Session X11: Photo-Production of Hadrons II

Live

We report on the photoproduction of $\eta$ mesons studied at the GlueX experiment at Thomas Jefferson National Laboratory in Newport News, VA. These particles are produced by a linearly polarized photon beam at energies between 8.2 and 8.8 GeV incident on protons in a liquid hydrogen target. Azimuthal angular distributions of the $\eta$ produced in the lab frame, with respect to the direction of the polarized photon facilitate the extraction of the beam asymmetry $\Sigma$ for the reaction $\vec\gamma p \rightarrow \eta p $. $\Sigma$ is measured as a function of four-momentum transfer $-t$. The data currently being analyzed is 3-4 times larger compared to previous GlueX results [1,2], thereby allowing us to extend these measurements to values beyond the previous limitation of $-t \leq$ 1.1 (GeV/$c$)$^2$. Preliminary results will be shown for events reconstructed from the decays of $\eta \rightarrow \pi^{+} \pi^{-} \pi^{0} $ and $\eta \rightarrow \gamma \gamma $. [1] S.~Adhikari {\it et al.} [GlueX Collaboration], Phys.\ Rev.\ C {\bf 100}, no. 5, 052201 (2019) [2] H.~Al Ghoul \textit{et al.} [GlueX],Phys. Rev. C \textbf{95}, no.4, 042201 (2017)   

Live

The GlueX experiment is a photoproduction experiment which is being carried out at Thomas Jefferson National Laboratory in Newport News, Virginia. We report on measurements of the beam asymmetry ($\Sigma$) in the reaction $\gamma p\rightarrow \eta' p$, using a tagged, linearly polarized 9 GeV photon beam incident on a liquid hydrogen target. This observable is sensitive to the exchange processes via Regge exchange. A previous measurement using $\approx20$\% of GlueX Phase-I data allowed the extraction of $\Sigma$ up to the momentum transfer $-$t=0.9 (GeV/c)$^2$ and this indicated that the production mechanism is dominated by natural parity exchange which include $\rho$ and $\omega$ meson exchanges while showing little variation with $-t$[1]. Analysis using $\approx80$\% of Phase-I data will allow us to further investigate and understand production mechanisms up to larger momentum transfer than before. We will present preliminary results of the ongoing analysis for azimuthal angular distributions, yield asymmetries and extracted beam asymmetries as a function of $-$t for different $\eta'$ decay modes.   

Live

The photoproduction mechanism studied in the GlueX experiment by impinging an 8.2-8.8 GeV linearly polarized photon beam on a liquid hydrogen target allows for the mapping of light mesons in unprecedented detail with particular interest in exotic meson candidates. Polarization observable such as beam asymmetry $\Sigma$ is extracted from azimuthal ($\phi$) angular distribution between the meson production plane and the polarized photon beam. Beam asymmetry $\Sigma$ will help understand and constraint quasi-particle t-channel exchange processes using Regge theory. We report preliminary results on the beam asymmetry measurements for $\eta$ in $\gamma$ p $\rightarrow$ $\eta$ $\Delta^+$. This reaction with a recoiling $\Delta^+$ will allow for comparison and validation of theoretical calculations and provide additional validation of the $\eta$ asymmetry with a recoiling proton. The differing isospin of the $\Delta^+$ imposes added restrictions that further constrain allowed Regge exchanges. Understanding the exchange mechanisms is a crucial ingredient in establishing new photoproduced light meson states.   

Live

The GlueX experiment has produced the largest statistics for peripheral photoproduction of mesons with a goal to unambiguously identify new and exotic mesons. Here we will present preliminary results on the reaction $\gamma p \rightarrow p$ $\pi^{+} \pi^{-} \pi^{0} \eta$. The data set was obtained at the Thomas Jefferson National Accelerator Facility utilizing the GlueX detector and a tagged linearly polarized photon beam of 8.0 to 9.0 GeV incident on a liquid hydrogen target. The focus of this study is to search for possible intermediate resonances which decay to $\omega \eta$. The $\omega$ is identified via the $\pi^{+} \pi^{-} \pi^{0}$ decay mode and the $\eta$ and $\pi^{0}$ are identified via the decay to 2 $\gamma$. General features of the data will be presented along with plans for future studies.   

Live

The GlueX experiment uses a beam of linearly polarized photons with a coherent peak near 9 GeV incident on a fixed hydrogen target. The preliminary analysis presented here considers the final state \(\eta'\eta\) which decays to 4\(\gamma\pi^{+}\pi^{-}\). This channel is motivated by the exotic \(\pi_{1}(1600)\) since it has a strong observation in \(\eta'\pi\). The \(\pi_{1}(1600)\) has isoscalar partners, the \(\eta_{1}\) and \(\eta_{1}^\prime\), which could possibly be observed in \(\eta'\eta\). General features of the data including data selection, mass spectra, and intermediate states will be presented along with plans for future studies.   

Live

The new experiment, JLab Eta Factory (JEF), in the experimental Hall-D at Jefferson Lab will extend the physics potential of the GlueX beyond the main spectroscopy program and study rare decays of eta mesons. Among various physics topics, the experiment will focus on decays of eta mesons to the $\eta\to\pi^0\gamma\gamma$ final state. This decay mode provides an important information for higher-order calculations in chiral perturbation theory. The final state is ideal for the search of the leptophobic dark $B$ boson in the reactions $\eta\to B\gamma$, $B\to\pi^0\gamma$ and the scaler dark matter mediator $S$ in the channel $\eta\to\pi^0S$, $S\to\gamma\gamma$. The experiment requires to upgrade the inner part of the forward lead glass calorimeter of the GlueX detector with high-granularity, high-resolution lead tungstate $\rm PbWO_{\rm 4}$ scintillating crystals. The detector will be ready to take data in 2023. I will give an overview of the JEF project.   

Live

The study of the decay $\eta'\to\eta\pi\pi$ is interesting in many ways. First, the decay can be used to analyze the properties of the resonances $f_0(500)$ (or $\sigma$), where the scalar resonances contribution is predominant even if the decay is thought to be dominated by the contributions of the $a_0$ resonance. Second, the study of the $\eta'\to\eta\pi\pi$ decay may supply information to test predictions from $\chi PT$. Last, it offers the opportunity to constrain $\eta\pi$ scattering. In this talk, we report the progress in the analysis of the Dalitz plot for photoproduced $\eta'$, $\gamma p \to p \eta'$, for the decay channel $\eta'\to\eta\pi\pi$ using data obtained from the GlueX experiment in Hall D at Jefferson Laboratory.