Prospects for Heavy-Ion Physics with the MPD Detector at NICA

Round 1

Reviewer 1 Report

The author of this manuscript discusses the physics topics at NICA, the status of the accelarator and the detector, as well as their performance compared with some simulation results. It is nice to know that the first collision will be carried out in 2021. The paper can be published after the author considere/addresse my following comments:
1)  The center-of-mass energy of NICA is from 4 to 11 GeV, while the non-monotical behaviors of various observables appear at around 20 GeV from the RHIC beam energy scan program, presumedly indicates the energy range of the QCD critical point. Does the author have any comments on this?
2) I wonder whether the author can summarize the advantages of NICA over facilities/programs addressing similar physics topics, such as the RHIC beam energy scan program and the FAIR compressed baryonic matter program.
3) It is written in the introduction: "According to lattice QCD calculations a first order phase transition from the hadronic phase to the phase of deconfined quarks and gluons - Quark-Gluon Plasma (QGP) is suggested at large values of baryochemical potential mu_B". Is the statement correct? As far as I know, LQCD always predicts a smooth cross over, and a first order phase transition is predicted by effective models rather than LQCD.
4) The resolution of Fig.10 is a little low. Can it be improved?
5) The English presentation is OK, but hope the author can avoid using too long sentences.

Author Response

1)  The center-of-mass energy of NICA is from 4 to 11 GeV, while the non-monotical behaviors of various observables appear at around 20 GeV from the RHIC beam energy scan program, presumedly indicates the energy range of the QCD critical point. Does the author have any comments on this?

Response 1: The author provide a better motivation for new measurements of higher moment at NICA aimed in the search for CEP. The text now reads:
"If the QCD critical point exists, it is expected that abnormal event-by-event fluctuations of conserved quantities  can be observed near this point (net-baryon, net-strangeness, and net-charge numbers). It is believed that the higher order moments of the multiplicity distributions of the conserved charges are able to give signatures for such critical phenomena. As experimental data indicate the curtosis of the net-proton multiplicity distribution show an interesting non-monotonic behavior at low energies deviating from the Poisson baseline: it drops below unity around 19.6-27 GeV and increases above unity below 11 GeV~\cite{star_netp}. In order to relate these observations to a possible signal for the critical point~\cite{stepanov} one has to unveil the details of the energy dependence of the net-proton higher moments at energies below 11 GeV, where the uncertainties in the measurements are too high.  Moreover, the moments of net-protons are changing dramatically if the apparatus has geometrical constrains  (i.e. not full acceptance), thus future high statistics measurements for the moments of the conserved charges over a large phase-space are highly desirable."

2) I wonder whether the author can summarize the advantages of NICA over facilities/programs addressing similar physics topics, such as the RHIC beam energy scan program and the FAIR compressed baryonic matter program.

Response 2: The following text has added:

"Currently, the future beam energy scan programs at finite net-baryon density include the phase II at RHIC, the upcoming SIS100 facility at FAIR, and the NICA program at JINR in Dubna. The maximal energy of the SIS100 accelerator is limited to 10 GeV per nucleon in the fixed target mode (equivalent to about 4 GeV in the center-of-mass), while at RHIC due to luminosity limitations at low energies the rate of useful physics events is very low below the center-of-mass energy of 10 GeV. The NICA facility will be capable to achieve a high level of luminosity for heavy ions (two orders of magnitude higher than at RHIC) in the energy range not accessible at FAIR."

3) It is written in the introduction: "According to lattice QCD calculations a first order phase transition from the hadronic phase to the phase of deconfined quarks and gluons - Quark-Gluon Plasma (QGP) is suggested at large values of baryochemical potential mu_B". Is the statement correct? As far as I know, LQCD always predicts a smooth cross over, and a first order phase transition is predicted by effective models rather than LQCD.

Response 3: The text in the Introduction has changed to:
"According to lattice QCD calculations a crossover phase transition from the hadronic phase to the phase of deconfined quarks and gluons - Quark-Gluon Plasma (QGP) is suggested at a vanishing baryon chemical potential $\mu_B$~\cite{crossover}. The order of the phase transformation is expected to change with the net baryon density: arguments based on several approaches of QCD~\cite{cep} predict both a first order phase transition at large $\mu_B$ values and the existence of a critical endpoint (CEP)."

4) The resolution of Fig.10 is a little low. Can it be improved?

Response 4: Done

5) The English presentation is OK, but hope the author can avoid using too long sentences.

Response 5: It has changed where it's possible.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper reviews current status of the NICA/MPD project. It is quite informative.

However, I have few remarks concerning the presentation.

“According to lattice QCD calculations a first order phase transition from the hadronic phase to the phase of deconfined quarks and gluons - Quark-Gluon Plasma (QGP) is suggested at large values of baryochemical potential.”

Lattice QCD calculations are performed only at zero baryochemical potential. Therefore, they do not suggest anything for large values of it.

“Figure 5. The joke of the MPD magnet after control assembling at VHM (Vitkovice, Czech Republic).”

Joke??? What is funny in the MPD magnet?

A similar “joke” is in the text.

I recommend publication of this article in “Universe” after the author considers my remarks.

Author Response

1)“According to lattice QCD calculations a first order phase transition from the hadronic phase to the phase of deconfined quarks and gluons - Quark-Gluon Plasma (QGP) is suggested at large values of baryochemical potential.”
Lattice QCD calculations are performed only at zero baryochemical potential. Therefore, they do not suggest anything for large values of it.

Response 1: The text in the Introduction has changed to:
"According to lattice QCD calculations a crossover phase transition from the hadronic phase to the phase of deconfined quarks and gluons - Quark-Gluon Plasma (QGP) is suggested at a vanishing baryon chemical potential $\mu_B$~\cite{crossover}. The order of the phase transformation is expected to change with the net baryon density: arguments based on several approaches of QCD~\cite{cep} predict both a first order phase transition at large $\mu_B$ values and the existence of a critical endpoint (CEP)."
 

2) “Figure 5. The joke of the MPD magnet after control assembling at VHM (Vitkovice, Czech Republic).”
Joke??? What is funny in the MPD magnet?
A similar “joke” is in the text.

Response 2: Corrected ("joke-->yoke")

Author Response File: Author Response.pdf