sPHENIX HCal discussion

[Edward Kistenev <kistenev AT bnl.gov>]

John,

if tiles used to build large tower are out of pilot shipment (easy to check - they should not be in A/M database) then the spread in performance is not excluded. Plastic used to produce those tiles was from the very initial production attempts made after the slit was modified to allow extrusion of 25cm wide band of polystyrene what is not a small feat (7mm thick plastic needs a lot of speed/temperature controls like SiPm’s). Surface quality, surface curvature etc, everything initially looked somewhat different. UNIPLAST believes that they now have technology settled but that happened not before all small tiles were made and some number of large tiles junked. Besides - pilot tiles were produced using old samples of BICRON 600 optical epoxy (remember the EPOTEC story). We also tuned the grooving and gluing procedures while I was at Uniplast in September.  

Here are my suggestions:

- first - I do not think the problem seen in large tower data is alignment problem, knowing Mike for longer then 20 years this is very unlikely;

- second - finish couple new tiles (one with a top quality grade, one with the bottom). Repeat it for every tile kind.  Measure them all under the same SiPM - trigger scintillators arrangement. Use the data to decide if we need to group tiles and not only SiPM’s. I see no problem with light yield varying tower to tower but would not agree to use random tile combinations within a tower if tiles are different in excess of 20%. We may need to preselect tiles (before SiPM’s are installed);

- finally - unwrap and visually inspect all 5 tiles tiles from existing large tower. I do not know what to look for but I would look for crazing on fibers first (even fibers used in pilot tiles were cut from different roll and travelled to Russia different road), air in the glue, surface damage and nonuniformity of coating ets (inject the light into both ends of the fiber using LED plugged into the coupler or something similar). It can be useful to cut one of those tiles (small piece) shave coating on one side without fibers and visually inspect coating on other side. Compare it to similar piece cut from one of smaller tiles we got in earlier shipments. 

This all sounds like small research project but … it already started.

Finally - I really would like to try different arrangement for fiber exits for the future (symmetrical with respect to tile  surfaces. It should simplify the light insulation (thicker coupler walls) and make the whole fiber package inside the tile more symmetrical with respect to light emission points (no fiber-by-fiber shadowing which can be one of the reasons for the hot spot at exit). UNIPLAST will try to produce for me couple of small and couple of big tiles with this kind of fiber arrangement (made from my sketches) using plastic similar to that in the large production tiles. They will probably come to BNL within a month for measurements (Richie may help to speed the whole process by generating professional drawings). We are also trying to understand if it may work - pushing fibers to the depth of 4 mm into plastic here at USM. 

Regards to everyone

Edward

Edward Kistenev, PhD

PHENIX Physicist

On Nov 23, 2015, at 2:07 AM, John Haggerty <haggerty AT bnl.gov> wrote:

Abhisek, Megan, and I set up a stack of five inner hcal tiles acquired
by Edouard from Uniplast, wrapped by Mike Lenz, with SiPM holders for
Sean's SiPM's from Richie and preamps from Steve and Sal on Friday (you
get the idea; it takes a village).  There's serious stuff to do, but I
thought this animated gif of cosmic rays was fun:

https://www.phenix.bnl.gov/WWW/p/draft/haggerty/sphenix/cosmic_1191.gif

It shows waveforms from the five tiles on the left and the discriminated
trigger scintillators on the right.  (The animated gif of 100 events
should play in your browser forever because it loops.)  The raw data are
in rcf at

/direct/phenix+user04/sphenix/bnl/buffer/rc-01191-0.prdf

--
John Haggerty
email: haggerty AT bnl.gov
cell: 631 741 3358
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