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    User name R. Michaels

    Log entry time 13:24:37 on June19,2004

    Entry number 126314

    Followups:

    keyword=prelim. Alum. background results

    I checked the Alum. background runs for HAPPEX DAQ data and
    spectrometer DAQ data. One thing I don't know for sure (groan)
    is the relative thickness of the alum. dummy cell walls compared
    to the 20 cm racetrack cell walls. Let this variable be "xt".
    I think xt = 0.1 (ratio of racetrack to dummy) but we need to find
    out for sure.

    First the raw data

    HAPPEX run 2244 production run
    I_beam ... det1 (L-arm) .... det3 (R-arm)
    26.5 uA..... 33200 ............ 28000

    HAPPEX run 2250 - 20 cm alum dummy target, nominal momentum
    I_beam .... det1 ....... det3
    24 uA ...... 2450 ......... 1980

    Spectr. DAQ runs
    Note from online :
    HV was same and amplitudes in ADC same (to be checked again).
    Acceptance of front and back foils of Al dummy tgt was same (tbca).

    Run 1121 ..... elastic peak on detector (good alignment)
    I_beam ......... L-arm rate (T4) ..... R-arm rate (T2)
    0.56 +/- 0.15 uA ... 79 kHz ............ 109 kHz

    Run 1144 .... 20 cm Alum dummy target
    I_beam ......... L-arm rate (T4) ..... R-arm rate (T2)
    1.89 +/- 0.6 uA .... 26.4 kHz ........ 34.5 kHz

    Results -- must normalize to beam current
    Ratio of signal for Alum dummy to 20 cm racetrack

    DAQ ....... L-arm ratio ........ R-arm ratio
    HAPPEX ..... 0.081 xt .......... 0.078 xt (error ~0.005 xt )
    Spectr ..... 0.099 xt .......... 0.093 xt (error ~ 0.01 xt )
    (Reminder: xt = ratio of racetrack to dummy tgt thickness
    i.e. the Aluminum component of racetrack).
    The error in spectr-DAQ result is bigger due to small beam current
    and error in beam current.

    Conclusions:
    1) HAPPEX DAQ and Spectr. DAQ are consistent.
    2) If xt = 0.1 as rumored (and we need to find out !) then the
    background from Alum is 0.9 +/- 0.2 % (error may go down later).
    3) See yesterday's halogs, the background is almost exclusively from
    tail of Q.E. peak. There is no (or very small) Alum elastic or
    other inelastic levels.
    4) For this year's He4 run, we need no more data on Alum backgrounds.