[d2n-analysis-talk] THaScintillator Class: fSize[1]

[David Flay]

Hi all,

Relaying my conversation with Ole concerning the THaScintillator code
involving fSize[1]:

    On 9/24/2010 9:13, David Flay wrote:
     Hi Ole,

     My name is David Flay, I am a graduate student from Temple University
working on the E06-014 (d2n) experimental data analysis.

     I've been working on calibrating the scintillators, and I have
noticed that the average time for a given paddle in the scintillator
plane is calculated as follows:

           fTime[i] = .5*(fLT_c[i]+fRT_c[i]) - fSize[1]/fCn;

     (line 632 in THaScintillator.C)

     I am not familiar with the quantity fSize[1].  I printed it to the
screen, and it turns out to be either 0.18 or 0.216... I am assuming
the units to be in meters, since fCn is the speed of light in the
scintillator material (in meters per second).  From what I can tell,
these two values correspond to either the S1 or S2m planes.  (S2m was
used for d2n).

     Could you shed some more light on this quantity fSize[1], and its
inclusion in the above calculation?

     Thank you very much,

    David



On Fri, Sep 24, 2010 at 1:40 PM, Ole Hansen <ole at jlab.org> wrote:

    Hi David,

    I admit that this is a bit confusing. fSize is the physical size of
the active area of the detector (half-size for x and y coordinates,
for historical reasons).  It is defined in THaDetectorBase.h, where
you can also find a comment about its definition. Hence, fSize[1] is
1/2 the y-size of the scintillator, and fSize[1]/fCn is the expected
average propagation time of the scintillation signal of a particle
that passes the scintillator at the center y-position to the PMT at
either end. fTime is supposed to be the time offset of the
scintillator signal with respect to the trigger and should be centered
at zero for tracks that make the trigger. Obviously, for fTime to be
calculated accurately, the scintillator TDC offsets need to be
calibrated, so fTL_c and fRT_c reflect the true time w.r.t. the
trigger. All of this is as precise as your calibration. Subtracting
fSize[1]/fCn only removes a trivial time offset.

Hope this helps.

Ole








-------------------------------------------------
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://quarks.temple.edu
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