The target asymmetry
T
, recoil asymmetry
P
, and beam-target double polarization observable
H
were determined in exclusive
π
0
and
η
photoproduction off quasi-free protons and, for the first time, ...off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the
γ
p
→
π
0
p
and
γ
p
→
η
p
reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the
η
n
system at
W
=
1.68
GeV
. A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the
S
11
(
1535
)
and
S
11
(
1650
)
resonances within the
S
11
-partial wave.
The quasifree
photon beam asymmetry,
, has been measured at photon energies,
, from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were ...collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49
to 148
. In this kinematic region, polarization observables are sensitive to contributions from the
and
(1440) resonances. The extracted values of
have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID and Bonn-Gatchina analyses; while a revised SAID fit, including the new
measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict
photoproduction observables, based on fits to published data in the channels
,
and
.
The quasifree
γ
→
d
→
π
0
n
(
p
)
photon beam asymmetry,
Σ
, has been measured at photon energies,
E
γ
, from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the ...first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49
∘
to 148
∘
. In this kinematic region, polarization observables are sensitive to contributions from the
Δ
(
1232
)
and
N
(1440) resonances. The extracted values of
Σ
have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID and Bonn–Gatchina analyses; while a revised SAID fit, including the new
Σ
measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict
π
0
n
photoproduction observables, based on fits to published data in the channels
π
0
p
,
π
+
n
and
π
-
p
.
Photoproduction of π0π±-pairs from quasifree nucleons bound in the deuteron has been investigated to study the helicity dependence of this reaction. Measurements with a liquid deuterium target were ...used to extract the unpolarized cross sections for reactions on protons and neutrons. A deuterated, longitudinally polarized solid-butanol target, together with a circularly polarized photon beam, determined the double polarization observable E. From these results the spin-dependent cross sections σ1/2 and σ3/2, corresponding to the anti-parallel and parallel spin configurations of the beam photon and target nucleon, have been derived. The measurements were performed at the Mainz MAMI accelerator with tagged, circularly-polarized photon beams produced via bremsstrahlung from longitudinally polarized electron beams. The reaction products were detected with an almost 4π solid-angle covering calorimeter composed of the Crystal Ball and TAPS detectors, supplemented by plastic scintillation detectors for charged particle identification. The results are sensitive to sequential decays of nucleon resonances via intermediate states and also to the decay of nucleon resonances by emission of charged ρ mesons, and are compared to recent model results.
Abstract
The target asymmetry
T
, recoil asymmetry
P
, and beam-target double polarization observable
H
were determined in exclusive
$$\pi ^0$$
π
0
and
$$\eta $$
η
photoproduction off quasi-free ...protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the
$$\gamma p \rightarrow \pi ^0 p$$
γ
p
→
π
0
p
and
$$\gamma p \rightarrow \eta p$$
γ
p
→
η
p
reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the
$$\eta n$$
η
n
system at
$$W = 1.68\ \textrm{GeV}$$
W
=
1.68
GeV
. A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the
$$S_{11}(1535)$$
S
11
(
1535
)
and
$$S_{11}(1650)$$
S
11
(
1650
)
resonances within the
$$S_{11}$$
S
11
-partial wave.
The target asymmetry
T
, recoil asymmetry
P
, and beam-target double polarization observable
H
were determined in exclusive
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\begin{document}$$\pi ^0$$\end{document}
π
0
and
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\begin{document}$$\eta $$\end{document}
η
photoproduction off quasi-free protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the
\documentclass12pt{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
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\usepackage{amssymb}
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\usepackage{mathrsfs}
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\setlength{\oddsidemargin}{-69pt}
\begin{document}$$\gamma p \rightarrow \pi ^0 p$$\end{document}
γ
p
→
π
0
p
and
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\begin{document}$$\gamma p \rightarrow \eta p$$\end{document}
γ
p
→
η
p
reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the
\documentclass12pt{minimal}
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\begin{document}$$\eta n$$\end{document}
η
n
system at
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\setlength{\oddsidemargin}{-69pt}
\begin{document}$$W = 1.68\ \textrm{GeV}$$\end{document}
W
=
1.68
GeV
. A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the
\documentclass12pt{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
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\begin{document}$$S_{11}(1535)$$\end{document}
S
11
(
1535
)
and
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\begin{document}$$S_{11}(1650)$$\end{document}
S
11
(
1650
)
resonances within the
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\begin{document}$$S_{11}$$\end{document}
S
11
-partial wave.
