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Inclusive radiative $J / ψ$ decays

D. Besson¹, T. K. Pedlar², D. Cronin-Hennessy³, K. Y. Gao³, J. Hietala³, Y. Kubota³, T. Klein³, B. W. Lang³, R. Poling³ et al. (CLEO Collaboration)

R. Poling³, A. W. Scott³, P. Zweber³, S. Dobbs⁴, Z. Metreveli⁴, K. K. Seth⁴, A. Tomaradze⁴, J. Libby⁵, A. Powell⁵, G. Wilkinson⁵, K. M. Ecklund⁶, W. Love⁷, V. Savinov⁷, H. Mendez⁸, J. Y. Ge⁹, D. H. Miller⁹, I. P. J. Shipsey⁹, B. Xin⁹, G. S. Adams¹⁰, M. Anderson¹⁰, J. P. Cummings¹⁰, I. Danko¹⁰, D. Hu¹⁰, B. Moziak¹⁰, J. Napolitano¹⁰, Q. He¹¹, J. Insler¹¹, H. Muramatsu¹¹, C. S. Park¹¹, E. H. Thorndike¹¹, F. Yang¹¹, M. Artuso¹², S. Blusk¹², S. Khalil¹², J. Li¹², R. Mountain¹², S. Nisar¹², K. Randrianarivony¹², N. Sultana¹², T. Skwarnicki¹², S. Stone¹², J. C. Wang¹², L. M. Zhang¹², G. Bonvicini¹³, D. Cinabro¹³, M. Dubrovin¹³, A. Lincoln¹³, P. Naik¹⁴, J. Rademacker¹⁴, D. M. Asner¹⁵, K. W. Edwards¹⁵, J. Reed¹⁵, R. A. Briere¹⁶, T. Ferguson¹⁶, G. Tatishvili¹⁶, H. Vogel¹⁶, M. E. Watkins¹⁶, J. L. Rosner¹⁷, J. P. Alexander¹⁸, D. G. Cassel¹⁸, J. E. Duboscq¹⁸, R. Ehrlich¹⁸, L. Fields¹⁸, R. S. Galik¹⁸, L. Gibbons¹⁸, R. Gray¹⁸, S. W. Gray¹⁸, D. L. Hartill¹⁸, B. K. Heltsley¹⁸, D. Hertz¹⁸, J. M. Hunt¹⁸, J. Kandaswamy¹⁸, D. L. Kreinick¹⁸, V. E. Kuznetsov¹⁸, J. Ledoux¹⁸, H. Mahlke-Krüger¹⁸, D. Mohapatra¹⁸, P. U. E. Onyisi¹⁸, J. R. Patterson¹⁸, D. Peterson¹⁸, D. Riley¹⁸, A. Ryd¹⁸, A. J. Sadoff¹⁸, X. Shi¹⁸, S. Stroiney¹⁸, W. M. Sun¹⁸, T. Wilksen¹⁸, S. B. Athar¹⁹, R. Patel¹⁹, J. Yelton¹⁹, P. Rubin²⁰, B. I. Eisenstein²¹, I. Karliner²¹, S. Mehrabyan²¹, N. Lowrey²¹, M. Selen²¹, E. J. White²¹, J. Wiss²¹, R. E. Mitchell²², and M. R. Shepherd²² (CLEO Collaboration)

¹University of Kansas, Lawrence, Kansas 66045, USA
²Luther College, Decorah, Iowa 52101, USA
³University of Minnesota, Minneapolis, Minnesota 55455, USA
⁴Northwestern University, Evanston, Illinois 60208, USA
⁵University of Oxford, Oxford OX1 3RH, United Kingdom
⁶State University of New York at Buffalo, Buffalo, New York 14260, USA
⁷University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
⁸University of Puerto Rico, Mayaguez, Puerto Rico 00681
⁹Purdue University, West Lafayette, Indiana 47907, USA
¹⁰Rensselaer Polytechnic Institute, Troy, New York 12180, USA
¹¹University of Rochester, Rochester, New York 14627, USA
¹²Syracuse University, Syracuse, New York 13244, USA
¹³Wayne State University, Detroit, Michigan 48202, USA
¹⁴University of Bristol, Bristol BS8 1TL, United Kingdom
¹⁵Carleton University, Ottawa, Ontario, Canada K1S 5B6
¹⁶Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
¹⁷Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA
¹⁸Cornell University, Ithaca, New York 14853, USA
¹⁹University of Florida, Gainesville, Florida 32611, USA
²⁰George Mason University, Fairfax, Virginia 22030, USA
²¹University of Illinois, Urbana-Champaign, Illinois 61801, USA
²²Indiana University, Bloomington, Indiana 47405, USA

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Phys. Rev. D 78, 032012 – Published 19 August, 2008

DOI: https://doi.org/10.1103/PhysRevD.78.032012

Abstract

Using data taken with the CLEO-c detector at the Cornell Electron Storage Ring, we have investigated the direct-photon momentum spectrum in the decay $J / ψ (1 S) \to γ g g$ , via the “tagged” process: $e^{+} e^{-} \to ψ (2 S)$ ; $ψ (2 S) \to J / ψ π^{+} π^{-}$ ; $J / ψ \to γ + X$ . Including contributions from two-body radiative decay processes, we find the ratio of the inclusive direct-photon branching fraction to that of the dominant three-gluon branching fraction [ $R_{γ} = B (g g γ) / B (g g g)$ ] to be $R_{γ} = 0.137 \pm 0.001 \pm 0.016 \pm 0.004$ , where the errors shown are statistical, systematic, and the model-dependent uncertainty related to the extrapolation to zero photon energy. The shape of the scaled photon energy spectrum in $J / ψ \to g g γ$ is observed to be very similar to that of $Υ \to g g γ$ . The $R_{γ}$ value obtained is roughly consistent with that expected by a simple quark-charge scaling [ $R_{γ} \sim (q_{c} / q_{b})^{2}$ ] of the value determined at the $Υ (1 S)$ , but somewhat higher than the value expected from the running of the strong coupling constant.