[Halld-cal] [EXTERNAL] FCAL light guide interactions

[Shepherd, Matthew]

Hi all,

I was chatting with Eugene in the hall this morning and we were discussing the response of FCAL modules to muons, which is relevant for CPP trigger studies.

At the May meeting there was also some discussions amongst small group of us.  I was reminding people of studies that David Lawrence showed many years ago.  See slides 14 and 15 of this:

> https://halldweb.jlab.org/wiki/images/5/56/20170727_ebode_jlab.pptx

Slide 15 is pretty strong evidence that the light guide plays an important role in the output of the module in response to a MIP.

Eugene was discussing the idea to build a standalone G4 simulation of a module that one can use to study the difference in the response of the block when the light guide is hit by the muon.

I was reminding Eugene, that our experience from the early design days of FCAL modules was that such simulations are quite non-trivial due to the angular distribution of Cherenkov light.  The non-specular reflections due to imperfections in the surface are very important.  Also one is operating at extreme angles where reflection is polarization dependent.  Some discussion of all this can be found in a very old GlueX document that describes the FCAL light guide design:

https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=850

I wanted to send these links to the mailing list so there is some archive for people that are interested.

Matt

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