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Register a new userTriangle relations for XYZ states
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Kai Zhu
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We propose novel triangle relations, not the well-known triangle singularity, for better understanding of the exotic XYZ states. Nine XYZ resonances, X(3872), Y(4230), Zc(3900), X(4012), Y(4360/4390), Zc(4020), X(4274), Y(4660), and Zcs(3985) have been classified into triples to construct three triangles based on the assumption that they are all tetra-quark states. We also suggest some channels deserving search for with high priority based on this hypothesis, as well as predictions of a few production/decay rates of these channels. We hope further experimental studies of the XYZ states will benefit from our results.
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Numerous exotic candidates containing a heavy quark and anti-quark (the so-called $XYZ$ states) have been reported since the observation of the $X(3872)$ in 2003. For these systems a study of the implications of the heavy quark spin symmetry and its breaking is expected to provide useful guidance towards a better understanding of their nature. For instance, since the formation of the complete spin multiplets is described with the same parameter sets, in some cases the currently available experimental data on the $XYZ$ states allows us to predict properties of spin partner states. To illustrate this point we extract the parameters of the two $Z_b$ states by analyzing the most recent experimental data within an effective-field theory approach which treats both short-ranged contact interactions and the long-ranged one-pion/one-eta Goldstone boson exchanges (OPE/OEE) dynamically. The line shapes and pole positions of their spin partners are then predicted in a parameter-free way and await to be tested by future experimental data.
The branching fractions of the $Upsilon(1S)$ inclusive decays into final states with a $J/psi$ or a $psi(2S)$ are measured with improved precision to be $BR(Upsilon(1S)to J/psi + {rm anything})=(5.25pm 0.13(mathrm{stat.})pm 0.25(mathrm{syst.}))times 10^{-4}$ and $BR(Upsilon(1S)to psi(2S) + {rm anything})=(1.23pm 0.17(mathrm{stat.})pm 0.11(mathrm{syst.}))times 10^{-4}$. The first search for $Upsilon(1S)$ decays into $XYZ$ states that decay into a $J/psi$ or a $psi(2S)$ plus one or two charged tracks yields no significant signals for $XYZ$ states in any of the examined decay modes, and upper limits on their production rates in $Upsilon(1S)$ inclusive decays are determined.
Charmonium, the spectroscopy of cbar{c} mesons, has recently enjoyed a renaissance with the discovery of several missing states and a number of unexpected charmonium-like resonances. The discovery of these new states has been made possible by the extremely large data samples made available by the B-factories at the Stanford Linear Accelerator Center and at KEK in Japan, and at the CESR e^+e^- collider at Cornell. Conventional cbar{c} states are well described by quark potential models. However, many of these newly discovered charmonium-like mesons do not seem to fit into the conventional cbar{c} spectrum. There is growing evidence that at least some of these new states are exotic, i.e. new forms of hadronic matter such as mesonic-molecules, tetraquarks, and/or hybrid mesons. In this review we describe expectations for the properties of conventional charmonium states and the predictions for molecules, tetraquarks and hybrids and the various processes that can be used to produce them. We examine the evidence for the new candidate exotic mesons, possible explanations, and experimental measurements that might shed further light on the nature these states.
I discuss the properties of some representative $XYZ$ mesons in the context of the most commonly proposed models for their underlying nature.
We investigate the anomalous triangle singularity (ATS) and its possible manifestations in various processes. We show that the ATS should have important impact on our understanding of the nature of some newly observed threshold states. Discussions on how to distinguish the ATS phenomena from genuine dynamic pole structures are presented.
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