Review Reports - Feasibility Studies for the Measurement of Open-Charm Mesons at ALICE-3 Using Decay Channels with Neutral Mesons and Photons in the Final State

Round 1

Reviewer 1 Report

The Authors present results of the feasibility studies for the measurement of open heavy-flavor mesons at the LHC using a multipurpose detector ALICE 3 experimental setup. One physics aim for this new initiative, described e.g. in [1], is a measurement of low transverse momentum photons in pp, p-Pb, and Pb-Pb collisions. In the study the event generator is used to simulate both the signals and background particles, in particular from decays of D0 (-> K- pi+ pi0) and D*0 (-> D0 gamma) mesons.

One of interesting result presented in the paper is that the invariant mass spectra reconstructed for the decays of excited states are very narrow which should result in better S/B ratios. To suppress the background several criteria of single particles were also given. This was done using a simplified approach to produce first-look estimations but the analysis appears to be useful for its stated purpose.

I recommend publish this manuscript in Particles in present form.

Author Response

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I recommend publish this manuscript in Particles in present form.
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We thank the referee for the high appraisal of importance of the obtained results and recommendation for publication of the draft.

No other comments to answer.

Reviewer 2 Report

I recommend to publish this paper in the special issue.

One suggestion: For all of the figures, move the labeling such as "(a)" and "(b)" to inside each plot.

Author Response

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I recommend to publish this paper in the special issue.
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We thank the referee for the high appraisal of importance of the obtained results and recomendation for publication of the draft.

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One suggestion: For all of the figures, move the labeling such as "(a)" and "(b)" to inside each plot.
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For figures we followed the recommendation of Journal described in the Word template file. We also personally prefer to label the plots on the outside since it simplifies usage of the plots in external presentations.

No other comments to answer.

Reviewer 3 Report

Dear authors,

I found the paper is well described for the feasibility studies for the measurement of open heavy-flavor mesons at ALICE-3.

I have two suggestions.

(1) Since you are treating only open-charm mesons here, the title should be "Feasibility studies for the measurement of open-charm mesons at ALICE-3".

(2) Page1, line 33-37
Please add appropriate references for
studying the production mechanisms of heavy c-quarks (particle yields)
involvement of heavy flavor particles in the 34 collective system expansion (particle flow coefficients)
scattering and energy loss of c- 35 quarks traversing the dense and hot partonic medium produced in the collisions (azi- 36 muthal angular correlations, nuclear modification factors).

Author Response

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Dear authors,

I found the paper is well described for the feasibility studies for the measurement of open heavy-flavor mesons at ALICE-3.
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We thank the referee for the high appraisal of importance of the obtained results and recommendation for publication of the draft.

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I have two suggestions.

(1) Since you are treating only open-charm mesons here, the title should be "Feasibility studies for the measurement of open-charm mesons at ALICE-3".
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The paper title was changed as proposed.

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(2) Page1, line 33-37
Please add appropriate references for
studying the production mechanisms of heavy c-quarks (particle yields)
involvement of heavy flavor particles in the 34 collective system expansion (particle flow coefficients)
scattering and energy loss of c- 35 quarks traversing the dense and hot partonic medium produced in the collisions (azi- 36 muthal angular correlations, nuclear modification factors).>
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We reshuffled the references and now provide 9 references for the topics of interest:

Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Rinella, G.A.; Agnello, M.; Agrawa, N.; Ahammed, Z.; Ahmad, S.; et al. [ALICE Collaboration] Prompt D0, D+, and D∗+ production in Pb-Pb collisions at √(s_NN ) = 5.02 TeV, JHEP 2022, 01, 174.
Acharya, S.; Acosta, F.T.; Adamová, D.; Adolfsson, J.; Aggarwal, M.M.; Rinella, G.A.; Agnello, M.; Agrawa, N.; Ahammed, Z.; et al. [ALICE Collaboration] Measurement of D0, D+, D∗+ and Ds+ production in Pb-Pb collisions at √(s_NN ) = 5.02 TeV. JHEP 2018, 1810, 174.
Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Rinella, G.A.; Agnello, M.; Agrawa, N.; Ahammed, Z.; Ahmad, S.; et al. [ALICE Collaboration] Measurement of prompt D0, Λc+, and Σc0,++(2455) production in pp collisions at √s = 13 TeV. Phys. Rev. Lett. 2022, 128, 012001.
Acharya, S.; Adamova, D.; Adhya, S.P.; Adler, A.; Adolfsson, J.; Aggarwal, M.M.; Rinella, G.A.; Agnello, M.; Agrawa, N.; et al. [ALICE Collaboration] Measurement of prompt D0, D+, D∗+, and Ds+ production in p-Pb collisions at √(s_NN ) = 5.02 TeV. JHEP 2019, 12, 92.
Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Rinella, G.A.; Agnello, M.; Agrawa, N.; Ahammed, Z.; Ahmad, S.; et al. [ALICE Collaboration] Investigating charm production and fragmentation via azimuthal correlations of prompt D mesons with charged particles in pp collisions at √s = 13 TeV. Eur. Phys. J.C 2022, 82, 4, 335, Eur. Phys. J. C 2022, 82, 335.
Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Rinella, G.A.; Agnello, M.; Agrawa, N.; Ahammed, Z.; Ahmad, S.; et al. [ALICE Collaboration] Azimuthal correlations of prompt D mesons with charged particles in pp and p–Pb collisions at √(s_NN ) = 5.02 TeV, Eur. Phys. J. C 2020, 80, 10, 979.
Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Aggrawal, M.M.; Rinella, G.A.; Agnello, M.; Agrawal, N.; Ahammed, Z.; et al. [ALICE Collaboration] Transverse-momentum and event-shape dependence of D-meson flow harmonics in Pb–Pb collisions at √(s_NN ) = 5.02 TeV. Phys. Lett. B 2021, 813, 136054.
Acharya, S.; Acosta, F.T.; Adamová, D.; Adler, A.; Adolfsson, J.; Aggrawal, M.M.; Rinella, G.A.; Agnello, M.; Agrawal, N.; et al. [ALICE Collaboration] Event-shape engineering for the D-meson elliptic flow in mid-central Pb-Pb collisions at √(s_NN ) = 5.02 TeV. JHEP 2019, 02, 150.
Adam, J.; Adamová, D.; Aggrawal, M.M.; Rinella, G.A.; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahn, S.U.; Aimo, I.; et al. [ALICE Collaboration] Centrality dependence of high-pT D meson suppression in Pb-Pb collisions at √(s_NN ) = 2.76 TeV. JHEP 2015, 11, 205, JHEP 2017, 06, 32.

No other comments to answer.

Reviewer 4 Report

Please see the attachments for my comments.

Comments for author File: Comments.pdf

Author Response

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General Comments
The paper “Feasibility studies for the measurement of open heavy-flavor mesons at ALICE3” discusses a prospective next-generation heavy-ion experiment envisaged to operate at the
future high-luminosity LHC (HL-LHC), namely, ALICE 3. The feasibility of studying open charm mesons (D mesons) produced in pp, p–Pb, and Pb–Pb collisions at the HL-LHC with the ALICE 3 experiment was assessed by the authors using a simplified model of the ALICE 3 detector and LHC collision events simulated using the Pythia event generator. Although the corresponding simulation results are well-validated, the methodology is appropriate, and the outcomes of the feasibility studies reported are positive, the clarity of the writing, the
background information provided in the introduction, and the discussion of the results could be improved considerably. Moreover, given that the ALICE 3 experiment has been proposed to operate at the HL-LHC (as described by the authors), the feasibility studies for ALICE 3 presented in this manuscript should be revised to be consistent with the correct center-of mass energies projected for pp and heavy-ion collisions at the HL-LHC that are reported in
the literature and typically used by other similar feasibility studies of proposed experiments, e.g., √s = 14 TeV for pp collisions. Consequently, major revisions are necessary before this manuscript should be accepted. Specific comments regarding the major and minor revisions that I have requested are detailed below.
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We thank the reviewer for the careful reading of the paper draft and the comments. We do not share many of the expressed concerns. To make message and positioning of the paper more clear, we largely reworked the introduction and conclusion subsections. Please see our detailed replies below.

