sPHENIX is a new detector at RHIC.

[woody <woody AT bnl.gov>]

Hi All,
  I just want to support what Rosi and John have said. I don't think we want to imply in the Descoping Document that "we're fine" with the proposed cuts in either the EMCAL or the HCAL, and I would not use words like "these losses are not catastrophic", since I believe that is exactly how this would be interpreted. For the EMCAL, I looked more carefully at how we would save the $1.1M before contingency from the EMCAL alone (not counting the electronics), and, because of the fixed costs involved in building the sectors, the cost savings does not scale exactly with reducing the acceptance, although it does to a fairly good approximation (|eta| < 0.82 rather than |eta| < 0.85). However, we should remember that the acceptance for the baseline design is |eta| < 1.1 so that we can have a fiducial regon of |eta| < 1.0 for physics, and we would still need to impose a similar fudicial cut on the reduced acceptance detector. This would imply our physics acceptance would be more like |eta| < 0.72, which would imply a loss of statistics of ~ 50% for the upsilon. Also, the boundary between the reduced acceptance EMCAL and the full acceptance HCAL (which may only be the outer HCAL) will certainly cause significant non-uniformities in jet reconstruction that we will presumably only really find out about after we've started actually analyzing the data. All of this certainly goes against the original design motivation for sPHENIX for having a larger acceptance jet spectrometer with uniform coverage, and I personally don't this this should be stated as "not catastrophic".

Craig

On 10/24/2017 8:35 AM, Rosi Reed wrote:

Hello Everyone,

First, attached are two plots for single jet and dijet containment.
For the single jet containment, this is the number of jets a given jet
pT within the EMCal acceptance over all jets of that pT.  For the
dijet containment plot, this is versus the leading jet transverse
momentum so they are on the same scale.  This is the ratio of the
number of leading jets of a given pT where both the leading and
subleading jet are within the EMCal acceptance (and the subleading jet
has pt > 5) over the total number of leading jets with that momentum.
The sub-leading and lead jets are |delta phi| > 2.35, there is no
requirement that the sub leading jet be the highest pt sub-leading
jet.

I think this shows the statistical hit that we take with the reduced
emcal, as we are unlikely to analyze Calo jets that are not fully
contained within both the HCal and the EMcal.  The reason we would
want to do this is illustrated in Figure 1.5.

I can adjust these plots as needed up until about 4 pm today.

Line 91: I highly doubt we can improve upon the nominal configuration
using the reduced configuration with corrections ... the JES and JER
are both affected for the worse, and this means the correction and
unfolding will be more difficult.  In lines with what John has stated,
I don't think we want to make it too optimistic.

Regards,

Rosi



On Tue, Oct 24, 2017 at 12:26 AM, John Haggerty <haggerty AT bnl.gov> wrote:

Gunther and Dave,

Speaking as a high official of the project, it is good to see that the
collaboration can agree on a plan to bring the costs within the boundaries
the lab has asked.  As you know, I have looked into more radical changes
without expending engineering effort on them, but I cannot see any better
alternative to this proposal that could come anywhere near being ready in
202{1,2,3}

Speaking as a member of the collaboration, I think we should try to convey
more of a sense of loss and sacrifice.  Cutting the emcal acceptance in
particular seems like a double whammy, because it not only cuts the
acceptance, it makes the whole calorimeter system thinner, and I have even
wondered whether the un-descoped detector is thick enough, and with the
Inner HCAL probably gone, the fiducial region is pretty small.  Experiments
often recover that region with endcap or end plug calorimeters, but I don't
think that's a viable option for us, because it introduces a boundary which
is inherently non-uniform.

Another concern is the unknown unknowns we have introduced with the odd
longitudinal segmentation in the calorimeters...  sure, there is now a lot
of evidence that the signals look not so bad with this arrangement, but
violating the conventional wisdom is often punished harshly by nature.  I
don't know that we can say with certainty that the vast background ocean of
low pt particles, jets, and slow secondaries which are now spinning around
inside the magnet but outside the emcal do not have some very unfortunate
effects.  I have not been able to put my finger on exactly what we should
look for, but I think we have to keep looking for trouble.

I know these are not very well formulated objections, and so may be
impossible to take account, but I thought it might be useful to put them out
there in case it inspires someone smarter than me to see more clearly where
we might be going off the rails.


On 10/21/17 12:02 AM, Gunther M Roland wrote:

Friends,

As discussed at the General Meeting today, we are forwarding draft 1 of
our document outlining the detector scope for a $32M cost cap. The pdf file
can be found at
https://www.dropbox.com/s/5wyutbndogozm5q/sPH-GEN-2017-002_v1.pdf?dl=0
(we'll provide another link tomorrow for those that can't access dropbox)

Please send your comments in reply to this mail, keeping the
[sPH-GEN-2017-002] tag in the subject line***. Comments received by
close-of-business on Monday, 10/23, will be most useful.

Cheers,

Gunther and Dave

***we will move future reviews to an sphenix-notes-l AT bnl.gov list, but the
list couldn't be generated in time for this note.
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John Haggerty
email: haggerty AT bnl.gov
cell: 631 741 3358

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