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

[Igal Jaegle]

My point is that the energy is used for determining the position which is true. So, what you are saying is that the matching is done using DFCALCluster and not DFCALShower/DFCALShower_factory Position line 274/275 (I see that DFCALShower is used and not DFCALCluster in TRACKING dir but I am misreading maybe) and that in any case, the energy is playing a negligible role even if completely miscalibrated which is the case for energy deposited below 1 GeV.

tks ig.


________________________________
From: Shepherd, Matthew
Sent: Tuesday, November 30, 2021 1:26 PM
To: Igal Jaegle
Cc: Mark Ito; halld-offline at jlab.org
Subject: [EXTERNAL] Re: [Halld-offline] HDGeant4 Meeting Minutes, November 29, 2021



> 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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