Strange molecular partners of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>Z</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>3900</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>Z</mml:mi><mml:mi>c</mml:mi></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>4020</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math>

Abstract

Quantum chromodynamics presents a series of exact and approximate symmetries which can be exploited to predict new hadrons from previously known ones. The ${Z}_{c}(3900)$ and ${Z}_{c}(4020)$, which have been theorized to be isovector ${D}^{*}\overline{D}$ and ${D}^{*}{\overline{D}}^{*}$ molecules [${I}^{G}({J}^{PC})={1}^{\ensuremath{-}}({1}^{+\ensuremath{-}})$], are no exception. Here we argue that from SU(3)-flavor symmetry, we should expect the existence of strange partners of the ${Z}_{c}$'s with hadronic molecular configurations ${D}^{*}{\overline{D}}_{s}\ensuremath{-}D{\overline{D}}_{s}^{*}$ and ${D}^{*}{\overline{D}}_{s}^{*}$ (or, equivalently, quark content $c\overline{c}s\overline{q}$, with $q=u$, $d$). The quantum numbers of these ${Z}_{cs}$ and ${Z}_{cs}^{*}$ structures would be $I({J}^{P})=\frac{1}{2}({1}^{+})$. The predicted masses of these partners depend on the details of the theoretical scheme used, but they should be around the ${D}^{*}{\overline{D}}_{s}\ensuremath{-}D{\overline{D}}_{s}^{*}$ and ${D}^{*}{\overline{D}}_{s}^{*}$ thresholds, respectively. Moreover, any of these states could be either a virtual pole or a resonance. We show that, together with a possible triangle singularity contribution, such a picture nicely agrees with the very recent BESIII data of the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{K}^{+}({D}_{s}^{\ensuremath{-}}{D}^{*0}+{D}_{s}^{*\ensuremath{-}}{D}^{0})$.

Topics & Concepts