sPHENIX EMCal discussion

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

Hello sPHENIX Calorimeter-ers,

Congratulations on all the hard work on the EMCal and HCal and test beam that went in to producing this draft manuscript.    There is a wealth of useful information presented and this puts the work on a good path for jet measurements in sPHENIX.  

I have included comments/suggestions below.   I recommend a full re-pass on the manuscript before a collaboration-wide release.   As a minor aside, I would prefer a version with all the line numbers instead of every 5 lines.

Sincerely,

Jamie

abs - "design ... were" -> awkward, designs were

abs - "to measure jets" -> this is quite restrictive even as the sPHENIX program might be broadening...  perhaps something like measure jets, heavy quarkonia, and associated observables..."

abs - The 15%/sqrt(E) and 100%/sqrt(E) are delicate numbers...     For the EMCal, the claim is that sPHENIX works for EIC.    Should we say that the 15% is specifically specs for the heavy ion program and may be exceeded?   For the HCal, is that the resolution of the combined calorimeter system?   or is that for jets?    Typically the jet performance is about 20% worse than the single hadron resolution for the combined calorimeters (e.g. CMS I believe).    

abs - split the sentences on the EMCal and HCal design - awkward sentence as it is now

line 1 - "sPHENIX is a proposed general purpose detector" - I think this is not true - sPHENIX is targeted to take advantage of 15 years of knowledge gain in the field and RHIC luminosity increases - so it is the opposite - quite targeted.

line 5 - "is especially designed" -> "is specifically designed"

line 6 - "occur early ... to probe" -> this implies the scattering occur early for the purpose of probing...   re-phrase

line 9 - "and tracking system" -> "a tracking system" and then watch for "have" versus "has"

line 12 - "preparation of the full construction" -  awkward sentence - the prototype was built and tested to verify the design performance and converge on the final full construction design....

line 18 - "Y suppression" -> "for the measurement of the Upsilon states and heavy flavor...."   suggest to also write out "Upsilon" here.

line 21 - "was built and testing using ..." it was not built using the Team Beam Facilty -- a comma might help or a sentence restructure

line 27 - one needs to have a sentence saying that sPHENIX is re-purposing the BaBar superconducting solenoid first - otherwise it is confusing...   One might also mention the inner radius of the magnet here.    

One additional piece, the BaBar detector had a rather non-compact EMCal - there is lots of space if you do not have the inner HCal (or for that matter a space clearance for the RICH).    Someone familiar with BaBar will find this sentence odd.    Of course, I am not sure if one wants to explain that this sPHENIX design is a compromise on cost and so moving part of the HCal inside saves money and further constrains the EMCal depth.

line 29 - *** My understanding of some aspects of the design may be out of date (so apologies), but I thought the 2-d projectivity is important for e/pi separation for the Upsilon program in particular (see Jin's studies), and expect that it has essentially zero impact on the jet program.     

line 33 - "an Upsilon decay to dieletrons"

line 34 - "typical cluster size is about 340 MeV" - that is a cluster energy, not size?   What is meant here?

line 35 - this seems like a very odd argument - though I realize that our justification for the specs on the resolution have always been an issue.    The EmCal resolution does not contribute to the Upsilon mass resolution - it only contributes to the signal / background via the e/pi separation.    Again, note that the EIC argument also may enter here...   One can say that it does not pay to have an EMCal resolution in central AA better than about 15%/sqrt(E) because better resolution is only then dominated by underlying event fluctuations.   We have shown that a performance dominated by underlying event fluctuations delivers the physics.    And then mention EIC?

line 40 - The phrasing is unclear to me here.   There was a SPACAL design (much earlier than work by the UCLA group) - in fact picked up by the Jack Sandweiss group at Yale back in the 1990's for the E864 calorimeter.    Here when it says the "SPACAL blocks" it seems to refer to the UCLA design -- perhaps a specific designation is needed to clarify this from the original SPACAL design?

line 45 - "by either by vibration" ?

line 45 - why is the density approximate?   is there an exact number?   Also it would be good to provide a comparison with pure tungsten.

line 49 - here is describes "blocks" and there is some confusion in the text/tables (and/or my mind) about "towers" versus "blocks"

First here it says the back of the block has a height of 2.39 cm, the front has a height of 2.07 cm.     This is almost square whereas the "block" shown in Figure 1D looks like a rectangle at the end (maybe two square towers together in a block)..   

Second, it would be better to say the "towers" (?).... are square on the end with the side dimension XX cm.    Height is odd here.

Table I - I find these values confusing and somewhat random.    First, towers and blocks need to be sorted out.  The tower length is listed at 144 mm, but in the text it is 13.9 cm? 

