We report the measurement of spin-density matrix elements 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 used a linearly polarized photon beam with \(E_\gamma=8.2-8.8\)~GeV and the statistical precision exceeds the previous measurement from SLAC by three orders of magnitude for the momentum transfer squared region \(-t < 1.4\) 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, which shows that the unnatural exchange plays an important role in the low \(-t\) region.
Phys. Rev. C 103, 022201 (2021) We report a measurement of the $\pi^-$ photoproduction beam asymmetry for the
reaction $\vec{\gamma} p \rightarrow \pi^- \Delta^{++}$ using data from the
GlueX ...experiment in the photon beam energy range 8.2--8.8 GeV. The asymmetry
$\Sigma$ is measured as a function of four-momentum transfer $t$ to the
$\Delta^{++}$ and compared to phenomenological models. We find that $\Sigma$
varies as a function of $t$: negative at smaller values and positive at higher
values of $|t|$. The reaction can be described theoretically by $t$-channel
particle exchange requiring pseudoscalar, vector, and tensor intermediaries. In
particular, this reaction requires charge exchange, allowing us to probe pion
exchange and the significance of higher-order corrections to one-pion exchange
at low momentum transfer. Constraining production mechanisms of conventional
mesons may aid in the search for and study of unconventional mesons. This is
the first measurement of the process at this energy.
Phys. Rev. C 102, 044322 (2020) The excitation function for the $pd\rightarrow$ $d p \pi^{0}$ reaction has
been measured by WASA-at-COSY experiment with the aim of searching for
...$^{3}\hspace{-0.03cm}\mbox{He}$-$\eta$ mesic nuclei. The measurement in the
vicinity of $\eta$ meson production was performed using a ramped proton beam.
The data analysis and interpretation was carried out with the assumption that
the $\eta$-mesic Helium decays via the formation of an intermediate
N$^{*}$(1535) resonance. No direct signal of the $\eta$-mesic nucleus is
observed in the excitation function. We determine a new improved upper limit
for the total cross section for the bound state production and decay in the
$pd\rightarrow$ $(^{3}\hspace{-0.03cm}\mbox{He}$-$\eta)_{bound} \rightarrow$ $d
p \pi^{0}$ process. It varies between 13 nb to 24 nb for the bound state with
width in the range $\Gamma \in (5,50)$ MeV.
Phys. Rev. C 101, 065206 (2020) We report measurements of the photon beam asymmetry $\Sigma$ for the reaction
$\vec{\gamma} p\to K^+\Sigma^0$(1193) using the GlueX spectrometer in Hall D at
Jefferson ...Lab. Data were collected using a linearly polarized photon beam in
the energy range of 8.2-8.8 GeV incident on a liquid hydrogen target. The beam
asymmetry $\Sigma$ was measured as a function of the Mandelstam variable $t$,
and a single value of $\Sigma$ was extracted for events produced in the
$u$-channel. These are the first exclusive measurements of the photon beam
asymmetry $\Sigma$ for the reaction in this energy range. For the $t$-channel,
the measured beam asymmetry is close to unity over the $t$-range studied,
$-t=(0.1-1.4)~$(GeV/$c$)$^{2}$, with an average value of $\Sigma = 1.00\pm
0.05$. This agrees with theoretical models that describe the reaction via the
natural-parity exchange of the $K^{*}$(892) Regge trajectory. A value of
$\Sigma = 0.41 \pm 0.09$ is obtained for the $u$-channel integrated up to
$-u=2.0$~(GeV/$c$)$^{2}$.
Two children showed evidence of alpha-pattern coma (APC). One case followed a phenobarbital sodium overdose with complete recovery. The second case occurred subsequent to cardiopulmonary arrest with ...unfavorable outcome. These cases and others that we reviewed emphasize that the prognosis of APC in children, as in adults, is variable and appears to be related to the cause.
We report on the experimental search for the bound state of an \(\eta\) meson and \(^{3}\hspace{-0.03cm}\mbox{He}\) nucleus performed using the WASA-at-COSY detector setup. In order to search for the ...\(\eta\)-mesic nucleus decay, the \(pd\rightarrow\) \(^{3}\hspace{-0.03cm}\mbox{He} 2\gamma\) and \(pd\rightarrow\) \(^{3}\hspace{-0.03cm}\mbox{He} 6\gamma\) channels have been analysed. These reactions manifest the direct decay of \(\eta\) meson bound in \(^{3}\hspace{-0.03cm}\mbox{He}\) nucleus. This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained excitation functions reveal a slight indication for a possible bound state signal corresponding to an \(^3\)He-\(\eta\) nucleus width \(\Gamma\) above 20 MeV and binding energy \(B_s\) between 0 and 15 MeV. However, the determined cross sections are consistent with zero in the range of the systematic uncertainty. Therefore, as final result we estimate only the upper limit for the cross section of the \(\eta\)-mesic \(^{3}\hspace{-0.03cm}\mbox{He}\) nucleus formation followed by the \(\eta\) meson decay which varies between \(2\) nb and \(15\) nb depending on possible bound state parameters.
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 \(-t<0.5\,\text{GeV}^{2}/c^{2}\).
This study outlines the processes used by University of Wisconsin--Extension, Lincoln County (UWELC), educators over an eight-year period to facilitate the development of a county land use plan and ...to guide committees through a review of the new proposed county zoning ordinances based on that plan. As a partner in these projects, UWELC helped create a model of public participation for other counties and municipalities conducting land use planning based on Wisconsin's comprehensive planning law passed in October 1999. UWELC educators drew on the expertise of University of Wisconsin system faculty based outside Lincoln County to provide information about land use and zoning issues.
Phys. Rev. C 100, 052201 (2019) We report on the measurement of the beam asymmetry $\Sigma$ for the reactions
$\vec{\gamma}p\rightarrow p\eta$ and $\vec{\gamma}p \rightarrow p\eta^{\prime}$
from the ...GlueX experiment, using an 8.2--8.8 GeV linearly polarized tagged
photon beam incident on a liquid hydrogen target in Hall D at Jefferson Lab.
These measurements are made as a function of momentum transfer $-t$, with
significantly higher statistical precision than our earlier $\eta$
measurements, and are the first measurements of $\eta^{\prime}$ in this energy
range. We compare the results to theoretical predictions based on $t$--channel
quasi-particle exchange. We also compare the ratio of $\Sigma_{\eta}$ to
$\Sigma_{\eta^{\prime}}$ to these models, as this ratio is predicted to be
sensitive to the amount of $s\bar{s}$ exchange in the production. We find that
photoproduction of both $\eta$ and $\eta^{\prime}$ is dominated by natural
parity exchange with little dependence on $-t$.
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