Observation of Υ(4S) decays to π+π-Υ(1S) and π+π-Υ(2S)

We present the first measurement of Upsilon(4S) decays to pi(+)pi(-)Upsilon(1S) and pi(+)pi(-)Upsilon(2S) based on a sample of 230x10(6)Upsilon(4S) mesons collected with the BABAR detector. We measure the product branching fractions B(Upsilon(4S)->pi(+)pi(-)Upsilon(1S))xB(Upsilon(1S)->mu(+)mu(-))=(2.23 +/- 0.25(stat)+/- 0.27(syst))x10(-6) and B(Upsilon(4S)->pi(+)pi(-)Upsilon(2S))xB(Upsilon(2S)->mu(+)mu(-))=(1.69 +/- 0.26(stat)+/- 0.20(syst))x10(-6), from which we derive the partial widths Gamma(Upsilon(4S)->pi(+)pi(-)Upsilon(1S))=(1.8 +/- 0.4) keV and Gamma(Upsilon(4S)->pi(+)pi(-)Upsilon(2S))=(2.7 +/- 0.8) keV.