Towards Improved Polarimetry at RHIC

1. Towards Improved Polarimetry at RHIC Yousef I. Makdisi Brookhaven National Laboratory For The RHIC Polarimetry Group

2. Outline • A brief introduction to the polarimetry components • The P-Carbon CNI polarimeters • Current R&D efforts • Upgrade plans • The Polarized Jet Target issues • Plans for the Jet for Run 9 • Summary

3. BRAHMS(p) Absolute Polarimeter (H jet) pC Polarimeters Siberian Snakes Spin flipper PHENIX (p) STAR (p) Spin Rotators (longitudinal polarization) Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake LINAC BOOSTER Helical Partial Siberian Snake Pol. H- Source AGS 200 MeV Polarimeter AGS Polarimeters Strong AGS Snake

4. The RHIC Polarimetry Complex The Polarized Hydrogen Jet target Self Calibrating p-Carbon Polarimeters Calibrated from the Jet Data

5. L Target Detector port (inner view) SSD (effective deadlayer) (adcC) p-Carbon Polarimeters E • 5.486 MeV (85%) • 5.443 MeV (12%) (t0,x)Kinematic Fit

6. p-Carbon Polarimeters Energy Correction Vipuli • Energy calibration uses alpha sources followed by a fit to TOF/ Energy relation to extract the dead layer thickness • The average thickness is ~ 80 gm/cm2>> 25-30 gm/cm2 expected • The energy correction in the silicon carbon could be charge dependent !!

7. R&D Effort At The Tandem Morozov • The BNL Tandem: Carbon beams to scan energies of interest with varying intensities up to 4.106/cm2: • 0.3 – 5 MeV (wider than the current range to reach the Alpha energy from the Americium source) • Charge of +1, +2, and +3 • This will provide a good energy calibration • Will decouple the time and energy dependences • Use alpha sources impinging forward and backward to determine the effective silicon thickness and assess potential degradation • Use a foil to simulate the polarimeter carbon target

8. p-Carbon Polarimeters – Looking Ahead • Test new Hammamatsu photodiode detectors and array under similar conditions • A factor of 4 energy resolution good for going to lower t • We will also test a duel-silicon detector system with • a thin 5 m followed by the 300 m detectors • Identify the carbon charge with the thin detector at energies between 0.3 – 1 MeV. This then drives the energy loss (dead layer) determination from the earlier data • An added bonus, the thin detector could provide a trigger. It is blind to minimum ionizing prompts, so less rate dependent • Test the existing charge amplifier with a lower shaping time • Test a new low capacitance cable between the detector and preamp • Test a current amplifier concept: better for high capacitance detectors and high rate environment. Are the noise levels acceptable? • For high rate we will try to reduce the silicon volume current by reducing area and thickness

9. Testing in situ w/ New Polarimeter Upgrade • Run 9: install the new detectors • in a two arm 450 configuration in • one of the duel polarimeters: • Compare its performance to the • existing systems under similar • beam conditions • Assess resilience to radiation • Include a detector to get a handle • on the prompts or t0 timing

10. Jet Target experienced higher background levelsH. Okada

11. Background Under The Jet Elastic Signal • Studied the contribution from • each beam separately the incident • beam and the displaced beam • If elastics, expected a beam related • Asymmetry. None was found • Two beam mode did not show • increased background! • With beam incident at the jet FWHM position • did not observe lower asymmetry within stats. • Collimators were removed this Run

12. The Polarized Jet Target Two Beam Mode y (+10, -10) mm +10 -10 x (0, -1.5) mm (0, -7) mm jet

13. For Run 9 • Re-install and survey the collimators albeit with a wider vertical opening for better two-beam acceptance. Re-establish conditions similar to Run6 • The two beam mode allows for simultaneous calibration of both the Blue and Yellow p-Carbon polarimeters instead of alternating between them. • Use one beam only impinging on the jet center and assess the associated background • Use one beam displaced by 10 x 10 mm in x and y respectively and determine the background under the signal if any • Use a two beam mode to see if the background is any different • Run with the beam at the FWHM position for enough statistics to see if there is any jet beam polarization profile • Repeat jet beam depolarization measurements with the two beam mode

14. Run 9 + • We need to revisit the molecular hydrogen background. • This still represents the largest systematic error on the jet measurement • Re-do the electron beam measurement with a time of flight measurement instead of the magnetic measurement of the outgoing products. • (A. Belov, INR) • A good statistical measurement and calibration at RHIC injection energy to couple the AGS and RHIC measurements and assure that we do not lose polarization on the RHIC ramp

15. Summary • We continue to strive for consistent polarimetry measurements from one run to the next • We are embarking on a significant R&D effort for better detector performance especially in anticipating higher rate environment • Continued efforts to understand the associated backgrounds and reduce the associated systematic errors • It is gratifying to see the analyses of both the polarimaters and jet data completed in half the earlier times. • A testimonial to the analysis maturity and thanks to the diligence of • Hiromi Okada (BNL Spin Phys. Group, now at KEK-Jparc) • Vipuli Dharmawardane (New Mexico State University)