A High-Precision Measurement of the Di-Electron Widths of the Upsilon(1S), Upsilon(2S), and Upsilon(3S) Mesons at CLEO-III

Abstract

The di-electron width of an Upsilon meson is the decay rate of the Upsilon into an electron-positron pair, expressed in units of energy. We measure the di-electron width of the Upsilon(1S) meson to be 1.354 +- 0.004 +- 0.020 keV (the first uncertainty is statistical and the second is systematic), the di-electron width of the Upsilon(2S) to be 0.619 +- 0.004 +- 0.010 keV and that of the Upsilon(3S) to be 0.446 +- 0.004 +- 0.007 keV. We determine these values with better than 2% precision by integrating the Upsilon production cross-section from electron-positron collisions over their collision energy. Our incident electrons and positrons were accelerated and collided in the Cornell Electron Storage Ring, and the Upsilon decay products were observed by the CLEO-III detector. The di-electron widths probe the wavefunctions of the Strongly-interacting bottom quarks that constitute the three Upsilon mesons, information which is especially interesting to check high-precision Lattice QCD calculations of the nuclear Strong force.