$ multipoles
• Quasi-free photoproduction of eta-mesons off 3He nuclei
• Photoproduction of pi0-mesons off neutrons in the nucleon resonance region
• Measurement of the ${}^{1}H$($\vec{\gamma }$, $\vec{p}$)${\pi }^0$ reaction using a novel nucleon spin polarimeter
• Differential Cross Section Measurements for $\gamma n\to {\pi }^{-}p$ Above the First Nucleon Resonance Region
• Photoproduction of Neutral Pions off Protons
• Evaluation of the gn-->pi-p differential cross sections in the Delta-isobar region
• First measurement of the polarization observable $E$ and helicity-dependent cross sections in single ${\pi }^0$ photoproduction from quasi-free nucleons
• Helicity-dependent cross sections and double-polarization observable E in eta photoproduction from quasi-free protons and neutrons
• Measurement of the beam-helicity asymmetry $I^{\odot }$ in the photoproduction of ${\pi }^0{\pi }^{\pm }$-pairs off protons and off neutrons
• Double-polarization observable G in neutral-pion photoproduction off the proton
• On the Extraction of Cross Sections for pi0 and eta Photoproduction off Neutrons from Deuteron Data
• Design of the Pluto Event Generator
• Photoproduction of eta mesons from the neutron: cross sections and double polarization observable E
• Complete kinematical study of the 3$\alpha$ breakup of the 16.11 MeV state in ${}^{12}$C
• Photon asymmetry measurements of $\overrightarrow{\gamma }\mathrm{p}\to {\pi }^0\mathrm{p}$ for E${}_{\gamma }$=320$-$650 MeV
• Quasi-free ${\pi }^0$ Photoproduction from the Bound Nucleon

Cited by in corpus (8)

• Light Baryon Spectroscopy
• Cross Section for $\gamma n\to {\pi }^{0}n$ measured at Mainz/A2
• Experimental study of the $\gamma p\to K^0{\Sigma }^{+}$, $\gamma n\to K^0\Lambda$, and $\gamma n\to K^0{\Sigma }^0$ reactions at the Mainz Microtron
• Extraction of $\gamma n\to \pi N$ observables from deuteron-target data
• Helicity-dependent cross sections for the photoproduction of ${\pi }^0$ pairs from nucleons
• First measurement of helicity-dependent cross sections in pi0-eta photoproduction from quasi-free nucleons
• Single-energy partial wave analysis for pion photoproduction with fixed-t analyticity
• Dynamical coupled-channels approach to electroweak meson productions on nucleon and deuteron