Guy Wilkinson

Abstract:

We report the first observation of the decay J/ψ→3γ. The signal has a statistical significance of 6σ and corresponds to a branching fraction of B(J/ψ→3γ)=(1.2±0.3±0.2)×10-5, in which the errors are statistical and systematic, respectively. The measurement uses ψ(2S)→π+π-J/ψ events acquired with the CLEO-c detector operating at the CESR e+e- collider. © 2008 The American Physical Society.

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(1S)→γgg, via the "tagged" process: e+e-→ψ(2S); ψ(2S)→J/ψπ+π-; J/ψ→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 [Rγ=B(ggγ)/B(ggg)] to be Rγ=0.137±0.001±0.016±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→ggγ is observed to be very similar to that of Υ→ggγ. The Rγ value obtained is roughly consistent with that expected by a simple quark-charge scaling [Rγ∼(qc/qb)2] of the value determined at the Υ(1S), but somewhat higher than the value expected from the running of the strong coupling constant. © 2008 The American Physical Society.

Abstract:

Using a sample of 2.59×107 ψ(2S) decays collected by the CLEO-c detector, we present results of a study of χcJ (J=0, 1, 2) decays into baryon-antibaryon final states. We present the world's most precise measurements of the χcJ→pp̄ and χcJ→ΛΛ̄ branching fractions, and the first measurements of χc0 decays to other hyperons. These results illuminate the decay mechanism of the χc states. © 2008 The American Physical Society.

Abstract:

We exploit the quantum coherence between pair-produced D0 and D̄0 in ψ(3770) decays to study charm mixing, which is characterized by the parameters x and y, and to make a first determination of the relative strong phase δ between doubly Cabibbo-suppressed D0→K+π- and Cabibbo-favored D̄0→K+π-. We analyze a sample of 1.0×106 D0D̄0 pairs from 281pb-1 of e+e- collision data collected with the CLEO-c detector at Ecm=3.77GeV. By combining CLEO-c measurements with branching fraction input and time-integrated measurements of RM≡(x2+y2)/2 and RWS≡Γ(D0→K+π-)/Γ(D̄0→K+π-) from other experiments, we find cosδ=1.03-0.17+0.31±0.06, where the uncertainties are statistical and systematic, respectively. In addition, by further including external measurements of charm mixing parameters, we obtain an alternate measurement of cosδ=1.10±0.35±0.07, as well as xsinδ=(4.4-1.8+2.7±2.9)×10-3 and δ=(22-12-11+11+9) °. © 2008 The American Physical Society.

Abstract:

We report determination of branching fractions for the decays ψ(2S)→h+J/ψ, where h=any, π+π-, π0π0, η, π0, and γγ through χc0,1,2. These measurements use 27M ψ(2S) decays produced in e+e- collision data collected with the CLEO detector. The resulting branching fractions and ratios thereof improve upon previously achieved precision in all cases, and in combination with other measurements permit determination of B(χcJ→γJ/ψ) and B(ψ(2S)→light hadrons). © 2008 The American Physical Society.