sPHENIX is a new detector at RHIC.

[Gunther M Roland <rolandg AT mit.edu>]

Hi - 

Let me add a piece of information from a separate email thread with Jin and Mike, and a personal opinion:

* regarding full MAPS vs IB + TPC: I understand from Jin and Mike's emails that a MAPS simulation (in particular for the middle/outer layers) with a realistic ladder geometry is not something that is in hand *right now*. Similarly, for a TPC a fully realistic simulation of space charge effects incl. event pileup is not available *right now*. Therefore both alternatives can be attacked regarding their level of realism, and there isn't much that we can do other than add some parametrization of the resulting corresponding effects based on our best estimates (e.g. for the TPC, the ALICE experts could certainly provident advice and have in fact volunteered to work with us). In my opinion starting simulations right now with the ITS IB + TPC option *right now* is the better option, as it is not as radical a departure from the $82M configuration. I am very optimistic that we would able to find additional funding at the $5M level that this option implies, finding the $10-15M *1.x that the full MAPS option implies is a much bigger jump. In light of the recent VTX pixel developments, I agree with other comments (and have said so on Monday) that now maybe the time to admit that this detector is not likely to be part of the solution.

* Regarding Ed's comment: 

" 1) Agree that whatever Tracker solution we adopt will be

    cost neutral, i.e $5M AY in material cost + 40% contingency.  That is what we should
    tell Berndt. Whatever solution we choose will be cost neutral."

I'm not sure how to read this statement. We will present Berndt with 1-2 "best worst case" configurations that fit into the $75M budget, and a discussion of what we would buy or buy back with additional funding. I don't think it would make sense to claim that VTX pixels + TPC is the tracking solution for the latter configurations. There is no convincing evidence that the VTX pixel + TPC solution is sufficient for ANY of the three pillars of our program, jet structure, heavy flavors and upsilons. The pixel detector may not work at all, and there is no proof that space-charge corrections for a TPC in the sPHENIX running conditions can be corrected without external tracking to anchor the corrections. Agreeing to a configuration where there is no evidence for, but many arguments against, its capabilities for any  relevant physics program seems ill-advised. In my judgement, a TPC + some functional additional tracking is the cheapest solution for which we have hope of arguing  that performance may be sufficient for our entire physics program. I don't think there is enough detail on the 5-layer strip tracker option that was brought up on Monday to form an opinion.

Best,

Gunther