Bunch-by-bunch (relative) polarization measurements using inner annuli of STAR BBC Andrew Gordon April 4, 2008

2 } { East-West Coincidence Bunch Crossing (7-bits) { Hank’s Scaler Boards } 24-bit word is histogrammed every clock cycle Inner tiles of BBC accumulated every clock cycle Discriminated phototube outputs

3 Require East-West coincidence Top and bottom of inner tiles clean to reduce dilution of asymmetry Keeps ~5% of all bunch crossings. Keeps 20% of the 5%=1% of all crossings pass both requirements. Typical numbers on the order of ~3M events per bunch per hour ~3.5  (statistical) measurement of polarization per bunch per hour Use tiles 5+6 for Left, tiles 2+3 for Right (Backgrounds from single beam accidentals less than ~1% of sample after this requirement.)

4 Yellow (east BBC) Blue (west BBC) sig Sig bx = Statistical uncertainties only (|P bx |- )  bx Width=1.22  0.15 Width=1.05  0.12

5 Yellow Blue sig Sig bx = Statistical uncertainties only (|P bx |- )  bx Width=1.12  0.14 Width=0.91  0.09

6 Yellow Blue sig Sig bx = Statistical uncertainties only (|P bx |- )  bx Width=1.16  0.13 Width=0.79  0.08

7 Yellow Blue sig Sig bx = Statistical uncertainties only (|P bx |- )  bx Width=1.06  0.16 Width=0.84  0.07

8 Conclusions We can see the relative polarization per bunch at a rate of several measurements per fill. Polarization is largely consistent across bunches. Can be extended to all Run 8 fills. Measurement requires calibration to determine polarization at STAR. To do