sPHENIX HCal discussion

[John Lajoie <lajoie AT iastate.edu>]

Hi Edward, John:

    I really wonder if grading the light response of the scintillator could go in the wrong direction. Wigmans makes the point that "Compensation relies on amplification of the signal from neutrons produced in the shower development, such as to overcome (i.e. compensate for) the effects of nuclear binding energy losses."  By grading the scintillator we are throwing out light in a depth-dependent manner. How this interacts with the distribution of where neutrons interact in the scintillator (the compensation) is something that we really can't rely on simulations to tell us (another point Wigmans continually makes). 

    If we are unlucky then in the real world we might end up making e/h *worse* with the graded tiles,  but as Edward points out this is something we will really only learn from the test beam. We should keep this in mind as we go into the reviews this fall and spring - I think what we are doing with the next prototype is some good old-fashioned calorimetry R&D.

Regards,
John

On 9/18/2015 7:39 AM, Edward Kistenev wrote:

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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John Lajoie

PHENIX Deputy Spokesperson

Professor of Physics

Iowa State University

 

(515) 294-6952

lajoie AT iastate.edu

Contact me: john.lajoie