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Register a new userImplications of spin symmetry for XYZ states
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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.
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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.
In recent years data have been accumulated at various experiments about states in the heavy quarkonium mass range that seem to be inconsistent with the most simple variants of the quark model. In this contribution it is demonstrated that most of those data are consistent with a dominant molecular nature of those states. It is also discussed which kind of observables are sensitive to the molecular component and which are not.
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.
In a local gauge-invariant theory with massless Dirac fermions a symmetry of the Lorentz-invariant fermion charge is larger than a symmetry of the Lagrangian as a whole. While the Dirac Lagrangian exhibits only a chiral symmetry, the fermion charge operator is invariant under a larger symmetry group, SU(2N_F), that includes chiral transformations as well as SU(2)_{CS} chiralspin transformations that mix the right- and left-handed components of fermions. Consequently a symmetry of the electric interaction, that is driven by the charge density, is larger than a symmetry of the magnetic interaction and of the kinetic term. This allows to separate in some situations electric and magnetic contributions. In particutar, in QCD the chromo-magnetic interaction contributes only to the near-zero modes of the Dirac operator, while confining chromo-electric interaction contributes to all modes. At high temperatures, above the chiral restoration crossover, QCD exhibits approximate SU(2)_{CS} and SU(2N_F) symmetries that are incompatible with free deconfined quarks. Consequently elementary objects in QCD in this regime are quarks with a definite chirality bound by the chromo-electric field, without the chromo-magnetic effects. In this regime QCD can be described as a stringy fluid.
Quantum correlation of bipartite states (beyond entanglement) in presence of environment is studied for Heisenberg XYZ spin system. It is shown that if the system is allowed to exchange energy with environment, the initial state evolves and settles down to uncorrelated state in asymptotic limit. We have also demonstrated that fidelity based measurement induced non-locality is a useful quantity in characterizing correlated quantum states.
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