First Observation of a Upsilon(1D) State

TL;DR

This paper reports the first observation of the Upsilon(1D) state via a four-photon cascade, confirming its mass and production rate, and compares results with theoretical models.

Contribution

First experimental evidence of Upsilon(1D) state production and precise measurement of its mass, supporting potential and lattice QCD predictions.

Findings

Significance of 10.2 standard deviations for the Upsilon(1D) signal

Measured mass of (10161.1±0.6±1.6) MeV for Upsilon(1D)

Product branching ratio consistent with theoretical estimates

Abstract

We present the first evidence for the production of Upsilon(1D) states in the four-photon cascade, Upsilon(3S)-->gamma chib(2P), chib(2P)-->gamma Upsilon(1D), Upsilon(1D)-->gamma chib(1P), chib(1P)-->gamma Upsilon(1S), followed by the Upsilon(1S) annihilation into e+e- or mu+mu-. The signal has a significance of 10.2 standard deviations. The measured product branching ratio for these five decays, (2.5+-0.5+-0.5)x10^(-5), is consistent with the theoretical estimates. The data are dominated by the production of one Upsilon(1D) state consistent with the J=2 assignment. Its mass is determined to be (10161.1+-0.6+-1.6) MeV, which is consistent with the predictions from potential models and lattice QCD calculations. We also searched for Upsilon(3S)-->gammachib(2P), chib(2P)-->gammaUpsilon(1D), followed by either Upsilon(1D)-->eta Upsilon(1S) or Upsilon(1D)-->pi+pi- Upsilon(1S). We find no evidence for such decays and set upper limits on the product branching ratios.