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

[David Flay]

On Wed, Apr 7, 2010 at 1:55 PM, Brad Sawatzky <brads at jlab.org> wrote:

> 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.
>

Are you talking about just the resolution, or the calculation as well?

I've been searching through my various timestamped directories, and they all
say 1875.  However, I'm not totally confident in that, because I created
'master' db_L.s1.dat, db_L.s2.dat files based off of run 20676 (20090313
directory) and copied those to each and every other directory (once I
figured out that the cratemap was wrong).

Also -- I fear that maybe the true TDC model # was lost when Matt and I
created the merged DB back in September -- however, even my earliest backup
shows 1875.  In which case, I've asked Vince.


>
> [ . . . ]
> > 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...
>

All I could find in the THaScintillator class is:

        // Time-walk correction parameters
        fAdcMIP = 1.e10;    // large number for offset, so reference is
effectively disabled





-- 
-----------------------------------------------------------
David Flay
Physics Department
Temple University
Philadelphia, PA 19122

office: Barton Hall, BA319
phone: (215) 204-1331

e-mail: flay at jlab.org
           flay at temple.edu

website: http://www.jlab.org/~flay <http://www.jlab.org/%7Eflay>
             http://quarks.temple.edu
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