Paper Versions:
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v0: drupal.star.bnl.gov/STAR/system/files/PtoPi_InJets_v0.pdf
v1: drupal.star.bnl.gov/STAR/system/files/PtoPi_InJets.pdf
v2: drupal.star.bnl.gov/STAR/system/files/PtoPi_InJets_v2.pdf

Minutes from first GPC meeting, September 17th, 2024:

====================
Participants:
PAs:  Gabriel Dale-Gau, Olga Evdokimov
GPC:  Jana Bielcikova, Ondrej Lomicky, Isaac Mooney, Richard Witt, Zebo Tang

Gabe presented an overview of his analysis and results and in discussion we clarified several things including choice of the jet pT constituent cut selection, background subtraction, fit of PID nsigma distributions and identified several key points that should be looked at by PAs in the coming weeks listed below. Ondrej and Gabe also started their work on code Q/A and will report on the progress in the coming weeks after Hard Probes.

1. Please check whether in the pseudo-embedding the vertex is aligned to that of the data

Response:

We built a version of the pseudo-embedding that incorporates vertex matching between events used to construct the Au+Au MCE and found that it does not impact the resulting output of combinatorial jets, both in rate of occurrence an per-jet particle yield. The addition of vertex matching greatly increases computational time for this step of the analysis, so we have left out this feature in the final version of the code.

2. It would be good to see and have it included in the analysis note as well, how well your corrected inclusive baryon-to-meson ratio agree with that in the published STAR data in PRL 637 (2006) 161 that is used in the paper.

Response:

We ran PID on inclusive charged hadrons for both systems and found that our method agrees with the previously published results. A figure demonstrating this point had been added to the analysis note and circulated to the GPC via email.

3. Can we also have a figure with R or delta(R) dependence in the paper?

Response:

Statistics for the jet sample used in this paper, specifically the p^{cons}_{T} > 3 GeV/c cut, do not allow for a precision measurement of the p/pi ratio as a function of deltaR. We are studying this dependence for the extension of this analysis to p^{cons}_{T} > 2 GeV/c and hope to present a preliminary plot at QM25.

4. Figure 3: it would be good to include some model comparisons (PYTHIA, HERWIG, AMPT ...) as well as e+/e- data and perhaps also consider plotting explictily p/pi inclusive data points istead of the curve (but we should definitely avoid to have a crowded figure, so it will depend what else will be added to the figure in terms of models).

5. Rewrite the analysis part in the ligth of recent development of background subtraction reported at the meeting (slide 16 and following of Gabe's presentation)

Response:

This rewrite has been completed and can be found in v1 of the paper.

====================

Comments from GPC members on v1 of the paper draft:

Jana:

Title: collisions → Collisions

Response:

Done.

Introduction
L2-L23: It would be good to smooth a bit the flow of the text in this introductory paragraph. I would avoid having a sentence “QGP is novel as it is a hot and dense phase consisting of deconfined quark and gluons”, you could  combine it with the previous sentence.

Response:

Reworked this paragraph for better overall flow. I tried to address all specific comments made as well, detailed below in response to each comment. Removed that sentence and added information to the previous sentence.

The sentence on L10 “Some key signatures of QGP observed through such comparisons …” could be misinterpreted because as written somebody could think that modification of charged particle spectra and jet quenching are necessarily indicating that coalescence mechanisms are at play also for these observables.

 Response:

Removed the mention of coalescence in medium from this paragraph, as it it covered in the next paragraph.

The sentence on L16 “Jet quenching-related phenomena can also be studied through hadron production measurements at high transverse momenta or with fully reconstructed jets.” It also need some tweeks because jet quenching is ideally to be studied with reconstruted jets not “also with reconstructed jets”, but “also” should apply to hadron production (pT) spectra measurements, which are used as a proxy for jet quenching studies.

