# An Improved Core-Corona Model for Λ and Λ Polarization in Relativistic Heavy-Ion Collisions

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## Abstract

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## 1. Introduction

## 2. A Core-Corona Model for $\mathrm{\Lambda}/\overline{\mathrm{\Lambda}}$ Polarization

## 3. $\mathrm{\Lambda}$ ($\overline{\mathrm{\Lambda}}$) Intrinsic Polarization z ($\overline{z}$)

## 4. Polarization in the Corona ${\mathcal{P}}_{REC}^{\mathrm{\Lambda}}$ (${\mathcal{P}}_{REC}^{\overline{\mathrm{\Lambda}}}$)

## 5. Results

## 6. Discussion

## 7. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Appendix A. The Ratio w

## Appendix B. The Ratio w′

## Appendix C. Λ and Λ Production in the Core and Corona

## References

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**Figure 1.**Sketch of a non-central heavy-ion collision. The non-homogeneity density of the fireball is illustrated by the color gradient. The core, in which $\mathrm{\Lambda}$s and $\overline{\mathrm{\Lambda}}$s are produced by QGP processes, and the corona which is dominated by nucleon nucleon/N + N) reactions. The figure is taken from Ref. [18]).

**Figure 2.**The interaction rate is obtained from the imaginary part of the self-energy, whose kinematics are defined by the one-loop self-energy quark diagram used to compute the interaction rate. The gluon line with a blob represents the effective gluon propagator at finite density and temperature. The blobs on the quark–gluon vertices represent the effective coupling between the quark spin and the thermal vorticity. The figure is taken from Ref. [22].

**Figure 3.**Intrinsic polarization z and $\overline{z}$ for different values of ${\tau}_{0}$. The figure is taken from Ref. [19]).

**Figure 4.**Global polarization ${\mathcal{P}}^{\mathrm{\Lambda}}$ and ${\mathcal{P}}^{\overline{\mathrm{\Lambda}}}$ as functions of collision energy and fixed values of the model parameters.

**Figure 5.**The panel on the left shows that the ratio ${\mathcal{P}}^{\overline{\mathrm{\Lambda}}}/{\mathcal{P}}^{\mathrm{\Lambda}}$ increases as $w/{w}^{\prime}$ decreases. For small enough $w/{w}^{\prime}$, it achieves values larger than 1 in the case ${N}_{\mathrm{\Lambda}\phantom{\rule{0.166667em}{0ex}}QGP}/{N}_{\mathrm{\Lambda}\phantom{\rule{0.166667em}{0ex}}REC}<1$, even though $\overline{z}<z$. The panel on the right shows the ratio $w/{w}^{\prime}$ as a function of the collision energy.

**Figure 6.**The red and blue shaded regions represent the global polarization ${\mathcal{P}}^{\mathrm{\Lambda}}$ and ${\mathcal{P}}^{\overline{\mathrm{\Lambda}}}$ as a function of the collision energy for the centrality range 20–50% obtained from the core-corona model. Data from STAR-BES Au+Au [14,15,16] and HADES Au+Au and Ag+Ag measurements [17].

**Figure 7.**$\mathrm{\Lambda}$ global polarization as a function of centrality. With (right plot) and without (left plot) ${\mathcal{P}}_{REC}^{\mathrm{\Lambda}}=4$% contribution for all centrality bins. Data for Au+Au at $\sqrt{{s}_{NN}}=3$ GeV [16].

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**MDPI and ACS Style**

Ayala, A.; Dominguez, I.; Maldonado, I.; Tejeda-Yeomans, M.E.
An Improved Core-Corona Model for Λ and Λ Polarization in Relativistic Heavy-Ion Collisions. *Particles* **2023**, *6*, 405-415.
https://doi.org/10.3390/particles6010022

**AMA Style**

Ayala A, Dominguez I, Maldonado I, Tejeda-Yeomans ME.
An Improved Core-Corona Model for Λ and Λ Polarization in Relativistic Heavy-Ion Collisions. *Particles*. 2023; 6(1):405-415.
https://doi.org/10.3390/particles6010022

**Chicago/Turabian Style**

Ayala, Alejandro, Isabel Dominguez, Ivonne Maldonado, and Maria Elena Tejeda-Yeomans.
2023. "An Improved Core-Corona Model for Λ and Λ Polarization in Relativistic Heavy-Ion Collisions" *Particles* 6, no. 1: 405-415.
https://doi.org/10.3390/particles6010022