A Search for the LHCb Charmed 'Pentaquark' using Photo-Production of \(J/{\psi}\) at Threshold in Hall C at Jefferson Lab

• Published in: arXiv.org 2016-09
• Main Authors: Z -E Meziani, Joosten, S, Paolone, M, Chudakov, E, Jones, M, Adhikari, K, Aniol, K, Armstrong, W, Arrington, J, Asaturyan, A, Atac, H, Bae, S, Bhatt, H, Bhetuwal, D, J -P Chen, Chen, X, Choi, H, Choi, S, Diefenthaler, M, Dunne, J, Dupré, R, Duran, B, Dutta, D, El-Fassi, L, Q Fu, Gao, H, H Go, C Gu, J Ha, Hafidi, K, Hansen, O, Hattawy, M, Higinbotham, D, Huber, G M, Markowitz, P, Meekins, D, Mkrtchyan, H, Nouicer, R, W Li, X Li, Liu, T, Peng, C, Pentchev, L, Pooser, E, Rehfuss, M, Sparveris, N, Tadevosyan, V, Wang, R, Wesselmann, F R, Wood, S, Xiong, W, Yan, X, L Ye, Z Ye, Zafar, A, Zhang, Y, Zhao, F, Zhao, Z, Zhamkochyana, S
• Format: Article
• Language: English
• Subjects: Angular momentum; Angular resolution; Bremsstrahlung; Calibration; Charm (particle physics); Cross-sections; Electron beams; Liquid hydrogen; Mesons; Momentum; Photon beams; Quarks; Radiators; Spectrometers
• ISSN: 2331-8422

We propose to measure the photo-production cross section of \(J/{\psi}\) near threshold, in search of the recently observed LHCb hidden-charm resonances \(P_c\)(4380) and \(P_c\)(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 \(J/{\psi}\) production from the threshold photo-production energy of 8.2 GeV, to an energy beyond the presumed \(P_c\)(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 \(J/{\psi}\) mesons 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 \(J/{\psi}\) 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 \(J/{\psi}\) 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 \(J/{\psi}\) production data for a calibration measurement. This calibration measurement in itself will greatly enhance our knowledge of \(t\)-channel elastic \(J/{\psi}\) production near threshold.