This work presents a simple method to determine the significant partial wave contributions to experimentally determined observables in pseudoscalar meson photoproduction. First, fits to angular ...distributions are presented and the maximum orbital angular momentum \(\text{L}_{\mathrm{max}}\) needed to achieve a good fit is determined. Then, recent polarization measurements for \(\gamma p \rightarrow \pi^{0} p\) from ELSA, GRAAL, JLab and MAMI are investigated according to the proposed method. This method allows us to project high-spin partial wave contributions to any observable as long as the measurement has the necessary statistical accuracy. We show, that high precision and large angular coverage in the polarization data are needed in order to be sensitive to high-spin resonance-states and thereby also for the finding of small resonance contributions. This task can be achieved via interference of these resonances with the well-known states. For the channel \(\gamma p \rightarrow \pi^{0} p\), those are the \(N(1680)\frac{5}{2}^{+}\) and \(\Delta(1950)\frac{7}{2}^{+}\), contributing to the \(F\)-waves.
We revisit Moravcsik's theorem on the unique extraction of amplitudes from polarization observables, which has been originally published in 1985. The proof is (re-) written in a more formal and ...detailed way and the theorem is corrected for the special case of an odd number of amplitudes (this case was treated incorrectly in the original publication). Moravcsik's theorem, in the modified form, can be applied in principle to the extraction of an arbitrary number of \(N\) helicity amplitudes. The uniqueness theorem is then applied to hadronic reactions involving particles with spin. The most basic example is Pion-Nucleon scattering (\(N=2\)), the first non-trivial example is pseudoscalar meson photoproduction (\(N=4\)) and the most technically involved case treated here is given by pseudoscalar meson electroproduction (\(N=6\)). The application of Moravcsik's theorem to electroproduction yields new results, which for the first time provide insights into the structure and content of complete sets for this particular process. The uniqueness-statements for the various reactions are compared and an attempt is made to recognize general patterns, which emerge under the application of the theorem.
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.
The spin-exotic hybrid meson $\pi_{1}(1600)$ is predicted to have a large
decay rate to the $\omega\pi\pi$ final state. Using 76.6~pb$^{-1}$ of data
collected with the GlueX detector, we measure the ...cross sections for the
reactions $\gamma p \to \omega \pi^+ \pi^- p$, $\gamma p \to \omega \pi^0 \pi^0
p$, and $\gamma p\to\omega\pi^-\pi^0\Delta^{++}$ in the range $E_\gamma =$ 8-10
GeV. Using isospin conservation, we set the first upper limits on the
photoproduction cross sections of the $\pi^{0}_{1}(1600)$ and
$\pi^{-}_{1}(1600)$. We combine these limits with lattice calculations of decay
widths and find that photoproduction of $\eta'\pi$ is the most sensitive
two-body system to search for the $\pi_1(1600)$.
We measure the spin-density matrix elements (SDMEs) of the
$\Delta^{++}(1232)$ in the photoproduction reaction $\gamma p \to
\pi^-\Delta^{++}(1232)$ with the GlueX experiment in Hall D at Jefferson ...Lab.
The measurement uses a linearly--polarized photon beam with energies from $8.2$
to $8.8$~GeV and the statistical precision of the SDMEs exceeds the previous
measurement by three orders of magnitude for the momentum transfer squared
region below $1.4$ GeV$^2$. The data are sensitive to the previously
undetermined relative sign between couplings in existing Regge-exchange models.
Linear combinations of the extracted SDMEs allow for a decomposition into
natural and unnatural--exchange amplitudes. We find that the unnatural exchange
plays an important role in the low momentum transfer region.
