Measurement of the direct photon spectrum from ϒ (1S) decays

Abstract

Using the Crystal Ball detector at the e+e-storage ring DORIS II, we have measured the energy spectrum of direct photons from "f(IS) decays. According to QCD, these photons result from the decays of the "f(IS) resonance into one photon and two gluons, T (1 S)-'l'gg-* T + hadrons. The shape of our spectrum does not agree with that calculated in lowest order QCD, but can be described well by a prediction incorporating gluon self-interaction. Using this fit, the ratio Rv=F('f-,'tgg)/F(F~ggg) is determined to be (2.7+0.2+0.4)%. From this ratio we deduce the strong coupling constant in the MS scheme at Q2=2.2 GeV 2 and find cq= 0.25 + 0.02 + 0.04.

Relativistic and binding energy corrections to direct photon production inϒdecay

“…However, the peak is still too sharp and close to z = 1. An earlier calculation by Field [4] predicts a much softer spectrum which fits the relatively recent data [5] quite well. This uses a parton-shower Monte Carlo approximation wherein the two gluons recoiling against the direct photon acquire a non-zero invariant mass by radiating further bremsstrahlung gluons.…”

“…The effect of final-state interaction corrections can be reasonably well estimated [3] provided one stays away from the end-point z = 1. In fig.2 we compare the data, taken from Ref [5], with the prediction of our model appropriately folded with the experimental photon energy resolution (assumed to be Gaussian). The effect of the binding and wavefunction corrections calculated in this work is sizeable, and tends to to increase the photon rate in the middle z range and to lower it for larger z.…”

Measurement of the direct photon momentum spectrum inΥ(1S),Υ(2S)Besson1, Henderson2, Pedlar3 et al. 2006Phys. Rev. DSelf Cite27110View full textAdd to dashboardCite

“…Given the poor resolution of the CLEO-I electromagnetic calorimeter, that measurement was also consistent with a subsequent modification to lowest-order QCD which calculated corrections at the endpoint [8] by summing leading logs of the form ln(1-x γ ). Higher statistics measurements by Crystal Ball [9] as well as ARGUS [10] corroborated this softened photon spectrum. 1 A subsequent CLEO analysis (CLEO-II) [11], based on ∼1 M Υ(1S) events, provided a highstatistics confirmation of a photon spectrum peaking at x γ ∼ 0.65, and was able to trace the direct photon momentum spectrum down to x γ ≈0.4; at that momentum, the direct photon signal becomes less than 10% relative to the background, whereas the systematic errors on the background estimate in that momentum region exceed 10%.…”

Inclusive radiativeJ/ψdecays

“…Although inclusive radiative decays have received considerable experimental attention in the case of bb [7,8,9,10,11,12], the cc system has had only one prior measurement, by the MARK-II Collaboration in 1981 [13]. The MARK-II analysis, which utilized a calorimeter with resolution σ E /E ∼ 0.12/ E(GeV ) resulted in a measurement for the inclusive partial branching fraction B(J/ψ → γX)=(4.1 ± 0.8)% limited to the range z γ >0.6.…”