Response to institutional review papers
Updated on Mon, 2021-06-28 12:29. Originally created by adams92 on 2021-06-23 17:00.
Isaac
Done.
/>/ 129: strongly interacting -> strongly-interacting
If the first word of a phrasal adjective is an adverb, then one shouldn't use hyphenation.
/>/ Fig 3: This plot seems to include the 62.4 GeV from the 2007 paper which is misattributed to the 2017 paper. Either add the 2007 paper citation or remove the point.
I don't follow; the line "Previous experimental results..." cites the 2007 paper (reference #9).
The comments below refer to version 14 of this draft, found here. [ https://drupal.star.bnl.gov/STAR/system/files/Global_Lambda_Polarization_at_3_GeV_v14.pdf ]
Comments yet to be directly addressed are highlighted.
Overall there are many comments expressing concern over our statements of QGP formation and its relation to vorticity and polarization:
- What can we cite to back up that there is no QGP formation at 3 GeV, but "some" QGP at 7.7+ GeV
- We are giving the impression that we're claiming QGP is needed for polarization, so we should rephrase things like "it's unclear what to expect for energies too low to form QGP"
- We talk about polarization in the context of hydrodynamics at first, implying that it's necessary for vorticity and polarization
Ben Kimelman
Comments yet to be directly addressed are highlighted.
Overall there are many comments expressing concern over our statements of QGP formation and its relation to vorticity and polarization:
- What can we cite to back up that there is no QGP formation at 3 GeV, but "some" QGP at 7.7+ GeV
- We are giving the impression that we're claiming QGP is needed for polarization, so we should rephrase things like "it's unclear what to expect for energies too low to form QGP"
- We talk about polarization in the context of hydrodynamics at first, implying that it's necessary for vorticity and polarization
Ben Kimelman
/>/ I have one comment regarding the Fixed-Target setup. On line 202, the
/>/ position of the target is incorrect. In the 2015 test run, the target was
/>/ located at z=210 cm (which is likely where you got the number), but it was
/>/ moved for the official physics run. Starting in 2018, the target has been
/>/ located at z=200 cm.
Corrected.
Wayne State University
Sure, on lines 183-187 the phrase "Our observation ... has significant theoretical implications" may be a bit self-congratulatory (now removed); however, I don't believe it's self-congratulatory saying that it's the lowest energy so far at which Lambda polarization has been measured, and that it's the largest yet observed. This is equivalent to saying we observe a continued trend of increasing polarization with falling energy as we search below the existing studies, which is simply summarizing our observation. On line 467 we say that this rapidity-dependent measurement is uniquely valuable because the other studies did not have access to the most forward-rapidity lambdas, and a potential explanation for the fall of polarization with energy is that the polarization is migrating to forward rapidity. I personally don't see how that is self-congratulatory at all.
I'm not sure if you're suggesting we remove the "high"-pT data point, but I don't think "hiding" data points is justified. I agree that the wording "suggested drop" is inappropriate; we only meant that, while the "high"-pT data point is eye-catching, one should not take that to mean low polarization at high pT. This is now changed to "Although the highest-$\pT$ data point is the lowest, there is no statistical significance in a $\pT$ dependent $\PLambda$."
This is the same notation used in other publications (e.g. the Nature paper); it indicates a global average.
/>/ Throughout, the text uses symbols as words, and even pluralizes them
Done, and hyphenated when used as a phrasal adjective.
/>/ Line 130-134: Viscous hydro has indeed emerged as a powerful tool to
Done.
Done.
/>/
/>/
Done.
UT Austin
/>/ 8) line 247 -- insert comma after "cuts"
Done.
/>/ 9) line 250 -- What was the Lambda efficiency for this 10:1 result?
This is integrated over all Lambdas, so roughly 0.25. I can get a more accurate number if need be.
Aha, you've met the most-altered and refined paragraph of this paper! Yes, it's "just" cowboys and sailors here, but the difference plays a significant role with fixed-target asymmetries. It's not clear exactly why the background is larger for the red distribution but in principle it's not at all surprising that the widths and backgrounds are different between the two decay classes.
Corrected.
Wayne State University
/>/ Why do the authors assume that a QGP is needed for global polarization
/>/ (or just vorticity) to occur? The paper makes this assumption
/>/ frequently. Can the paper defend this assumption, with references? The
/>/ root-s "threshold" for QGP production is not mentioned explicitly (or,
/>/ as far as we know, known) yet the authors assume 3 GeV is too small
/>/ for QGP and then make the additional assumption that a QGP is
/>/ necessary for there to be global polarization. The discussion also
/>/ neglects other potential aspects besides "QGP on vs off," e.g. due to
/>/ increased stopping and the immense baryon doping at lower root-s. The
/>/ paper also seems to assume a strong dependence of the global
/>/ polarization on viscosity - which is likely overemphasised. In any
/>/ case, all this requires references and an explicit and clear
/>/ discussion. There are several places referring to these assumptions,
/>/ including abstract (lines 123-126), and several others for example,
/>/ lines 176-179, 423-425, 460-463...
/>/ The paper starts by saying that hydro models successfully describe a
/>/ large body of measurements at top RHIC and LHC energy assuming a QGP
/>/ fluid. The paper also has the expectation (which we questioned above)
/>/ that the polarization should vanish when the QGP is turned off. Thus,
/>/ the finite polarization measured in this paper suggests the QGP is not
/>/ "off" at 3 GeV. Is the paper thus arguing against one of its main
/>/ assumptions? It was hard to tell from the text. Later, hadron gas-like
/>/ models with transport are shown and claimed they can reproduce
/>/ qualitatively or even quantitatively the observed polarization. These
/>/ same models also predict non-vanishing polarization at higher beam
/>/ energies. Thus, on that basis, one can then argue that no QGP is
/>/ needed to explain the polarization at ANY root-s. It is thus not at
/>/ all clear what this paper is trying to argue here, but it appears to
/>/ making these arguments based on assumptions that we already question.
