references on the precision TOF

[Andrei Semenov <semenov@jlab.org>]

Hall D PID Mail List:


Elke:

You can find the PDF file with the paper you asked for on the meeting
(viz., CERN NA49 detector description) on the web address
http://www.jlab.org/~semenov/na49-detector.pdf (it's too big for the
attachment); and the reference is NIM A430 (1999) 210.
TOFR wall (of about 2 m^2 area and 900 PMTs) was made
by Marburg U. group, and used Philips XP-2972 tubes; the overall TOF
resolution (viz., including start counter contribution as well as
electronics resolution and the 900-channels calibration misallignment) was
about 60 ps (sigma). TOFL wall (same area, same # of PMTs) was made by
Dubna group (myself included); it used Russian FEU-87 PMTs, and the
overall time resolution was about 75 ps (sigma). Surely, these detectors
are the "pixel" ones, but my point is that absolutely no special
"stabilization" of PMTs was necessary to reach such a resolution. Critical
decision (to reach such a resolution) was to remove the light guides and
couple PMTs directly to the scintillators. Another important moment was to
use the hit position from the TPC. And (of course) the quality of the
cables from PMTs to CFDs...

You might be interested to have a look on the TOF paper from BESII/BESIII
experiment: http://www.jlab.org/~semenov/besII-tof.pdf or
NIM A555 (2005) 142. The guys used 230x5x6 cm^3 bars, and got about
90 ps resolution per bar. Again, it was more thick bar, and they used
fine-mesh Hamamatsu R5924 PMTs, but light dispersion should be about the
same => it's not an absolute limit that does not allow to reach a good
time resolution, and the optimization is possible.

Thanks,
Andrei



On Mon, 30 Jul 2007, beni zihlmann wrote:

>
> I probably did not express myself properly. The 150ps I quoted as TOF
> resolution
> is for one plane.
> So one can assume that for two planes (horizontal+vertical) the timing
> resolution
> from the full device could reach 150ps/sqrt(2)=106ps. So there is
> justified hope
> that for the full device we can reach 100ps or even below. The only
> caveat is that
> while the efficiency will be high it will be not 100%, in particular
> because we
> do not stager the paddles but they are on top of each other or side by side.
>
> cheers,
> Beni
>