sPHENIX HCal discussion

[Edward Kistenev <kistenev AT bnl.gov>]

Hi, Jamie,

available options to correct visible spike in the tile light yield are unlikely even to include changing the fiber embedding pattern. It is driven by geometry of bends and has little freedom. The spike likely saturated by two contributions - direct collection of scattered LED light and retaining cladding light at the end of the fiber. It is very probable that both could be handled by painting last couple cm of fiber black. This will definitely help to kill some of the cladding light but can be too strong a remedy for excess light collection if any. It is tempting to look into simply reducing the thickness of scintillator close to fiber exits - can easily be done together with grooving. 

What may help to disentangle contributors to the spike is  scanning tile  with different wave length LED light. If most of the spike is from scattered direct light then moving away from PoPOP absorption peak will change the measured profile and help to tune the simulation.

Edward

Edward Kistenev, PhD

PHENIX Physicist

On Nov 12, 2015, at 12:50 PM, Jamie Nagle <jamie.nagle AT colorado.edu> wrote:

Hello All,

Using the LED tile scans shown earlier by Ron and Sebastian, I have written a light simulation program that does a reasonable job reproducing the relative light yield across the large panel.    Details are shown in the attached slides.

http://www.phenix.bnl.gov/WWW/publish/nagle/sPHENIX/nagle_sphenix_hcaltilesimulation_11122105.pdf

One question is whether the LED light penetrating through the white coating on the non-fiber side of the scintillator really has the right response in terms of how quickly the signal falls off as one moves away from the fiber.   There is a good comparison of the LED data and the cosmic data, but that does not have the resolution to discriminate this type of feature.    A natural follow up that Ron would like to coordinate on is using this type of simulation map in the sPHENIX GEANT simulation to test if there is any impact on the resolution, tails, etc.    I assume that is a prerequisite to considering any modification of the fiber pattern since one would need a measurement metric to compare patterns.

Sincerely,

Jamie

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