Measurement of the branching fraction for the decay Upsilon(4S) -> Upsilon(1S)pi+pi-

TL;DR

This paper measures the probability and decay width of the Upsilon(4S) transitioning to Upsilon(1S) via charged pion emission, providing precise experimental data on this rare decay process.

Contribution

The study provides the first precise measurement of the branching fraction and decay width for Upsilon(4S) to Upsilon(1S) pi+ pi- transition using a large data sample from the Belle detector.

Findings

Measured product branching fraction: (2.11 +/- 0.30(stat.) +/- 0.14(sys.)) x 10^(-6)

Partial decay width: (1.75 +/- 0.25(stat.) +/- 0.24(sys.)) keV

Results improve understanding of bottomonium transitions.

Abstract

We study transitions between Upsilon states with the emission of charged pions using 604.6/fb of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. The measured product branching fraction is B(Upsilon(4S) -> Upsilon(1S)pi+pi-) * B(Upsilon(1S) -> mu+mu-) = = (2.11 +/- 0.30(stat.) +/- 0.14(sys.))*10^(-6) and the partial decay width is Gamma(Upsilon(4S) -> Upsilon(1S)pi+pi-) = = (1.75 +/- 0.25(stat.) +/- 0.24(sys.)) keV.