A current scan was made for the Yellow and Blue beam spin rotators at STAR during fill 16576 (March 16-17, 2012) in preparation for longitudinal running at 500 GeV.  Seven combinations of current settings were used.  STAR collected 3 ZDC polarimetry runs for each of these combinations.

The attachments give the settings and realtime results from the scaler-based analysis.  The analysis based on trigger-data shows consistent results, with an order of magnitude worse precision.

Following the scan, an optimal set of currents was applied and 3 additional ZDC polarimetry runs were taken (13077012-14). Initial online results indicate that the residual transverse components are at the level of 6% for the Yellow beam and at the level of 1% for the Blue beam.  No evidence for systematics larger in size than ~twice the statistical uncertainties was found from the ZDC polarimetry measurements at negative xF.  Typical asymmetry values observed during the preceding fills 16567 and at the start of 16570 were used to normalize instead of the CNI online values communicated through CDEV.

Thanks to the crews of the evening and night shift at STAR and MCR, including in particular Vahid Ranjbar.

Len Eun / Ernst Sichtermann