Absolute Polarization Measurement at RHIC in the Coulomb Nuclear Interference Region September 30, 2006 RHIC Spin Collaboration Meeting RIKEN, Wako, Japan K. Oleg Eyser University of California, Riverside 2005

Jet Polarimeter Setup 96 silicon strips: 6 x 2 x 8 geometry reflects kinematics in: x y jet ~ 80 cm 8 cm 5 cm scattered recoil displacement of beams

Recoil Protons T R (MeV) t TOF (ns) prompt events (large yield, filtered) ADC (peak or integral) Calibration Am (5.486 MeV) Gd (3.183 MeV) TDC ¼ rise time scale 1.19 ns T 0 calibration from proton signals recoil protons from elastic scattering single strip (example) TDC (a.u.) ADC (a.u.) a typical waveform

< T R < 3.5 MeV 1.5 < T R < 2.0 MeV 2.0 < T R < 2.5 MeV 2.5 < T R < 3.0 MeV strips Beamgas background from empty target runs: 2.4% - 3.4% strips elastic signal 1.0 < T R < 1.5 MeV

MeV 1.5 – 2.0 MeV 2.0 – 2.5 MeV 2.5– 3.0 MeV 3.0 – 3.5 MeV 3.5– 4.0 MeV bunch distributions, including all cuts blue and yellow detector sides separated abort gaps (example: blue 120 bunch mode) blue abort gapyellow abort gap not for both beams on jet !!! yellow 60 blue 60 yellow 120 blue – 1.5 MeV1.2% 1.3%1.2% 1.5 – 2.0 MeV2.1%2.0%2.1%1.6% 2.0 – 2.5 MeV1.5%2.1% 1.9% 2.5 – 3.0 MeV2.4%2.1%2.7%2.6% 3.0 – 3.5 MeV3.6%2.8% 2.9% 3.5 – 4.0 MeV4.7%2.0%5.0%3.1%

Asymmetries and Polarization Target Yellow beam Blue beam

bunch shuffling 5000 shuffles asymmetry ratio (beam / target) divided by its statistical error yellow beam centered 120 bunch mode  blue  blue  yellow  yellow both yellow blue yellow blue too large where statistical errors are small include systematic errors from abort gaps !!!  consistent with 1 within accuracy of number of filled bunches fit gaussian

variations of proton signal regions beam and target asymmetries pick up more background, ratio (polarization) is very stable 1 stripall strips2 strips3 strips4 strips5 strips

Systematic Error Summary yields include (s)ignal and (b)ackground simple asymmetries: left-right, up-down relative luminosity: no monitor use integrated left-right yields  cut dependence acceptance asymmetry: detector alignment efficiency asymmetry: detector efficiency Background should have no effect at all on the determination of the beam polarization !!! Issues when dealing with physical properties (analyzing power). background yield 5% to 7%. (same for physics quantities) systematic errors of beam polarization smaller than 2%. (strip signal region variations, previous slide) if not polarization dependent !!!

Beam Polarizations yellow beamP  stat 120 b. mode45.4 %1.4 % 60 b. mode41.1 %2.9 % both beams41.9 %2.9 % blue beamP  stat 120 b. mode49.4 %1.7 % 60 b. mode48.2 %3.8 % both beams43.8 %2.8 % Target Yellow beam Blue beam 120 bunch mode Target Yellow beam Blue beam 120 bunch mode

Polarizations: comparison to online numbers from Carbon polarimeters  one sigma bands pC online meas. both beams on jet (60 bunch mode) yellow beam on jet (60 & 120 bunch modes) blue beam on jet (60 & 120 bunch modes) 205 GeV/c blue measurements yellow measurements