/>/ It might be better to simplify the narrative to a careful description of
/>/ what was measured, and how will to the standard models work, then
/>/ in a separate discussion section present the thinking about whether
/>/ qgp is required for polarization, possible relation of observed polarization
/>/ to viscosity, etc.. As the paper reads now, the solid and
/>/ beautiful experimental results are mixed up with a lot of conjecture
/>/ on what the results might mean it makes it hard to know what's
/>/ solid and measured vs. what may be.
/>/ This paper is doing a complicated analysis in fixed target mode where
/>/ the acceptance in rapidity is no longer symmetric. The paper mentions
/>/ this (257, 295—297) but we believe space should be taken to provide a
/>/ few plots from the detailed simulations (mentioned line 329, and the
/>/ "suite of tests to check for unexpected systematic effects" line 348)
/>/ to show that this very different mode of star running has not biased
/>/ this complicated measurement. The PAs are certainly experts on the
/>/ main biases - we'd suggest a few plots to comfort the reader on the
/>/ performance of this measurement in the fxt mode compared to collider
/>/ mode. Also, the discussion of the systematic errors (348-352) seems
/>/ insufficient. Effects such as feed-down, which we recall being
/>/ important in previous measurements (although at higher energies), are
/>/ not mentioned at all. All the feeddown is precisely zero? We believe this
/>/ analysis is sufficiently complicated, and the STAR configuration
/>/ sufficiently different to the previous STAR polarization papers, that
/>/ this paper should make a greater effort to show the reader that all
/>/ known systematics are under complete control.
I agree, and we actually had a much more detailed discussion originally on the systematics, etc. but that got parsed down by the GPC to the very brief explanation you now see. Because of the numerous such comments in institutional review, I have added a more detailed discussion.
/>/ A lot of jargon is used, and many technical terms are presented
/>/ without a proper context or explanation.
These were addressed more specifically in other comments; now fixed.
/>/ Sentences like 183-187, 467, are extremely self-congratulatory and
/>/ should just be dropped (or at the very least phrased more soberly).
Sure, on lines 183-187 the phrase "Our observation ... has significant theoretical implications" may be a bit self-congratulatory (now removed); however, I don't believe it's self-congratulatory saying that it's the lowest energy so far at which Lambda polarization has been measured, and that it's the largest yet observed. This is equivalent to saying we observe a continued trend of increasing polarization with falling energy as we search below the existing studies, which is simply summarizing our observation. On line 467 we say that this rapidity-dependent measurement is uniquely valuable because the other studies did not have access to the most forward-rapidity lambdas, and a potential explanation for the fall of polarization with energy is that the polarization is migrating to forward rapidity. I personally don't see how that is self-congratulatory at all.
/>/ Figure 5 Inclusion of the pt=1.8 data point produces the (unjustified)
/>/ impression that the polarization might be decreasing with increasing
/>/ pT. The text says (correctly we think) that the polarization is
/>/ "independent of transverse momentum" on line 412. But, the caption to
/>/ Fig 5 says "There is a suggested drop in PΛ at higher pT, but this is
/>/ not statistically significant." We disagree - there is no such
/>/ "suggested drop" in Fig 5! Please remove this sentence from the
/>/ caption. FIg 6 caption is also somewhat of a mess. Please consider
/>/ putting items like the 2nd sentence of this caption to the main text, and
/>/ the keep the captions to just the clinical description of what is shown in
/>/ the figure (axes, point and line styles).
I'm not sure if you're suggesting we remove the "high"-pT data point, but I don't think "hiding" data points is justified. I agree that the wording "suggested drop" is inappropriate; we only meant that, while the "high"-pT data point is eye-catching, one should not take that to mean low polarization at high pT. This is now changed to "Although the highest-$\pT$ data point is the lowest, there is no statistical significance in a $\pT$ dependent $\PLambda$."
/>/ ---- detailed comments...
/>/
/>/ notation - why is there an overline for P_H?
This is the same notation used in other publications (e.g. the Nature paper); it indicates a global average.
/>/ Throughout, the text uses symbols as words, and even pluralizes them
/>/ sometimes! "$\Lambda$" and "$\Lambda$s" are not words. Use words: e.g.
/>/ "$\Lambda$ hyperons" (which indeed is done often in the paper,
/>/ inconsistently though). Please check globally?
Done, and hyphenated when used as a phrasal adjective.
/>/ Line 130-134: Viscous hydro has indeed emerged as a powerful tool to
/>/ describe AA collisions at top RHIC energy and at the LHC. But hydro
/>/ models have yet to be properly instrumented to deal with the non
/>/ trivial formation time of AA collisions at low RHIC energy e.g., 3 GeV
/>/ presented in this paper. Calculations must account for large baryon
/>/ chemical potential, large stopping effects, and the finite amount of
/>/ time it takes to create the system. So opening the paper with this
/>/ line does not seem appropriate. Of greater interest is how vorticity
/>/ evolves with beam energy and whether and how this may translate into
/>/ the production of globally polarized lambdas. In any case, measuring
/>/ lambda polarization at 3 GeV is surely not about tuning hydro. One
/>/ should instead discuss whether and how vorticity could arise in purely
/>/ hadronic systems (e.g., no QGP) and how these could yield lambda
/>/ polarization on their own.
/>/ Line 133: Remove "so-called"
Done.
Done.
/>/ Line 137: considerable experimental and theoretical effort has focused
/>/ —> considerable experimental and theoretical efforts have focused
Done.
/>/ Line 155-159: The discussion of Cooper-Frye is of interest.
/>/ Clarification as to what the issues are, or might be, is lacking.
