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[Hugo Pereira Da Costa <hugo.pereira-da-costa AT cea.fr>]

Hello Ross, Tony, Christof, others

Following up on discussions we had yesterday I looked a bit into how the electron drift velocity is handled in the TPC code.

It turns out that

1/ Tony was right, there is no drift velocity used anywhere outside of PHG4ElectronDrift

2/ in PHG4ElectronDrift the only place were it is used, once you have properly compacted the multiply and divided by velocity, to convert G4Hit time into a position offset in the TPC (due to out-of-time pileup collisions and propagation time along the particle path). Everywhere else, we effectively use z, which we convert into a z_bin in the TPC length, via LayerGeom->get_zbin(z) and at clustering back to z via: z = z_bin x (tpc_length/2) / n_zbins.  (or rather, LayerGeom->get_zcenter(zbin))

So it is unclear to me

- how one can include a discrepancy of drift time between generation and reconstruction, to mimic an incorrect velocity ? Adding some discrepancy between LayerGeom->get_zbin(z) and LayerGeom->get_zcenter(zbin)) ? adding some correction factor after LayerGeom->get_zcenter(zbin) ?

- how we will handle that when processing real data

Maybe we can have a discussion dedicated to this next week ? (either Monday at the tracking meeting, or Tuesday during the TPC calibration ?

Hugo

On 10/25/21 20:41, Ross Corliss via sPHENIX-calibration-l wrote:

      Dear Distortions Folks,
      
      A reminder that the distortion meeting will take place tomorrow at
      the usual coordinates and time, 11AM EDT.  If you let me know in
      advance, I will add a slot to the agenda for you, but impromptu
      updates are also welcome.
      
      https://stonybrook.zoom.us/j/94081538941?pwd=Y256N3ptUC9zV2M4cjNtUGgyWnJYdz09
      
      https://indico.bnl.gov/event/12844/
      
      -Ross

==========
Dr. Ross Corliss
Research Assistant Professor
Center for Frontiers in Nuclear Science
Stony Brook University
ross.corliss AT stonybrook.edu

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