Session Q13: Photoproduction of Hadrons

Live

The primary motivation of the GlueX experiment at Jefferson Lab experimental Hall D is the search for light hybrid mesons that are quark-antiquark pairs coupled to gluonic field excitation. GlueX uses a $\approx 9\;\mathrm{GeV}$ linearly-polarized real photon beam incident on $\mathrm{LH}2$ target and a solenoid based, large-acceptance detector. The facility completed the initial phase of data taking in 2018 and has many analysis efforts well underway. These studies include understanding the production mechanisms and potential final states of interest for well-established hadronic states at GlueX beam energies, where little data is available from other photoproduction experiments. There are also ongoing searches for the $\pi_{1}\;(1600)$ hybrid meson with exotic $J^{PC}=1^{-+}$. Contributions of resonances with different spins in the mass spectrum of the $\eta^{\left( '\right) }\pi$ system are studied via partial wave analysis, where we use a newly developed model for photo-production via linearly polarized beam. The status of these efforts will be reported.   

Live

The GlueX experiment at Hall-D in Jefferson Lab uses a tagged photon beam with linear polarization peaking around 9 GeV on a liquid hydrogen target to study the spectrum of conventional mesons and search for hybrid exotic mesons. The spectrometer is designed to have an almost 4$\pi$ acceptance and good efficiency especially suited to study multi-particle final states in both charged and neutral modes. This talk will report on the analysis of $\gamma p \rightarrow \eta^{\prime} \pi^0p$ focusing on the background systematics underneath the $\eta^{\prime}$ signal and preliminary results from amplitude analysis of the $\eta^{\prime} \pi^0$ invariant mass spectrum.   

Live

Direct production in photon-induced reactions is a promising way to gain insight into exotic mesons, the so-called XYZ states, and pentaquark-like signals. To this end, I will discuss recent JPAC efforts to motivate searches for exotics in photoproduction facilities. We provide phenomenological predictions of production cross-sections which are important for existing experiments at JLab as well as future facilities such at the EIC.   

Live

We report on the Jefferson Lab Hall C experiment E12-16-007 ($J/\psi$-007) where we measured the 2D $J/\psi$ photoproduction cross-section versus momentum transfer $t$ and photon energy $E_{\gamma}$ in the kinematic region of the LHCb hidden-charm pentaquark states. The experiment used a high-intensity real photon beam generated by a 10.6 GeV incident electron beam traversing a copper radiator upstream of a liquid hydrogen target. The two high momentum spectrometers of Hall C, HMS, and SHMS were used to detect the $e^{+} e^{-}$ and $\mu^{+} \mu^{-}$ di-lepton $J/\psi$ decay pairs in coincidence. The spectrometers momentum and angle settings scan a photon beam energy range between 9.1 GeV and 10.6 GeV and $|t|$ up to 5 $GeV^{2}$. The measurements' sensitivity to the $s$-channel resonant pentaquarks signals is maximal at larger $|t|$. We will present preliminary results of the differential and total $J/\psi$ photoproduction cross-section.   

Live

Within the broader efforts to study the spectrum of light-quark mesons, the GlueX experiment provides a large photoproduction data set with nearly 4$\pi$ acceptance that allows the study of a wide variety of final states. In this talk we will discuss the analysis of the reaction $\gamma p \to K^+K^- \pi^+ \pi^-p'$ as measured by the GlueX experiment. This reaction was selected to study the photoproduction of the $\phi(2170)$, a state with a yet undetermined interpretation seen in several measurements in $e^+e^-$ experiments. This analysis will focus on various properties of the final state particles as we lay the ground work for the amplitude analysis likely necessary for understanding the rich number of processes involved.   

Live

The quasifree $\gamma $d $\to \pi^{\mathrm{0}}$n(p) photon beam asymmetry,~has been measured at photon energies~from 390 to 610 MeV, corresponding to CM~energies, W, from 1.271 to 1.424 GeV, for the first time. The data was collected in the A2 Hall of the~MAMI electron beam facility with the Crystal Ball and~TAPS calorimeters covering pion CM angles from 48 to 148 degrees.~In these kinematic regions, polarization observables are sensitive to contributions from~the $\Delta $(1232) and N$^{\mathrm{\ast }}$(1440) resonances. The extracted values of $\Sigma $ have been compared to predictions based~on~PWAs of the existing pion-photoproduction database. We include 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 $\pi ^{\mathrm{0}}$n photoproduction observables, based~on fits to~published~data in the channels $\pi^{\mathrm{0}}$p, $\pi ^{\mathrm{+}}$n, and $\pi^{\mathrm{-}}$p.