[A1n_d2n] [EXTERNAL] Re: Brad's questions about parameters

[Brad Sawatzky]

Thanks Mark, much appreciated!

On Wed, 23 Dec 2020, Mark Jones wrote:

> 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 Of course this is superceded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
> [1]https://hallcweb.jlab.org/DocDB/0009/000970/001/hodo_calib.pdf
> Cheers,
>            Mark
> 
> References
> 
>    Visible links
>    1. https://hallcweb.jlab.org/DocDB/0009/000970/001/hodo_calib.pdf

-- 
Brad Sawatzky, PhD <brads at jlab.org>  -<>-  Jefferson Lab / Hall C / C111
Ph: 757-269-5947  -<>-  Fax: 757-269-5235  -<>- Pager: brads-page at jlab.org
The most exciting phrase to hear in science, the one that heralds new
  discoveries, is not "Eureka!" but "That's funny..."   -- Isaac Asimov