Discussion of sPHENIX note sPH-cQCD-2017-001

[Jamie Nagle <jamie.nagle AT colorado.edu>]

Hello All,

I have read through the LOI draft dated June 1, 2017 (as sent around on May 23, 2017).   Let me start by saying that from my heavy ion perspective, I would love to have additional sPHENIX calorimetry coverage from eta = 1-4 units.   I believe that this would really help the jet program in two regards.   First, you could make a version of Figure 1.8 with a outlined region with the kinematic coverage of just the sPHENIX barrel for photon-jet and jet-jet and then another (different color) outlined region with the extended kinematics with the additional forward calorimetry.     That would be a nice money plot - and it applies to p+p, p+A, A+A.    One could also make a projected uncertainties plot (just statistics) for jet pT spectra at different pseudorapidities.    Second, the extended coverage would be very useful for different techniques of subtracting the underlying event including flow fluctuations and looking for very large angle medium response.   I think just as an argument for the forward calorimetry at least from units 1-3, this will resonate.

Now for the document as a whole, I think it is important to have a very crisp connection for non-experts from a short (longer is not more helpful).   I will probably get this wrong (so apologies), but here is my attempt...

The fsPHENIX goals are to address:

(1) how the proton works?   spin-spin and spin-momentum correlations of partons inside the nucleon which gets at the physics of orbital motion etc.

       Where is the money plot (just one)?   Figure 4.9?    Needs to be larger and very sharp.    Is there a way to make a 

       single panel with the theory and projected fsPHENIX uncertainties?     You want fsPHENIX projected measurement          clearly highlighted on the figure.

       The case is filled with jargon.   That is fine as long as up front the basic motivation is given - in a paragraph.

       There is also a sentence on line 36 that says "and some can uniquely be addressed in transversely polarized

       hadron-hadron collisions" -- This needs a very clear back up - what is unique, and why...    Just resolving the

       origin for Figure 1.1 is unique, but not the real motivation.

(2) how antiquarks move around in nuclei?    antiquarks only come from quantum fluctuations in the proton and in nuclei and can tell us a lot about QCD.    Antiquark distributions in protons have already shown some big surprises.   Measure antiquarks via DY in p+A.    

       Where is the money plot?  Apologies here, but I do not find any such plot.   Something with the x-distribution of                  anti-up or anti-down in nuclei at a given Q^2 with experimental uncertainties ...  overlay with EPPS16 fit results.

       Figure 1.7 is okay, but not a delivery/money plot.    

       A couple other questions on DY.   For Figure 1.7, what is the DY mass range assumed to be accessible?   

       I am also interested in how one compared the deliverable from forward direct, real photons to these DY virtual

       photons.    I think that needs a crisp answer/discussion.

       Anti-quarks are unique (?) to hadron-hadron, in other experiments by running to separate proton+neutron and

       proton+proton one can get at anti-up versus anti-down.   That is not the case here...   One gets at the sea via

       DIS, so the real argument is in the kinematic coverage?

(3) Hot QCD studies - My personal impression is that this text (Section 1.2.1, 1.2.2, and 4.5) actually worsen the case.

       Where is the money plot?  - Figure 4.13 - a mostly blue color plot?     There is no good evidence that overall

       texture or energy decompositions reveal anything.    In fact that was something PHOBOS and ATLAS/CMS 

       with large coverage can mostly do, but just has not been particularly fruitful.   The summary is that "this exercise

       clearly demonstrates that the simultaneous 2-D Fourier transformation gives n overall look at the correlation

       of observables."      

       The Section 1.2.2 section also bothers me because it completely downplays what people at RHIC have been

       learning about small systems.  "Adding a forward spectrometer to sPHENIX will allow similar measurements 

       to be performed at RHIC energies where it is currently unclear to what extent these phenomena persist." 

       The only reference is Ron Belmont's nice QM proceedings.    Maybe the PHENIXian's involved in this writing

       missing all our published papers, PPG205, PPG206 in progress, etc.    Also, what is smaller than p+Au, well 

       p+Al which we have also shown nice results from Qiao on at QM17.    How would forward sPHENIX better

       measure correlations in the only smaller system p+p left?    There are no figures, no projections...

I would actually remove the entire item (3) or replace it with something as mentioned above about extending calorimeter coverage for jet physics in A+A.    Simple and with money plots is better than hand waving arguments that also are not up to date and with no specific measurement (e.g. the small system section with nothing in the performance section).

The overall document needs another edit pass for type-O's etc.   In addition, there are a large number of qualifiers on many sentences that makes it hard to simply read smoothly.   

Sincerely,

Jamie

 

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