sPHENIX HCal discussion

[Edward Kistenev <kistenev AT bnl.gov>]

Dear Jamie et al,

sorry for not explaining the philosophy of the whole project with those tiles. The assumption - we do not need to scan whole tile (we do not have automated scanner here at BNL) - instead I was planning to measure light from individual fibers. All what one does need (if it works like dreamed) is to calibrate individual channels with single pixel signals and then measure the light yield in the reference area (along one short side of the tile where coating is untouched, coating is to some extent foaming polyurethane - it is not removable without damage to the base material) then do a similar measurements in each of the bands (there is a bit of an issue with exposing tile in the fiber area so we do have a wide gap on one side of the central fiber). 

There are also tiles with round spots instead of bands. It is not clear how big should be the damaged area to allow enough light to exit so the spots has different diameters (band is an extreme spot) and different density of remaining coating.

All damage to the coating is an effect of exposure to high intensity laser. Controls are speed of laser light displacement and laser intensity. When done exposed areas loose reflectivity in controlled way and light is allowed to leak (extinction in damaged area is also unknown - we may need some black paper on top). 

At BNL we will have all 8 fibers coupled to SiPM’s. No  grease, we will use different setup to compare air gap to cookie and to calibrate coupling. 

All 8 channels will go into HBD readout, trigger will require some level of coincidence between digitized amplitudes from individual fiber ends. 

I asked Steeve for preamps with the dual gain, lower corresponding to ~200mkV per pixel and x32 higher. In this setup we will work with high gain only. 

As an extra I am converting 20tiles from T1044 prototype (outer) into tiles resembling what we’ll have in sPHENIX. Both fiber ends will be constrained in the fiber holder attached to the tile. On exiting the holder the fibers will be glued into the grove identical to that planned for the exit from production tiles. Single SiPM will be used to collect the light from tile. 5 SiPM’s (tiles) will be passively ganged together and coupled to the single preamp (similar to one used for multi fiber tiles). The whole arrangement will simulate vertical column of 4 towers - to study cosmic muon calibration for HCal (or any other calorimeter is sPHENIX) with muon tracks. I have not decided yet but most likely we’ll have cookies between fibers and SiPM’s. This part of the project is to close the gap between the time when we got square tiles and will get the prototype real tiles (delayed by export control at BNL and whatever holds StGobain from delivering BC600 ordered more then 2 months ago).

Best regards

Edward

Edward Kistenev, PhD

PHENIX Physicist

On May 11, 2015, at 7:05 PM, Jamie Nagle <jamie.nagle AT colorado.edu> wrote:

Hello Edward (cc sphenix-hcal-l list and Shawn, Sebastian, Sebastian),

We just received the shipment of HCal scintillator tiles at the University of Colorado today!     In the attached slides we have cataloged the different panels by the markings on the plastic cover and the visible coating patterns.   We do not want to remove the wrapping under the plastic cover on some of the tiles before learning more.

A full scan with detailed resolution will probably take about one-day per tile.     Additionally, all tiles in the past have had the fibers extending beyond the end and that is where we coupled the SiPM to the fiber.  On all of these panels the fibers are cut flush to the scintillator end, and it is not so clear they are polished.    We can put together a coupling device, though are concerned that the optical grease we have been using is known (by our experience) to eat away at the white coating (the exact material properties we are not aware of).    A quick answer to this question would be great to get a first test underway.

It would be great if we can set up a separate meeting or part of the larger HCal meeting, to go through the optimal testing of these tiles.    For example, we can easily run with a two SiPM coincidence on the ends of one fiber as long as we can use optical grease, and are unclear on the 4 fibers purpose in each tile.

Sincerely,

Jamie (for Shawn, Sebastian, and Sebastian)

 

||--------------------------------------------------------------------------------
|| James L. Nagle   
|| Professor of Physics, University of Colorado, Boulder
|| EMAIL:   jamie.nagle AT colorado.edu
|| SKYPE:  jamie-nagle        
|| WEB:      http://spot.colorado.edu/~naglej 
||---------------------------------------------------------------------------------

<Scintillator Panel Catalog 05-11-15.pdf>