Probing the structure of $f_{0}(980)$ from the elliptic flow in p-Pb collisions at the LHC

TL;DR

This study uses a coalescence model to analyze the elliptic flow of the $f_0(980)$ meson in p-Pb collisions, supporting its interpretation as a $Kar K$ molecule and highlighting the importance of realistic modeling for understanding its internal structure.

Contribution

The paper demonstrates that the $f_0(980)$ behaves as a $Kar K$ molecule in high-energy collisions, challenging the simple quark-antiquark interpretation and emphasizing the need for detailed coalescence calculations.

Findings

Reproduces CMS elliptic flow data with $Kar K$ coalescence model.

Supports the $Kar K$ molecular structure of $f_0(980)$.

Shows violation of number-of-constituent scaling for $v_2$ in p-Pb collisions.

Abstract

The $f_{0}(980)$ is a light scalar meson whose internal structure remains under debate and investigation. 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 ($v_2$) 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 with reasonable values for the $f_0(980)$ radius successfully reproduce the elliptic flow measured by CMS over the range $0 < p_{T} < 12$ GeV and also agree with the $p_T$-spectra from ALICE. 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 because most $f_0(980)$ are produced from the coalescence of kaons that have different momenta. Our study 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model calculations and also explains why the CMS interpretation of the $f_0(980)$ as an ordinary $q\bar q$ meson is no longer valid by interpreting the measured $v_2$ with a simple scaling formula based on the assumption of equal momentum coalescence. The investigation also provides a novel way to explore the internal structure of light exotic hadrons that can be abundantly produced in relativistic heavy and/or light ion collisions.