Λ Polarization and Vortex Rings in Heavy-Ion Collisions at NICA Energies

Round 1

Reviewer 1 Report

Referee report on "$\Lambda$ Polarization and Vortex Rings in Heavy-Ion Collisions at NICA Energies", by Yuri B. Ivanov, Alexei A. Soldatov, submitted to Particles. 

The present paper calculates the global $\Lambda$ hyperons polarization and the ring observable $R_{\Lambda}$ in heavy-ion collisions at RHIC energies using the three-fluid dynamics (3FD) model with two different equations of state. The meson-field contribution to the global $\Lambda$ hyperons polarization was taken into account by using the relativistic mean-field (RMF) model. The paper presents some interest and it is well-written. I recommend publication of this paper in the present form in Particles. Nevertheless, below there are a few comments or questions that I would suggest the authors considering.

1.) In the tensor $S^{\mu}$ in eq.(2), the Fermi-Dirac distribution given in the point $x$ means that each continuum point $x$ of infinitely small size contains a local equilibrium open system of fermions. However, the $\Lambda$ baryons have the finite spatial size. Are there no contradictions in this?

2.) The statement that the Boltzmann statistics dominates in the high-temperature regions is controversial. Experimental data on high-energy heavy-ion and proton-proton collisions show the opposite. 

3.) In the present paper the global $\Lambda$ hyperons polarization is calculated using the contributions of two models: 3FD model and RMF model. These two different models describe the same physical system. Will it lead to double counting in the global $\Lambda$ hyperons polarization?  

4.) It would be helpful if the authors could provide a reference to an experimental paper that explains how the experimentalists calculate the global $\Lambda$ hyperons polarization. 

Comments for author File: Comments.pdf

Author Response

1.) In the tensor $S^{\mu}$ in eq.(2), the Fermi-Dirac distribution given in the point $x$ means that each continuum point $x$ of infinitely small size contains a local equilibrium open system of fermions. However, the $\Lambda$ baryons have the finite spatial size. Are there no contradictions in this?

This is a common approximation in heavy-ion physics, when the hydrodynamical description is used. The continuum point $x$ is understood as a small volume, definitely larger than the hadron size. Moreover, such kind of description is applicable only to collisions of heavy nuclei, where the number of constituent particles is large. However, there are statements in the literature that hydrodynamical description is applicable even to proton-proton collisions  at LHC energies, where the number of newly produced particles is huge. 

 

2.) The statement that the Boltzmann statistics dominates in the high-temperature regions is controversial. Experimental data on high-energy heavy-ion and proton-proton collisions show the opposite. 

Sorry, I do not know about proton-proton collisions, but the particle production in heavy-ion  collisions at moderately relativistic energies is well described by the statistical model, see e.g. A. Andronic, P. Braun-Munzinger and J. Stachel, Nucl. Phys. A 772, 167 (2006). While this model formally operates with Fermi-Dirac and Bose statistics, the resulting temperatures and chemical potentials indicate dominance of the  Boltzmann statistics. 

 

3.) In the present paper the global $\Lambda$ hyperons polarization is calculated using the contributions of two models: 3FD model and RMF model. These two different models describe the same physical system. Will it lead to double counting in the global $\Lambda$ hyperons polarization?  

An important comment is added in the end of subsect. 2.2: 

"It is important to note that we do not apply the RMF-model for describing the matter dynamics. This dynamics is still described by the 3FD model with the aforementioned EoS's. Only the interaction, splitting the polarization of  $\Lambda$ and ${\bar{\Lambda}}$, is taken from the RMF-model. This splitting is an additional contribution to the global polarization which is absent in the 3FD model. "

 

4.) It would be helpful if the authors could provide a reference to an experimental paper that explains how the experimentalists calculate the global $\Lambda$ hyperons polarization. 

A brief explanation with references is added in the first paragraph of sect. 2. 

 

Reviewer 2 Report

particles-2207477-peer-review-v1 review report

I’ve read through the manuscript thoroughly. I found it very well written and containing nice results.

During reading I encountered a few acronyms, that I thought should be resolved, e.g. EoS (which I found explained at its first instance), or NICA (which is a well-known name of the facility in Dubna). Later I found the Abbreviations section at the end of the manuscript, so this was also considered by the authors.

I only found one minor typo to be corrected:

In line 415 there is „Quark GIuon Plasma”. It was probably a different font type during the editing of the manuscript. Now Gluon is spelled with a capital L, such as GLuon. It is clearly visible in the font of the downloaded PDF, because this font type shows it clearly. Please change it to lowercase l, such as Gluon.

 

 

Author Response

We are grateful to the Referee for pointing out the misprint. It is corrected.