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Helicity dependent asymmetry of the Bar Rate

To quantify the helicity dependent asymmetry of the Bar rate A_b we can use scaler values:

$\begin{displaymath}A_{b}=\frac{b^{\downarrow }-b^{\uparrow }}{b^{\downarrow }+b^... ...row }=\frac{B^{\uparrow \downarrow }}{T^{\uparrow \downarrow }}\end{displaymath}$

$B^{\uparrow \downarrow }$ and $T^{\uparrow \downarrow }$ denote the scaler counts of ``B Pretrigger'' and ``1 MHz Clock'' respectively with the up arrow indicating the positive helicity² and the down arrow indicating the negative helicity. Note that this is the asymmetry of the raw Bar rates not normalized for beam current. According to the explanation in the previous section it is the raw rate that affects the electronics dead-time. A_b was calculated for all Q²=0.5runs that made the DEC99 replay. For further insight the beam current asymmetry was calculated for the same runs too. Fig.

shows the results of this study.

**Figure:** The top graph shows beam current asymmetries vs. run number. The two solid red lines indicate the averages for positive and negative target polarization, which are basically equal. The bottom graph shows Bar pretrigger rate asymmetries vs. run number for positive (green) and negative (blue) target polarization. The two corresponding solid lines indicate the averages and the red line is again the average of the beam current asymmetry.
$\resizebox*{0.85\textwidth}{!}{\includegraphics{a_Bptr.ps}}$

The average beam current asymmetry is in the order of $6.5\cdot 10^{-4}$ and is the same for both signs of the target polarization as one would expect. The Bar rate however has an intrinsic asymmetry of the same order as the beam current asymmetry. This intrinsic asymmetry flips sign with the orientation of the target polarization. As a consequence we have an asymmetric behavior behavior with respect to the two signs of the target polarization! The asymmetry of the raw bar rate is basically 0 for the positive target polarization and significant for the negative target polarization. The numbers are $A_{b}=(-7.6\pm 0.2)\cdot 10^{-5}$ for positive and $A_{b}=(-1.134\pm 0.002)\cdot 10^{-3}$ for negative target polarization.

Side note 1: The spread in the distribution of bar asymmetries becomes smaller and is much more correlated with the beam current after run 21000, which is due to the synchronization of the raster with the helicity.

Side note 2: The intrinsic Bar rate asymmetry has the opposite sign to the coincidence rate asymmetry and is one order of magnitude smaller.

Next: Impact on Physics Asymmetries Up: E93-026 Technical Note: Electronics Previous: Electronics dead-time during Gen98

Marko Zeier
2000-05-04