Measurement of the direct photon momentum spectrum inΥ(1S),Υ(2S)

Abstract

Using data taken with the CLEO III detector at the Cornell Electron Storage Ring, we have investigated the direct photon spectrum in the decays Υ(1S) → γgg, Υ(2S) → γgg, Υ(3S) → γgg. The latter two of these are first measurements. Our analysis procedures differ from previous ones in the following ways: a) background estimates (primarily from π 0 decays) are based on isospin symmetry rather than a determination of the π 0 spectrum, which permits measurement of the Υ(2S) and Υ(3S) direct photon spectra without explicit corrections for π 0 backgrounds from, e.g., χ bJ states, b) we estimate the branching fractions with a parametrized functional form (exponential) used for the background, c) we use the high-statistics sample of Υ(2S)→ ππΥ(1S) to obtain a tagged-sample of Υ(1S)→ γ + X events, for which there are no QED backgrounds. We determine values for the ratio of the inclusive direct photon decay rate to that of the dominant three-gluon decay Υ → ggg (R γ = B(ggγ)/B(ggg)) to be: R γ (1S)=(2.70±0.01±0.13±0.24)%, R γ (2S)=(3.18±0.04±0.22±0.41)%, and R γ (3S)=(2.72±0.06±0.32±0.37)%, where the errors shown are statistical, systematic, and theoretical model-dependent, respectively. Given a value of Q 2 , one can estimate a value for the strong coupling constant α s (Q 2 ) from R γ .

Hadron spectroscopy: theory and experiment

“…Masses are in agreement with unquenched lattice QCD calculations [163]. Direct photons have been observed in 1S, 2S and 3S decays, implying estimates of the strong fine-structure constant consistent with others [164]. The transitions χ b (2P ) → ππχ b (1P ) have been seen [165,166].…”

Flavor cosmology: dynamical yukawas in the Froggatt-Nielsen mechanism

“…In general, the larger the starting point for σ, the larger the effective Yukawas and the stronger The limits come from the CHARM beam dump experiment [19][20][21], searches for Υ → γ + Inv. at BABAR [22], Υ → γgg at BABAR [23] and CLEO [24,25] and limits on K → π + Inv. from E949 [26,21].…”