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    User name jpchen

    Log entry time 16:45:32 on April 9,1999

    Entry number 24

    This entry is a followup to: 22

    keyword=addition to 3/17 minutes


    Detail of Zhengwei's optics analysis for the week of 3/10-3/17:

    Filtered the hadron arm's optics data for each target foil and sieve slit
    phi strip. Tried first y_tg optimization for hadron arm. The result shows
    the optization procedure is resonable. All the optimized y_tg point move
    to their real position.

    Nilanga advised me to do the t000 optimization before y_tg optimization.
    And he also found an error in my calculation of th_tg. I checked my
    calculation,the problem is that all the holes have one hole's shift along
    phi and theta direction. After correction of this hole shift problem and
    using the new target to sieve distance, I repeated my geometry
    calculation. The t000 optimization is been doing again. And I will
    restart the y_tg optimization right after t000 optimization. Hopefully,
    the y_tg optimizated results can be got before this weekend.

    At the same time, I am also doing the electron arm's data filtering. It
    will be finished by this weekend,too.

    After the y_tg optimization, I will do the th_tg and ph_tg optimization
    and dp optimization.

    Detail of Seonho's analysis work for 3/10-3/17:
    After the preparation for the collaboration meeting last Friday, I started
    to look at Cerenkov detectors.

    >From ADC pulse heights with or without TDC signal, I can see that there
    were some problems of pedestal subtraction with some phototubes. The
    requiring TDC signal does not clean up completely the pedestal signal.
    Beside that, most of the signals look reasonable although the gains are
    not completely matched between different mirrors.

    As to the efficiency, about 5% of the events did not record a valid hit
    (ADC AND TDC signal). 76% of them has one and only one valid hit, 17% of
    them has two mirrors fired. The rest of the events fired 3 or 4 mirrors.

    For the events which have one valid hit, the mirrors close to the
    beam line (mirror numbers 3, 5 and 7 for hadron arm) have more hits than
    the mirrors far from the beam line (4, 6 and 8 for hadron arm). This is
    due to the rapid change in cross section with respect to the scattering
    angle.

    If I compare individual ADC signals for various mirrors, some mirrors have
    lower amplitude than others and these amplitudes need to be corrected by a
    software gain.

    For the events with two valid hits, the hit pattern (the first mirror
    versus the second) is consistent with known geometry of the Cerenkov
    detectors, i.e. the adjacent mirrors are illuminated more often than any
    pair else. If I look at the two ADC values for these adjacent mirrors, I
    can identify a class of events which deposits one photo electron in one
    mirror and the rest in the other mirror. The two amplitudes of the
    adjacent mirrors should be added together and treated as one entity in the
    further analysis. (Of course, the relative gain should be matched before
    summing the amplitudes.)

    For multi hit events (two hits on non-adjacent mirrors or three and more
    hits), the track information from the drift chamber should be used to pick
    up the correct mirror corresponding to valid tracks. When there are two or
    more tracks AND two or more hits in the Cerenkov, the analysis may get a
    little more complicated but should work out.