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The structure of the $X(3915)$ meson and its production in heavy ion collisions

Sungtae Cho, Aaron Park, Su Houng Lee, Sungsik Noh

TL;DR

This work combines a full quark-model analysis with a Yukawa-type hyperfine interaction to reproduce the X(3915) mass and argues that its ground state favors a well-separated $D_s\bar{D}_s$ configuration, i.e., a hadronic molecular state, rather than a compact $c\bar{c}s\bar{s}$ tetraquark. It then applies a coalescence model in relativistic heavy-ion collisions to compare production for three internal structures (charmonium, tetraquark, and hadronic molecule), deriving distinct transverse-momentum distributions and yields. The results show charmonium production can exceed thermal expectations, while tetraquark and molecular productions are significantly suppressed, with the molecular case sensitive to chemical vs. kinetic freeze-out scenarios. Together, these analyses provide a practical strategy to identify the internal structure of X(3915) through heavy-ion collision observables like $p_T$ spectra and integrated yields.

Abstract

We study the structure of the $X(3915)$ meson in a quark model and explore how its production in heavy ion collisions depends on its internal structure. We first analyze the $X(3915)$ as a $c\bar{c}s\bar{s}$ state and solve the Hamiltonian with color-spin interactions within the quark model. We find that the ground state of the $c\bar{c}s\bar{s}$ with total spin 0 obtained from the quark model analysis favors a separated $D_s \bar{D}_s$ state. To probe its structure further, we study its production in relativistic heavy ion collisions for various proposed configurations. We calculate the transverse momentum distributions and yields for the $X(3915)$ assuming its structure to be either a charmonium, a tetraquark, or a hadronic molecular state. We argue that by measuring the transverse momentum distributions and yields of the $X(3915)$ produced in heavy ion collisions, one can identify the structure of the $X(3915)$.

The structure of the $X(3915)$ meson and its production in heavy ion collisions

TL;DR

This work combines a full quark-model analysis with a Yukawa-type hyperfine interaction to reproduce the X(3915) mass and argues that its ground state favors a well-separated configuration, i.e., a hadronic molecular state, rather than a compact tetraquark. It then applies a coalescence model in relativistic heavy-ion collisions to compare production for three internal structures (charmonium, tetraquark, and hadronic molecule), deriving distinct transverse-momentum distributions and yields. The results show charmonium production can exceed thermal expectations, while tetraquark and molecular productions are significantly suppressed, with the molecular case sensitive to chemical vs. kinetic freeze-out scenarios. Together, these analyses provide a practical strategy to identify the internal structure of X(3915) through heavy-ion collision observables like spectra and integrated yields.

Abstract

We study the structure of the meson in a quark model and explore how its production in heavy ion collisions depends on its internal structure. We first analyze the as a state and solve the Hamiltonian with color-spin interactions within the quark model. We find that the ground state of the with total spin 0 obtained from the quark model analysis favors a separated state. To probe its structure further, we study its production in relativistic heavy ion collisions for various proposed configurations. We calculate the transverse momentum distributions and yields for the assuming its structure to be either a charmonium, a tetraquark, or a hadronic molecular state. We argue that by measuring the transverse momentum distributions and yields of the produced in heavy ion collisions, one can identify the structure of the .
Paper Structure (9 sections, 33 equations, 2 figures, 4 tables)

This paper contains 9 sections, 33 equations, 2 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Quark model description
  3. Short range interaction
  4. Production of the $X(3915)$ meson in heavy ion collisions
  5. The $X(3915)$ meson in a two-quark state
  6. The $X(3915)$ meson in a four-quark state
  7. The $X(3915)$ meson in a hadronic molecular state
  8. Yields and transverse momentum distributions of the $X(3915)$
  9. Conclusions

Figures (2)

  • Figure 1: Transverse momentum distributions of the $D_s$ meson, $dN_{D_s}/dp_T$ at mid-rapidity at $\sqrt{s_{NN}}=5.02$ TeV with and without feed down contributions, denoted by $D_s$ and $D_s^{tot}$, respectively.
  • Figure 2: (a) Transverse momentum distributions of the $X(3915)$ meson, $dN_{X(3915)}/dp_T$ at mid-rapidity at $\sqrt{s_{NN}}=5.02$ TeV for various possible states, or a charmonium state, $c\bar{c}$, a tetraquark state, $c\bar{c}s\bar{s}$, a hadronic molecular state formed from $D_s$ mesons at chemical freeze-out, $D_s\bar{D}_s$, and a hadronic molecular state formed from $D_s$ mesons at kinetic freeze-out, $D_s^{tot}\bar{D}_s^{tot}$. (b) Transverse momentum distribution ratios between the $X(3915)$ of various states and the $D_s$ meson.