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Specific Comments
Major Revisions
1. The introduction of the manuscript is sparse and does not provide sufficient background or adequate coverage of the corresponding literature. Notably, no discussion of, or reference to, any past measurements involving open charm mesons at accelerator facilities was included. The introduction should be revised to include more background on previous measurements of open heavy-flavor mesons performed at particle accelerators, focusing, in particular, on energy-frontier measurements already performed at the LHC (e.g., by the ALICE and LHCb experiments). Additionally, more detail on what improvements
and upgrades, in particular, make ALICE 3 unique and superior to ALICE 2 would be beneficial; it seems to me that a key improvement is that a much larger range of rapidity is covered by ALICE 3, but this is never made clear to the reader. Please revise accordingly. Lastly, I feel that the introduction would also benefit from some discussion of the current state of heavy-ion physics at the LHC.
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We largely revised the introduction to better position the paper in the world of heavy-flavor measurements. ALICE-3 has been designed to provide state-of-the-art measurements for heavy-flavor hadrons in decay channels with charged particles in the final state in pp, p-A and A-A collisions at LHC energies. Pefrormance of ALICE-3 for the measurements, comparison with the previous, current and future measurements by LHCb/CMS/ATLAS are discussed in [1]. Focus of the paper is to present the first estimates for ALICE-3 capabilities to measure open heavy flavor mesons in specific decay channels with neutral mesons/photons in the final state and compare the obtained results with those published in [1] for other channels. The main incentive behind is that measurements in the considered decay channels can utilize data samples collected with dedicated triggers and thus sample larger integrated luminosities compared with minimum bias samples and extend measurements of mesons to higher momenta. In other words, the paper focus on the measurements in new decay channels and comparison of the obtained results with those published in [1]. Comparison of ALICE-3 to other facilities and its competitive advantages are discussed in [1].

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2. The feasibility of the ALICE 3 experiment for measuring open charm mesons at the HL-LHC should be assessed using the correct center-of-mass energies projected for the HL-LHC: √s = 14 TeV for pp, √sNN = 8.8 TeV for p–Pb, and √sNN = 5.52 TeV for Pb–Pb. Please revise the analyses, figures, and manuscript accordingly. Additionally, adding references/citations regarding these values is recommended.
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The estimations presented in the paper remain valid in a wide collision energy range. There will be marginal difference in the results if we compare pp collisions at 13 or 14 GeV, Pb-Pb collisions at 5.02 or 5.52 TeV. Using collision energies of Run-1,2 we keep the possibility of direct comparison with the published results. Needless to say that results at other collision energies are not available for publications. Collision energies of √s = 14 TeV for pp, √sNN = 8.8 TeV for p–Pb, and √sNN = 5.52 TeV for Pb–Pb are foreseen for the centralized full-event Geant-based simulations to be used for more realistic estimations in the future.

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3. The last paragraph of Sec. 2 (lines 177–182) discusses results obtained for studies involving D mesons produced in p–Pb and Pb–Pb collisions; however, the data/results being discussed were not provided. Please provide these results (which should also be revised with the correct center-of-mass energies) either in the revised manuscript or in a supplementary material file.
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The text was modified to make the presented results more clear.

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4. Comparisons between the results obtained in the manuscript (regarding the feasibility of measuring open charm mesons at ALICE 3) and other experiments (both past and future) are not provided, although such comparisons are natural to include and would be beneficial to readers and the scientific community. Please include the following comparisons (when available)
Comparisons with performance studies of other future experiments, such as the
estimated performances of LHCb and ALICE 2 in Run-3 and Run-4, as well as CMS in Run-4 (using the MIP Timing Detector upgrade). For example, estimates of the performance of the upgraded CMS experiment at the HL-LHC with regards to measurements of heavy-flavor particles (including D0 → π + K) can be found here.
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The purpose of the paper is to compare results obtained for D mesons with measurements in other decay channels in the same apparatus. Principal comparison of ALICE-3 capabilities for heavy flavor measurements with other existing and future experiments is present in [1]. Measurements of D meson in the studied decay channels in A-A- collisions have never been undertaken.

