First observations of Y(1S)->gamma pi(+)pi(-) and Y(1S)->gamma pi(0)pi(0)

Abstract

We report on a study of exclusive radiative decays of the Y(1S) resonance collected with the CLEO II detector operating at the Cornell Electron Storage Ring. We present the first observation of the radiative decays Y(1S) --> gamma pi(+)pi(-) and Y(1S) --> gamma pi(0)pi(0). For the dipion mass regime m(pi pi) > 1.0 GeV, we obtain N(Y(1S) --> gamma pi(+)pi(-)) = (6.3 +/- 1.2 +/- 1.3) x 10(-5) and B(Y(1S) --> gamma pi(0)pi(0)) = (1.7 +/- 0.6 +/- 0.3) x 10(-5).