as a follow up on my previous email, i did an analysis of the tof
efficiency based on events with ep-elastic wc-tracks in both sectors. i
made histograms with the new 'ntl,ntr'-like coordinates 'swl,swr'
formed by the intersection of the wc track with the (polygonal) plane of
the tof's. note that because of the spacing between groups of paddles,
the boundaries are not at exact integer values of swl,swr.
the magenta curve shows all events with two good wc tracks, while the
red curve is the subset of those events missing a tof hit. the green
curve = 1-(red/magneta).
conclusions:
a) the 'inefficiency' turned out to be explained mostly by events which
fall through the cracks between the tofs.
b) unfortunately, this method is only an upper bound of the tof
efficiency; otherwise one would not see dips between each paddle in the
magenta histogram, only in the red one. i'm not quite sure why the wc
misses these events; either the wc reconstruction is messed up by not
having the tof timing, or somehow the singles trigger is inefficient
(even after prescaling). perhaps it could be fixed by loosening up the
wc cuts.
c) this method works better in the right sector because of the lads bars
behind to supplement the singles trigger.
d) it could be extended to the CC's and NC's if needed.
--chris
Chris Crawford wrote:
> hi john,
> i'm pretty sure the big spike around TOF 12 corresponds to the gap
> between TOF's 3,4. i just talked with chi about the possibility of
> adding a couple of variables "swl,swr", which would be floats between
> 0-16, projections of the wc track to the relative position where it
> crosses the tof's. (3.5=middle of TOF 3) with this in hand, we could do
> the sort of thing you are thinking about. i just need the extra time
> (or help?) to add this.
> another improvement would be to cut on the CC or NC (especially for the
> right sector!)
> --chris
>
> John Calarco wrote:
>
>> Hi Tancredi, Chris,
>>
>> When we originally tuned up the TOFs (gain setting and matching)
>> efficiencies were essentially 99% as measured with the start counter
>> and small paddles behind the TOFs. This certainly measures the
>> efficiency near the TOF center. Chris, in your analysis, can you
>> make cuts to constrain the tracks with no TOF to project to near
>> the center of the missing TOF, or is that not possible? Can the
>> cosmics runs be used to gain any info on this?
>>
>> John
>>
>>
>>
>>
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