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

TL;DR

This paper reports the first observation of specific Upsilon transitions near the Upsilon(5S) resonance, revealing unexpectedly large partial widths for these dipion transitions compared to lower Upsilon states.

Contribution

It provides the first measurements of e+e- -> Upsilon(nS)pi+pi- near the Upsilon(5S) resonance and quantifies their partial widths, highlighting significant enhancements over previous lower state transitions.

Findings

First observation of Upsilon(1S)pi+pi- and Upsilon(2S)pi+pi- production near Upsilon(5S)

Evidence for Upsilon(3S)pi+pi- and Upsilon(1S)K+K- production

Partial widths exceed previous measurements by over two orders of magnitude

Abstract

We report the first observation of e+e- -> Upsilon(1S)pi+pi-, Upsilon(2S)pi+pi-, and first evidence for e+e- -> Upsilon(3S)pi+pi-, Upsilon(1S)K+K-, near the peak of the Upsilon(5S) resonance at sqrt{s}~10.87 GeV. 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.