Abstract
We report the observation of ϒ(2S)→γη_{b}(1S) decay based on an analysis of the inclusive photon spectrum of 24.7 fb^{-1} of e^{+}e^{-} collisions at the ϒ(2S) center-of-mass energy collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We measure a branching fraction of B[ϒ(2S)→γη_{b}(1S)]=(6.1_{-0.7-0.6}^{+0.6+0.9})×10^{-4} and derive an η_{b}(1S) mass of 9394.8_{-3.1-2.7}^{+2.7+4.5} MeV/c^{2}, where the uncertainties are statistical and systematic, respectively. The significance of our measurement is greater than 7 standard deviations, constituting the first observation of this decay mode.
Highlights
Background shapeBin=range N1⁄2Υð2SÞ γ efficiency Selection criteria Total χb1ð1PÞ Æ0.5 Æ0.0þ0.1 −0.0 þ0.0 −0.2 ÁÁÁ ÁÁÁ ÁÁÁ Æ0.5 χb2ð1PÞ initial-state radiation (ISR) Æ0.5 þ1.2 −2.2 þ0.2 −0.0 þ0.3 −0.4 þ0.1 −2.0 þ0.0 −0.4
We report the observation of Υð2SÞ → γηbð1SÞ decay based on an analysis of the inclusive photon spectrum of 24.7 fb−1 of eþe− collisions at the Υð2SÞ center-of-mass energy collected with the Belle detector at the KEKB asymmetric-energy eþe− collider
Further evidence was provided by BABAR in Υð2SÞ → γηbð1SÞ decay [3] and subsequently by the CLEO experiment [4]. These analyses studied the inclusive photon spectrum from Υ decays to measure the ηbð1SÞ mass and production branching fractions based on the photon line associated with the hindered M1 radiative transition
Summary
Simulation and data, we fit the energy spectrum with the MC-determined line shapes for the Υð2SÞ → γχbJð1PÞ and χbJð1PÞ → γΥð1SÞ transitions, allowing the energy scale and resolution to vary in order to reproduce the expected EÃγ values [20] of the χbJð1PÞ peaks in the data.
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