[Halld-tagger] microscope beam test

[Richard Jones]

Alex,

Yes, we are in essential agreement about the time resolution, I think.  If you look at your 2D time walk plots, you can see that the regions where you get less than 300ps resolution are out in the tails of the amplitude distribution where there are hardly any events.  We should not consider those regions very relevant for measuring performance properties.

https://halldweb1.jlab.org/wiki/index.php/BLTWG_Meeting_10/31/2011

The only one of the 3 summed channels that has a clear enough amplitude peak to see it clearly separated from the threshold cutoff is the "sum 2" (your first one).  In that one, the peak amplitude is around 900 adc channels.  There you are getting about the same time resolution as I am, around 350ps.  In the other two sum channels you show, unfortunately the gains seem to be somewhat lower, and the threshold cutoff actually cuts into the peak distribution, and trying to pick off a time resolution at the intensity peak is impossible.  Going way out into the tail where there are a few dozen events out of 50,000 (like looking at sum channel 3, adc 1300 where you get less than 300ps rms) doesn't really work, I would say.

Thanks for showing this.  I do not doubt any of the results that you show.  I just want to make sure that any claims of resolution that we make based on these data are solidly supported by the bulk of the data, and not cherry picking results in a corner of parameter space that look artificially good.  I think we agree about this.

-rtj




On 11/2/2011 10:57 AM, Alexander Somov wrote:
> Hello Richard,
>
> Just following up our discussion during the beamline meeting
> regarding the microscope beam test, I have linked a few time
> resolution plots to the appendix of our last meeting
> https://halldweb1.jlab.org/wiki/index.php/BLTWG_Meeting_10/31/2011
> (I made these plots quite time ago)
>
> The time resolutions  were computed with respect to the RF signal;
> I also applied time walk corrections.
>
> In general, the resolutions are consistent with that you have
> presented.
>
> Cheers,
>          Alex


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