 Response:

Flipped the ordering of this sentence, and removed use of the word “also”

L26: it would be good to mention here what pT range we refer to when speaking about intermediate momenta

Response:

Added a parenthetical to this line “(2.0 < p_T < 5.0 GeV/c)”

L35: .. very question … it sounds a bit colloquial, I propose to reformulate

 Response:

Changed to “This study searches for modification in in-jet hadro-chemistry by combining…”

L39-L48: as the paper is intended for PRL, I think we do not really need this introductory paragraph  explaining what is covered in each section in case we need to gain some space for the main text of the paper

Response:

This section was added on a recommendation from the HP-PWG conveners. I have removed it for now.

L52 for Au+Au … for p+p → for Au+Au collisions  …. for p+p collisions

 Response:

Done.

L53 sqrt(s) = 200 GeV/c → sqrt(s_NN) = 200 GeV. In fact you could combine this with the previous sentence.

 Response:

Corrected and combined with the previous sentence.

L54-L55:  The STAR Time Projection Chamber (TPC) [6] provides angular location, momentum, and energy loss, dE/dx. → I would add here explicitly … of charged-particle tracks. Perhaps, for a better flow of the text you could consider to say: Charged-particle tracks are reconstructed in the Time Projection Chamber (TPC) [6] that provides angular location, momentum, and energy loss, dE/dx. In addition, the Time of Flight …

 Response:

Done.

L63-64 No need to repeat here TPC and TOF definitions, nor that these are STAR detectors.

 Response:

Removed the unnecessary redefinition.

L66 also no need to repeat STAR TPC, just TPC is sufficient

 Response:

Done

L68 and following: As you use the BEMC HT trigger, you should somewhere explicitly say which threshold you use and whether the BEMC information is used in jet reconstruction. Also from the current paper it is not at all obvious where you actually use minimum bias events and where HT triggered ones. Also add the number of events you analyzed for both systems.

 Response:

Added information on the HT trigger used. Also separated mention of the minimum bias events in this paragraph to avoid confusion. I have also clarified later in the paper when minimum bias events are employed. Added the number of events used as well.

In addition, in this paragraph, you should probably refer to the vertex reconstruction or at least refer other STAR papers relevant for your particular data set.

 Response:

Added two references on vertex position determination. One on algorithmic location and one on VPD. I employ a cut of |vzz - vpd| < 3.0, I haven’t explicitly written that cut in the paper but I can add it if you think it is necessary.

L73 … jet cone sits … → it sounds a bit colloquial, reformulate

 Response:

Changed to “entire jet cone is contained within…”

L76 phi has not been defined yet

 Response:

Added definition in line

L84: I would consider refering to Figure 1 already at the beginning of this paragraph and not wait with it to L92. This will allow the reader to follow the text much better. Reformulate accordingly.

 Response:

Moved this referral to the second sentence of the section to draw attention before explaining the process.

L89: it would be good to be here quantitative and say explicitly how close the centrality and vz bins for mixed events are.

 Response:

Removed mention of “similar centrality and vertex position” from this sentence, given that I ran the mixed event with and without tight vertex cuts and found it had no impact on the resulting correction. A cut on centrality of 0-10% and |vz| < 25 is sufficient for this step. These are the same cuts used for the entire sample of events, so I think it is unnecessary to mention here.

L117-118: When the reader comes to this point, it will not be clear to him, how/why you actually perform PID for the low and high-pT regimes, and its details come only later on L156-L168. Please reshuffle and change the text accordingly to fit. Btw. there is no need to have the PID description repeated in the caption of Figure 2.

 Response:

Reorganized the text to introduce PID earlier in the methods section. I also cut down the text in the caption of the PID figure. One concern I have about this reorganization is that now the PID figure comes first in the paper before introducing jet-track correlation. In order to streamline the number of figures included, I had an overlay of in-jet and underlying event mass squared in the figure describing PID. I think this is a useful demonstration, but perhaps it could be removed, given that now it appears in the paper before discussing the identification of “jet” and “U.E.” I removed this overlay for now, but I can add it back in if others prefer.

L172, 177, 184 Gev/c → GeV/c

 Response:

Done.

