The anomalous Upsilon(1S)pi+pi- and Upsilon(2S)pi+pi- production near the Upsilon(5S) resonance

TL;DR

This study investigates anomalously large dipion transition rates from the Upsilon(5S) resonance to lower Upsilon states, revealing partial widths much greater than previously observed, based on data from the Belle detector.

Contribution

The paper provides the first measurement of partial widths for Upsilon(5S) decays to Upsilon(1S)pi+pi- and Upsilon(2S)pi+pi-, showing significantly enhanced transition rates.

Findings

Partial widths for Upsilon(5S) to Upsilon(1S)pi+pi- are 0.59 MeV.

Partial widths for Upsilon(5S) to Upsilon(2S)pi+pi- are 0.85 MeV.

Transition rates are over two orders of magnitude larger than lower Upsilon transitions.

Abstract

We report the study of e+e- -> Upsilon(1S)pi+pi-, Upsilon(2S)pi+pi-, Upsilon(3S)pi+pi-, and Upsilon(1S)K+K-, near the peak of the Upsilon(5S) resonance. The results are based on a data sample of 21.7 fb^-1 collected with the Belle detector at the KEKB e+e- collider. Attributing the signals to the Upsilon(5S) resonance, the partial widths Gamma(Upsilon(5S)->Upsilon(1S)pi+pi-) = 0.59+-0.04(stat)+-0.09(syst) MeV and Gamma(Upsilon(5S)->Upsilon(2S)pi+pi-) = 0.85+-0.07(stat)+-0.16(syst) MeV are obtained from the observed cross sections. These values exceed by more than two orders of magnitude the previously measured partial widths for dipion transitions between lower Upsilon resonances.