sPHENIX is a new detector at RHIC.

[Craig Woody <woody AT bnl.gov>]

Dear All,
   I think the LoI looks very nice and provides a very reasonable plan 
as to how sPHENIX could evolve into a very capable EIC detector that 
would be ready to take physics data at the startup of eRHIC. It's clear 
that a lot work went into preparing it and it contains a great deal of 
very useful information. I didn't try and go through the entire document 
and edit it in great detail,  but I thought I would share a few detector 
related comments.
   The first is regarding the DIRC. Figure 2.1 shows the DIRC which 
looks like it goes back to the original ePHENIX LoI.  It shows the DIRC 
bars extending for ~ 5 m, which are presumably the actual radiator bars 
used by the BaBar DIRC. We talked about using these without any 
modification at the time of the ePHENIX LoI (circa 2013-2014), but in 
the present detector concept in which we would have either a focusing 
DIRC or a TOP DIRC, I don't see why the radiators bars would need to 
extend out to 5 m (assuming we would use a solid state photodetector 
like a SiPM or APD, or a MCP). We don't show the expansion volume that 
was part of the ePHENIX LoI, so we must be assuming we would use some 
form of readout of this type (and we even say this in the current LoI). 
It then looks odd to me to see the radiator bars extend so far. Since 
the figure is really just a cartoon anyway, I would shorten the Barrel 
DIRC region to just beyond the EMCAL in the electron going direction. We 
should also keep in mind that the some of the original BaBar DIRC bars 
have already been given or promised to other experiments (GlueX and 
TORCH), and that they probably couldn't be used in sPHENIX anyway 
without some significant modification (the are contained in so-called 
bar boxes which probably won't fit inside the EMCAL envelope). I think 
showing a DIRC for PID in the central region is fine, but I would keep 
it more generic at this stage of the design. This might also affect what 
is shown in Figure 2.4, but I don't see where this figure is actually 
referred to in the text anyway.
  The only other comment I had was regarding Figure 2.3 and the 
discussion about the sPHENIX EMCAL resolution. The left hand plot in 
Figure 2.3 is fine since this is now published (or about to be) in our 
IEEE TNS paper. However, the right hand plot for the large eta prototype 
is for the V2 prototype that was measured in 2017. The new V2.1 
prototype which we measured in 2018 showed better resolution (~ 
14-15%/SQRT(E) with ~ 3% constant term). The analysis of that data is 
being done at UIUC and may not be quite finalized yet, and it may not 
make a great deal of difference as far as what we say about it in the 
LoI, but since these kinds of documents often wind up getting 
distributed and quoted in far away places, it may be best to put our 
best foot forward in terms of what we show here. We could check with 
Anne Sickles and see if those test beam analysis results are ready to be 
made public yet. Also, just better clarity, we should say the the large 
eta measurements were done for eta ~ 0.9 (not just eta > 0.15), which 
was the case for both the 2017 and 2018 data.

Cheers,
Craig


On 9/14/2018 8:29 PM, David Morrison wrote:
> Dear collaborators,
>
> We're pleased to announce that a draft response to ALD Berndt Mueller's
> charge asking for an update to the 2013 sPHENIX/EIC letter of intent is
> available for review.  A big thanks to Christine and Nils for
> shepherding this effort, and as they note below, a big thanks also to
> the many people who've contributed to the studies and writing that
> comprise the draft.  The current draft can be downloaded here:
>
> https://www.sphenix.bnl.gov/web/draft-sphenixeic-loi
>
> Please provide comments by the end of the day on September 26, 2018.  We
> are due to deliver the document to the ALD by September 30, 2018.
>
> As the draft was authored both by sPHENIX collaborators and by EIC
> interested friends from outside the collaboration, we'll need to be
> flexible about how we collect comments on the draft.  We have the
> sPHENIX mailing list sPHENIX-notes-l, which is intended for discussion
> of note drafts among sPHENIX collaborators.  And there is also the
> eic-DSG-l mailing list, which is not limited to sPHENIX collaborators
> and was set up for discussions of the EIC detector study group.  Send
> your comments to either of these lists and we'll ask the note's authors
> to compile the responses.
>
> Regards and happy reading,
> Dave and Gunther
>
> -------- Forwarded Message --------
>
> Dear Dave and Gunther,
>
> please forward the attached draft of the document for "An EIC Detector
> Based On sPHENIX" to the collaboration for review.
>
> The draft is the product of many people pushing this concept over the
> years and focused activities in the more recently established EIC
> Detector Study Group. We thank all the people who have contributed to
> it. Please have a look and let us know your thoughts and suggestions by
> September 26th.
>
> The document is still work in progress. While most of the content we
> intend to include is there (we only need to add the Executive Summary
> and Conclusions), the text likely needs some editing. Therefore, when
> reviewing the draft, please focus on the content, messages, and figures
> first. We will keep you posted about major updates to the draft.
>
> Best,
> Christine & Nils