# Search for the QCD Critical Point by Transverse Velocity Dependence of Anti-deuteron to Deuteron Ratio

## TL;DR

This paper proposes using the transverse velocity dependence of anti-deuteron to deuteron ratios as a new observable to detect the QCD critical point in heavy-ion collisions, supported by model simulations and experimental data analysis.

## Contribution

It introduces the $eta_T$ dependence of particle ratios as a novel method to identify the QCD critical point and analyzes existing experimental data for signs of critical behavior.

## Key findings

- Focusing effect causes anomalous $eta_T$ dependence of particle ratios near the critical point.
- Observed negative slope in $eta_T$ dependence of $ar{d}/d$ ratio at 19.6 GeV suggests passing through the critical region.
- Future measurements can refine the critical point's location and properties.

## Abstract

We propose the transverse velocity ($\beta_T$) dependence of the anti-deuteron to deuteron ratio as a new observable to search for the QCD critical point in heavy-ion collisions. The QCD critical point can attract the system evolution trajectory in the QCD phase diagram, which is known as focusing effect. To quantify this effect, we employ thermal model and hadronic transport model to simulate the dynamical particle emission along a hypothetical focusing trajectory near critical point. We found the focusing effect can lead to anomalous $\beta_T$ dependence of $\bar{p}/p$, $\bar{d}/d$ and $^3\overline{\text{He}}/^3\text{He}$ ratios. We examined the $\beta_T$ dependence of $\bar{p}/p$ and $\bar{d}/d$ ratios of central Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7 to 200 GeV measured by the STAR experiment at RHIC. Surprisingly, we only observe a negative slope in $\beta_T$ dependence of $\bar{d}/d$ ratio at $\sqrt{s_{NN}}$ = 19.6 GeV, which indicates the trajectory evolution has passed through the critical region. In the future, we could constrain the location of the critical point and/or width of the critical region by making precise measurements on the $\beta_T$ dependence of $\bar{d}/d$ ratio at different energies and rapidity.