Magnetic and quadrupole moments of the $Z_{c}(4020)^+$, $Z_{c}(4050)^+$, and $Z_{c}(4600)^{+}$ states in the diquark-antidiquark picture

TL;DR

This paper calculates the magnetic and quadrupole moments of exotic $Z_c$ states using QCD light-cone sum rules, providing predictions that can help understand their internal quark-gluon structure.

Contribution

It introduces a novel calculation of magnetic and quadrupole moments of $Z_c$ states within the diquark-antidiquark model using light-cone sum rules.

Findings

Magnetic moments are sizable and measurable experimentally.

Quadrupole moments are small but non-zero, indicating non-spherical charge distribution.

Results offer a basis for future experimental verification and structural analysis.

Abstract

The magnetic and quadrupole moments of the $Z_{c}(4020)^+$, $Z_{c}(4050)^+$ and $Z_{c}(4600)^{+}$ states are calculated within the QCD light-cone sum rules. The compact diquark-antidiquark interpolating currents and the distribution amplitudes of the on-shell photon are used to extract the magnetic and quadrupole moments of these states. The magnetic moments are acquired as $\mu_{Z_{c}} = 0.50 ^{+0.22}_{-0.22}~\mu_N$, $\mu_{Z^{1}_{c}}=1.22 ^{+0.34}_{-0.32}~\mu_N$, and $\mu_{Z^2_{c}}=2.40 ^{+0.53}_{-0.48}~\mu_N$ for the $Z_{c}(4020)^+$, $Z_{c}(4050)^+$ and $Z_{c}(4600)^{+}$ states, respectively. The magnetic moments evaluated for the $Z_{c}4020)^+$, $Z_{c}(4050)^+$ and $Z_{c}(4600)^{+}$ states are sufficiently large to be experimentally measurable. The magnetic moment is an excellent platform for studying the internal structure of hadrons governed by the quark-gluon dynamics of QCD because it is the leading-order response of a bound system to a weak external magnetic field. The quadrupole moment results are $\mathcal{D}_{Z_c}=(0.20 ^{+0.05}_{-0.04}) \times 10^{-3}~\mbox{fm}^2 $, $\mathcal{D}_{Z_c^1}=(0.57 ^{+0.07}_{-0.08}) \times 10^{-3}~\mbox{fm}^2 $, and $\mathcal{D}_{Z_c^2}=(0.30 ^{+0.05}_{-0.04}) \times 10^{-3}~\mbox{fm}^2 $ for the $Z_{c}(4020)^+$, $Z_{c}(4050)^+$ and $Z_{c}(4600)^{+}$ states, respectively. We obtain a non-zero, but small, value for the quadrupole moments of the $Z_c$ states, which indicates a non-spherical charge distribution. The nature and internal structure of these states can be elucidated by comparing future experimental data on the magnetic and quadrupole moments of the $Z_{c}(4020)^+$, $Z_{c}(4050)^+$, and $Z_{c}(4600)^{+}$ states with the results of the present study.