J/Psi Photoproduction off the proton and neutron with CLAS12

Lead Research Organisation: University of Glasgow
Department Name: College of Science and Engineering


Understanding hadronic structure and interactions in terms of quark and gluon degrees of freedom,
within the framework of Quantum Chromodynamics (QCD), is the main goal of modern
nuclear/hadron physics. An important tool to further explore these fundamental properties is the
study of heavy quarkonia with hadronic matter. The production of heavy quarkonia directly probes
the local colour (gluonic) fields in the nucleon and can reveal properties such as their spatial
distribution (building a picture of the internal components of the nucleon), the response to
momentum transfer within the system (how does the picture vary with energy) and the correlation
with valence quarks (the quarks that give the nucleon its properties such as charge).
The first state of heavy quarkonia is the two quark system comprising of a bound charm-anti-charm
pair, namely the J/Psi meson. With the available beam energy at Jefferson Lab now upgraded to 12
GeV and a new detector system, CLAS12 in Hall-B on-line, the photo- and electroproduction
ofJ/Psi can now be studied. There is a considerable amount of J/Psi photoproduction data at high
energies but no data near threshold. Given the considerable change in dynamics between high
energy and the near-threshold regions, two recent experiments carried out on a proton and a
deuterium target at CLAS12 will provide unique information on the gluonic fields within the
nucleon at "real-world" hadronic energy scales.
In addition to the studies of these fundamental QCD degrees of freedom, recent claims of the
discovery of pentaquark (5 quark) like structures from the LHCb have renewed interest in this
charmonium threshold region. These states, should they exist, are within the energy range available
in the above measurements and this data has the potential to provide compelling evidence for or
against such states. Furthermore, CLAS12 is in the unique position to provide measurements from
production off a neutron (within deuterium) and thus check the necessity for isospin invariance to
hold true regarding any "new" resonance claims. In simple terms, if a pentaquark resonance is
produced decaying to a J/Psi and proton, then one must also exist which decays to J/Psi and a
The project aims and objectives are currently defined to:
Study the particle identification efficiency of the CLAS12 detector system through the analysis of
electron-positron pairs.
Develop a standard cuts based analysis for the data
Develop a machine learning algorithm to replicate and verify the above standard approach. The
exploitation of machine learning is still in its infancy within the hadronic physics community and
any such development will provide valuable guidance for future analysis projects.
Ultimately extract the cross-sections (the production probabilities) of J/Psi-proton and J/Psineutron.
The project will be undertaken within the CLAS Collaboration at Jefferson Lab.


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Studentship Projects

Project Reference Relationship Related To Start End Student Name
ST/T506102/1 30/09/2019 29/09/2023
2284628 Studentship ST/T506102/1 30/09/2019 30/03/2023 Richard Tyson