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Run 8 Polarization measurements from STAR BBC

Run 8 Polarization measurements from STAR BBC. Andrew Gordon September 12, 2008. Inner tiles of BBC accumulated every clock cycle. {. Hank’s Scaler Boards. }. Discriminated phototube outputs. 24-bit word is histogrammed every clock cycle. {. East-West Coincidence. }.

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Run 8 Polarization measurements from STAR BBC

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  1. Run 8 Polarization measurements from STAR BBC Andrew Gordon September 12, 2008

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

  3. Requirements: Outer left and right phototubes (9,10,11 and 14,15,16) 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: updown updown   - NL NR NR NL p = updown updown   + NL NR NR NL 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/0501072v1, 28 Jan 2005 and C.A.Whitten (STAR), Proceedings PSTP 2007, p. 390.

  4. Background level from abort gaps low Yellow beam Background fraction <Blue Empty & Yellow Filled> = <Blue Filled & Yellow Filled> Blue beam Background fraction <Blue Filled & Yellow Empty> = <Blue Filled & Yellow Filled> Yellow filled & Blue filled Yellow filled & Blue empty Yellow empty & Blue filled Yellow empty & Blue empty Star preliminary

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

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

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

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

  9. Polarization dependence not always smooth decay Star preliminary

  10. Polarization dependence not always smooth decay Star preliminary

  11. Effective decay rates of polarization vs Fill Polarization of each fill fitted to P = A e-t <>=1.7±0.1 separately for each beam. Yellow beam decay rate more consistently non-zero than blue beam. <>=0.7±0.1 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 1000. Star preliminary

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

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

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