Possibility of Exotic States in the Upsilon system

Recent data from Belle show unusually large partial widths Υ(5S) → Υ(1S)ππ and Υ(5S) → Υ(2S)ππ. The Z(4430) narrow resonance also reported by Belle in ψπ spectrum has the properties expected of a c̄cud̄ charged isovector tetraquark T c̄c . The analogous state T b̄b in the bottom sector might mediate anomalously large cascade decays in the Upsilon system, Υ(mS) → T b̄b π → Υ(nS)ππ, with a tetraquark-pion intermediate state. We suggest looking for the b̄bud̄ tetraquark in these decays as peaks in the invariant mass of Υ(1S) pi or Υ(2S)π systems. The b̄bus̄ tetraquark can appear in the observed decays Υ(5S) → Υ(1S)KK as a peak in the invariant mass of Υ(1S)K system. We review the model showing that these tetraquarks are below the two heavy meson threshold, but respectively above the Υππ and ΥKK̄ thresholds. e-mail: [email protected] e-mail: [email protected]