L195: As in ALICE, we have not yet published p/pi ratios in jets, I encourage to refer here also to the measurement I have done with my group and a couple of other colleagues in ALICE for Lambda/K0S ratios in jets vs inclusive in pp and p-Pb collisions published in Phys. Lett. B 827 (2022) 136984

 Response:

Updated to employ and argument from physics rather than trying to cite unpublished in-jet measurements. Added a new citation for a paper on Color Reconnection in p+p collisions that uses pythia to model inclusive hadron measurements from ALICE.

“This feature is not unexpected, as data from ALICE shows that the inclusive hadron particle production at low $p_{\rm{T}}$ (around $3$ GeV/$c$) cannot be described in a purely vacuum-like fragmentation framework, instead requiring Color Reconnection (CR) at the partonic level to describe the full particle production~\cite{CR}. Our in-jet selection biases the yield towards fragmentation from hard scattering, removing the low $p_{\rm{T}}$ baryonic enhancement that results from CR.”

For Pb-Pb,  we did not have sufficient statistics and Run 2 analysis is still ongoing, so for these one could only refer to similarly unpublished thesis of my student Vit Kucera.  However, in STAR we are commonly not citing thesis in publications, so if you want to cite something from the LHC, then I would cite published conference proceedings from the above mentioned PhD analyses (QM/Hard Probes … I would need to have a look where it has been shown in public).

Figures:

Figure 1: In the figure and caption it should be explicitly noted what collision system, energy, centrality and pT cuts were used. In addition, please unify the font size and usage of capital letters for “Raw Correlation”, “Mixed Event” and “After acceptance correction” labels. Btw. I would change the labels to read “Raw Correlation”, “Mixed Event Correlation” and “Acceptance Corrected Correlation”. Please also note that the y-axis is completely missing a label!

Response:

Added details on jet collection and collision system/energy to the caption.

Remade this figure with updated axes labels and uniform title sizing. Used your suggested change in titles.

Figure 2: as above, unify font size, usage of capital, letters + missing units of pT bins in the legend, missing collision system and energy labels. Also for clarity the y-axis labels for the left and right panels would be better to have from the outside, not inside the panels. Please also note that for these two panels, the values on y-axis appears to be cut on the left hand side (probably you have overlapping panels in canvas or touch their border). Also unify usage of in-jet vs. In-jet (figure vs caption).

 Response:

Updated figure aesthetics. Added units of pT in legend. Removed overlay in mass squared as I believe it was causing unnecessary confusion.

Figure 3: collision energy is missing in the legend. Caption: no need to say what we see in the figure, i.e. remove the sentence “In-jet ratios show no significant …..”.

 Response:

Added collision energy label to the figure. Removed the final sentence from caption, left only descriptive text.

References: there is no need to spell out paper names, please use the PRL bibtex style

 Response:

I am currently using the suggested bibliography format for PLB papers, \bibliographystyle{nature}, but I agree there is something strange going on with my reference formatting. I am getting errors when I try to compile my bibliography in any other formatting style. I will look into this further in the next few days and send an update when it is resolved. Sending a new draft out now to update everyone on the main content of the paper in the meantime.

Zebo

1. Introduction

I feel the first paragraph need to be rephrased. 

Response:

Implemented significant rephrasing following Jana’s comments as well.

L5-7, I am not sure about the relationship of this sentence and the following sentences. To me, if one don't want to list the evidences of the existence of QGP at RHIC, I would skip the flow and directly go to L8 to discuss about the jets. If one would like to anyhow show some evidence about QGP, I guess flow and reference 1 are not enough.

Response:

Deleted this sentence for now. I can put in more references if defending the existence of QGP is useful, but maybe this is not the place to levy such an argument given that it’s existence is widely accepted.

While jets are defined at L18, it has been discussed in L12 and L16.

Response:

Moved the definition of jets before discussion of jet properties.

