Possibility of Exotic States in the Upsilon system

TL;DR

This paper explores the potential existence of exotic tetraquark states in the Upsilon system, proposing experimental signatures and discussing theoretical models for these states, which could explain anomalous decay patterns observed in recent data.

Contribution

It introduces the possibility of bottom tetraquarks mediating unusual Upsilon decays and suggests experimental searches for these states in specific invariant mass spectra.

Findings

Tetraquarks may exist below heavy meson thresholds but above Upsilon decay thresholds.

Proposed decay channels could reveal bottom tetraquarks as peaks in invariant mass distributions.

Theoretical models support the stability of these tetraquarks in the Upsilon system.

Abstract

Recent data from Belle show unusually large partial widths Upsilon(5S) --> Upsilon(1S) pi^+pi^- and \Upsilon(5S) --> \Upsilon(2S) pi^+ pi^-. The Z(4430) narrow resonance also reported by Belle in psi' pi^+ spectrum has the properties expected of a (cbar c u dbar) charged isovector tetraquark T^{+-}_cc The analogous state T^{+-} in the bottom sector might mediate anomalously large cascade decays in the Upsilon system, Upsilon(mS) --> T^{+-}_bb pi^{-+} --> Upsilon(nS) pi^+ \pi^-, with a tetraquark-pion intermediate state. We suggest looking for the (bbar b u dbar) tetraquark in these decays as peaks in the invariant mass of Upsilon(1S) pi or Upsilon(2S) pi systems. The (bbar b u sbar) tetraquark can appear in the observed decays Upsilon(5S) --> Upsilon(1S) K^+ K^- as a peak in the invariant mass of Upsilon(1S) K system. We review the model showing that these tetraquarks are below the two heavy meson threshold, but respectively above the Upsilon pi pi and Upsilon K Kbar thresholds.