Measurement of branching fractions for B -> J / K decays and search for a narrow resonance in the J / final state

Le résumé fourni par la source

We report an observation of the |$B^{\pm } \to J/\psi \eta K^{\pm }$| and |$B^0 \to J/\psi \eta K^0_S$| decays using |$772\times 10^{6}B\overline {B}$| pairs collected at the |$\Upsilon (4S)$| resonance with the Belle detector at the KEKB asymmetric-energy |$e^+e^-$| collider. We obtain the branching fractions |${\mathcal B}(B^{\pm }\rightarrow J/\psi \eta K^{\pm })=(1.27\pm 0.11(\hbox {stat.})\pm 0.11(\hbox {syst.}))\times 10^{-4}$| and |${\mathcal B}(B^0\to J/\psi \eta K^0_S)=(5.22 \pm 0.78 (\hbox {stat.}) \pm 0.49 (\hbox {syst.}))\times 10^{-5}$|⁠. We search for a new narrow charmonium(-like) state |$X$| in the |$J/\psi \eta $| mass spectrum and find no significant excess. We set upper limits on the product of branching fractions, |${\mathcal B}(B^\pm \to XK^\pm){\mathcal B}(X \to J/\psi \eta)$|⁠, at |$3872\,\hbox {MeV}\,c^{-2}$| where a |$C$|-odd partner of |$X(3872)$| may exist, at |$\psi (4040)$| and |$\psi (4160)$| assuming their known mass and width, and over a range from 3.8 to |$4.8\,\hbox {GeV}\,c^{-2}$|⁠. The obtained upper limits at 90% confidence level for |$X^{C\hbox {-}{\rm odd}}(3872)$|⁠, |$\psi (4040)$|⁠, and |$\psi (4160)$| are |$3.8\times 10^{-6}$|⁠, |$15.5\times 10^{-6}$|⁠, and |$7.4\times 10^{-6}$|⁠, respectively.

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