sPHENIX HCal discussion

[John Lajoie <lajoie AT iastate.edu>]

Dear HCAL Folks:

    Recently there has been a lot of discussion about the different scintillator testing efforts going on at BNL and Colorado, specifically the goals and deliverables that we expect from each effort.  This email is an attempt to summarize what we see as the testing strategy going forward.

    Currently there are two efforts going on at BNL, one at Colorado, and a nascent effort getting underway at GSU. Over the next several months the main thrust of these efforts will be to characterize the light output, uniformity, and sources response of a large HCAL scintillator tile.
 
BNL (Edward and Abilene students):  
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Edward made a presentation at an HCAL meeting several weeks ago:

https://indico.bnl.gov/conferenceDisplay.py?confId=1308

Edward has been using the multi-fiber small tiles from Uniplast ("smartTiles") in a setup that allows him to localize the passage of a cosmic ray to within a few cm. This has allowed him to make measurements to verify the effect of coating the tile to reduce the light yield along the tile, a technique we hope to use to even out the sampling fraction as a function of longitudinal depth, especially in the outer HCAL.

BNL (Abhisek and others):
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As Abhisek described at yesterday's HCAL meeting, a group at BNL is planning to set up cosmics test stand with multiple tiles, trigger counters and finger scintillators to localize the cosmics.  The goal of this effort is to get an absolute calibration of the light yield per MIP.  This is an *extremely important* number - a lot of our planning and performance for the HCAL will depend critically on this number, and how much light we have to play with.

While the setup is being done with smaller tiles, the plan is to have the setup debugged and running for the arrival of the long tiles from Uniplast, which are expected by the end of the fiscal year.

Colorado (Sebastian V., Sebstian S., and others):
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While Colorado can do cosmics as well, they also have the ability to scan a tile quickly with a source (in fact, right now they are the *only* place we have that can do this). This presents some unique challenges (like self-triggering)  but is extremely valuable because we are thinking about using a quick source scan as a fast QA check on production scintillator tiles. Having both cosmics results on the absolute light yield and correlating these with source results will give us a better idea about what we can really learn from a source test.

Colorado has previously upgraded their setup to handle larger tiles, so we intend to send them some of the large tiles from Uniplast when they arrive, and possibly exchange tiles so that we have both cosmics and source measurements for a set of tiles.  They are currently working with the light coupling and new preamps to geth their electronics chain fully up and running, and thinking about trigger options.

GSU (Xiaochun, Megan and others):
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The GSU group is also setting up to measure light output, and we think it's desirable to make as many measurements as possible with different instrumentation chains as possible to build confidence in our measurements.  It also provides valuable experience that will probably be needed when we have to test and calibrate 15,000 tiles in production.

We hope this helps clarify what testing is currently ongoing and how we see it fitting together.

Regards,
John Haggerty
John Lajoie

John Lajoie

PHENIX Deputy Spokesperson

Professor of Physics

Iowa State University

 

(515) 294-6952

lajoie AT iastate.edu

Contact me: john.lajoie