sPHENIX HCal discussion

[Edward Kistenev <kistenev AT bnl.gov>]

Dear Jamie, I agree 100% with your proposal to purchase well made tiles of certified plastic with precision machined groves. Possible suppliers are StGobain and Eljen (I have quote from ELJEN, simply do not remember what drawings were used to produce those quotes). I am sure JL already had similar quotes and contacts with FNAL and FNAL option probably is not excluded at all too. I will use JH definition - and call new proposals new “lines of attack” (in fact I have one of my own - Precision Plastic here on LI is still looking into production options for our tiles).

The reason why I did nothing along those lines - at this stage my priority is to get prototype built and on time. I am not going to discuss visual quality of the tiles which you have. We made light yield and uniformity measurements on our first prototype tiles at INR, they gave >40 pixels per MIP on two SiPM’s and uniformity better then 20% and tiles were of similar quality. 

To make next step I invented my “smart tiles” with 4 fibers which you do not like so much but which allowed me to study the light propagation in the plastic, ways to trigger sPHENIX, ways to calibrate SiPM’s, ways to organize QC on production site, uniformity and many other problems which this time I would like to solve before going into beam. 15 years ago I had mass peak in EMCal at exactly pi0 mass with the very first collisions in RHIC and I would like this to be repeated with calorimetry system at sPHENIX. 

Just to explain why these tiles are smart I attach few pictures showing set-up, examples of SiPM calibration (NO LED’s USED TO CALIBRATE SiPM’s) and uniformity measurements done with gradually modified tile coating. The first two do not need an explanations, the third one needs few:

- vertical axis is in units of pixels fired in 8 SiPM’s viewing 8 ends of 4 fibers;

- horizontal axis are in [cm], tile is 15x25cm2;

- fibers are along X;

- fibers at Y<7.5cm are spaced by 2.5 cm, above by 5 cm (see the first picture);

- every square (5x3cm2) in that picture integrate data for muons crossing tile in that square.

As expected the hot corner is lower left (fibers spacing is small), the coolest one is top right (fiber spacing is like in our actual tiles, maximum loss of light due to modifications of coating). Effect of modifications is about 25% (one side modifications), effect of fiber spacing (light attenuation in the tile) is of similar order of magnitude.

This is just very preliminary - many other questions are still only touched. 

Now about large tiles. Prototype tiles for sPHENIX prototype are still in Vladimir. Nothing I did helped to win over obstacles set on the road to shipping fibers and optical cement which Uniplast could not purchase directly. It took from January till this last Tuesday for boxes with fibers and cement to travel from BNL to UNIPLAST.  The first thing Uniplast will do is to glue fibers into large prototype tile and ship those to BNL. You will have your copies probably towards the end of August. 

Hope that first delivery of production tiles for prototype (uniformly coated) will come towards September end.

Best regards

Edward

 она и