Doubly Heavy Tetraquarks and Baryons

Abstract

During the last three years strong experimental evidence from $B$ and charm factories has been accumulating for the existence of exotic hadronic quarkonia, narrow resonances which cannot be made from a quark and an antiquark. Their masses and decay modes show that they contain a heavy quark-antiquark pair, but their quantum numbers are such that they must also contain a light quark-antiquark pair. The theoretical challenge has been to determine the nature of these resonances. The main possibilities are that they are either "genuine tetraquarks", i.e. two quarks and two antiquarks within one confinement volume, or "hadronic molecules" of two heavy-light mesons. In the last few months there as been more and more evidence in favor of the latter. I discuss the experimental data and its interpretation and provide fairly precise predictions for masses and quantum numbers of the additional exotic states which are naturally expected in the molecular picture but have yet to be observed. In addition, I provide arguments in favor of the existence of an even more exotic state - a hypothetical deuteron-like bound state of two heavy baryons. I also consider "baryon-like" states $Q{Q}^{\prime }\bar{q}{\bar{q}}^{\prime }$, which if found will be direct evidence not just for near-threshold binding of two heavy mesons, but for genuine tetraquarks with novel color networks. I stress the importance of experimental search for doubly-heavy baryons in this context.

Invited plenary lecture at International Conference on New Frontiers in Physics, Aug. 28-Sep. 2013, Kolymbari, Crete, Greece

References in corpus (6)

• Observation of a charged charmoniumlike structure Z_c(4020) and search for the Z_c(3900) in e+e- to pi+pi-h_c
• Observation of anomalous Upsilon(1S)pi+pi- and Upsilon(2S)pi+pi- production near the Upsilon(5S) resonance
• Measurement of the Bc meson mass in the exclusive decay Bc --> Jpsi Pi
• Search for a new bottomonium state decaying to Upsilon(1S) pi+ pi- in pp collisions at sqrt(s) = 8 TeV
• The Constituent Quark Model Revisited - Quark Masses, New Predictions for Hadron Masses and KN Pentaquark
• Possibility of Exotic States in the Upsilon system

Cited by in corpus (4)

• Evidence for a $B_s^0{\pi }^{\pm }$ State
• How tetraquarks can generate a second chiral phase transition
• Production of $X_b$ via ${\rm Y}(5S,6S)$ radiative decays
• Fate of the doubly heavy spin$-3/2$ baryons in a dense medium