Discussion of sPHENIX note sPH-cQCD-2017-001

[Nathan Grau <ngrau AT augie.edu>]

Hi all,

I have read things rather quickly since I am unavailable over the holiday weekend. I apologize for anything that is not clear. I would be happy to try and clarify my comments early next week. I compiled my list starting the Type B questions/suggestions and then the list of Type A. I fell into the trap of trying to proofread. The significant number of grammar, predication, and pronoun issues made it interesting to read. There are definitely a couple of places that need some pretty thorough revisions before submission. I hope that my suggestions are helpful.

Thanks,

Nathan

Type B:

Page 11, Line 20--23: The sentences seems to imply gamma+jet correlations as a function $x$ can access quark flavor since there will be a mixture of "parton flavors" as the relative pseudorapidity between the photon and the jet is varied. Does this really mean quark flavor or do you mean parton flavor as in quark or gluon? Either way, It isn't clear what this statement adds. You would need to clarify exactly how you can separate quark flavor in gamma+jet measurements. If it is the latter, at leading q+g --> q+gamma, initial state quark vs. gluon mixtures changing will affect the rate of gamma+jets. Could my last sentence be what you meant?

Page 17, Lines 23 -- 30: The sentences focus on the beam rapidity difference between RHIC and LHC. I am ignorant of the freezeout time difference between the LHC and RHIC. Presumably it is longer, which compensates somewhat for the reduced eta-beam y. I don't think that the freezeout time would be twice as long. But what is written is a qualitative argument and factors of 2 could matter.

Page 29, Line 46 -- Page 30, Line 1: What exactly is the 2-APD readout? This should be explained how this can help.

Page 33 Section 3.1 -- This is unfortunately lean. What cuts are used? What kind of simulation -- single particle, p+p, p+A HIJING? What kind of occupancy issues in HI do you expect. This needs more fleshing out. Figure 3.2 is even incomplete. Some of the text on Page 41, Lines 28--35 may be appropriate here.

Page 36, Line 3: The expected resolution is 70%/sqrt(E). Why is this expected? Is this from GEANT or is a citation missing?

Page 37 discussion of jet reconstruction: Why is the jet energy > 18 GeV? What weighting do you use in the anti-kt? pT or E? That matters at forward rapidity and needs to be documented. How do you match the truth and reconstructed jets? Just by position? What is the shift in the jet energy?

Page 41, Line 12--13: The PYTHIA trigger is on pT and not energy. The calorimeters measure energy and the triggering would need to know the module position to trigger on pT. Am I missing something?

Page 42, Line 2--4: How is the EMCAL energy corrected? This is not discussed.

Page 42, Lines 15--16: Why throw out the event? How much does this affect the signal? Presumably the additional electrons and positrons is for conversions and you don't know which pair is conversion and which could be signal.

Page 43, Lines 2--4: Should refer to Q^2 range, i.e Figure 1.7. It would be good to mention precisely what is plotted since I first read that Q^2 would be known to < 0.06 GeV^2 and then wondered if this was the wrong units or what. But you are plotting a stdev(Q^2_meas - Q^2_true)/Q^2_true I guess.

Page 45, Lines 17--18: (2) reason confuses me. The charge of that initiates a parton shower must have little affect on the leading hadron. Gluons fragment and they have zero electric charge. So, I'm not sure how to reconcile this statement with gluons and Figure 4.7. Also, in a string breaking model, the charge of the initiating parton pair has basically nothing to do with what the string breaks into. Therefore, i would think that the charge matters very little in the fragmentation process.

Page 46, Line 15: I don't agree that efficiency is flat at 15%. In fact, I would think that Figure 4.8 would come before Figure 4.7. First identify the statistics hit and then see if the purity of the same increased.

Page 47, Lines 12 -- Page 48: The discussion of the model I'm not evaluating without the final Figure 4.9

Pages 51 -- 53: The discussion of heavy ion observables needs someone to complete rewrite several places. There are too many weak statements include "may" and "could". If this isn't a definitive part of the proposal, then I would consider dropping it completely.

Page 58, Line 1-3: I don't understand what this paragraph means, it needs context either with explanations previous or here.

Type A:

Page 2, Line 5: "extremely" --> "very", this occurs in a few places and I will try to mark them.

