Log entry time 16:12:37 on June13,2004

Entry number 125586

Followups:

• 125590 06/13/04 16:33 Armstrong correction

 
Counting rate estimate

  We are running with a beam energy of 3.026 GeV, rather than the
3.2 GeV assumed in the proposal. 

  Thus we are at a Q2 of about 0.09 GeV2, not 0.1 GeV2 (using an acceptance-averaged central angle of 5.72°).

  The counting rate I get, per arm, for 100 µA at this Q2
is 17 MHz, compared to the 12 MHz in the proposal. Scaling
to 30 µA,  I get a predicted detector asymmetry pulse-pair
width of 1720 ppm. 

  Unfolding the boiling contribution of about 600 ppm for the 4x4
raster at 30 µA, I get, from Bryan's analysis of the boiling
studies,
   Detector 1 (right arm): 1650 ppm
   Detector 3 (left arm) : 1960 ppm 

  so Detector 1 looks reasonably consistent with the predicted rate
(within the uncertainty of the calculation), but Detector 3 appears
to have a significantly lower rate - 40%??

  The cross section goes like 1/theta6 for small
angles, so if this counting rate difference is correctly estimated, 
and is due entirely to detector mispointing, it would indicate
a 0.35° larger angle for the left arm. This seems large
to me! Does anyone know if this is consistent (even in sign) 
with what has been learned from hypernuclear?

  It would be of interest to look at our spectrometer DAQ runs to
compare the elastic peak trigger rates between the two arms, and
double-check the centering of the elastic peak. This will tell 
us if we need to refine the centering of the elastic peak on 
the detector for the left arm. 

  volunteers?