Implications of spin symmetry for XYZ states

TL;DR

This paper investigates how heavy quark spin symmetry influences the properties of XYZ states, using effective-field theory to predict spin partner states based on experimental data, guiding future experimental tests.

Contribution

It introduces a method to analyze XYZ states with effective-field theory, predicting properties of spin partners by exploiting heavy quark spin symmetry and recent experimental data.

Findings

Predicted line shapes and pole positions of spin partner states.

Extracted parameters of Z_b states from experimental data.

Provided parameter-free predictions for future experiments.

Abstract

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.