The quasifree
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\begin{document}$$\overrightarrow{\gamma } d\rightarrow \pi ^0n(p)$$\end{document}
γ
→
d
→
π
0
n
(
p
)
photon beam asymmetry,
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\begin{document}$$\varSigma $$\end{document}
Σ
, has been measured at photon energies,
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\begin{document}$$E_\gamma $$\end{document}
E
γ
, from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49
\documentclass12pt{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
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\setlength{\oddsidemargin}{-69pt}
\begin{document}$$^\circ $$\end{document}
∘
to 148
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\begin{document}$$^\circ $$\end{document}
∘
. In this kinematic region, polarization observables are sensitive to contributions from the
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\begin{document}$$\varDelta (1232)$$\end{document}
Δ
(
1232
)
and
N
(1440) resonances. The extracted values of
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\begin{document}$$\varSigma $$\end{document}
Σ
have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID and Bonn–Gatchina analyses; while a revised SAID fit, including the new
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\begin{document}$$\varSigma $$\end{document}
Σ
measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict
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\begin{document}$$\pi ^0n$$\end{document}
π
0
n
photoproduction observables, based on fits to published data in the channels
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\begin{document}$$\pi ^0p$$\end{document}
π
0
p
,
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\begin{document}$$\pi ^+n$$\end{document}
π
+
n
and
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\begin{document}$$\pi ^-p$$\end{document}
π
-
p
.
Physics Letters B, Volume 847, 10 December 2023, 138273 Photoproduction of $\pi^0\pi^{\pm}$-pairs from quasifree nucleons bound in
the deuteron has been investigated to study the helicity dependence ...of this
reaction. Measurements with a liquid deuterium target were used to extract the
unpolarized cross sections for reactions on protons and neutrons. A deuterated,
longitudinally polarized solid-butanol target, together with a circularly
polarized photon beam, determined the double polarization observable $E$. From
these results the spin-dependent cross sections $\sigma_{1/2}$ and
$\sigma_{3/2}$, corresponding to the anti-parallel and parallel spin
configurations of the beam photon and target nucleon, have been derived. The
measurements were performed at the Mainz MAMI accelerator with tagged,
circularly-polarized photon beams produced via bremsstrahlung from
longitudinally polarized electron beams. The reaction products were detected
with an almost $4\pi$ solid-angle covering calorimeter composed of the Crystal
Ball and TAPS detectors, supplemented by plastic scintillation detectors for
charged particle identification. The results are sensitive to sequential decays
of nucleon resonances via intermediate states and also to the decay of nucleon
resonances by emission of charged $\rho$ mesons, and are compared to recent
model results.
The quasifree $\overrightarrow{\gamma} d\to\pi^0n(p)$ photon beam asymmetry,
$\Sigma$, has been measured at photon energies, $E_\gamma$, from 390 to 610
MeV, corresponding to center of mass energy ...from 1.271 to 1.424 GeV, for the
first time. The data were collected in the A2 hall of the MAMI electron beam
facility with the Crystal Ball and TAPS calorimeters covering pion
center-of-mass angles from 49 to 148$^\circ$. In this kinematic region,
polarization observables are sensitive to contributions from the $\Delta
(1232)$ and $N(1440)$ resonances. The extracted values of $\Sigma$ have been
compared to predictions based on partial-wave analyses (PWAs) of the existing
pion photoproduction database. Our comparison includes the SAID, MAID, and
Bonn-Gatchina analyses; while a revised SAID fit, including the new $\Sigma$
measurements, has also been performed. In addition, isospin symmetry is
examined as a way to predict $\pi^0n$ photoproduction observables, based on
fits to published data in the channels $\pi^0p$, $\pi^+n$, and $\pi^-p$.
Photoproduction of \(\pi^0\pi^{\pm}\)-pairs from quasifree nucleons bound in the deuteron has been investigated to study the helicity dependence of this reaction. Measurements with a liquid deuterium ...target were used to extract the unpolarized cross sections for reactions on protons and neutrons. A deuterated, longitudinally polarized solid-butanol target, together with a circularly polarized photon beam, determined the double polarization observable \(E\). From these results the spin-dependent cross sections \(\sigma_{1/2}\) and \(\sigma_{3/2}\), corresponding to the anti-parallel and parallel spin configurations of the beam photon and target nucleon, have been derived. The measurements were performed at the Mainz MAMI accelerator with tagged, circularly-polarized photon beams produced via bremsstrahlung from longitudinally polarized electron beams. The reaction products were detected with an almost \(4\pi\) solid-angle covering calorimeter composed of the Crystal Ball and TAPS detectors, supplemented by plastic scintillation detectors for charged particle identification. The results are sensitive to sequential decays of nucleon resonances via intermediate states and also to the decay of nucleon resonances by emission of charged \(\rho\) mesons, and are compared to recent model results.
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