First Observation of Upsilon(1D) States

TL;DR

This paper reports the first observation of Upsilon(1D) states through a four-photon cascade in Upsilon(3S) decays, providing experimental evidence and measurements consistent with theoretical predictions.

Contribution

First experimental evidence of Upsilon(1D) states via a specific four-photon cascade in Upsilon(3S) decays, with measured mass and branching ratios.

Findings

Significance of 9.7 standard deviations for Upsilon(1D) detection

Measured mass of 10162.2 ± 1.6 MeV/c^2 for Upsilon(1D_2)

Product branching ratio of (3.3 ± 0.6 ± 0.5) x 10^{-5}

Abstract

The CLEO III experiment has recently accumulated a large statistics sample of 4.73 x 10^6 Upsilon(3S) decays. We present the first evidence for the production of the triplet Upsilon(1D) states in the four-photon cascade, Upslion(3S) -> gamma chi_b(2P), chi_b(2P) -> gamma Upsilon(1D), Upsilon(1D) -> gamma chi_b(1P), chi_b(1P) -> gamma Upsilon(1S), followed by the Upsilon(1S) annihilation to e+ e- or mu+ mu-. The signal has a significance of 9.7 standard deviations. The measured product branching ratio for these five decays, (3.3 +- 0.6 +- 0.5) x 10^{-5}, is consistent with the theoretical estimates. We see a 6.8 standard deviation signal for a state with a mass of 10162.2 +- 1.6 MeV/c^2, consistent with the Upsilon(1D_2) assignment. We also present improved measurements of the Upsilon(3S) -> pi0 pi0 Upsilon(1S) branching ratio and the associated di-pion mass distribution.