[A1n_d2n] Brad's questions about parameters

[Mark Jones]

To answer a few of Brad's question:

 hcer_num_regions = 3  ; This is used for efficiency calculations mainly as a check if the
   the HMS cerenkov is working ok during the online experiment. I have never seen
an experiment actually use this. Of course this is superceded
  by a real efficiency offline calculation.

phodo_neg_sigma, phodo_pos_sigma are not used in the present HCANA. There are leftover from
the 6 GeV FORTRAN code.

Just as a note phodo_NegSigma and phodo_PosSigma are used in weighting the contribution when
determining the time of flight by fitting the time versus distance from each paddle's time and position.

phodo_neg_invadc_adc, phodo_neg_invadc_offset    phodo_pos_invadc_adc, phodo_pos_invadc_offset
This are parameters that are used in an OLD hodo calibration method.

PARAM/HMS/HODO/hhodo_calib_1267.param
  - c1-* params have large spread -- is this normal/reasonable?

The c1 parameters are not actually used in HCANA. The timewalk is the
tw_corr = c1 + 1/(amp/pTDC_threshold)^c2

So a spread in c1 , just reflects possible different cable lengths etc.

pTDC_threshold is set in the calibration code and then in the parameter file.

"pTDC_threshold=120 ;units of mV"
It is not used as a threshold cut anyway.

In HCANA  , the time walk correction is the correction relative the correction
at amp = 200mV, so
tw_corr_corr= 1/(amp/pTDC_threshold)^c2 -1/(200./pTDC_threshold)^c2
which is done for each PMT.

One has to remember that the hodo calibration does the time walk correction calibration separate
from the velocity/time offset correction. So if one redoes the time walk correction then the data needs to
be replayed with the new time walk calibration parameters before doing the next step of determining
the velocity/time offset correction.

You need to be careful about choosing the data for calibration. Need to cover the entire area of paddles.
We did not change HV or cables during the experiment


The hodo calibration procedure is described in
https://hallcweb.jlab.org/DocDB/0009/000970/001/hodo_calib.pdf

Cheers,
           Mark



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