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Comparisons with past/present experiments, such as ALICE 1 and ALICE 2. For
example, it should be possible to compare the estimated signal-to-background ratio as a function of pT for D0 mesons produced in Pb–Pb collisions obtained for ALICE 3 with measurements from ALICE 1 and ALICE 2 (at least for a particular centrality and rapidity interval).
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Such a comparison is present in [1]. In this work we compare results for the new decay channels with those reported in [1]. The revised version of the paper now compares S/B ratios for different decay channels and discusses the implications. In conclusion we now discuss the obtained results in more detail to make positioning of the study more clear.

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5. I am missing some discussion of the results obtained. Several items that I feel should be discussed are as follows: The significance of the results, in particular, with regards to the goals of the LHC’s heavy-ion program mentioned at the beginning of the manuscript. For example, given the feasibility of the measurement of open charm mesons at ALICE 3 reported, what insights into the properties of strongly interacting matter could be obtained through such measurements.
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The brief overview of open charm measurements in A-A collisions and physical goals of the measurements is presented in [1]. Such a discussion would be outside of the paper scope. The paper is not an overview of modern situation, it rather presents results for the specific study.

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I get the impression that this study is intended to largely serve as a benchmark
study for the measurement of heavy-flavor particles at the HL-LHC with ALICE 3
in general. If so, please add some discussion of how the results reported in the
manuscript serve as a benchmark for other similar scenarios. For example, do the positive results obtained regarding the feasibility of measuring open charm mesons with ALICE 3 suggest that any other heavy-flavor particles (e.g., Λc) could likely be measured as well?
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We did not consider the obtained results from this point of view and we have nothing to add to the discussion. Reconstruction of Lc and multi-charmed baryons is discussed in [1].

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Lastly, in conjunction with the previous comment (#4), a discussion of how ALICE 3 performs in comparison to other LHC experiments (past, present, and future) would improve the manuscript considerably, i.e., how competitive is ALICE 3? For example, for measurements of D0 mesons, do the results suggest that ALICE 3 exclusively outperforms ALICE 1, ALICE 2, LHCb, and CMS over the pT range studied? How much better, quantitatively, is the estimated reconstruction performance of ALICE 3 vs. ALICE 2? Can ALICE 3 probe regions of parameter space that ALICE 2 and/or LHCb, CMS, etc., cannot?
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Ref [1] claims that ALICE-3 will outperfrom all existing and future detectors at the LHC in respect of heavy-flavor measurements in A-A collisions. We do not discuss this claim in the paper draft since it is a way beyond the scope.

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Minor Revisions
1. For publications that involve studies using Pythia, both the most recent version of the manual and the paper(s) introducing the physics model you are using must be cited according to the Pythia documentation. The following references should be added and cited accordingly:
• SciPost Phys. Codebases 8-r8.3 (2022) [arXiv:2203.11601];
• Eur. Phys. J. C 74, 3024 (2014);
• J. High Energy Phys. 2018, 134 (2018).
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Thanks for the references, these were added to the draft

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2. The font size of the axis labels and tick labels for Figure 1 should be increased, preferably to a size that is consistent with all the other figures provided in the manuscript.
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The Figure 1 was replotted to comply with the comment.

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3. Figure 1a would benefit from the addition of a legend; although the caption clarifies the meaning of the points and the solid line, a visual indication on the plot that makes it immediately clear would be an improvement.
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Legends were added to Figure 1.

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4. Please clarify the percentage ranges stated in the sentence spanning lines 77–80. It is not clear if these are meant to indicate the percent difference or agreement or, instead, the centrality. I get the impression that it is the latter, but this should be clarified; moreover, if this is indeed the case, then the legend in Figure 1b could also be updated accordingly to make the meaning of the percentage ranges more clear.
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We added an explanation to the text - "... , where numbers in brackets are for centrality binning in percentage of a total inelastic nu-cleus-nucleus cross-section". Figure 1b) was modified accordingly.
The Figure 1b was revised as suggested.

