sPHENIX EMCal discussion

[Craig Woody <woody AT bnl.gov>]

Sean,
  Thanks for making the measurement of the light guide transmission so 
quickly. Admittedly we should have checked this before, but the light 
guides came in so late that we didn't really think about this at the 
time. From your plot it does look like the NN light guide has lower 
transmission, but since the lower transmission extends to very long 
wavelengths, I worry whether this is just a surface effect. I presume 
Bill machined and polished the ends of the sample you measured ? Also, I 
presume you avoided the screw hole in all cases ?
   Just as a reminder, it was decided at the "Light Guide Design 
Review" to switch to the UVT material based on measurements that were 
done with completely different material than the one actually used to 
manufacture the light guides we got from the supplier. They were based 
on samples of UVT and UVA acrylic that we had on hand (or maybe Bill 
ordered) that were irradiated with gammas up to 1 Mrad (far higher than 
we will ever see at RHIC). If you look at the radiation induced 
absorption coefficient from those measurements, the difference between 
UVA and UVT is imperceptible at 100 Krad.
    I'm not so sure the comparison of the transmission of the 4 samples 
you measured yesterday is telling us the whole story, and a 9% loss in 
light output won't explain our current problems with the lack of the 
detector response at low energies, but we may want to revisit the 
transmission issue of the light guides before ordering more of them.

Craig

On 3/13/2018 7:25 PM, Sean Stoll wrote:
> I added some slides to the Indico page for today's mtg comparing the 
> optical transmission of the V2.1 lightguides to the V2.0 lightguides. 
> Bottom line - they have ~9% lower absolute transmission at the BCF12 
> emission peak (though they transmit further into the UV.  As a 
> reminder, we selected the UVT material because the transmission edge 
> is further from the BCF12 emission peak, and so will be less likely to 
> change over time with accumulated gamma exposure.
>
> Sean
>
>
> On 3/11/2018 3:40 PM, Sickles, Anne M wrote:
> > Hi,
> >
> > We’ll have an sPHENIX EMCal meeting on Tuesday.  The primary item for 
> > discussion is the progress on the data taking at Fermilab.  I expect 
> > a discussion of the current status led by John.  Jin, could you 
> > provide a summary of the up to date plots from the slack channel?
> >
> > The agenda is here:
> >
> > https://indico.bnl.gov/event/4355/
> >
> > Best,
> > Anne
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