L11-14, sounds weird to me. First, three comparisons are listed: 1) significant modification of charged particle spectra; 2) jet quenching; 3) enhancement of relative baryon to meson production. These three things are correlated. For example, jet quenching can result in modification of charged particle spectra; the modification of charged particle spectra includes the enhancement of relative baryon to meson ratio. Second, when you say "indicating the presence of a coalescence ...", it is not clear to me whether you are referring only to 3) or from 1) to 3). Third, coalescence is not the only reason for the enhancement of baryon to meson production in general, radial flow can also enhance the baryon to meson ratio at intermediate pT due to different blue shifts.

Response:

Removed mention of coalescence from this paragraph, as I agree it was confusing to place at the end of such a list. Instead it is mentioned in the next paragraph during the discussion of particle production. Also added specific mention of hydrodynamic flow as a contribution to baryon enhancement.

L39-49, I don't think one need to go into such detail in the introduction for such a letter.

Response:

Following Jana’s comment as well, I have removed this section.

2. Analysis Procedure

I don't recall clearly, but I feel the style for the subsection is different from PLB style.

Response:

I am using the “Elsarticle Bundle” provided for PLB submissions, and this is the default subsection heading style.

https://www.overleaf.com/latex/templates/elsevier-physics-letters-b-journal-template/vdymppdhcwrx

Let me know if this seems wrong to you still, and I can adjust.

L53, the unite for energy is GeV instead of GeV/c. And \sqrt(s) is inaccurate for Au+Au collisions. \sqrt(s_NN) is better.

Response:

Ah yes, this was a typo, good catch.

L54, "angular location, momentum", momentm is often referred to 3D vector and includes the angular location.

Response:

Removed “angular location”. I had originally separated these in the list to highlight where we get information for jet-track correlation.

L56, "velocity of tracks within the detector", I am not sure what detector are you talking about. The measured velocity is not the velocity in ToF, but the average velocity from the primary vertex to ToF by definition.

Response:

Rephrased for clarity, I agree my previous wording was confusing and inaccurate. It now reads:

“provides the relativistic velocity, β, of tracks from the primary vertex to the TOF detector, which can be used to calculate mass.”

L64, TPC and ToF

Response:

Done

L73-L74, repeat what said in L60

Response:

Done

L103, it is not clear to the reader how exactly the region for UE is selected. How far it is away from the jet peak?

Response:

Added two sentences explicitly describing the area selected for UE, and the gap in eta between in-jet and UE selections.

“The area selected for UE consists of two semi-circlular regions with radii of $0.3$ positioned with the flat side of each semi-circle at $|\Delta\eta| = 1.0$. This leaves a gap in pseudorapidity of $0.4$ between the edge of the in-jet selection and the edge of the UE selection.”

I think the discussion on efficiency correction is missing. For example, when you count on proton based on m2 distribution at (relative) low-pT, what is the mass window and what is the efficiency for the mass window. And when extract the yield of pion, do you require the TOF-matching as well to cancel out the TOF-matching efficiency? Are we sure the TOF-matching efficiency is the same for pion and proton? Caution also need to be paid when calibrate nsigma with TOF-match and apply it to those tracking don't require TOF-match. The resolution is likely different. 

Response:

TOF-matching is required for all tracks considered in the analysis, and the TOF matching efficiency is equivalent for proton’s and pions in out pT regime. I have included a plot here of the TOF matching efficiency by particle species from run 14 to demonstrate this. I will add this plot to the analysis note.

Added a sentence mentioning TOF-matching in the experimental setup and datasets section.

Figure 2, since the GeV/c is used for momentum, it is better use GeV^2/c^4 for m2

Response:

Updated units in figure axis label.

Figure 2, left plot, it looks like there is significant pion yield produced in jets and almost no (even negative) proton in jets if UE is subtracted. Does the p/pi ratio shown in this plot consistent with those shown in Fig. 3?

Response:

I have removed this figure for now, as it no longer fits within the logical flow of the paper after restructuring the methods section. The original plot was taken from the actual data used for the analysis, so the extracted ratio does indeed agree with the points shown in Fig. 3. However there are a few factors that made that figure appear misleading to the naked eye: first, the figure was integrated for 4 of my pT bins (2.0 < pT < 2.6), but dominated by yields in the lowest bin (2.0 < pT < 2.2), and second, I applied rebinning to the distributions for this figure in attempt to make the picture clearer to the reader. However, this rebinning made the UE appear more dominant near the center of the mass squared region selected for protons.

