Minutes of the CALCOM analysis meeting April 25, 1997.


  Agenda:
          
    B. Niczyporuk  DC time calibration (cont)
        
    K. Egiyan      Effective speed of light in EC scintillators

    V. Giourdjian  Status of cosmic ray analysis on LAEC


Summary:

(1) Kim Egiyan presented his conclusions on the effective speed of light 
measurements using runs triggered on electrons. The method was briefly 
described in the minutes of the last CALCOM meeting (see web page). 
After applying time walk corrections he obtains a value of 
16.0 +/- 0.4 cm/nsec. When he extracts the combined time resolution for 
a single EC stack and the related TOF bar the resulting 
resolution is worse (dT ~ 1.1 ns) than the combined resolution of 
two EC stacks (~0.85 ns). This shows a much larger than expected 
contribution from the TOF counter indicating a need for improvements
in the TOF calibration.

(2) Volker Burkert reminded everybody of the importance of the TOF 
calibration. This task requires increased attention immediately so
that we may fully employ the TOF information for particle id during 
the upcoming commissioning runs in June - August.
Maurik Holtrop from UNH has recently joined this effort. 

(3) Vartan Giourdjian reported on the status of the cosmic ray data taking
and analysis of the large angle em. calorimeters (LAEC). Data a currently 
taken alternating with the forward EC. The goal is to perform the 
PMT gain matching with min. ion. signals in the center of the scintillator 
stacks. The hope is to do this with similar accuracy as it was done in 
the lab in Italy (O(1-2% rms). 
Vartan showed that in the retracted position the LAEC is currently in,
the trigger arrives late and cuts into the fastest signal from the stacks 
(nearest to the PMTs) so that not the full stack length can be covered.

Next meeting:  
Due to the CLAS collaboration meeting there will be no CALCOM analysis
meeting this week. On Saturday May 3, several brief reports from the 
CALCOM analysis effort will be presented to the collaboration. The next 
CALCOM analysis meeting will be on Friday May 9.

Volker Burkert

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Individual report:
 
B. Niczyporuk:
============= 
    The data, Run# 781.b01 (85072 triggers, Itorus = 1929A and Iminit = 6000A)
    has been processed with the SDA. The 13919 tracks (Q=-1) were reconstructed
    for Theta < 60 degrees. The SDA takes only < 4 ms > to process one trigger.
    
    The 11235 electrons were identified by matching the DC tracks with the 
    corresponding hits in SC and EC. The losses of 19% are mainly due to the
    geometry of EC. The corresponding MC prediction is about 14%.
    
    The hits in DC and SC of the identified electons were used to derive the
    calibration constants (time offsets:) for drift chambers, it is:
    
             Cdelay = DL1 - (Dcable)dc + (Dcable)sc   [ns]
    where
             DL1         - Level1 trigger delay to stop DC tdc (common stop)
             (Dcable)dc  - signal wire cable delay to start DC tdc  
             (Dcable)sc  - DC signal wire cable delay to stop SC tdc 
             
    After corrections: for time of flight (ToF), time of propagation along SC 
    slab, time of propagation along signal wire, and adding the raw tdc for SC
    hit with the raw tdc for DC hits on the reconstructed tracks (to get rid 
    trigger jitter), the Cdelay has been determined with resolution of < 10 ns.
    Thus, having the DC filled with the slow gas (velocity about 15 microns/ns),
    the calibration constant resolution will contribute about 0.02 cm to the
    distance of closest approach (Dca).
    
    For Region 1 the constant "Cdelay" has two values: 1200 ns and 1130 ns.
    The smaller value of the "Cdelay" corresponds to the following wires:
    <25 (la 1), <24 (la 2), <24 (la 3), <23 (la 4), <29 (la 7), <28 (la 8),
    <28 (la 9), <27 (la 10), <27 (la 11), <26 (la 12).
      
    Having the calibration constants "Cdelay" the drift times "Td" in a cell has
    been obtained. From "Td" distributions the functions: Dca = f(Td)  for each
    Superlayer have been derived. It has been found that for Superlayer 3 the
    shape of  Dca = f(Td)  funcion does not depend on the strength of magnetic
    field (slow gas). The Figures (postscript files) are available on request.