/>/
/>/ Line 160: An initial measurement —> The first measurement
Done.
Done.
/>/ Line 164: "significant" is not substantive in this context. Presumably
/>/ you mean non vanishing I.e., with statistically significant deviations
/>/ from null polarization. Or are these measurements significant in some
/>/ other way?
No, just in the sense you thought; done.
No, just in the sense you thought; done.
/>/ Line 167: falls —> decreases, or is decreased
Done.
/>/ Line 168-169: The notion of "energy required for QGP formation"
/>/ is not clearly articulated or justified. Is the production of QGP
/>/ absolutely necessary to obtain a system with finite angular momentum
/>/ and finite vorticity? The paper should defend its position on this point
/>/ with references.
/>/ The angular momentum (precollision) of two nuclei colliding with
/>/ finite impact parameter is non vanishing whether sqrt{s} is close to
/>/ m_NN or much larger. This needs to be clarified.
Maybe I'm missing something; E^2=p^2+m^2, so p -> 0 (and therefore so does J) as 2m_N -> \sqrt{s_{NN}}
Maybe I'm missing something; E^2=p^2+m^2, so p -> 0 (and therefore so does J) as 2m_N -> \sqrt{s_{NN}}
/>/ The authors use the word "here" several times in the paper. This is
/>/ poor form. Phrases such as "in this work" or "In this paper" would be
/>/ more appropriate for the journals considered. Line 175, 188, 251, .
Done.
Done.
/>/ Line 176: "presumably below that which is required" The use of
/>/ "presumably" is not a useful statement in the context of a scientific
/>/ paper. WHy do the authors presume this?
/>/ It would be OK to acknowledge that there is still debate as to whether
/>/ there is evidence for the formation of QGP at energies as low as 3 GeV
/>/ or even higher RHIC energies. But this paper makes this a primary
/>/ assumption without any references. This assumption needs to be shored
/>/ up with some supported evidence in the paper.
/>/ Line 183: The notion of "overlap region" is not defined or discussed
/>/ before this mention and thus stands undefined except for those who
/>/ know the jargon
Changed to "... region of nuclei overlap", which should be self explanatory.
Changed to "... region of nuclei overlap", which should be self explanatory.
/>/ Line 213: It is confusing for readers to use the expression "forward
/>/ rapidity" (which normally associated with positive and "large"
/>/ rapidity) with a value stated as $\eta < -2.55$. Also, "forward
/>/ rapidity" is prime example of jargon.
Added the line "Here and henceforth we use the term ``forward" to mean large $|\eta|$ or $|y|$."
Added the line "Here and henceforth we use the term ``forward" to mean large $|\eta|$ or $|y|$."
/>/ Fig1, legend notation for "antiparallel" looks strange.
I don't follow; do you mean B_{STAR}||-\hat{z} in the caption? In what way does it look strange?
I don't follow; do you mean B_{STAR}||-\hat{z} in the caption? In what way does it look strange?
/>/ Line 241—243: the word "cut" is jargon of the field. A better/clearer
/>/ phrase is "selection criterion". Alternatively, one can state that
/>/ protons are required to have pT in excess of 0.4 GeV/c in order to
/>/ suppress contamination from secondary protons produced
/>/ by spallation processes in the beam pipe.
On the first instance of the word cut, I now specify:``cuts" (selection criteria)
On the first instance of the word cut, I now specify:``cuts" (selection criteria)
/>/ Line 247-249: this sentence is very awkward and should be rewritten.
/>/ It also raises a number of questions about the numerical soundness of
/>/ the analysis near of below a pT of 0.7 GeV/c. The word "unstable"
/>/ raises a red flag. Where is the analysis "stable" and what is meant
/>/ by unstable?
It is now read as "Finally, we select $\Lambda$ hyperons with $\pT>0.7$~GeV/c as results on $\PLambda$ begin to vary when varying topological cuts below $\pT=0.7$~GeV/c and reconstruction efficiency on $\Lambda$ hyperons also becomes very small below $\pT=0.7$~GeV/c."
It is now read as "Finally, we select $\Lambda$ hyperons with $\pT>0.7$~GeV/c as results on $\PLambda$ begin to vary when varying topological cuts below $\pT=0.7$~GeV/c and reconstruction efficiency on $\Lambda$ hyperons also becomes very small below $\pT=0.7$~GeV/c."
/>/
/>/ Line 260: In general, by convention, one should spell out the words
/>/ "Figure" or "Equation" only when they begin a sentence while the
/>/ abbreviations "Fig." and "Eq." Or "Eqs." should be used within
/>/ sentences.
Done.
Done.
/>/
/>/ Line 260-262: The event plane is not a person and thus cannot carry
/>/ out a measurement.
I won't tell my event planes you said that... "measures" -> "estimates" (is better?)
I won't tell my event planes you said that... "measures" -> "estimates" (is better?)
/>/
/>/ Line 266: Remove "so-called"
Done.
Done.
/>/
/>/ Line 270: 40% exactly? As is, it reads like a ballpark number
/>/ and perhaps could be more quantitative.
$=$ ->$\approx$
$=$ ->$\approx$
/>/
/>/ Line 273: "Disproportionately positive" is non-substantive and
/>/ arbitrary.
The point is that there are more positively-charged particles produced, so I feel "Disproportionately positive" is completely appropriate
The point is that there are more positively-charged particles produced, so I feel "Disproportionately positive" is completely appropriate
/>/ Before Eq 2: What is the "sine" term?!? The paper is again
/>/ assuming everyone knows your jargon.
Well, maybe everyone should know my jargon! "sine term" -> "sine term in Eq. 1"
Well, maybe everyone should know my jargon! "sine term" -> "sine term in Eq. 1"
/>/
/>/ Line 276: The polarization for \Lambda —> the \Lambda polarization.
