A CLAS Collaboration Proposal to PAC47 Search for a φ−N Bound State from φ Production in a Nuclear Medium

In light of recent experimental results of the hidden charm pentaquark candidates at LHCb, a renewed interest is invoked for other multi-quark states also. The QCD van de Waals interaction, mediated by multi-gluon exchanges, is expected to dominate the interaction between two hadrons when they have no common quarks, which led to the prediction that a bound state between a J/ψ and a light nucleus can exist. It has also been suggested by theoretical studies that a φ-meson and a nucleon may form a bound state. Studies also suggest that such a bound state can be produced via two steps: first the production of a φ-meson from a nucleon near the threshold or below the threshold in a nuclear target, and then the φ-meson interacts with another nucleon inside the nucleus to form the bound state. Since the φ−N bound state can be viewed as a hidden strange pentaquark state, a comparison with the hidden charm pentaquark candidates could help unveil the flavor dependent effect in hadron physics. We propose to perform a measurement of quasi-real photo-production from a nuclear target to search for a φ−N bound state with a predicted mass value near 1950 MeV and a total decay width of 4 MeV. Because the probability of the formation of the bound state is enhanced at a low relative velocity between the φ-meson and the nucleon, we propose to search for this bound state through the suband near-threshold φ-production on a gold target in Hall B at JLab. The scattered electrons would be detected by the forward tagger, and the proton, K+, and K− in the final state would be detected by the ALERT detector and the CLAS12 forward detector to reconstruct the bound state. The total beam time requested is 45 days for this experiment. The proposed experiment will be a pioneer to explore the strange multi-quark final states in the JLab 12 GeV era and lead a new way of studying hadron physics and non-perturbative QCD through searches of exotic QCD states.