sPHENIX HCal discussion

[John Haggerty <haggerty AT bnl.gov>]

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*
> Professor of Physics
> Iowa State University
>
> (515) 294-6952
> lajoie AT iastate.edu
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--
John Haggerty
email: haggerty AT bnl.gov
cell: 631 741 3358