Page 2, Lines 17 -- 19: "Studying hadrons and their interactions can teach us about fundamental aspects of QCD as a theory." (otherwise there is a predication issue)

Page 2, Line 31: "The proton, the simplest stable QCD bound state, is..."

Page 3, Line 1 -- 5 remove "It was" at the beginning and "that" just before "inspired"

Page 3, Line 6 -- 8: I don't understand "observed in the lab in terms of hadron".

Page 3, Line 8 -- 10: "Broadly speaking, there are ... that contribute to..."

Page 3, Line 13: "Here, ..."

Page 3, Line 13: Run on. ";" --> "."

Page 4, Line 4: FF needs to be defined here, first use

Page 4, Line 8: "long-standing"

Page 11, Line 3: "Moreover, there is..."
Page 11, Line 4: change "with respect to" --> "compared to"

Page 11, Line 7: "in turn" should be offset with commas

Page 11, Line 9-10: "RHIC will help to further constrain quark and gluon nPDFs."

Page 11, Line 13: remove "furthermore"

Page 12, Line 14: remove "nearly"

Page 12, Line 21: remove "so"

Page 12, Line 27: change "will be" to "is"?

Page 12, Line 35 -- 37: this is awkward and needs to be reworded for clarity. For example, "The BRAHMS experiment measured antiparticle-to-particle ratios as a function of rapidity and observed the net baryon density increases with increasing rapidity."

Page 13, Lines 21 -- 24: "Even with the theoretical and experimental efforts over the past two decades in QCD, we know little about the formation mechanisms of QCD systems such as hadrons, nuclei and the quark-gluon plasma."

Page 14, Lines 13 -- 20: "Experiment results (see, for instance, Ref. [30]) confirm the short duration of the pre-equilibrium stage compared to the later thermodynamic equilibrium stage. The later stage ends with at kinetic freezeout of the hadronic gas at $\tau_{freeze} \sim 20$ fm/$c$. Both pre-equilibrium and equilibrium stages contain several sub-stages ..."

Page 14, Lines 20 -- 23: This reads a bit awkward but don't have time to make a good suggestion.

Page 14, Line 26 -- Page 15, Line 6 can be simplified. "Earlier times of the collision can be studied experimentally through correlations between quantities with large rapidity separation. Any physical correlation must have been established when the two regions were causally connected, as long as any subsequent evolution is local like hydrodynamics. Figure 1.11 shows the space time diagram for heavy ion collisions. The dashed lines are the past light cones of a fluid cell at y=+1.5 and y=-1.5 units at freezeout. These two regions were causally connected very early in the equilibrium stage. Widening the rapidity gap probes earlier in the collision time."

Page 17, Line 1 "As an example, if we take $\eta_1 = -1$, $\eta_2 = 3$, and $\tau_{freeze} = 10$ fm/$c$, we will ..."

Page 17, Line 3: What is "this"?

Page 17, Line 5: New paragraph and "Utilizing correlations...is similar to..."

Page 18, Line 7--8: "...unexpected collective behavior..." and remove "which were unexpected"

Page 18, Line 12: "which" --> "that"

Page 18, Line 13: remove "be the physical" and "of"

Page 18, Line 31: comma after "thus"

Page 19, Line 23: "This" --> "Fixing the hard-scattering kinematics"

Page 19, Line 24: run-on, ";" --> "."

Page 20, Line 2: missing "s" on "hadrons"

Page 20, Line 10: "...this will permit the first comparison between..."

Page 20, Line 13: "... proton's internal spin-momentum..." remove "present in the proton"

Page 20, Line 15: "of" --> "with"

Page 21, Line 8: remove "moreover"

Page 21, Line 13--14, comma around "in fact" or just remove.

Page 21, Line 22 "extremely" --> "very"

Page 23, Line 3: "to extend" --> "an extension of"

Page 27, Line 14: "\eta" -- missing forward slash

Page 27, Line 23: "For the studies in this document" -- changed the second "for" to "in"

Page 27, Line 25: Spell out "R&D"

Page 27, Line 28: "This will worsen the momentum resolution by 40\%."

Page 27, Line 37: remove "and to do so"

Page 28, Line 3: "concern" --> "concerning"

Page 28, Line 5: "facing" --> "face"

Page 29, Lines 14 -- 18: I got confused momentarily by 11x11x37.5 cm on line 15 compared to 5.5x5.5x37.5 in line 4 (and repeated line 17). There is redundant information lines 14--18 and in line 4 of the same page. It is not easy to disentangle. One simple thing is not to repeat the tower size. The flow should be say a block is 2x2, the towers are 37.5 cm long corresponding to 18 X_0.