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5. It seems that the feasibility of the measurements described also relies heavily on background reduction/rejection. How are the backgrounds going to be dealt with experimentally? Are there any noteworthy detector components/systems of ALICE 3 that will aid in background reduction with regards to reconstructing heavy-flavor decays?
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The comment is not fully understood. A part of the study is evaluation of S/B ratio for D-meson measurements where B stands for combinatorial background. The same detectors that are used for signal reconstruction are used to suppress the background using different single particle and pair selections as described in the text. There are no special-purpose detectors in ALICE-3 for suppression of background. In the studies, we accept only particles that could be reconstructed in the real detector, reconstructed parameters of the particles are smeared according to expected energy/spatial resolution of different subsystems. The same selections that were used for tracks and their combinations in the simulations are foreseen for analysis of experimental data.

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6. Although the ALICE 3 detector is described in detail in one of the cited references, which the reader is informed of, the paper would stand better on its own if some of the key information regarding the ALICE 3 detector was provided in the manuscript (a few sentences should suffice). For example, information on the principal components, detector/subdetector systems, tracking systems, etc., would help the reader better understand how ALICE 3 reconstructs charged particles.
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Such a discussion was added in the introduction.

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7. The sentence beginning on line 161 appears to reference the incorrect figure and should be corrected. Additionally, the end of this sentence, which mentions “a statistical significance of ten” should be revised for clarity. Should this read “a statistical significance of 10%” instead?
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Thanks for spotting the problem with figure number, the reference was changed to Figure 5. We also changed text to say "with a statistical uncertainty of 10%" instead of statistical significance of 10.

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8. The centrality intervals corresponding to the results stated in lines 179–182 differ from those that were previously used in the analyses reported earlier in the manuscript (0–20% vs. 0–10%); please verify that these are indeed correct.
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We fixed the typo, changed 0-10% to 0-20%.

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9. My understanding is that the ALICE detectors are embedded in a magnetic field; however, no magnetic field is mentioned in the manuscript. Please clarify if the feasibility studies reported included a magnetic field or not. If the former is the case, then please specify the strength and configuration of the magnetic field used in the studies; otherwise, if the latter is the case, then please provide a discussion in the manuscript as to why the magnetic field was ignored and how this affects the results.
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The magnetic field was accounted in the simulations but indirectly. The main effect of the magnetic field is that it bends low-pT track trajectories so that they do not reach the tracking system and PID detectors. Magnetic field also defines momentum resolution of the tracker at given spatial/angular resolution of detectors. These effects have been accounted as described in the text:

"For reconstruction and identification of the charged particles it was required that they cross all eight layers of the central tracking system and fall in the acceptance of the time-of-flight (TOF) and ring imaging Cherenkov (RICH) detectors. The subsystem ac-ceptance, efficiency of charged particle track reconstruction and momentum resolution as a function of particle momentum and rapidity were applied as reported in [1]. "

The mentioned (1) efficiency of charged particle track reconstruction, (2) momentum resolution as a function of particle momentum and rapidity were taken as reported in [1] for the case of 2T magnetic field. We explicitly mention in the draft that we use a simplified approach for simulation of ALICE-3 response to D-meson decays. This is one of the elements of simplification. The simplified approach is used in the absence of the Geant-based framework for the full ALICE-3 detector simulation needed to precisely account for all effects of the magnetic field.

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10. The article title could be more specific, as the article seems to focus exclusively on open charm mesons. Either the title should be revised, or some discussion of how these results serve as a benchmark for the feasibility of measuring other open heavy-flavor mesons should be added.
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The title was revised to be more specific. Now it says that 1) we study only open charm mesons and 2) we do that only for specific decay modes.

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11. On line 74, it is mentioned that the p–Pb collision data is not shown. Please either provide the data (in the article or as supplemental material) or a reference to the data if it has already been published.
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The p-Pb data is referenced in Ref.9. Corresponding plot was added to the supplemental materials.

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12. Several statements would benefit from the addition of citation(s) (e.g., line 165).
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The reference was added.

