W. Kollman

Bio: W. Kollman is an academic researcher from Harvard University. The author has contributed to research in topics: Crystal Ball & Particle detector. The author has an hindex of 6, co-authored 6 publications receiving 186 citations.

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.

Decay J/. pi. -->. 3. gamma. and a search for the eta/sub c/

Abstract: The decay $\frac{J}{\ensuremath{\psi}}$ into $3\ensuremath{\gamma}$ final states has been studied. No evidence is found for the existence of the $X(2.83)$ or any heavy narrow state (e.g., the ${\ensuremath{\eta}}_{c}$) decaying into two photons. Upper limits are given on the branching ratio $\frac{J}{\ensuremath{\psi}}\ensuremath{\rightarrow}{\ensuremath{\eta}}_{c}$, ${\ensuremath{\eta}}_{c}\ensuremath{\rightarrow}2\ensuremath{\gamma}$ for ${\ensuremath{\eta}}_{c}$ masses in the 2.7-3.0-GeV region. In addition, the branching ratios $\frac{J}{\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\eta}}$, $\ensuremath{\gamma}{\ensuremath{\eta}}^{\ensuremath{'}}$ are measured. It is found that the ${\ensuremath{\eta}}^{\ensuremath{'}}$ branching ratio is higher than previously reported.

DecayJψ→3γand a Search for theηc

Abstract: The decay $\frac{J}{\ensuremath{\psi}}$ into $3\ensuremath{\gamma}$ final states has been studied. No evidence is found for the existence of the $X(2.83)$ or any heavy narrow state (e.g., the ${\ensuremath{\eta}}_{c}$) decaying into two photons. Upper limits are given on the branching ratio $\frac{J}{\ensuremath{\psi}}\ensuremath{\rightarrow}{\ensuremath{\eta}}_{c}$, ${\ensuremath{\eta}}_{c}\ensuremath{\rightarrow}2\ensuremath{\gamma}$ for ${\ensuremath{\eta}}_{c}$ masses in the 2.7-3.0-GeV region. In addition, the branching ratios $\frac{J}{\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\eta}}$, $\ensuremath{\gamma}{\ensuremath{\eta}}^{\ensuremath{'}}$ are measured. It is found that the ${\ensuremath{\eta}}^{\ensuremath{'}}$ branching ratio is higher than previously reported.

Observation of the Production of $\eta$ Mesons in Two Photon Collisions

Abstract: Using 2674 nb/sup -1/ of data taken at ..sqrt..s from 5.00 to 7.25 GeV with a trigger sensitive to decays of lower-mass particles produced in two-photon collisions, we have observed 56 +- 12 events consistent with the reaction e/sup +/e/sup -/..-->..e/sup +/e/sup -/eta, eta..--> gamma gamma... Background has been subtracted using separated-beam data. We obtain GAMMA/sub gammagamma/(eta) = 0.56 +- 0.16 keV and the pseudoscalar-nonet mixing angle theta/sub P/ = -17.6/sup 0/ +- 3.6/sup 0/.

Design and Performance of a Modularized NaI(Tl) Detector (The Crystal Ball Prototype)

Abstract: A prototye NaI(Tl) detector (the Cluster of 54) of spherical geometry subtending a solid angle of 7.5% of 4? at its center, has recently been assembled and tested. This detector consisted of 54 close-packed but optically isolated NaI(Tl) modules and the associated electronic circuitry. The Cluster of 54 is the predecessor of an almost complete spherical detector, the Crystal Ball, which will cover 94% of 4?. The latter detector is now under construction and is especially designed for the study of ?-rays produced in electron-positron collisions at colliding beam facilities. This article will outline the mechanical, optical, and electronic assembly of the prototype system. Cluster of 54 test data will be presented.

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.

Baryon spectroscopy

Abstract: About 120 baryons and baryon resonances are known, from the abundant nucleon with $u$ and $d$ light-quark constituents up to the recently discovered $\Omega_b^-=bss$, and the $\Xi_b^-=bsd$ which contains one quark of each generation In spite of this impressively large number of states, the underlying mechanisms leading to the excitation spectrum are not yet understood Heavy-quark baryons suffer from a lack of known spin-parities In the light-quark sector, quark-model calculations have met with considerable success in explaining the low-mass excitations spectrum but some important aspects like the mass degeneracy of positive-parity and negative-parity baryon excitations are not yet satisfactorily understood At high masses, above 18 GeV, quark models predict a very high density of resonances per mass interval which is not observed In this review, issues are identified discriminating between different views of the resonance spectrum; prospects are discussed how open questions in baryon spectroscopy may find answers from photo- and electro-production experiments which are presently carried out in various laboratories