Z. E. Meziani, S. Joosten, et al.
Jefferson PAC Proposal PR12-16-007 (2016)
Publication year: 2016

We propose to measure the photo-production cross section of J/ψ near threshold, in search of the recently observed LHCb hidden-charm resonances Pc(4380) and Pc(4450) consistent with ‘pentaquarks’. The observation of these resonances in photo-production will provide strong evidence of the true resonance nature of the LHCb states, distinguishing them from kinematic enhancements. A bremsstrahlung photon beam produced with an 11 GeV electron beam at CEBAF covers the energy range of J/ψ production from the threshold photo-production energy of 8.2 GeV, to an energy beyond the presumed Pc(4450) resonance. The experiment will be carried out in Hall C at Jefferson Lab using a 50{\mu}A electron beam incident on a 9% copper radiator. The resulting photon beam passes through a 15 cm liquid hydrogen target, producing J/ψmesons through a diffractive process in the t-channel, or through a resonant process in the s– and u-channel. The decay e+e pair of the J/ψ will be detected in coincidence using the two high-momentum spectrometers of Hall C. The spectrometer settings have been optimized to distinguish the resonant s– and u-channel production from the diffractive t-channel J/ψ production. The s– and u-channel production of the charmed 5-quark resonance dominates the t-distribution at large t. The momentum and angular resolution of the spectrometers is sufficient to observe a clear resonance enhancement in the total cross section and t-distribution. We request a total of 11 days of beam time with 9 days to carry the main experiment and 2 days to acquire the needed t-channel elastic J/ψ production data for a calibration measurement. This calibration measurement in itself will greatly enhance our knowledge of t-channel elastic J/ψ production near threshold.

Leave a Reply

Your email address will not be published. Required fields are marked *