Run 8 Polarization measurements from STAR BBC Andrew Gordon September 12, 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 Requirements: Outer left and right phototubes of small tiles have no hits. Left Hit=Hit in 2 or 3 AND no hit in 5 and 6 Right Hit=Hit in 5 or 6 AND no hit in 2 and 3 Polarization: pp  N L N R up down N R N L up down  -  N L N R up down N R N L up down  + = For effective analyzing power use final Run 6 polarizations and Run 6 BBC data: Yellow Polarization (%)=  p (East)/(6.9±0.1(stat))x10 -5 Blue Polarization (%)=  p (West)/(7.1±0.1(stat))x10 -5 See also J. Kiryluk (STAR) ArXiv:hep-ex/ v1, 28 Jan 2005 and C.A.Whitten (STAR), Proceedings PSTP 2007, p. 390.

Effective Analyzing Power BBC Polarimeter Analysis from available run-6 data  more complete analysis still to do Event data suggests BBC very similar year to year  assume same effective analyzing power for run 8

5 Example: Rates for start of Fill 9949 East-West Coincidence Rates for each crossing 100 Yellow filled & Blue filled crossings 7 Yellow Empty & Blue Filled bunches 7 Yellow Filled & Blue Empty bunches Yellow Background ~ 0.1% Blue Background ~ 0.2% ~0.5 MHz Star preliminary

6 Background level from abort gaps low Yellow filled & Blue empty Yellow empty & Blue empty Yellow empty & Blue filled Yellow filled & Blue filled Yellow beam Background fraction = Blue beam Background fraction = Star preliminary

Example: Background for Fills 9949 and 9951 Note change of scale on y- axis Background fractions low and relatively stable, except for event in blue beam at around 3 hours. Time=midpoint of run relative to start of fill, ~ 10 minutes Star preliminary

Example: Multiplicity for Fills 9949 and 9951 Average number of BBC phototubes with hits is relatively stable. (Event in blue beam 9949 not detectable.) East BBC West BBC Star preliminary

9 Sample polarization time dependence Decline visible in fill 9949, but 9951 more stable. Time=midpoint of run relative to start of fill, ~ 10 minutes Star preliminary Flat line fits shown

10 Polarization dependence not always smooth decay Star preliminary

11 Polarization dependence not always smooth decay Star preliminary

12 Effective decay rates of polarization vs Fill Polarization of each fill fitted to P = A e -  t separately for each beam. Yellow beam decay rate more consistently non-zero than blue beam. Star preliminary Comparing to Whitten PSTP 2007, roughly same rates as for Run 6. Polarization in units of percent. The values for  are the y-axis values divided by 100. =1.7±0.1 =0.7±0.1

13 Fill averaged polarizations Run 6 calibration of BBC asymmetries applied to Run 8 data. Star preliminary

Comparison of Polarization to CNI results For each fill calculate STAR/pC Error bars are uncorrelated errors only. pC data from Sasha, September 12, Uncertainties dominated by pC uncertainty estimates. Mean=1.026±0.023 Mean=0.929±0.012

15 Conclusions Absolute polarization can be derived from Run 6 calibration. Polarization shows dependence on time. Some fills show a step downward in middle of fill Stronger for the yellow beam STAR can measure polarization at relatively small time steps.