[Frost] New findings for FROST momentum problems

[Eugene Pasyuk]

Hi Brian,

You did interesting study.
The shift in vertex time for different ST paddles by itself is not 
alarming. All times in CLAS are measured with respect to the trigger 
time. If trigger time shifts all times shift. Trigger time depends on 
which detector fired the trigger. For that reason we never use vertex 
time for event selection and PID. What we us is vertex time difference 
obtained from different detectors. Particularly, time difference between 
track vertex time and beam vertex time. When we look at the time 
differences those shifts due to the different trigger time cancel out. 
The differences between g11 and g9a can be explained by the differences 
in electronics. It was not exactly the same.
So, the time shifts you observe are not necessarily bad thing.
However, the difference in occupancies may indicate some problems with 
trigger efficiency. We need to do more studies of this. Particularly 
sectors 6 looks odd.

Having said that I don't see how those timing shifts can affect momentum 
reconstruction.

-Eugene




On 11/17/10 2:34 PM, Brian Vernarsky wrote:
> Greetings all,
>
> I have been continuing to work on finding the source of the momentum
> discrepancies we see between the butanol and CH2 targets.  I tried to
> look into the tracking code, but could not find any problems there.
> So I started to look at some other reactions than the gamma p ->  p pi+
> pi- () reaction, and when I looked at the single track reactions I
> found what might be the source of our problem, the start counters.  I
> have written up all of my findings in a presentation you can find at:
>
> http://www.andrew.cmu.edu/user/bvernars/FROST_update_2010-11-17.pdf
>
> It is a somewhat large file, around 10 Mb.  Please let me know if you
> have any questions or ideas.  Thanks
>
> Brian
> _______________________________________________
> Frost mailing list
> Frost at jlab.org
> https://mailman.jlab.org/mailman/listinfo/frost