Thanks for more details. I'm sure you have discussed in depth
these issues and I apologize that I missed it and now am rising
these questions again. So, probably my concern now is only about
the way you present it. On your slide you show only one direction
- increasing the angle decreases non-uniformity. No doubt! As I
said 20 or 30 degrees will improve it farther. Do we want to got
there? - Probably not. So, it is really a trade-off, and this
should be somehow mentioned.
Sasha.
Hi Sasha,
Thanks very much for your comments. Yes, you are right, there
is a price to be paid for tilting the towers both in eta and
phi, and we have discussed this at great length within the EMCAL
group. As Jin showed in his simulations, having perfect
projectivity produces the narrowest shower size, which is good
for not only measuring electrons and photons, but also for our
e/h rejection. However, because of the vertex distribution, the
pointing will never be perfect, and the effect of the
non-uniformities in the blocks is quite large. As we've seen
from the test beam data, the tilting does improve the uniformity
considerably, and while it is indeed a tradeoff, the benefit of
tilting is very substantial. It may degrade the position
resolution slightly, but our position resolution for photons
will already be degraded significantly by the underlying event
in central collisions.
Also, the tilt angles we are talking about are actually quite
small. In the current sPHENIX configuration, the eta tilt is
only about 8 degrees for the projective part of the calorimeter,
and the phi tilt decreases with eta from less than 5 degrees at
central rapidity to less than 3 degrees at large eta (see the
attached plot that Jin generated showing this). We believe that
we need a tilt greater than about 4 degrees to really see an
improvement in the uniformity, which is why we've just tested
the V2.1 prototype at larger phi tilt angle at Fermilab this
week. We haven't seen the results of that test yet, but
hopefully we'll see some improvement.
Cheers,
Craig
On 5/3/2018 4:13 PM, Alexander Bazilevsky wrote:
Dear Craig and All,
I have one major concern on your slides. Probably it is not
an issue at all, but just the way you present it.
On slide 4 you justify the necessary of (increasing of) the
tilt angle by the uniformity of the EMCal response. I'm afraid
this logic is not completely right. Obviously, the larger the
tilt angle (or the larger shower size on the projection on
EMCal plane) the better uniformity. If you checked 20 or even
30 degrees tilt in test beam (or even in simulation), you
would get even better uniformity. What matters here is EMCal
efficiency (1 minus fraction of photons/electron tunneled
without inducing a shower) and resolutions. Introducing the
(large) tilt angle you deteriorate other things, e.g. position
resolution, the ability of shower profile for photon/electron
ID etc. So, those should also be judged when moving to larger
angle. ... Probably 10 degrees is still ok: e.g. it will add
(only?) ~1.2mm to position resolution.
Position dependence of the measured energy would not be a
problem at all if it is correctable. And I believe it is (as
shown by Joe). My personal feeling is that what important
here is not the (average) response non-uniformity but a
fraction of tunneled photons/electrons (or the size of the
tail to very low energy in EMCal response to a fixed energy
photon/electron), and the average EMCal response vs position
doesn't directly reflect it.
... my 2 cents.
Sasha.
On 5/3/18 12:32 PM, Craig Woody
wrote:
Sorry,
but in my haste to get this out, I forgot one important item
on the last slide. Please have a look at these slides instead
of the first ones I sent out.
Thanks,
Craig
On 5/3/2018 12:22 PM, Craig Woody wrote:
Dear All,
There has been a lot of discussion lately about what we
say in the CDR about the energy resolution for the EMCAL and
how we present this to the CD-1 Review Committee. During the
practice for the plenary talks yesterday, Gunter showed our
"Ultimate Performance Parameters", which are physics
deliverables that we claim that we will be able to achieve
in the final detector. They are important quantities since
we are essentially promising the DOE that we will be able to
deliver these levels of performance, and we better be sure
we can achieve them.
I've prepared a few slides that I plan to show at the
General Meeting tomorrow (or at least some subset of them)
which I wanted to distribute before then to get feedback
from people about how they think we should present this.
Please have a look at the attached slides and let me know
your comments.
Many thanks,
Craig
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Alexander Bazilevsky
Brookhaven National Laboratory, Bldg. 510D, 2-232
Upton, NY 11973 Tel: 631-344-3712
Email: shura AT bnl.gov
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