sPHENIX HCal discussion

[John Lajoie <lajoie AT iastate.edu>]

Hi John, Edward:

    Thanks for the discussion. I don't remember seeing anything from previous test beams on the variation of scintillator slats within a tower, but Abhisek did make a plot of the deviation of the cosmics response for *towers* for the 2017 test beam setup, normalized to the simulation to take out the geometry effect.  I'm attaching that here as this is something that we might want to compare with this year.

    It sounds like we really don't need to worry about grouping tiles+SiPMs for the inner HCAL for this test beam.

Regards,
John

On 12/21/2017 10:01 AM, John Haggerty wrote:

Edward et al.,

I copied to root files off the laptop to

/direct/sphenix+data+data03/phnxreco/sphenix/caen5702/ihcaltiles

You probably have notes on files-to-tiles which we might want to put with them.

I agree that if the tile-to-tile variation is "about the same" as the variation with in a tile, that there would be no point to sorting the tiles by light output.  I couldn't find or make a histogram of the variation in light output of last year's small tiles form the tile mapper, maybe someone on this list has that handy, that would provide quantitative comparison to this.

One could also question whether the precision that the tile-to-tile variation can be measured without being extremely meticulous about the coupling of the SiPM to the fibers, the temperature of the SiPM's, and the amplifier gain variation.  I know you've tried to be careful, but even so, if the tiles are the same within the measurement errors, it seems unnecessary to sort the tiles.

So does all the evidence point to putting the tiles together?  I can imagine a number of possibilities for cosmic testing that would give us some additional information on variation once they're in the absorber.

On 12/20/17 6:11 PM, Edward Kistenev wrote:

Hi, John,
I am done with 2017 testing of tile to tile uniformity. Cosmic data in some form are  available for 24 tiles of HInner calorimeter. After all other testing and tweaking 12 tiles of one configuration (S30)  were used to equalize the channel gains in the CAEN box I am currently using. They were then removed and 12 new randomly chosen tiles of a different configuration (S32)  were then placed into the same kluge.  Both data taking runs were made under the same running conditions and resulted in essentially identical numbers (peak positions, see two pictures below - before and after).  The ratio is 1.01 with rms of 10%. This is essentially a very good upper limit to configuration dependence of the light yield and tile-to-tile spread we have for the small tiles in the recent batch as it came from UNIPLAST. Its contribution to HInner induced constant term is certainly lower then that “estimated” as due to 20% across the tile non-uniformity or LCG fluctuations in calorimeter with depth dependent sampling fraction (which can be accounted for on event-by-event basis).
My best guesstimate for today is that we do not need tile grouping for this prototype, visual inspection of fiber luminosity when tile is out of its protective wrap should be sufficient to answer live/dead question after shipment.
And we will definitely pay attention to tile-LED data when they will be available in January.
Edward





On Dec 20, 2017, at 4:32 PM, John Lajoie <lajoie AT iastate.edu <mailto:lajoie AT iastate.edu>> wrote:

Dear HCAL'ers:

     In the HCAL meeting today we had a discussion of the assembly of the inner HCAL for the test beam, the testing of the tiles, and whether or not it would be valuable to try to match cosmics response of the HCAL tiles within a tower.  In principle this should be a "good thing", and I would imagine that if there is a large variation between the tiles in a tower that could contribute to the constant term in the energy resolution.

     Doing this would require mating the scintillators with their SiPM's followed by cosmics testing to mix-and-match the scintillators before they are installed. It's my understanding that at BNL they will be ready to start installing scintillator soon, so if we want to do this then we need to get organized quickly.  Of course, we would only be doing this for the inner HCAL as the outer HCAL is the same as last year.  I think I would be assassinated if I suggested we disassemble the outer HCAL and match the tiles.

     In past test beams the variation within a tower was not carefully controlled, so if we did this it would be a good way to test the effect on the energy resolution. However, if we only do it for the inner HCAL it is likely of limited utility.

     Comments? Suggestions?

Regards,
John Lajoie


*John Lajoie*
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Iowa State University

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John Lajoie

Professor of Physics

Iowa State University

 

(515) 294-6952

lajoie AT iastate.edu

Contact me: john.lajoie

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