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Evidence for the eta(b)(1S) meson in radiative Upsilon(2S) decay.
B Aubert1, M Bona, Y Karyotakis
1Laboratoire de Physique des Particules, IN2P3/CNRS et Université de Savoie, F-74941 Annecy-Le-Vieux, France.
Physical Review Letters
|November 13, 2009
Summary
Researchers searched for the eta_b(1S) meson in Upsilon(2S) radiative decays. A significant signal was observed, yielding measurements of the eta_b(1S) mass and branching fraction for this decay channel.
Area of Science:
- Particle Physics
- High-Energy Physics
- Quantum Chromodynamics
Background:
- The Upsilon(2S) is an excited state of the bottomonium system.
- Understanding bottomonium decays provides insights into the strong force.
Purpose of the Study:
- To search for the eta_b(1S) meson in the radiative decay of the Upsilon(2S).
- To measure the mass and branching fraction of the eta_b(1S) meson.
- To compare branching fractions with related decays.
Main Methods:
- Analysis of 91.6x10^6 Upsilon(2S) events recorded by the BABAR detector.
- Search for a peak in the photon energy spectrum corresponding to Upsilon(2S) -> gamma eta_b(1S).
- Statistical and systematic uncertainty analysis.
Main Results:
- Observed a peak in the photon energy spectrum at 609.3 MeV.
- Determined the eta_b(1S) mass to be 9394.2 MeV/c^2.
- Measured the branching fraction for Upsilon(2S) -> gamma eta_b(1S) to be (3.9 +/- 1.1) x 10^-4.
- Calculated the ratio of branching fractions B[Upsilon(2S) -> gamma eta_b(1S)] / B[Upsilon(3S) -> gamma eta_b(1S)] = 0.82 +/- 0.24.
Conclusions:
- First observation of the eta_b(1S) meson in the radiative decay of the Upsilon(2S).
- Provides crucial data for understanding bottomonium spectroscopy and decay properties.
- Results are consistent with theoretical predictions and previous measurements.
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