[Halld-pid] f1TDC timing resolution

[Beni Zihlmann]

Hi Sasha,
attached are two fits to the same data with different bin sizes.
one very fine with 25ps/channel and one with 56ps/channel
the actual bin size of the F1TDC. As you can see the fit results
do change a little but not drastically. The chi2/ndf is bad in
both cases because it is not really a Gaussian distribution
but closer to a square.

cheers,
Beni

> 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
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