# Observation of the Decay $B \Rightarrow J/\psi \eta K$ and Search for $X(3872) \Rightarrow J/\psi \eta$

Abstract : We report the observation of the $B$ meson decay $B^\pm\to J/\psi \eta K^\pm$ and evidence for the decay $B^0\to J/\psi \eta K^0_S$, using {90} million $BBbar$ events collected at the $\ensuremath{\Upsilon{(4S)}}\xspace$ resonance with the $BaBar$ detector at the PEP-II $e^+ e^-$ asymmetric-energy storage ring. We obtain branching fractions of $\cal{B}$(B^\pm\to J/\psi \eta K^{\pm})=(10.8\pm 2.3(\rm{stat.})\pm 2.4(\rm{syst.}))\times 10^{-5} and \cal{B}$(B^0\to J/\psi\eta K_{\rm{S}}^{0}$)=$(8.4\pm 2.6(\rm{stat.})\pm 2.7(\rm{syst.}))\times 10^{-5}$. We search for the new narrow mass state, the X(3872), recently reported by the Belle Collaboration, in the decay $B^\pm\to X(3872)K^\pm, X(3872)\to \jpsi \eta$ and determine an upper limit of $\cal{B}$$(B^\pm \to X(3872) K^\pm \to \jpsi \eta K^\pm$) $<7.7\times 10^{-6}$ at 90% C.L.
Document type :
Journal articles

http://hal.in2p3.fr/in2p3-00023356
Contributor : Claudine Bombar <>
Submitted on : Friday, November 26, 2004 - 3:29:37 PM
Last modification on : Wednesday, April 21, 2021 - 8:36:02 AM

### Citation

B. Aubert, R. Barate, D. Boutigny, F. Couderc, J.M. Gaillard, et al.. Observation of the Decay $B \Rightarrow J/\psi \eta K$ and Search for $X(3872) \Rightarrow J/\psi \eta$. Physical Review Letters, American Physical Society, 2004, 93, pp.041801. ⟨10.1103/PhysRevLett.93.041801⟩. ⟨in2p3-00023356⟩

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