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arXiv · 0806.3027

Observation of Upsilon(2S) -> eta Upsilon(1S) and search for related transitions

CLEO Collaboration·Q. He
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Abstract

We report the first observation of the transition Upsilon(2S) > eta Upsilon(1S), with branching fraction B=(2.1+0.7-0.6(stat.)+-0.3(syst.)) x 10^{-4} and statistical significance 5.3 sigma. Data were acquired with the CLEO detector at the CESR e+ e- symmetric collider. This is the first process observed involving a b-quark spin flip. Upper limits at 90% confidence level for related processes, in units of 10^{-4}, are B[Upsilon(2S) -> pi0 Upsilon(1S)] < 1.8, B[Upsilon(3S) -> eta Upsilon(1S)] < 1.8, B[Upsilon(3S) -> pi0 Upsilon(1S)] < 0.7, and B[Upsilon(3S) -> pi0 Upsilon(2S)] < 5.1.

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CLEO Collaboration, Q. He. 2008-11-07. Observation of Upsilon(2S) -> eta Upsilon(1S) and search for related transitions. https://doi.org/10.1103/physrevlett.101.192001

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