Amplitudes for the reaction
π
−
p
→
ΛK
0
are reconstructed from data on the differential cross section d
σ
/d
Ω
, the recoil polarization
P
, and on the spin rotation parameter
β
. At low energies, ...no data on
β
exist, resulting in ambiguities. An approximation using
S
and
P
waves leads only to a fair description of the data on d
σ
/d
Ω
and
P
; in this case, there are two sets of amplitudes. Including
D
waves, the data on d
σ
/d
Ω
and
P
are well reproduced by the fit but, now, there is a multitude of distinct solutions which describe the data with identical precision. In the range where the spin rotation parameter
β
was measured, a full and unambiguous reconstruction of the partial wave amplitudes is possible. The energy-independent (single-energy) amplitudes are compared to the energy-dependent amplitudes which resulted from a coupled-channel fit (BnGa2011-02) to a large data set including both pion- and photo-induced reactions. Significant deviations are observed. Consistency between energy-dependent and energy-independent solutions is obtained by choosing the energy-independent solution which is the closest to the energy-dependent solution. In a second step, the
known
energy-dependent solution for low (or high) partial waves is imposed and only the high (or low) partial waves are fitted leading to smaller uncertainties.
A measurement of the double-polarization observable
for the reaction
is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol ...(C
H
OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from
to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.
The new single-channel, single-energy partial wave analysis method based on a
simultaneous use of amplitude and partial wave analysis called AA/PWA,
developed and tested on $\eta$ photoproduction in ...ref. Svarc et al, PRC 102,
064609 (2020), is applied to the $K^{+} \Lambda$ photoproduction for the
center-of-mass energy range of 1625 MeV $< W <$ 2296 MeV. A complete set of
multipoles has been created. The advantages of the method have been confirmed,
and a comparison with the only existing single-energy partial wave analysis of
$K^{+} \Lambda$ photoproduction given in refs. Anisovich et al PRL 119 062004
(2017) and Anisovich et al Eur. Phys. J. A 53: 242 (2017) is presented. We
confirm the size and shape of Bonn-Gatchina multipoles, but we do not confirm
the unambiguous interpretation of the structure in the $M_{1-}$ multipole as a
$N(1880) \frac{1}{2}^{+}$ resonance. The decisive role of the self-consistency
of the world database is emphasized.
High-statistics measurements of the photon asymmetry Σ for the $\overrightarrow{\gamma}p \rightarrow \pi^{0} p$ reaction have been made in the center-of-mass energy range W = 1214–1450 MeV. The data ...were measured with the MAMI A2 real photon beam and Crystal Ball/TAPS detector systems in Mainz, Germany. The resulting measurements significantly improve the existing world data and are shown to be in good agreement with previous measurements, and with the MAID, SAID, and Bonn-Gatchina predictions. We have also combined the photon asymmetry results with recent cross-section measurements from Mainz to calculate the profile functions, $\check{Σ}$ (= σ0Σ), and perform a moment analysis. Comparison with calculations from the Bonn-Gatchina model shows that the precision of the data is good enough to further constrain the higher partial waves, and there is an indication of interference between the very small F-waves and the N(1520)3/2- and N(1535)1/2- resonances.
.
High-statistics measurements of the photon asymmetry
Σ
for the
γ
→
p
→
π
0
p
reaction have been made in the center-of-mass energy range
W
=
1214
-
1450
MeV. The data were measured with the MAMI A2 ...real photon beam and Crystal Ball/TAPS detector systems in Mainz, Germany. The results significantly improve the existing world data and are shown to be in good agreement with previous measurements, and with the MAID, SAID, and Bonn-Gatchina predictions. We have also combined the photon asymmetry results with recent cross-section measurements from Mainz to calculate the profile functions,
Σ
ˇ
(
=
σ
0
Σ
)
, and perform a moment analysis. Comparison with calculations from the Bonn-Gatchina model shows that the precision of the data is good enough to further constrain the higher partial waves, and there is an indication of interference between the very small
F
-waves and the
N
(
1520
)
3
/
2
-
and
N
(
1535
)
1
/
2
-
resonances.
High-statistics measurements of the photon asymmetry Σ for the γ → p → π 0 p reaction have been made in the center-of-mass energy range W = 1214 - 1450 MeV. The data were measured with the MAMI A2 ...real photon beam and Crystal Ball/TAPS detector systems in Mainz, Germany. The results significantly improve the existing world data and are shown to be in good agreement with previous measurements, and with the MAID, SAID, and Bonn-Gatchina predictions. We have also combined the photon asymmetry results with recent cross-section measurements from Mainz to calculate the profile functions, Σ ˇ ( = σ 0 Σ ) , and perform a moment analysis. Comparison with calculations from the Bonn-Gatchina model shows that the precision of the data is good enough to further constrain the higher partial waves, and there is an indication of interference between the very small F-waves and the N ( 1520 ) 3 / 2 - and N ( 1535 ) 1 / 2 - resonances.
The complete experiment problem in the truncated partial wave analysis of pseudoscalar meson photoproduction with suppressed t-channel exchanges is investigated. The focus is set to ambiguities of ...the group S observables with the unpolarized differential cross section, \(\sigma_0\), and the three single-spin observables, \(\Sigma\), \(T\) and \(P\). For this purpose, the approach and formalism already worked out by Omelaenko in 1981 is revisited in this work. A numerical study using multipoles of the PWA solution MAID2007 shows how only one additional double polarization observable can resolve all ambiguities. Therefore, the possibility emerges to perform a complete experiment with only five observables.
This work presents ideas for the determination of complete experiments using graphs, which are based on a recently published, modified form of Moravcsik's theorem. The lucid representation of ...complete experiments in terms of graphs, which is at the heart of the theorem, leads to a fully automated procedure that can determine complete experiments for in principle any reaction, i.e. for any number of amplitudes \(N\). For larger \(N\) (i.e. \(N \geq 4\)), the sets determined according to Moravcsik's theorem turn out to be slightly overcomplete. A new type of directional graph has been proposed recently, which can decrease the length of the complete sets of observables in some of these cases. The presented results are relevant for reactions with larger numbers of spin-amplitudes, which are at the center of interest in forthcoming measurements, such as single-meson electroproduction \((N=6)\), two-meson photoproduction \((N=8)\) or vector-meson photoproduction \((N=12)\).
Amplitude- and truncated partial-wave analyses are combined into a single procedure and a novel, almost theory-independent single-channel method for extracting multipoles directly from measured data ...is developed. In practice, we have created a two-step procedure which is fitted to the same data base: in the first step we perform an energy independent amplitude analysis where continuity is achieved by constraining the amplitude phase, and the result of this first step is then taken as a constraint for the second step where a constrained, energy independent, truncated partial-wave analysis is done. The method is tested on the world collection of data for \(\eta\) photoproduction, and the obtained fit-results are very good. The sensitivity to different possible choices of amplitude phase is investigated and it is demonstrated that the present data base is insensitive to notable phase changes, due to an incomplete database. New measurements are recommended to remedy the problem.
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