Abstract
We report the first observation of the processes e+e−→ϒ(1S,2S)η at s=10.866 GeV, with significance exceeding 10σ for both processes. The measured Born cross sections are σ(e+e−→ϒ(2S)η)=2.07±0.21±0.19 pb, and σ(e+e−→ϒ(1S)η)=0.42±0.08±0.04 pb. We also set the upper limit on the cross section of the process e+e−→ϒ(1S)η′ to be σ(e+e−→ϒ(1S)η′)<0.037 pb at 90% C.L. The results are obtained with the data sample collected with the Belle detector at the KEKB asymmetric-energy e+e− collider in the energy range from 10.63 to 11.02 GeV.Received 11 August 2021Accepted 12 November 2021DOI:https://doi.org/10.1103/PhysRevD.104.112006Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHadronic decaysPhysical SystemsBottom mesonsParticles & Fields
Highlights
Bottomonium states above the BBthreshold have unexpected properties
The results reported here are based on the reconstruction of exclusive decays and are independent of the published results
For the Υð2SÞη1⁄2γγ, Υð2SÞη1⁄23π, anpd ffiΥffiffiffiðffiffi1ffiffiffiSffiffiÞffiffiηffiffi1⁄2ffiffi3ffiffiπffiffiffiffiffimffiffiffiffioffiffiffidffiffieffiffis we evaluate the signal significance as 2 log 1⁄2LðNÞ=Lð0Þ, where LðNÞ=Lð0Þ is the ratio between the likelihood values for a fit that includes a signal yield N and a fit with a background hypothesis only
Summary
Bottomonium states (bound states of bb ) above the BBthreshold have unexpected properties. For bottomonium states below the BBthreshold, the QCDME model predictions are consistent with measurements: ΓðΥð2SÞ→Υð1SÞηÞ ΓðΥð2SÞ→Υð1SÞπ þ π − Þ ð1.64. Υð1SÞη is studied in the decay chain Υð1SÞ → μþμ−, η → πþπ−π0, π0 → γγ, denoted as Υð1SÞη1⁄23π. The process eþe− → Υð1SÞη0 is studied in two different modes: the first, Υð1SÞ → μþμ−, η0 → πþπ−η, η → γγ, denoted as. Υð5SÞ resonance and 21 fb−1 collected during a scan of center-of-mass energies in the range 10.63–11.02 GeV by the Belle detector [13,14] at the KEKB asymmetric-energy eþe− collider energy of the [15,16]. For Υð2SÞ → Υð1SÞπþπ−, we use a dipion invariant mass distribution according to the Voloshin and Zakharov model [5] measured in [19]. For the η → πþπ−π0 decay, final state particles are distributed in phase space according to the model from [20]. The simulation takes into account variations of the detector configuration and beam conditions
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