Page 29, Line 19: "Wavelength-shifting"

Page 30, Line 2: "keeps providing" --> "provides"

Page 30, Line 19: "hadrons" (missing the s)

Page 30, Line 25: Sentence is redundant, remove.

Page 31, Line 1: "wave length shifting" --> "wavelength-shifting"

Page 31, Line 4: "similarly" --> "similar"

Page 31, Line 16: add "to" before "dramatically"

Page 31, Line 16-17: change to "QCD" since it is already defined.

Page 32, Line 9: Spell out DIRC since it is the first usage

Page 32, Line 14: remove "which is" or add a comma before "which"

Page 32, Line 16: "which" --> "and" (and do not remove the comma)

Page 33, Line 1: "In this chapter we summarize the performance evaluation..." (predication issue)

Page 33, Line 27: move "of" after "nominally"

Page 35, Line 9--10: "The effect of the flux return on the energy resolution of the forward hadron calorimeter is quantified using the GEANT4 simulation of sPHENIX with the forward instrumentation." (predication issue)

Page 35, Lines 14 --16: "For thicker steel plate, the average reconstructed energy reduces and the width of the distribution increases."

Page 39, Line 5: add "s" to "interactions"

Page 41, Line 17: should be lower-case $\psi$ on $J/\psi$.

Page 41, Line 22: "an" --> "and"

Page 41, Line 36: "fit" --> "fitted"

Page 41, Line 37: this is the first time that clusters are mentioned. Is it necessary?

Page 41, Line 43: missing "$" around < for math mode

Page 42, Line 27: "event general level-triggered"

Page 43, Line 1: "``One electron'' backgrounds consist..."

Page 43, Line 2--3: "...electron is light meson decays dominated..." and remove "and decays of other mesons."

Page 43, Line 5: "contribute less-than-10%" --> "are less than 10%", "while" --> "and"

Page 43, Line 7: "``Two electron'' background consist"

Page 43, Line 9: "Dalitz decays"

Page 43, Line 12: comma after "cuts"

Page 45, Line 4--6: Remove the word "By" at the beginning and end with "...charged hadrons changes the partonic contribution of the processes initiating the jets."

Page 45, Line 10: change "this selection" --> "selecting $z>$0.5 hadrons with any charge sign"

Page 45, Lines 11--14: This sentence just needs rewritten for clarity. I don't have time to make a clear suggestion.

Page 46, Lines 1--2: "Jets in the acceptance will also arise from gluons and, to a much lesser extent, from proton beam remnants..."

Page 46, Lines 4--5 "contribution shows up 3 times.

Page 46, Lines 16--17 through Page 47, Lines 1--4: I would just kill this paragraph, it adds nothing.

Page 47, Lines 5--11: This is a long sentence. Break it up.

Page 49, Line 8: comma after "energies"

Page 50, Lines 4 -- 7: Reword for clarity.

Page 50, Line 7: comma after "Consequently,"

Page 50, Line 8: no dash with "up-quark"

Page 50, Line 10: -1 is not superscript

Page 50, Line 16: incomplete reference.

Page 50, Line 14: "distributions. But,"

Page 50, Line 15: comma after 0.3

Page 50, Line 20: "two-to-two" --> "$2\rightarrow2$"

Page 50, Line 21: "high x-coverage" --> "high-x coverage", "allows giving" --> "provides"

Page 50, Line 22: "understand" --> "understanding"

Page 51, Lines 1--2: Remove this paragraph, weak transition

Page 56, Lines 4--5: remove "for forward sPHENIX subsystems"

Page 56, Lines 5--6: remove "listed below are for direct costs only and in the cost table we also"

Page 56, Lines 8--9: "...detector design [17]. Hence, ..."

Page 57, Lines 6: remove ",scaled to a total 2044 towers, the cost"

Page 57, Line 12: remove "to"

Page 57, Line 14, 21: "PbW" --> "PbWO$_4$"

Page 57, Line 15: comma after "estimate"

Page 57, Line 23: "done" --> "is"

Page 57, Line 25: "of the one"

--

Nathan Grau

Associate Professor of Physics

Augustana University

2001 S Summit Ave

Sioux Falls, SD 57197
(605) 274-5012