A new data set for the helicity-dependent differential cross section of the
single-meson photoproduction reaction $\gamma p \to p \pi^{0}$ was obtained for
the photon energy interval 150-400 MeV. The ...experiment was performed at the A2
tagged photon facility of the Mainz Microtron MAMI using a circularly polarized
photon beam and a longitudinally polarized proton target. The reaction products
were detected with the large acceptance Crystal Ball/TAPS calorimeter covering
97\% of the full solid angle. These new results, obtained with a fine energy
and polar angle binning, greatly increase both the existing quantity and
quality of the data available for this observable. A moment analysis, based on
a finite expansion in Legendre polynomials, was applied to these data by using
a bootstrap-based fitting method to correctly account for their systematic
uncertainties. From the resulting decomposition of the differential cross
sections, the $E2/M1$ ratio for the $N\to \Delta(1232)$ transition was
determined to be $-2.38 \pm 0.16{\hbox{ (stat.+sys.)}} \pm 0.10 {\hbox{
(model)}} \%$. Combining this value with previous results also allowed us to
evaluate the most precise available estimate of the $E2/M1$ ratio to be used
for all further reference and model comparisons.
The Crystal Barrel is an electromagnetic calorimeter consisting of 1380 CsI(Tl) scintillators, and is currently installed at the CBELSA/TAPS experiment where it is used to detect decay products from ...photoproduction of mesons. The readout of the Crystal Barrel has been upgraded in order to integrate the detector into the first level of the trigger and to increase its sensitivity for neutral final states. The new readout uses avalanche photodiodes in the front-end and a dual back-end with branches optimized for energy and time measurement, respectively. An FPGA-based cluster finder processes the whole hit pattern within less than 100 ns. The important downside of APDs -- the temperature dependence of their gain -- is handled with a temperature stabilization and a compensating bias voltage supply. Additionally, a light pulser system allows the APDs' gains to be measured during beamtimes.
We discuss unitarity constraints on the dynamics of a system of three interacting particles. We show how the short-range interaction that describes three-body resonances can be separated from the ...long-range exchange processes, in particular the one-pion-exchange process. It is demonstrated that unitarity demands a specific functional form of the amplitude with a clear interpretation: the bare three-particle resonances are dressed by the initial- and final-state interaction, in a way that is consistent with the considered long-range forces. We postulate that the resonance kernel admits a factorization in the energy variables of the initial- and the final-state particles. The factorization assumption leads to an algebraic form for the unitarity equations, which is reminiscent of the well-known two-body-unitarity condition and approaches it in the limit of the narrow-resonance approximation.
Phys. Rev. C 108, 055204 (2023) The GlueX experiment at Jefferson Lab studies photoproduction of mesons using
linearly polarized $8.5\,\text{GeV}$ photons impinging on a hydrogen target
which is ...contained within a detector with near-complete coverage for charged
and neutral particles. We present measurements of spin-density matrix elements
for the photoproduction of the vector meson $\rho$(770). The statistical
precision achieved exceeds that of previous experiments for polarized
photoproduction in this energy range by orders of magnitude. We confirm a high
degree of $s$-channel helicity conservation at small squared four-momentum
transfer $t$ and are able to extract the $t$-dependence of natural and
unnatural-parity exchange contributions to the production process in detail. We
confirm the dominance of natural-parity exchange over the full $t$ range. We
also find that helicity amplitudes in which the helicity of the incident photon
and the photoproduced $\rho(770)$ differ by two units are negligible for
$-t<0.5\,\text{GeV}^{2}/c^{2}$.
We report the total and differential cross sections for $J/\psi$
photoproduction with the large acceptance GlueX spectrometer for photon beam
energies from the threshold at 8.2~GeV up to 11.44~GeV ...and over the full
kinematic range of momentum transfer squared, $t$. Such coverage facilitates
the extrapolation of the differential cross sections to the forward ($t = 0$)
point beyond the physical region. The forward cross section is used by many
theoretical models and plays an important role in understanding $J/\psi$
photoproduction and its relation to the $J/\psi-$proton interaction. These
measurements of $J/\psi$ photoproduction near threshold are also crucial inputs
to theoretical models that are used to study important aspects of the gluon
structure of the proton, such as the gluon Generalized Parton Distribution
(GPD) of the proton, the mass radius of the proton, and the trace anomaly
contribution to the proton mass. We observe possible structures in the total
cross section energy dependence and find evidence for contributions beyond
gluon exchange in the differential cross section close to threshold, both of
which are consistent with contributions from open-charm intermediate states.