Done.
Done.
/>/
/>/ Same comment for the background. Additionally, consider whether it is
/>/ actually appropriate to consider the "background" as polarized. This
/>/ is dubious at best. The background pair are NOT polarized but their
/>/ distribution may however mimic effects of polarization.
Changed to while the term $\PolarizationCorrelationTerm\bg$ is the false polarization of the combinatoric background."
Changed to while the term $\PolarizationCorrelationTerm\bg$ is the false polarization of the combinatoric background."
/>/
/>/ Line 295—297: "with these effects" is somewhat terse in this
/>/ context. What are these effects and how does one control them?
/>/ A lengthier discussion with a monte carlo closure test would be
/>/ appropriate in this context
Changed to "This symmetry-breaking effect is present in all STAR data sets; however, when running in fixed-target mode there is an additional asymmetry that is correlated with this effect." I believe "This symmetry-breaking effect" should clearly refer to the preceding paragraph.
Changed to "This symmetry-breaking effect is present in all STAR data sets; however, when running in fixed-target mode there is an additional asymmetry that is correlated with this effect." I believe "This symmetry-breaking effect" should clearly refer to the preceding paragraph.
/>/
/>/ Line 324: again, the paper uses symbols as words,
/>/ "where $c$ depends" —> "where the coefficient $c$ depends"
Done.
Done.
/>/
/>/ Line 334: some islands in the Caribbean are dependencies of the
/>/ Netherlands because each island alone is itself a dependency.
/>/ The word you wanted here was "dependence" (or worse but o.k.
/>/ "dependences").
Done; apparently I've been using that word incorrectly for years...
Done; apparently I've been using that word incorrectly for years...
/>/
/>/ Line 336: two more small corrections —> two additional corrections
Done.
/>/ Line 343: on on —> on
Done; are you making fun of my studder?
Done; are you making fun of my studder?
/>/
/>/ Line 348: this text on the systematic uncertainties seems woefully
/>/ inadequate. Here, it would be nice to have a detailed breakdown of the
/>/ various contributions of systematic sources of uncertainties
/>/ considered, perhaps in table form. Such a discussion of the largest
/>/ sources of systematic uncertainties is a standard feature of STAR
/>/ papers, and we think it is even more important to include this
/>/ information when using a completely different star configuration to do
/>/ this complicated analysis. Was a barlow check used? How is the
/>/ treatment for track splitting, merging, and crossing treated in the
/>/ systematic uncertainties?
Addressed above: I agree, and we actually had a much more detailed discussion originally on the systematics, etc. but that got parsed down by the GPC to the very brief explanation you now see. Because of the numerous such comments in institutional review, I have added a more detailed discussion.
Addressed above: I agree, and we actually had a much more detailed discussion originally on the systematics, etc. but that got parsed down by the GPC to the very brief explanation you now see. Because of the numerous such comments in institutional review, I have added a more detailed discussion.
/>/ What about feed down contributions from Sigmas or other strange
/>/ baryons? This does not seem to be discussed in the paper at all and
/>/ yet we recall feed-down was an important consideration in previous
/>/ polarization papers. We understand of course that at this energy
/>/ feed-down should be much smaller. The paper should be clear that this
/>/ correction was ignored (if that is the case). If it was ignored, is
/>/ this choice treated in the systematic error estimation?
We're not considering feed-down at because there's virtually nothing decaying into Lambdas at this energy. I personally don't feel it needs to be addressed in the paper.
/>/ Line 353-354: After a paragraph on systematic errors, using the phase
/>/ "world systematics" is awkward.
Removed.
Removed.
/>/ Line 366-372: The discussion in this paragraph is incomplete or
/>/ unclear. Make this text understandable or remove it?
I guess it belongs more to the preceding paragraph; moved.
I guess it belongs more to the preceding paragraph; moved.
/>/ Line 378-382: Very awkward text. Please rephrase?
Now reads as "Calculations were performed using one equation of state in which the deconfinement transition is characterized as first order and using another assuming a crossover transition; the resulting difference in polarization between these two methods is much smaller than the width of the band."
Now reads as "Calculations were performed using one equation of state in which the deconfinement transition is characterized as first order and using another assuming a crossover transition; the resulting difference in polarization between these two methods is much smaller than the width of the band."
/>/ Line 390-394: on the surface, this paragraph appears to contradict the
/>/ previous discussion.
I'm not sure how; it's stated that the hadronic model reproduces the low-energy data better than the hydro model which isn't contradicted previously as far as I can see.
I'm not sure how; it's stated that the hadronic model reproduces the low-energy data better than the hydro model which isn't contradicted previously as far as I can see.
/>/ Line 401: this sentence is either missing an important clause, or is
/>/ very awkwardly written. Please rephrase.
"predicted that" -> "made such predictions"
"predicted that" -> "made such predictions"
/>/ Line 407: "Born" is the past participle of the verb "bear" only when
/>/ it’s used in the sense of birth. It is also used as an adjective in
/>/ the same sense. "Borne" is the past participle of the verb "bear" in
/>/ all senses *except* the one related to birth -> You want "borne" not
/>/ "born" here.
Done.
Done.
/>/ Line 413: "again similar". Why "again"? Remove "again". State clearly
/>/ what is and is not similar between the results at 3 and 200 GeV.
"... again similar to the dependence ..." ->"... similar to the lack of dependence ..."
"... again similar to the dependence ..." ->"... similar to the lack of dependence ..."
/>/ Line 423-424: What is meant by "viscosity driven decay"? If viscosity
/>/ is suppressing the vorticity of the medium, it means a large amount of
/>/ angular momentum must be dissipated. How is that done? Please clarify
/>/ what is meant in this paragraph.
/>/ Line 428:429: The notion of "migration of vorticity to forward
/>/ rapidity" is rather obscure and should be explained at the very least.
