sPHENIX HCal discussion

[Edward Kistenev <kistenev AT bnl.gov>]

I am forwarding couple of messages exchanged between Craig and myself on the LED subject. Unless it was not already discussed in the open yesterday - they may contain an answer to the spike in light yield in earlier picture (I have not seen the new one yet).

Edward

Edward Kistenev, PhD

PHENIX Physicist

Begin forwarded message:

From: Craig Woody <woody AT bnl.gov>

Subject: Re: [Sphenix-hcal-l] Wavelength shifting

Date: November 18, 2015 at 10:47:56 AM GMT-3

To: Edward Kistenev <kistenev AT bnl.gov>

Hi Edward,
   This sounds like a very detailed study, which may indeed be interesting, but in the talk we heard yesterday from Ron Belmont, they were using the LED you suggested they use to measure the uniformity of the tile. If I understood correctly, the emission of this LED is in the blue (> 400 nm), so it's not exciting the scintillator or any of the fluors, but only injecting light into the plastic. Therefore, this isn't really measuring the uniformity you would get from charged particles. However, there are deep UV LED which emit in the 300 nm range, and these could be used to excite the plastic. I suggested they try one of those, which I think would give a much closer response to what you would get in terms of uniformity and light collection from charged particles.

Cheers,
Craig 

On 11/17/2015 5:08 PM, Edward Kistenev wrote:

Craig, this all depends on the purpose (most of LED’s we are using do have a long emission tail into red - except if it is filtered out by plastic) - if the purpose is just to get light into the fiber and to the photon detector - one can use almost anything. I think what we are discussing now is using LED to prove that the spike in LED response in the double fiber area in HCal tile is not from light which reached LED in some peculiar way (rescattering in core and/or cladding, rescattering in scintillator - area exposed to SiPM is at least 10mm2 out of which only <2mm2 are fibers itself) but from PS->PT->POPOP reemission chain. My earlier suggestion to Jamie/Ron was to repeat scanning using few LED’s with different emission peak - I suggested to use one with emission peak at POPOP absorption maximum and a second one at POPOP emission maximum and the third one at WLS fiber emission maximum. If spike survives this abuse - this is just an artifact of scattered light, if disappears - this is mostly a cladding effect which may or may not disappear if fiber ends are painted black.

Edward

PS. I remember the cost of LED Steve and I were using on my test bench is ~0.3 $US.

Edward Kistenev, PhD

PHENIX Physicist

On Nov 17, 2015, at 5:49 PM, woody <woody AT bnl.gov> wrote:

Maybe this slide will make things clearer as to what we're trying to do
<Principle_of_Wavelength_Shifting.pdf>_______________________________________________
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