3. Results,

The ratio of inclusive p and pi in 0-20% Au+Au is plotted in Fig. 3, but not discussed in this section.

 Response:

Added mention of the inclusive hadron measurement at the beginning of the results paragraph discussing Au+Au results. Also added a sentence contrasting agreement between in-jet ratios and difference in inclusive hadron measurements.

Do you want to discuss possible influence of weak decay of strange baryons? For example, if Lambda is different between in-jets and inclusive, it may have impact on p/pi ratio, as one Lamba contribute one proton and one pion.

Response:

Indeed, weak decays can contribute to the inclusive p/pi ratio, although a tight DCA cut selecting primaries would suppress this contribution. However, what we test is possible shower-thermal recombination in the jet, and lambda decay contributions would play no role here. As we isolate jet peak and subtract background contributions in an entirely data-driven way, the presence/absence of weak decay daughters in the BG is irrelevant - all UE particles are subtracted by the procedure.

Richard:

Second line of abstract:  “compared to p+p baseline.” => “compared to a p+p baseline.”

 Response:

Done.

First line of Fig.2 caption: “in-jet and Underlying Event (U.E.)” => “in-jet and underlying event (UE)”  I don’t think you need to capitalize underlying event and you should only use UE here since you drop the periods later anyway (see lines 104 and 109).  It’s more consistent.

 Response:

Removed this portion of the figure following restructuring comments from Jana and Zebo. If we decide to add it back, I will make sure to unify usage of UE with that of the text.

Lines 62-65:  The sentence is a bit run-on.  Please consider splitting it into something like “A jet-track … fully reconstructed jets.  Particle identification (PID) is achieved using information from the Time Projection Chamber (TPC) and the Time of Flight (ToF) detectors [references].”

 Response:

Split this into multiple sentences following comments from Jana and Zebo as well.

Lines 67-68: “to ensure PID.” => “to ensure uniform acceptance for PID.”

 Response:

Done.

Line 128: The (MCE) definition should go here at first mention.  “… mixed constituent events (MCE).”  And deleted from line 129.

 Response:

Good point, moved this definition up.

Line 132: Starting here and for the rest of the page you refer to “signal” as an entity, i.e.. “… sampled from signal to determine ….”.  But it’s unclear to me what signal really mean here.  Is it a signal distribution (i.e. the population of tracks correlated with the jet axis)?  Is it a signal region (i.e. the anti-kt R=0.3 region around a jet axis)?  It might be good to explicitly define in a single sentence what is referred to as “signal” ,or if the various mentions (lines 140, 148, 150, and 155)are contextually different, consider just saying explicitly each time what signal you mean.

 Response:

Ah yes, this is a good point. For clarity I added the following sentence to the first mention of “signal” in this section:

 “per event is sampled from our collection of high tower events, referred to as ”signal” from here on out, to determine how many tracks to place in MCE.”

Lines 134-136: You mention using only minbias events to create the MCE pool to avoid contamination from hard processes.  But minbias events surely contain hard processes as well, just not as many as purely central triggers.  So, please consider mentioning this fact to indicate that you’ve considered it  Something like “To minimizes the introduction of tracks from hard processes into the combinatorial background, minbias events were used to create the MCE pool.”.

 Response:

Switched to “minimize” rather than “avoid”. I agree this is more accurate.

And, of course, don’t forget the Acknowledgements section.  ;)

 Response:

It is my understanding that acknowledgements are standard and issued by management after collaboration review. Per the star authors page:

“Once the GPC Chair has informed the Collaboration management that the paper has been signed-off by the GPC and is ready for Institutional review the Collaboration management will send the PA acknowledgements for inclusion in the paper draft.”

https://www.star.bnl.gov/central/collaboration/authors/

If my interpretation of this guideline is incorrect and I need to draft an initial version of the acknowledgements, let me know. For now, I have left the section to management.