[d2n-analysis-talk] THaScintillator Class: Calculation of the Timewalk Correction

[Brad Sawatzky]

On Tue, 06 Apr 2010, David Flay wrote:

> So I've been investigating the THaScintillator class for how the analyzer
> implements the coefficients.
> 
> I found in the ApplyCorrections member function:
> 
>     if (fLT[i] != 0.) {
>        fLT_c[i] = (fLT[i] - fLOff[i])*fTdc2T - TimeWalkCorrection(i,kLeft);
>        nlt++;
>      }
>      if (fRT[i] != 0.) {
>        fRT_c[i] = (fRT[i] - fROff[i])*fTdc2T - TimeWalkCorrection(i,kRight);
>        nrt++;
>      }
> 
> Where fTdc2T = resolution of the TDC = 0.1e-9 s/channel.

This is only true for an 1875.  I don't think we used that model TDC.
Make sure the this resolution number corresponds to the TDC you're
getting your data from.

[ . . . ]
> now, the ReadDatabase() member function does:
> 
>    // timewalk coefficients for tw = coeff*(1./sqrt(ADC-Ped)-1/sqrt(ADCMip))
>    for (int i=0; i<fNTWalkPar; i++) fTWalkPar[i]=0;
> 
> ADCMip is a very large number, so we don't need to worry about it, as
> 1/sqrt(ADCMip) ~ 0.

What is ADCMip supposed to represent?   It must be some holdover from
ancient times...  Its function seems far better handled by the t0
offsets...

> comparing these two member functions, I'm thinking that the correction
> would be  to determine the slope of TDC vs. 1/sqrt(ADC) => coeff above. 

You certainly must use the same function in your fit as is applied in
the TimeWalkCorrection() method.

-- Brad

-- 
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