sPHENIX HCal discussion

[Edward Kistenev <kistenev AT bnl.gov>]

John, once again - the answer for sPHENIX HCal is more complicated then it was in all of the configurations considered by Richard. This worries me - attempts to place this detector into the framework of a published references. On the back of the envelope the physics tells us that there should be few reasons for e/h not being unity: (1) different particle content in showering (no neutrals in em showers); (2) differences in dE/dx (no Dirk law, no columnar effect, no energy transfer to nucleus in em showers); (3) no depth leakage in em showers in hadronic calorimeters - they are always totally absorbed. Maybe more but they all work the same way  - dumping hadronic response (e/h>1). Unless you want to manipulate the absorber your only tool to improve e/h (if needed) is to act on photon component which is dominant in em but to much lesser extent in hadronic showers (and it is by default is different as it comes from large Z absorber into H-dominated scintillator). Here comes critical energy and simulation.

I am hesitant to suggest but I would think that HCal with variable sampling fraction may have advantage in this aspect - it acts differently on showers in early and late parts, maybe this explains why e/h measured in T1044 is not 1.5 but (need to verify) rather 1.2 or 1.3. Real can of worms - guess how it will be affected by patterning of the coating.

Edward

Edward Kistenev, PhD

PHENIX Physicist

On Sep 18, 2015, at 7:05 AM, Craig Woody <woody AT bnl.gov> wrote:

Hi John,
  The e/h for the whole calorimeter obviously depends on what EMCAL you
put in front of the HCAL, and can often make e/h worse than just the e/h
of the pure HCAL alone if the composition of the two calorimeters are
very different (where might that occur..?). However, I would think
something in the range of about 1.5 would be what you might expect.

Cheers,
Craig

On 9/18/2015 12:06 AM, John Haggerty wrote:

While doing some writing on the pCDR, I was looking up some papers by
Richard Wigmans, a prominent calorimeter expert (who visited with us
early in sPHENIX history), which I put here:

https://www.phenix.bnl.gov/WWW/p/draft/haggerty/sphenix/calorimeter_papers/

If you page through only one, look at

https://www.phenix.bnl.gov/WWW/p/draft/haggerty/sphenix/calorimeter_papers/wigmans_calor11.pdf

which has good advice like

If one wants to make real progress in this field, it is imperative that scientific integrity be the guiding principle.

in addition to a very clear telling of the history of compensation, and
his evidence that you can make e/h = 1 by adjusting the sampling
fraction. I couldn't find the exact reference for Fe/scintillator, but
the plot of e/h here:

https://www.phenix.bnl.gov/WWW/p/draft/haggerty/sphenix/calorimeter_papers/Screen_Shot_2015-09-15_at_12.00.15_AM.png

seems to be consistent with our experience, where the sampling fraction
of the outer HCAL is about 3.5% and the inner is about 7% and we
evidence for e/h in the ballpark of 1.3 to 1.6.

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