Dynamical Freeze-Out Phenomena: The Case of K±, φ Transverse Momentum Spectra in Collisions of Au(1.23 A GeV) + Au
Round 1
Reviewer 1 Report
Inspired by a controversy of the KaoS and HADES results on the K-\phi production the authors performed BUU simulations of the collisions Au (1.23 A GeV) + Au and studied the time evolution of the slope parameters. Their simulations show that within their approach there is neither the need nor the possibility to determine in an unambiguous manner the freeze-out temperature at a certain instant of time. They interpret such a behavior as dynamic freeze-out. Presented results can serve as useful reference of analyses of strangeness dynamics for
the future experiments. Therefore I think that the manuscript should be published in ``Particles.’’
However, since the authors failed to reproduce the \phi multiplicity and the K^\pm \phi slope parameters in the analyzed reaction Au(1.23 A GeV) +Au (see Fig. 2) although the same code describes the available data of the reaction Ar (1.756 A GeV) + KCl, it would be worthwhile to give some extra clarifications and a discussion in the text.
As the result, Fig. 10 demonstrates that slope parameters of K^+ and K^- deviate only by 10 MeV (see Fig. 10). But the authors use a simplified m^*=m+\pho \delta m relation, although some previous works used that the scalar potential shifts the mass but the vector potential shifts the chemical potential. Also the p-wave K^-N-hyperon interaction might be strong. May these changes result in a larger difference between the slope parameters of K^+ and K^- resulting in a closer relation with previous calculations, which were performed with a simplified dynamics but with some extra in-medium effects included, where K^+ (and \phi) go off to infinity earlier than K^- , that results in appearance of the chemical potential for K^- till their freezeout?
Would be helpful to briefly clarify from Fig. 14 (lower row) a reason why the role of \rho\Delta seems to be larger for 1.23 A GeV than for a higher energy 1.76 A GeV, and why \Delta N give so much for low energy collision (1.23 A GeV) compared to NN, whereas for a higher energy 1.76 A GeV NN give more?
Fig. 2 shows appropriate fit to data for the value b=9 for Au (1.23 A GeV) , whereas the same code for Ar (1.756 A GeV) gave appropriate fit for essentially smaller b=3.9. Would be helpful to explain the reason. And then, if you did calculations for smaller b, e.g. for b=0, would you again get T\simeq const for K^\pm and \phi or not?
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This manuscript presents a study of the K+, K- and $\phi$ meson freeze-out, within a BUU-type transport model. The results provide a new interpretation of the data, which indicates time-independent transverse momentum slope parameters after 20 fm/c.
The authors show that their approach cannot reproduce the experimental slope parameters for any of the three particle species that they are investigating. Even though they mention in the text that this is a shortcoming of their model and they admit that their conclusions are hampered by these findings, I do not think the manuscript can be accepted in its present form, as the main conclusion is based on Figure 10, which is inconsistent with the data. How is it possible that the fit shown in Fig. 2 (right) yields the temperature shown in Fig. 10? The authors need to elaborate on these points and describe the source of this inconsistency and/or try to mitigate it, before they can draw conclusions on the temperature behavior as a function of t. For this reason, I cannot accept the manuscript in its present form.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
This is a competent paper on a timely topic, and I recommend publication.
One thing I found unclear is, the relevance of the "sub-threshold" part in
the dynamics. It is obvious that sub-threshold means any particle creation
is due to many-body effects, but the authors do not seem
to find any practical effect of threshold physics for their observables.
Perhaps it would be good, for some of the figures 8 onwards, to compare
the results with a similar system ran at SUPER-threshold energies, to see the
effect on the time dependence of the observable.
The authors also use "T" for what is really a slope rather than a "real" temper$
requiring approximate local equilibrium.
Perhaps it is worth, in the T vs time figures, to specify "how thermal" the
distribution is. This might be done by simply plotting the chi^2 of the fit
w.r.t. equation (1) vs time.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors have responded to my criticism and I can now accept the manuscript for publication.
