sPHENIX EMCal discussion

[Edward Kistenev <kistenev AT bnl.gov>]

Looks like I am repeating myself. From pictures of observed nonuniformities the half width of affected area is ~4mm. Let’s take the extreme - EM shower deposits more then 50%  of its energy around showmax (~1X0). . If shower started in response depleted area you want it to leave that area ~ 1X0 later (this is all back of the envelope). Close to 30 degrees and easy to check with simulation. Yes - everything is correctable (to some extent) but it is a lot of rock solid coding.

Unfortunately  tilt does not really improves the intrinsic uniformity of the detector - detector stays the same. It also can’t help with drops in light collection on tower edges and in the corners. But it improves efficiency (see Sasha's mail) by suppressing channeling. Fortunately there is even better way to suppress channeling - consider everything producing signals in the vicinity of the tower border as unreliable - introduce effective region. Unfortunately tilt is the enemy of effective regions (merges towers) - whatever good is done by 2D-pointing can easily be killed by tilting towers. Our EMC is very much like crystal calorimeters - I do not remember any with towers tilted in phi.

Edward 

On May 3, 2018, at 4:13 PM, Alexander Bazilevsky <shura AT bnl.gov> 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
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Email: shura AT bnl.gov
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