A few sentences that really start with tower, block, module, sector would really help.

line 52 - again check for consistency, and also explain why (are they glued together, mechanical support, etc.?)

line 68 - "at the same time to insure" - I would rephrase, "at the same time" as what?    during a period of the curing, pouring, what frequency of vibration (there are huge studies on this to maximize packing fraction).

line 75 - 1 x 2D may not be clear to some readers...

line 76 - "design developed by Oleg Tsai" - reference is needed here.    Also, is SPACAL the right word?

line 81 - the light guide is not larger, but smaller on the readout face - thus "an area large enough" is opposite by my reading

Figure 1 - the caption refers to a-f, but there are only 4 diagrams a-d.  

Figure 3 - cannot read the text, unclear thus what is shown...

line 87 - "spectrometer beam" - this is not described, what beam?

line 102 - "71 %" - no space needed, also is there an uncertainty on this value?

line 103 - I am not following this discussion.   Figure 4 does not look flat, and so I am just not understanding the "insensitive to any non-uniformities"

Figure 4 - not sure from the caption what is really shown and also on the flat part of the graph?

line 118 - convert to a real equation (i.e. not sqrt())

line 120 - "the beam hits the light guides" - again what beam, in what situation?

line 124 - THP ?   Again some introduction is needed here...   

line 128 - Vikuiti ERS - what is this?  reference?   properties?

line 133 - "pcb" -> "PCB"?

line 134 - "GE Silicones .." - needs reference and properties

As an aside, what are the aging and flow properties for this optical grease.   I would think this might be a concern for the duration of sPHENIX?

line 146 - again, what is this resolution really?   hadrons into just an HCal, into the EmCal + HCal, jets?    This is not really so modest...   

line 156 - probably need to say for the test beam data taking..

line 159 - It would be good to add that the three pieces model the cryostat (middle) and the container?    Also, mention the radiation and nuclear interaction lengths...

line 174 - what is the coating - at least the properties and a reference?  I know it is proprietary, but the properties must be known.

line 184 - I note that there is no optical grease mentioned here, in contrast to the EMCal coupling

line 188 - "estimate" or measured?

line 192 - "by and industrial" - "by an"

line 197 - "are the" -> "are then"

line 208 - "both long term and ongoing" - suggest to remove this phrase

line 211 - "for each" is awkward - just remove

Figure 8 - where is that first mentioned in the text?

line 228 - good to mention the UV LED with properties and reference

Figure 9 - needs label for "inner" and "outer"

Here I note that much of the discussion uses nomenclature of inner radius and outer radius, but there is no diagram of the calorimeters in sPHENIX (maybe good to add at the start).   Since the diagram for the test beam setup is linear (no obvious circle for a radius), some of these references are confusing.

Black text cannot be read.

line 255 - This needs some explanation - is this good, bad, ?  

line 271 - "cardboard" - just regular cardboard?    How was that made light tight?

line 293 - how is phi defined for the diagram?

line 293 - "In each run, four vertical"

line 302 - "AD timing samples" - some explanation is needed on the readout first...

For the second half, it will need a careful read by a different set of eyes.   A couple quick items that I noticed.

Figure 27 - legends cover part of real distributions (not optimal).  Also, all the numbers are too hard to read anyway.  

Numbers are far too small on many of the figures.  

If one gets 12.3%/sqrt(E) + 2.6% should that be quoted in the abstract (key result relative to spec)?

Figure 37 and others need very clear labeling as to whether they are HCal I+O only (with no EMCal in front) or with all three as we will have for real hadrons in the real sPHENIX.

In the acknowledgements, we have also had technical assistance at the University of Colorado Boulder for putting together the test stand and characterizing the tiles.

Also, some groups like UIUC are NSF funded and so should that be noted in the acknowledgements.    I know that was an issue for the PHENIX RPCs - funded by NSF, but with clear DOE funds for group / technical support.

  

  

On Mon, Sep 26, 2016 at 3:55 PM, Ron Belmont <ron.belmont AT colorado.edu> wrote:

Dear HCal and EMCal enthusiasts,

The T-1044 2016 paper is ready to be reviewed by the experts prior to our release to the collaboration at large.  The draft is linked on the test beam publication page (https://wiki.bnl.gov/sPHENIX/index.php/T-1044_publication) and can be accessed directly here: https://wiki.bnl.gov/sPHENIX/images/e/eb/Beam-test-results.pdf

Please note that, as always, editing the Overleaf is not allowed without first consulting with the section chairs as listed on the test beam publication page.

In principle we have no customary or official deadline for comments at this point, in contrast with official collaboration release, but we do want to release to the collaboration as soon as possible, so please send comments not more than two weeks from now (the sooner the better).

Best regards,

Abhisek, Jin, Megan, Vera, and Ron (the test beam publication committee)

--

-----------------------------------------------------
Ron Belmont
Postdoctoral Research Associate
University of Colorado, Boulder
ron.belmont AT colorado.edu
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