[d2n-analysis-talk] VDC t_0 Check

[Brad Sawatzky]

These look good.  Thanks for doing the check.

-- Brad

On Wed, 07 Jul 2010, David Flay wrote:

> Hey Brad,
> 
> Attached are four plots of the drift time (of all active wires) for planes
> U1, U2, V1, and V2.
> 
> Utilizing the variable 'L.vdc.u1.time[i],' we can examine the TDC values
> of the ith active wire.  If we use no index, we look at all (active)
> wires.
> 
> t_0 would be the amount we need to shift the main peak to zero.  In these
> plots, we can see that there is no need to shift the main peak, so such
> plots indicate that a t_0 correction is not needed.
> 
> Each plot has a structure to it, which is closely correlated to how close
> to the wire the track is.  There are four distinct regions: a 'shoulder'
> region, a 'plateau' region, a 'rise' region, and a 'peak' region.
> 
> The 'shoulder' region is due to large-angle tracks that intersect with a
> small portion of a 'drift cell' (defined as a region of +/- 2.12mm
> centered on a sense wire).  This leads to less ionization of the gas,
> leading to less number of events per time bin (= dN/dt).
> 
> dN/dt may be written as:
> 
> dN/dt = (dN/ds)(ds/dt)
> 
> where ds = an element of distance along the E-field lines; dN/ds = the
> linear density of counts along ds; ds/dt = mean drift velocity of
> ionization in an element ds.
> 
> The 'plateau' region is due to a 'flat response' -- the electric field
> lines are parallel in a particular section of a drift 'cell,' which leads
> to a constant dN/dt.
> 
> The 'rise' region is due to the section in the drift cell where the
> E-field lines become quasi-radial.  The mean drift velocity of the
> ionization is approximately constant, whereas dN/ds increases => dN/dt
> increases.  In the plots, this corresponds to the section of each
> histogram where we see a transition from the plateau to the main peak.
> 
> The 'peak' region is due to the E-field becoming elliptical, where dN/ds
> goes through a maximum, and ds/dt increases as one gets closer to the
> wire.
> 
> Dave
> 
> 
> -------------------------------------------------
> 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
> -------------------------------------------------
> 
> 





-- 
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