Searching for Hybrid Mesons with GlueX

Abstract

Hybrid mesons consist of a quark-antiquark pair bound together by a gluonic field that is in an excited state. Measuring the spectrum of these states will provide valuable information on the gluonic degrees of freedom of QCD in the quark-confinement regime. A rich spectrum of hybrid meson states has been predicted, but only a few experiments have reported evidence of their existence. The GlueX experiment at Jefferson Lab is designed to search for and measure the spectrum of light-mass hybrid mesons, and it has began its physics run in Spring 2017. For the experiment, a 12 GeV electron beam incident on a diamond radiator is used to produce a linearly-polarized, coherent bremsstrahlung tagged-photon beam with a coherent peak at 9 GeV. The linearly-polarized photon beam is incident on a proton target located within the hermetic GlueX detector, which can detect many different final states to which the hybrid mesons are predicted to decay. Measurements with these initial data are discussed, including beam asymmetry measurements, the search for photoproduced X baryons, and near-threshold charm production.

Nucleon resonances with hidden charm in γp reactions

“…[9], except blue open spares are from Ref. [88] larger in magnitudes than the previous data, as can be seen more clearly in the right side of Fig.2. While these data can be better described by the 2g+3g exchange model, as also shown by the GlueX collaboration, they need further confirmation from separate experiments at JLab.…”

“…In parallel to these theoretical efforts, an experiment [86,87](JLab(E12-16-007)) on γ p → J/ψ p near threshold at JLab(E12-16-007) was approved in 2016 and the data from this effort will soon become available. A separate effort at JLab using GlueX detector [88] has recently published [89] their measured total cross sections of γp → J/ψ p. The main purpose of this work is to provide information for examining whether the N * cc predicted by the available meson-baryon coupled-channel models can be observed in the data from these two experiments.…”

Determination of the Pole Position of the Lightest Hybrid Meson Candidate

“…their masses, widths, and decay patterns-provides a unique opportunity for a systematic study of low-energy gluon dynamics. This has motivated the COMPASS spectroscopy program [20,21] and the 12 GeV upgrade of Jefferson Lab, with experiments dedicated to hybrid photoproduction at CLAS12 and GlueX [22,23].…”

Searches for Exotic Hadrons at GlueX

“…1. The experiment has been described elsewhere in detail [6,8,7], which we briefly summarize in the following. The electron beam from the CEBAF accelerator strikes a thin diamond and produces a beam of photons through bremsstrahlung, including a component with a high degree of linear polarization due to coherent bremsstrahlung.…”