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13. Finally, I feel that the manuscript would benefit from some discussion of the challenges involved in performing measurements of open heavy-flavor mesons with ALICE 3.
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Challenges for the measurement of open heavy-flavor mesons are the same for all experiments. Due to smaller production rate compared to light-flavored hadrons, extraction of D meson raw yields from the invariant mass distributions suffers from huge combinatorial background. This background can be suppressed by reliable hadron identification and high resolution of the secondary vertex reconstruction, i.e. by tight decay topology selections. Both requirements are accounted in the tentative scheme of the proposed ALICE-3 detector, which has superb vertexing resolution and hadron identification with TOF and RICH subsystems in the wide momentum/rapidity range. There is hardly anything else could be done to improve the detector capabilities with the available detector technologies. The situation with open heavy-flavor measurements can be improved by sampling larger luminosities, which can be achieved by using specialized triggers. For example, one can preferentially select events with high-energy photons and then reconstruct D-mesons using decay channels with pi0/photons in the final state. However, performance of the LHC and ALICE-3 DAQ system is not yet well defined and the final conclusions are not possible. The purpose of the presented study is to provide the estimations that could be used later to make the right decisions and choices on the detector and accelerator strategy.

No other comments to answer.

Round 2

Reviewer 4 Report

Dear authors,

Thank you for taking the time to address all of my comments and for providing clear responses along with a revised version of the manuscript, particles-2163463-v2, which includes numerous modifications based on the suggestions of the referees. The revised version is a significant improvement over the original version of the manuscript. In particular, this is apparent in the revised Introduction and Conclusion sections as well as in the overall presentation of the study, which is much clearer.

Regarding my concern with the center-of-mass energies used in the analyses presented in the manuscript, I agree with the response that any differences in the results obtained for, e.g., pp collisions at 13 vs. 14 TeV, will largely be marginal (maybe even negligible); however, given the response of the authors that one of the goals of the study is to "compare the obtained results with those published in [1] for other channels" where the studies do appear to use the correct projected c.o.m. energies for the future LHC runs (i.e., 14 TeV for pp collisions at the HL-LHC, etc.), it is perhaps a bit of a questionable decision—making the comparisons at the same collision c.o.m. energy would be more natural. Nevertheless, it is okay if the authors prefer to keep their analysis at the c.o.m. energies used to allow direct comparisons with the current literature and data instead. This is reasonable given their stated plan to perform future studies using full-event Geant simulations and the center-of-mass energies projected for pp and heavy-ion collisions at the HL-LHC.

Based on the detailed responses provided by authors and the corresponding revisions made to the manuscript, I only have two remaining minor concerns that should be addressed before publication:

Are the units provided on the y-axis of Figure 1a correct? They are written as "(ub GeV/c)^-1, with ub^(-1)"; however, I believe that the correct units should be "(ub c/GeV)". Please verify.
I see no reason to exclude the supplementary figure from the manuscript, especially given that the results from this figure appear to be discussed in the manuscript (lines 125 to 126 of the revised version). Please add the provided supplementary figure to the manuscript as a subfigure of Figure 1.

If the manuscript is revised with these final concerns taken into consideration, I would be happy to recommend publication.

Author Response

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Thank you for taking the time to address all of my comments and for providing clear responses along with a revised version of the manuscript, particles-2163463-v2, which includes numerous modifications based on the suggestions of the referees. The revised version is a significant improvement over the original version of the manuscript. In particular, this is apparent in the revised Introduction and Conclusion sections as well as in the overall presentation of the study, which is much clearer.

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Based on the detailed responses provided by authors and the corresponding revisions made to the manuscript, I only have two remaining minor concerns that should be addressed before publication:

Are the units provided on the y-axis of Figure 1a correct? They are written as "(ub GeV/c)^-1, with ub^(-1)"; however, I believe that the correct units should be "(ub c/GeV)". Please verify.
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Thanks for spotting the typo in the Y-axis title. The figure was corrected and updated in the draft.

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I see no reason to exclude the supplementary figure from the manuscript, especially given that the results from this figure appear to be discussed in the manuscript (lines 125 to 126 of the revised version). Please add the provided supplementary figure to the manuscript as a subfigure of Figure 1.
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Figure 1b was added as proposed.

No other comments to reply.

Author Response File: Author Response.docx