I personally feel this clearly communicates the idea that vorticity is (potentially) dominant at the forward-rapidity region; is there an alternative you is better?
I personally feel this clearly communicates the idea that vorticity is (potentially) dominant at the forward-rapidity region; is there an alternative you is better?
/>/ Line 439: What is "complete" about the range -0.2<y<y_beam? Complete
/>/ might be -y_beam<y<y_beam. Why is -0.2<y<y_beam said to be complete?
/>/ Remove "complete"
Now reads "While all previous measurements were confined to the mid-rapidity region and were unable to reconstruct the most forward-rapidity $\Lambda$ hyperons, the present measurement covers the range $-0.2<y<y_{\rm beam}$ in the collision center-of-momentum frame which reaches the upper limit of $y_\Lambda$ at this collision energy."
Now reads "While all previous measurements were confined to the mid-rapidity region and were unable to reconstruct the most forward-rapidity $\Lambda$ hyperons, the present measurement covers the range $-0.2<y<y_{\rm beam}$ in the collision center-of-momentum frame which reaches the upper limit of $y_\Lambda$ at this collision energy."
/>/ Fig 5 caption: remove "There is a suggested drop in P at higher pT,
/>/ but this is not statistically significant."
Changed; addressed above.
Changed; addressed above.
/>/ Fig 6 caption: the 2nd sentence should nclude specific references for
/>/ "numerous models predict a strong dependence". This sentence also has
/>/ several other grammar issues. It should just be removed and this kind
/>/ of "learning" from the plot discussed in the _text_ not a caption.
/>/ Line 445: "Similar quantitative comparisons with other models will
/>/ provide tighter constraints than the mid-rapidity value alone (figure
/>/ 3)." This is pure speculation about a study that has not been done and
/>/ thus, as a sentence in *this* paper, it is completely useless. Remove
/>/ it.
/>/ Line 457-462: this sounds like a circular argument and it also comes
/>/ in contradiction to statements made earlier in the paper. You say that
/>/ there are models that predict non-vanishing polarization in the hadron
/>/ phase, but in the introduction your motivation made it sound as if
/>/ there was no such thing: i.e., that only a QGP could produce
/>/ polarization and that by turning off the QGP, one would turn off the
/>/ polarization. The paper needs to be much clearer.
/>/ Line 464: "as in other publications" and then you reference
/>/ just [17]. Replace "other publications" with "Ref."
Done.
Done.
/>/ Line 466: "with an effect driven by" is unclear. Please rephrase.
Now reads "... that is consistent with increasing $|\Jsys|$."
Now reads "... that is consistent with increasing $|\Jsys|$."
/>/ Line 467-468: "drops off with with our detector acceptance" we did not
/>/ follow this argument at all. The yield of measured particles always
/>/ decreases near and beyond the boundaries of the acceptance of a
/>/ detector! The more relevant question is how this, and changes of the
/>/ efficiency within the acceptance, can induce biases (or fake
/>/ polarization!) in the measurement. Please clarify this statement.
/>/ 473-480 is one long and **truly awful** sentence. Please try again.
Well now you're just being mean... Now reads "A migration of $\PLambda$ towards forward rapidity has been offered as a potential explanation of the monotonic fall of $\PLambda$ with $\sNN$~\cite{Jiang:2016woz}. Given our observation, such an explanation may be dubious, though this does not dispel such arguments as the state of the system at higher energy is notably different; measurements of $\PLambda$ using the STAR forward upgrade will provide indispensable comparisons to the work presented here."
Well now you're just being mean... Now reads "A migration of $\PLambda$ towards forward rapidity has been offered as a potential explanation of the monotonic fall of $\PLambda$ with $\sNN$~\cite{Jiang:2016woz}. Given our observation, such an explanation may be dubious, though this does not dispel such arguments as the state of the system at higher energy is notably different; measurements of $\PLambda$ using the STAR forward upgrade will provide indispensable comparisons to the work presented here."
/>/ Also the use of the word "dubious" makes it sound as though
/>/ you do not trust your own results.
We're saying the "migration to forward-rapidity" argument used to explain the energy dependence is dubious when considering our rapidity dependence.
We're saying the "migration to forward-rapidity" argument used to explain the energy dependence is dubious when considering our rapidity dependence.
UT Austin
/>/ General comments:
/>/
/>/ The abstract and introduction seem to be written from a
/>/ QGP-hydrodynamic perspective even though, at the energy studied
/>/ here, a hadronic transport picture of the collision seems more
/>/ reasonable. The latter point eventually comes through in the
/>/ text, however the paper starts off from a higher energy, hydro-
/>/ fluid position. Is this intentional? For instance, in the
/>/ abstract the usage of "fluid" and "thermalization" are
/>/ unnecessary.
/>/ Also, I assume that the anti-Lambda yield was very, very small
/>/ since its production requires multi-hadron interactions. Is it
/>/ worth mentioning what the anti-Lambda yields were and saying
/>/ why the analysis only considered Lambdas?
Yes, I forget what the anti-Lambda yields were but they were far, far too small to gain any information from. I personally think it's not worth saying, but I don't feel strongly.
Yes, I forget what the anti-Lambda yields were but they were far, far too small to gain any information from. I personally think it's not worth saying, but I don't feel strongly.
/>/ Previous papers discuss in detail the possible mu-dot-B
/>/ contributions to the global polarization from the transient B-
/>/ field. Why is there no mention of this contribution here? Based
/>/ on the energy trend in Fig.3 and the increasing
/>/ P(anti-Lambda) > P(Lambda) with reduced sqrt(sNN), the mu-dot-B
/>/ contribution to the present measurement could be large.
