[Halld-offline] [EXTERNAL] Re: HDGeant4 Meeting Minutes, November 29, 2021

[Shepherd, Matthew]

> On Nov 30, 2021, at 1:12 PM, Igal Jaegle <ijaegle at jlab.org> wrote:
> 
> As far as I understand the code: the position is determined by looking at the block position with the largest energy deposited among all blocks making a cluster. 

This is not the case.  DFCluster positions are at fixed z but with x,y determined by all hits in the cluster.  (Lines 190 and 191 of DFCALCluster.cc)  Then at the shower stage the energy is used to get the depth (z).   An energy miscalibraiton will cause the depth to be incorrect which will result in an incorrect angle for photon four-vector.  This leads to shift in x,y on the front face of the FCAL, which is presumably the plane where track-matching is done.  But this shift is so tiny around the beam hole, I don't see how it can practically make a difference.

Matt
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