sPHENIX is a new detector at RHIC.

[Ran Bi <biran AT mit.edu>]

Dear Jamie,

I've read through the SPHENIX BUP, and listed some minor typos and thoughts on the 2026-2027 run proposal below:

Typos:

- all beam-use summary tables: cyro weeks -> cryo weeks

- line 79: for selected observables in ???

Overall, I felt that 2.5 weeks of setup time is somewhat long for just 2 weeks of beam time for every additional collision system. I felt that it wasn't clear from the proposal if there is a need for collisions of two different small-nuclei systems. Given the focus of sPHENIX on hard probes, and that the point of using smaller nuclei is to probe the 'peripheral' region of large-nuclei collisions, it seems to me that choosing just one system may perhaps be enough?

This would convert 2.5 weeks of setup + ramp-up time to beam time, for a total of 6.5 weeks of beam time for one system, compared to the current nominal beam time of 2 weeks per system. At the LHC, the highest luminosities are achieved only at the last week or so of a 4-week run period, and so the gain in recorded luminosities may be greater than the gain in beam time, if the situation is similar at RHIC. Having more data of one collision system would allow measurements to be made more differentially in centrality, which would be effectively similar to having measurements that are less differential in centrality, in multiple collision systems, though the tradeoff would be the more limited range of Npart/Ncoll that canbe accessed. More speculatively, it might also be possible that a more precise measurementcan be conclusive, whereas two less precise measurements in separate systems, that cannot be easily combined, may not.

The major downside would be the risk of choosing the 'wrong' nuclei and potentially miss out on interesting physics. To some extent, the choice of nuclei can be guided by similar plans for running smaller collision systems at the LHC, although the lack of concrete plans also makes this rather unreliable.

Another possible way to increase beam time for the smaller collision systems would be to take 1-2 weeks of beam time away from the polarised pp running, since the relative gains are much greater for oxygen and argon collisions.​

Best,

Ran

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From: sPHENIX-l <sphenix-l-bounces AT lists.bnl.gov> on behalf of Jamie Nagle <jamie.nagle AT colorado.edu>
Sent: 21 August 2020 17:13
To: sphenix-l AT lists.bnl.gov
Subject: [Sphenix-l] Draft sPHENIX Beam Use Proposal document for Collaboration Comment (comment deadline Tuesday, August 25, 2020)

 

Hello sPHENIXians,

As discussed at the sPHENIX Fortnightly Meeting today, the sPHENIX BUP Taskforce is sending around the draft BUP Document -- it is linked on Indico below.

https://indico.bnl.gov/event/9236/contributions/40706/attachments/30061/46923/sPHENIX_BUP_2020_draftrelease08212020.pdf

The document is essentially complete with a few places with red text to indicate that a figure needs updating or a reference is missing.    Comments by line number will be most appreciated.   The more constructive and specific the comments (i.e. feel free to suggest specific re-writing or specific figure changes), the better since time is short and we want to produce the best document we can.   There was a lot of good discussion about the option for pp running in Year-1 (2023).    Specific suggestions for how to reference or modify this discussion - currently in Chapter 5 on Commissioning - are most welcome.       

Deadline for comments is close of business on Tuesday, August 25, 2020.    That gives the Taskforce sufficient time to take input seriously and improve the document before the submission deadline of August 31, 2020.

Comments can be sent directly as responses to this email on the list.   If you want to discuss some points in more detail in person, feel free to reach out to me or any of the Taskforce members

Sincerely,

Jamie, for the sPHENIX BUP Taskforce (Sasha Bazilevsky, John Haggerty, Jin Huang, Dennis Perepelitsa, ex-officio Dave Morrison, Gunther Roland)

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|| James L. Nagle   
|| Professor of Physics, University of Colorado Boulder

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