/>/
/>/ Specifics:
/>/
/>/ 1) line 137 -- omit "considerable"
I think it's fair to say "considerable" here, considering the sheer number of theoretical and experimental work surrounding this subject.
I think it's fair to say "considerable" here, considering the sheer number of theoretical and experimental work surrounding this subject.
/>/ 2) line 152 -- How does the hadronic phase following the hydro
/>/ evolution change the Lambda polarization; a lot, or a little?
/>/ 3) line 168-169 -- Why is a QGP relevant here? Wouldn't sigma-dot-L
/>/ coupling arise in a hadronic gas?
/>/ 4) lines 175-182 -- These lines also exemplify the QGP-hydro
/>/ perspective of the paper mentioned above. Terms such as
/>/ "equilibration" and "QGP droplets" are probably irrelevant here.
/>/ If the purpose is to contrast the 3 GeV system with the 200 GeV
/>/ system then OK, but it is not clear why this higher energy
/>/ perspective seems to be the dominant viewpoint. Setting the
/>/ context perhaps?
/>/ 5) lines 211-212 -- Please say "barrel time-of-flight (BTOF)"
/>/ detector to distinguish it from the eTOF. Was the eTOF used in
/>/ this analysis?
Fixed; and no, no eTOF
Fixed; and no, no eTOF
/>/ 6) line 222 primarily -> mainly, as in 'primary tracks are mainly'
/>/ instead of 'primary tracks are primarily'
Fixed.
Fixed.
/>/ 7) lines 242-243 -- How large was the p-spallation contamination
/>/ below 0.4 GeV/c?
Not significant, but we want to remain consistent with other STAR polarization cuts as much as possible.
Not significant, but we want to remain consistent with other STAR polarization cuts as much as possible.
/>/ 8) line 247 -- insert comma after "cuts"
Done.
/>/ 9) line 250 -- What was the Lambda efficiency for this 10:1 result?
This is integrated over all Lambdas, so roughly 0.25. I can get a more accurate number if need be.
/>/ 10) line 253 -- Lambda frame -> Lambda rest frame (I assume?)
Done.
Done.
/>/ 11) lines 260-263 -- Please move this explanation of symbols in
/>/ Eq.1 to the preceding paragraph where such is discussed.
Done.
Done.
/>/ 12) line 277 -- I do not find the background contribution discussed
/>/ in the paper. I assume side-bands were used, but this needs to be
/>/ discussed in some detail as it is significant for at least half the
/>/ Lambdas.
Side bands were not used as they were in the Nature paper; we use the invariant-mass method which fits the correlator w.r.t. m_inv. according to equations 1 and 2. In what manner should the background contribution be discussed beyond its contribution to equation 2?
Side bands were not used as they were in the Nature paper; we use the invariant-mass method which fits the correlator w.r.t. m_inv. according to equations 1 and 2. In what manner should the background contribution be discussed beyond its contribution to equation 2?
/>/ 13) line 284-294 -- This paragraph is confusing. Isn't the issue
/>/ just the extra tracking inefficiencies for "sailors" compared to
/>/ "cowboys"? Also, why does the crossing inefficiency lead to the
/>/ increased background in Fig.1?
Aha, you've met the most-altered and refined paragraph of this paper! Yes, it's "just" cowboys and sailors here, but the difference plays a significant role with fixed-target asymmetries. It's not clear exactly why the background is larger for the red distribution but in principle it's not at all surprising that the widths and backgrounds are different between the two decay classes.
/>/ 14) line 339 -- What are those rapidity cuts?
/>/ Can they be listed here?
The rapidity cuts are listed earlier
The rapidity cuts are listed earlier
/>/ 15) lines 347-352 -- This discussion of systematic uncertainty is
/>/ far too brief. The fact that the signal in Eq.3 and Fig.2 is only
/>/ ~1/10-th of the raw measurement, while the systematic error in P
/>/ is only 3%, gives one pause. A much more complete explanation of
/>/ systematic errors for this, first FXT data is essential.
Addressed above: I agree, and we actually had a much more detailed discussion originally on the systematics, etc. but that got parsed down by the GPC to the very brief explanation you now see. I am, however, confused about the problem with the systematic error. The extreme behavior seen in Fig. 2 is independent of
Addressed above: I agree, and we actually had a much more detailed discussion originally on the systematics, etc. but that got parsed down by the GPC to the very brief explanation you now see. I am, however, confused about the problem with the systematic error. The extreme behavior seen in Fig. 2 is independent of
/>/ 16) line 366 -- This first sentence refers back to the previous
/>/ paragraph, which includes both hydro and transport models. It
/>/ attributes thermalization to all calculations. Shouldn't it only
/>/ refer to the 3FD hydro model?
/>/ line 375 -- check sign in denominator of rapidity equation, + -> -
What's the matter, you don't like fancy definitions of 0? Good catch; fixed.
What's the matter, you don't like fancy definitions of 0? Good catch; fixed.
/>/ Fig.4 -- Naively we might expect P -> 0 for 0% centrality, but
/>/ the 0-10% bin averages over a finite range of impact parameter
/>/ leading to non-zero, global L. A comment to this effect with
/>/ the Glauber estimated range of b would serve to make the point
/>/ that the first datum is not expected to trend down to zero.
/>/ Or is it?
The first point shouldn't be zero for precisely the reason you say; I personally think it's obvious and not worth stating explicitly but I'm not stubborn about it if you feel strongly.
The first point shouldn't be zero for precisely the reason you say; I personally think it's obvious and not worth stating explicitly but I'm not stubborn about it if you feel strongly.
/>/ lines 395-400 -- I don't see why these results provide any evidence
/>/ of thermalization and temperature at this collision energy. Don't
/>/ the transport models provide counter-evidence?
Wlodek
Wlodek
Just one comment in support of a comment from WSU:
>/ Why do the authors assume that a QGP is needed for global polarization
/>/ (or just vorticity) to occur?
