Speaker
Description
The study of exotic hadrons has long been a topic of great interest for the understanding of Quantum Chromodynamics (QCD). As one of the light exotic hadrons, the structure and constituent quark content of $f_0(980)$ have been debated for decades, with theories suggesting it could be a tetraquark state ($s\bar sq\bar q$) or a hadronic molecule ($K\bar K$). Assuming that the $f_0(980)$ is a $K\bar K$ molecule that can only survive at the kinetic freeze-out of the evolving bulk matter, we implement the coalescence model to study its transverse momentum ($p_T$) spectra and elliptic flow $v_2(p_T)$ in high-multiplicity p-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV. Using the well-tuned kaon phase-space distributions from the Hydro-Coal-Frag model, our $K\bar{K}$ coalescence calculations for the $f_0(980)$ successfully reproduce the elliptic flow measured by CMS over the range $0 < p_{T} < 12$ GeV and are also agree with the $p_T$-spectra from ALICE with a reasonable range of values for the $f_0(980)$ radius. These results in heavy ion collisions are consistent with the $K\bar K$ molecular picture of the $f_0(980)$. We also find that the number-of-constituent scaling of $v_2$ for the $f_0(980)$ is violated in p-Pb collisions at the LHC, due to a large proportion of the coalescing kaons having different momenta. This demonstrates the necessity of realistic coalescence model calculations and also explains why the CMS interpretation of the $f_0(980)$ as an ordinary $q\bar q$ meson is no longer reliable, since the measured $v_2$ was analyzed by applying a simple scaling formula based on the assumption of equal momentum coalescence. Our investigation provides a novel way to explore the internal structure of light exotic hadrons that are abundantly produced in relativistic heavy and/or light ion collisions.
References
[1] Y. Wang, W. Zhao, C. M. Ko, F. Guo, J. Xie, H. Song, in preparation.
