J. O'Reilly

Bio: J. O'Reilly is an academic researcher from Stanford University. The author has contributed to research in topics: Crystal Ball & Branching fraction. The author has an hindex of 14, co-authored 19 publications receiving 730 citations.

Observation of an eta eta Resonance in J/psi Radiative Decays

Abstract: Evidence for a new resonance theta..-->..etaeta in the process J/psi..--> gamma..etaeta is presented. The resonance parameters of the theta are M = 1640 +- 50 MeV and GAMMA = 220/sup +100//sub -/70 MeV. J/sup P/C = 2/sup + +/ is preferred over 0/sup + +/.

Charmonium Spectroscopy from Inclusive psi-prime and J/psi Radiative Decays

Abstract: Results from a detailed study using the Crystal Ball detector at the SLAC ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ storage ring SPEAR of the inclusive photon spectra from 1.8\ifmmode\times\else\texttimes\fi{}${10}^{6}$ \ensuremath{\psi}' and 2.2\ifmmode\times\else\texttimes\fi{}${10}^{6}$ J/\ensuremath{\psi} decays are presented. Radiative transitions from the \ensuremath{\psi}' to the ${\ensuremath{\chi}}_{2}$,1,0 states are observed with photon energies of 126.0\ifmmode\pm\else\textpm\fi{}0.2\ifmmode\pm\else\textpm\fi{}4, 169.6\ifmmode\pm\else\textpm\fi{}0.3\ifmmode\pm\else\textpm\fi{}4, and 258.4\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\pm\else\textpm\fi{}4 MeV and branching ratios B(\ensuremath{\psi}'\ensuremath{\rightarrow}\ensuremath{\gamma}${\ensuremath{\chi}}_{2}$,1,0) =(8.0\ifmmode\pm\else\textpm\fi{}0.5\ifmmode\pm\else\textpm\fi{}0.7)%, (9.0\ifmmode\pm\else\textpm\fi{}0.5\ifmmode\pm\else\textpm\fi{}0.7)%, and (9.9\ifmmode\pm\else\textpm\fi{}0.5\ifmmode\pm\else\textpm\fi{}0.8)%, respectively. Values for the natural linewidths of the \ensuremath{\chi} states are obtained: \ensuremath{\Gamma}(${\ensuremath{\chi}}_{2}$,1,0)=0.8--4.9, l3.8, and 13--21 MeV, respectively (90% C.L.). Improved values are found for the branching ratios B(\ensuremath{\psi}'\ensuremath{\rightarrow}\ensuremath{\gamma}${\ensuremath{\eta}}_{c}$) =(0.28\ifmmode\pm\else\textpm\fi{}0.06)% and B(J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}${\ensuremath{\eta}}_{c}$)=(1.27\ifmmode\pm\else\textpm\fi{}0.36)%, and for the natural width \ensuremath{\Gamma}(${\ensuremath{\eta}}_{c}$)=11.5\ifmmode\pm\else\textpm\fi{}4.5 MeV.

Identification of a Pseudoscalar State at 1440 MeV IN Jpsi Radiative Decays. : Observation of a Pseudoscalar State at 1440-MeV in J/psi Radiative Decays

Abstract: From a partial-wave analysis of the en system in the decay J/$ -f yK+K-TO, it is determined that the quantum numbers of the K& resonance at 1440 MeV, previously identified as the E(1420), are J PC = O-+ . We have named this new particle the 1. Submitted to Physical Review Letters Jc Work supported in part by the Department of Energy under contracts DE-AC03-76SF00515 (SLAC), DE-AC02-76ER03064 (Harvard), DE-AC03-81ER40050 (CIT) , and DE-AC02-76ER03072 (Princeton); and by the National Science Foundation, contracts PHY81-07396 (HEPL), PHY79-16461 (Princeton), and PHY75-22980 (CIT).

Identification of a pseudoscalar state at 1440 MeV in J/psi radiative decays

Abstract: From a partial-wave analysis of the KK-bar..pi.. system in the decay J/psi..--> gamma..K/sup +/K/sup -/..pi../sup 0/, it is determined that the quantum numbers of the KK-bar..pi.. resonance at 1440 MeV, previously identified as the E(1420), are J/sup P/C = 0/sup - +/. This new particle has been named the iota.

Observation of an eta'/sub c/ candidate state with mass 3592 +- 5 MeV

Abstract: An eta'/sub c/ candidate state is observed at a mass M = 3592 +- 5 MeV and with a natural linewidth GAMMA<8 MeV (95% confidence level), by using the ''crystal ball'' NaI(Tl) detector at the Stanford Linear Accelerator Center (SPEAR). The evidence is found in the inclusive photon spectrum in decays of the psi'(3684), where a signal is observed corresponding to a radiative transition to this state with branching ratio between 0.2% and 1.3% (95% confidence interval, including an uncertainty due to correlation with width).

Heavy quarkonium: progress, puzzles, and opportunities

Abstract: A golden age for heavy-quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the B-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations at BESIII, the LHC, RHIC, FAIR, the Super Flavor and/or Tau-Charm factories, JLab, the ILC, and beyond. The list of newly found conventional states expanded to include h(c)(1P), chi(c2)(2P), B-c(+), and eta(b)(1S). In addition, the unexpected and still-fascinating X(3872) has been joined by more than a dozen other charmonium- and bottomonium-like "XYZ" states that appear to lie outside the quark model. Many of these still need experimental confirmation. The plethora of new states unleashed a flood of theoretical investigations into new forms of matter such as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of c (c) over bar, b (b) over bar, and b (c) over bar bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. Lattice QCD has grown from a tool with computational possibilities to an industrial-strength effort now dependent more on insight and innovation than pure computational power. New effective field theories for the description of quarkonium in different regimes have been developed and brought to a high degree of sophistication, thus enabling precise and solid theoretical predictions. Many expected decays and transitions have either been measured with precision or for the first time, but the confusing patterns of decays, both above and below open-flavor thresholds, endure and have deepened. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark-gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.