[Halld-pid] f1TDC timing resolution

[Alexander Ostrovidov]

Hi Beni,

Thanks for making these measurements! I have a quick question 
about your timing resolution plot. Why did you choose a bin size of 
50ps for this histogram? After all, TDC measurements (and their
differences) are integers, and it would be natural to histogram them 
in these units, with a bin size of 1 TDC count or, at least, with the
proportional 56.6ps bin size. With your bin size choice, a bin with 
about 3000 counts is followed by a bin with 0 counts, followed by
a bin with 5000 counts. This is "statistically unnatural" and is a
pure artifact of a non-aligned binning. Fitting a very narrow
(literally, a couple of bins) histogram to a gaus might be very
sensitive to how the binning is done. Seeing chi2 / ndf = 4892 / 9
makes me wonder how stable the obtained 36.7ps resolution value
is. Would it be possible to plot your data with the "natural" bin size
of one TDC count? Thanks.

Sasha

On Monday, February 21, 2011, Beni Zihlmann wrote:
> Hi All,
> to follow up on the discussion about the timing resolution of our F1TDC
> I looked at the data I took to test the Hamamatsu H10534 PMT.
> Attached is a plot that shows the timing difference between the trigger
> signal going to the TI board and the trigger signal output from the TI
> board. The Gaussian fit gives a width of 36.7ps while the position is
> 31.85 ns. This means that the TI response time to the triggers was
> 31.85ns with a timing resolution of 36.7ps. This resolution includes
> the timing jitter
> of the TI board as well as the intrinsic timing resolution of the F1TDC.
> In other words the intrinsic timing resolution of the F1TDC is expected
> to be better than 36.7ps.
> 
> On a side note: looking at the open PMT and its base the active base
> circuitry
>                           is based on 3 transistors.
> cheers,
> Beni