/
Lambda polarization was observed in 1976 at Fermilab in Proton Beryllium Scattering. No QGP there.
Lambda0 Hyperon Polarization in Inclusive Production by 300-GeV Protons on Beryllium.
DOI:10.1103/PhysRevLett.36.1113
https://inspirehep.net/files/0039d31f2b126ed540695b9fd6cb167a <https://inspirehep.net/files/0039d31f2b126ed540695b9fd6cb167a> <https://inspirehep.net/files/0039d31f2b126ed540695b9fd6cb167a <https://inspirehep.net/files/0039d31f2b126ed540695b9fd6cb167a>>
Isaac
Regards, Wlodek
Wlodek, this is a polarization, but not a *global* polarization. The
distinction is that the polarization is along a global axis (the angular
momentum of the system) rather than an axis perpendicular to the plane
spanned by the Lambda momentum and the beam direction (the "production
plane" -- as in the paper you have cited). The physical mechanism for these
effects are different. Even if you have a production-plane polarization
aligned with the event-plane (which may not be the case) such a
polarization is explicitly cancelled in even-acceptance. For this
measurement the acceptance may not be even, but the methodology the authors
made to cancel a different effect actually also removes any such possible
contribution.
- Isaac Upsal
What Isaac said...
Rice
What Isaac said...
Rice
/>/ Here are the comments as I've compiled them. Naturally some are rewritten to combine comments from multiple perspectives.
/>/
/>/ General comments:
/>/
/>/ 1) The authors state (without source) that 3 GeV likely does not have a QGP (a statement not many would challenge) and that this constitutes proof that physics mechanisms which give rise to global polarization do not require a QGP.
/>/ I do not think it is a general assumption in the field that global polarization requires a QGP. The authors might not agree that this is stated, but I believe it’s implied and a reader unfamiliar with the measurement would get this impression.
/>/ If the only previously-published result was from 200 GeV this seems like a reasonable statement, but it seems to ignore the BES-I measurements. This is the first proof that polarization does not require a QGP if you have concluded that there is no QGP at 3 GeV but some at 7.7 GeV. This datapoint is extremely precise compared to the BES-I measurement, so perhaps it is a matter of degrees, but one could combine Lambda + AntiLambda for the three lowest BES-I data if you want to make a comparison.
/>/ Perhaps the language can be softened and more emphasis can be put on how the precision of the data at low rootS is helpful for drawing these sorts of conclusions. Examples of this innuendo are 168-169 and 448-453.
/>/ 2) Similarly the first few paragraphs of the introduction discuss the QGP and hydrodynamics in great detail. Some of this might not be so relevant to the measurement, which is interesting on its own.
/>/ 3) We find the physics statements made by comparing to 3FD (388-394) to be excessive. It's a 30% overshoot, but (seemingly) statistically insignificant. Furthermore it seems to rely on some sort of reasoning that hydro working implies QGP. The hydro has error bars, but, of course, we can’t know if there are other systematic sources of error in the model. It’s unclear if all calculations are corrected for feed-down effects, but it’s clear that UrQMD is not. These additional points still pale in comparison to the first one though, which is that the 3FD does not seem to be inconsistent with the data.
/>/ 4) Line 175 to 187: The paper says a lot of important questions raised by the observation. However, the logic between the observation to these key questions is not clear in the paper. It would be better to expand this part in the conclusion paragraph. This whole discussion could be moved to the conclusion.
/>/ 5) The authors could mention that the corrections they make for uneven acceptance also remove possible contributions from production-plane polarization.
Done.
Done.
/>/ 6) It should be explicitly stated that this is a midrapidity measurement the collision-frame rapidity of this measurement is -1 to 1.
Done.
Done.
/>/ 7) It is a pity that the authors put significant work into generalizing the polarization measure for this difficult geometry and this work is reduced to a few paragraphs. We have a description in the analysis note, but it would be nice to have some more details public. The target journal is PRC so there should not be particular words/page limitations.
Yes, I feel the same; however, my rather lengthy explanations were parsed down already by the GPC to what you see now.
Yes, I feel the same; however, my rather lengthy explanations were parsed down already by the GPC to what you see now.
/>/ 8) Consider adding the 200 GeV measurements of the polarization dependence on rapidity, pt, and centrality. If so you could consider scaling them to fit on the same plot (?)
I personally think it's better kept separate, especially with the models at 3 GeV; they each make the same point separately, rather than in Fig. 3 where they are together part of a larger overall trend.
I personally think it's better kept separate, especially with the models at 3 GeV; they each make the same point separately, rather than in Fig. 3 where they are together part of a larger overall trend.
/>/ Detailed response
/>/
/>/ Title: Isn't it PRL style that ‘Polarization’ and ‘Collisions’ be capitalized?
I'm not sure about PRL, but it's not the case for PRCL.
I'm not sure about PRL, but it's not the case for PRCL.
/>/ Abstract: The abstract should first state what was measured and then what was observed. It should cite the number here as in 355.
/>/
/>/ 122: for “Direction of global angular momentum” sounds like jargon. I think this is because of the (unnecessary) ‘global’. We think ‘global’ should be removed. Even so it may not be obvious to a reader unfamiliar with the field what the angular is or where it’s coming from. The authors might add a statement about how the finite-size of heavy ions allows for this to happen in the abstract or introduction.
/>/ 123: The → An
I disagree; I think "The" is more appropriate
I disagree; I think "The" is more appropriate
/>/ 123: "Substantial" should be quantified. A number.
Done.
/>/ 129: strongly interacting -> strongly-interacting
If the first word of a phrasal adjective is an adverb, then one shouldn't use hyphenation.
/>/ 140: "very recently" -> ", very recently,"
Fixed.
Fixed.
