First Measurement of J/ψ Photoproduction on Neutron
Physicists report the first measurement of near-threshold J/ψ particle production from a neutron target, enabling a direct comparison with bound protons to
Physicists have made the first measurement of near-threshold J/ψ photoproduction on the neutron. The results, obtained using the CLAS12 detector at the Thomas Jefferson National Accelerator Facility, also provide incoherent cross sections for the bound proton.
This work enables the first direct comparison of this specific particle production process on bound protons and neutrons. The data were collected using a liquid-deuterium target. The team reports both total and momentum-transfer-differential cross sections.
Probing Gluonic Structure
The measurements are interpreted within several theoretical frameworks, including Vector Meson Dominance, holographic QCD, and Generalized Parton Distribution (GPD) models. According to the researchers, the data allow for an investigation of the gluonic structure of bound nucleons. Near-threshold J/ψ photoproduction is considered a important probe for this structure.
Comparing the new results with existing data from free protons reveals hints of modifications. The analysis suggests the gluon structure of nucleons may be altered within the nuclear medium. The researchers note these hints are dependent on the assumptions of the extraction method and the underlying production mechanism.
A Direct Nucleon Comparison
The core achievement is the direct comparison between bound neutron and bound proton cross sections. This comparison provides new constraints on the near-threshold J/ψ production mechanism. Establishing this process as a reliable probe of the nucleon's gluonic structure depends on such constraints.
The experiment was conducted at the Thomas Jefferson National Accelerator Facility, also known as Jefferson Lab. The CLAS12 detector in Hall B was used for the measurements.
Implications for Nuclear Physics
The findings, detailed in a paper submitted to the arXiv preprint server, offer a fresh lens on nucleon substructure. By studying how the J/ψ particle is produced from neutrons and protons struck by photons, scientists can test models of how gluons are distributed. The team states the data are interpreted within multiple frameworks to investigate this gluonic structure.
The reported measurement is specifically for the "near-threshold" energy region. This region is important for isolating the interaction dynamics. The paper is titled "First Measurement of Near-Threshold J/ψ Photoproduction on the Neutron."
