Re: TDC difference mystery mostly solved

[David Lawrence <davidl@jlab.org>]

Hi Alex,

    Blake is correct. Channels 1 and 13 were plugged into a different 
TDC and it is entirely possible that the North and South inputs were 
reversed. Since we rarely see any energy deposited there in beam data 
and have focused on z=0 runs up to now, we wouldn't have noticed it. 
Nice catch.

Regards,
-David

Blake Leverington wrote:
> Hi Alex,
>
> If I remember correctly 1 and 13 were put into a different tdc 
> "grouping"  as they were not part of the trigger since they see such 
> little energy or events. It is quite possible that they were reversed.
>
> -Blake
>
> George Lolos wrote:
>> Hi Alex:
>>
>> Interesting observation.  Since the was no reason to manipulate any of
>> the BCAL cables for the cosmic ray runs, were the TDC cables also
>> reversed for the photon runs?
>>
>> George
>>
>>   
>>>>> Alex Dzierba <dzierba@indiana.edu> <mailto:dzierba@indiana.edu> 06/22/07 4:53 AM >>>
>>>>>         
>> Dear Friends
>>
>> In the note that I sent out yesterday titled "BCAL Test
>> Module - Studies with Cosmic Rays" - referring to Fig 5,
>> we noted that the North-South TDC difference spectra
>> showed multiple peaks.  For the cosmic runs where the
>> trigger paddles were located at z .ne. 0 there is a primary
>> peak at the 'right' TDC difference and a secondary peak
>> with the opposite sign.  The 'right' answer is dt=2*z/c where
>> c is the effective speed of light in the module,
>> about 16 cm/ns.   For runs at z = -50 and -150 cm there are
>> smaller additional peaks.
>>
>> The secondary peaks for all the  z .ne. 0 runs appear to have a
>> trivial explanation -- the cables for segments 1 and 13 must have
>> been reversed going into the TDC's.  I determined this by
>> looking at TDC differences  for modules separately for
>> events in which more than 90% of the energy is contained
>> in a single layer.  Segments 1 and 13 are the top and bottom
>> segments in the first layer (as seen by the photon beam).
>> In the plots of Figure 5, the ratio of events in the primary
>> to secondary peaks is approximately 9 to 1 -- consistent with
>> this conclusion as there are 18 entries per event - corresponding
>> to the 18 segments.
>>
>> I am in the process of trying to track down the other
>> smaller peaks for the z = -50 and -150 cm runs.
>>
>> Cheers
>> Alex
>>   

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