/>/ 161: This paper also includes a 62.4 GeV measurement.
Fixed.
Fixed.
/>/ 160-174. Results from ALICE could be mentioned.
Done.
Done.
/>/ 169: The energy for QGP formation should be quantified, if only roughly, even if assumed on some basis.
/>/
/>/ 175: "here" can be dropped
Addressed above; fixed.
Addressed above; fixed.
/>/ 217: this is incredibly nit-picky, but I get -5.49. I'm using tile size = 9.64 cm and distance = 375 + 210, so
/>/ root [0] TVector3 f(0,0.5*9.64,375+210);
/>/ root [1] f.Eta()
/>/ (double) 5.4920021
Fair enough! Fixed.
Fair enough! Fixed.
/>/ 221: People outside of the field do not know what ‘centrality’ is. Perhaps add a sentence giving an intuitive feeling.
Now reads "The centrality of an event, which describes the degree to which the colliding nuclei overlap,..."
Now reads "The centrality of an event, which describes the degree to which the colliding nuclei overlap,..."
/>/ 222: delete "primarily"
Originally I didn't have this, but apparently there is a very high chi^2 cut as well, and I believe there might be primary-vertex refitting.
Originally I didn't have this, but apparently there is a very high chi^2 cut as well, and I believe there might be primary-vertex refitting.
/>/ 245: The sentence starting at l. 245 is not clear currently. It can be read: varying topological cuts become very small. ? More punctuation or shorter sentences.
Reworded; now reads "Finally, we select $\Lambda$ hyperons with $\pT>0.7$~GeV/c as results on $\PLambda$ begin to vary when varying topological cuts below $\pT=0.7$~GeV/c and reconstruction efficiency on $\Lambda$ hyperons also becomes very small below $\pT=0.7$~GeV/c."
Reworded; now reads "Finally, we select $\Lambda$ hyperons with $\pT>0.7$~GeV/c as results on $\PLambda$ begin to vary when varying topological cuts below $\pT=0.7$~GeV/c and reconstruction efficiency on $\Lambda$ hyperons also becomes very small below $\pT=0.7$~GeV/c."
/>/ Eq. (1): one too many closing brackets in the equation, suggest to remove the first “)” since the next one looks more like “\right)"
Good catch! Those are surprisingly easy to miss. Fixed.
Good catch! Those are surprisingly easy to miss. Fixed.
/>/ 258: ‘Operating STAR in fixed-target mode’ should, perhaps, be ‘Operating RHIC...’
Good point; changed to RHIC/STAR
Good point; changed to RHIC/STAR
/>/ 328: vorticity-driven is a hypothesis, not something STAR measured, and need not be mentioned here. You could instead say spin alignment to a global direction.
/>/
/>/ 330-334: Perhaps I'm mistaken, but isn't the even acceptance of those previous analyses also important. I think it should cancel even with large directed flow, and that seems like a more central point.
Yes, good point; fixed.
Yes, good point; fixed.
/>/ 343: “on on” → “on"
Addressed above; fixed.
Addressed above; fixed.
/>/ Fig 2 caption: consider v1 → “directed flow”
Added v_1 definition after first instance, so now should be fine.
Added v_1 definition after first instance, so now should be fine.
/>/ 354: “world systematics” seems strange. Maybe ‘world data’ (?)
Addressed above; fixed.
Addressed above; fixed.
/>/ 358: state the lambda threshold value
/>/
/>/ Fig 3: Using a slightly-larger star for the symbol might not be very clear, but I won't insist.
I'll keep it as is unless others feel the same.
I'll keep it as is unless others feel the same.
/>/ Fig 3: This plot seems to include the 62.4 GeV from the 2007 paper which is misattributed to the 2017 paper. Either add the 2007 paper citation or remove the point.
I don't follow; the line "Previous experimental results..." cites the 2007 paper (reference #9).
/>/ Fig 3 caption: “b” → “impact parameter”. The same for figures 4-6
Done.
Done.
/>/ 384: As mentioned previously the agreement between UrQMD or 3FD and the data are nearly statistically identical. It is not possible to say that one agrees and the other doesn't at various energies as the text now does. So the plot does not suggest anything statistically meaningful and the statement in lines 390-394 cannot be made.
/>/
/>/ 395-400 This seems like a subject for a theory discussion, not a statement STAR could or needs to make with any confidence. Actually the paragraph seems vague and confusing as a whole. For example: 401: have predicted what? it is not clear.
/>/
/>/ 389: higher energy -> higher-energy
Done.
Done.
/>/ 403: This looks like an unfinished sentence. Actually what's happening is that the "that" in line 401 is doing a lot of work and I think it's actually unclear what it means. I think it should be clarified what exactly is predicted.
Addressed above; fixed.
Addressed above; fixed.
/>/ 407: born → borne
Done.
Done.
/>/ Fig 6: add: ... no dependence within large statistical uncertainties.
Done.
Done.
/>/ 466-470: we have the most forward-rapidity Lambdas of what? Of the two non-trivial measurements of polarization that have published this plot (namely this one and STAR's more-recent 200 GeV paper)? Can't we get Lambdas with greater backwards rapidity in 7.7 FXT collisions? Is this compared to all other detectors (e.g. HADES)?
We have access to the most forward-rapidity lambdas of all emitted Lambdas. The specific wording used is "... the $\Lambda$-hyperon yield distribution with respect to $y$ drops off with our detector acceptance; we therefore have access to the most forward-rapidity $\Lambda$ hyperons." but perhaps this isn't clear?
We have access to the most forward-rapidity lambdas of all emitted Lambdas. The specific wording used is "... the $\Lambda$-hyperon yield distribution with respect to $y$ drops off with our detector acceptance; we therefore have access to the most forward-rapidity $\Lambda$ hyperons." but perhaps this isn't clear?
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