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Atomic Beam Polarization Measurement of the RHIC Polarized H-Jet Target

Atomic Beam Polarization Measurement of the RHIC Polarized H-Jet Target. A. Nass, M. Chapman, D. Graham, W. Haeberli, S. Kokhanovski, A. Kponou, G. Mahler, Y. Makdisi, W. Meng, J. Ritter, T. Wise, A. Zelenski, V. Zubets. Outline. Setup of the JET

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Atomic Beam Polarization Measurement of the RHIC Polarized H-Jet Target

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  1. Atomic Beam Polarization Measurement of the RHIC Polarized H-Jet Target A. Nass, M. Chapman, D. Graham, W. Haeberli, S. Kokhanovski, A. Kponou, G. Mahler, Y. Makdisi, W. Meng, J. Ritter, T. Wise, A. Zelenski, V. Zubets

  2. Outline • Setup of the JET • Design of the High Frequency Transitions (HFT) • Accuracy of Breit-Rabi-polarimeter (BRP) measurement • Efficiencies of the HFT’s and atomic polarization • Depolarizing effects • Velocity at the Interaction Point and target density • Summary Alexander Nass, Brookhaven National Laboratory SPIN 2004, Oct 14 2004

  3. Setup of the JET • Atomic beam produced by expansion of a dissociated H beam through a cold nozzle into vacuum chamber • Nuclear polarization achieved by HFT’s (SFT, WFT) after focusing with sextupole magnets • After passing RHIC beam BRP sextupoles focus the atomic beam into the detector • Determination of the efficiencies of these HFT’s and the polarization of the beam by comparing the detector signals while running different HFT’s, e.g.: • ABS SFT • ABS WFT • ABS SFT + ABS WFT • BRP HFT’s for calibration

  4. High Frequency Transitions • HFT’s located in a shielding box to reduce large z-field of main target magnet and avoid non adiabatic regions • Water cooling to reduce resonance drifting effects of cavity due to thermal expansion • Possible creation of short-lived (up to 10s) plasma inside the SFT cavity due to reduced pumping due to shielding box which slows down the turn on but didn’t affect polarization

  5. Solving the problem • Creation of plasma depends on surrounding magnetic field, gas density and RF-power • Not convenient to change magnetic fields and necessary RF-power. • Solution: Pulsing of dissociator power to reduce density for a short period (~10 ms)

  6. Accuracy of the BRP measurement • 1/3 of the full jet beam analyzed in BRP • 2 beam blockers to remove atoms in states |3> and |4> and molecules from beam • Chopped beam signal to subtract background • High signal to noise ratio due to improved signal processing (noise reduction, signal amplification, proper grounding) • Determination of HFT efficiencies to a relative error of DS/S < 0.1% in t < 1 min

  7. Efficiencies and nuclear polarization • Due to beam blockers only atoms in state |1> and |2> reaching the BRP detector • Using 4 HFT’s in ABS and BRP to create and analyze the nuclear polarization • Parameters are the efficiencies (1- e1-3), (1-e2-4), (1-e’1-3), (1-e’2-4) and the transmission ratio N2/N1 of state |2> to |1> through sextupoles • Polarization: (q=arctan BC/BJET, BC=50.7 mT, BJET=120 mT)

  8. Efficiencies and nuclear polarization Stable behavior over the whole 2004 run, mean values for nuclear polarization of the atoms: P+ = 0.957±0.001 and Pˉ = -0.959±0.001

  9. Stability of nuclear polarization

  10. Depolarizing effects • Majorana depolarization if change of direction of magnetic fields in rest frame of the atoms along atomic beam path is too rapid • No depolarization if field changes are adiabatic, i.e. slow compared to Larmor time tL ~ 1/B

  11. Depolarizing Effects • Beam induced depolarization due to bunched structure of p-beam  transient magnetic fields transverse to the beam direction • Closely spaced depolarizing resonances in the usable range of the surrounding target holding field • High uniformity of the target holding field necessary Required at JET: DB/B=6ּ10-3 achieved 5ּ10-3 No depolarization with 60 bunches in RHIC Toms theoretical values to be added

  12. Velocity at the IP with RHIC • Measurements done using a fast chopper and a QMA • TOF signal influenced by opening function of the chopper window • Influence decreases as speed of chopper increases  Measurements at different chopper speeds • Result: v=1562±20 m/s • Variation in dissociator parameters showed only small (±50 m/s) variations in velocity spectrum since it is almost fixed by the transmission of the sextupole magnets

  13. Areal density of the Jet • FWHM of the JET (comp. tube measurement): 5.5mm • Measured intensity: (12.4±0.2)ּ1016 atoms/s • Using measured velocity: rz=(7.94±0.13)ּ1010 atoms/mm • Assuming Gaussian distribution: • Density for RHIC interaction (square of 1 mm2): = (1.33 ± 0.02) 1012 atoms/cm2

  14. Velocity distribution at the BRP • Measurement done using the ABS-SFT and a QMA in BRP chamber • TOF spectrum measured using SFT pickup amplitude as trigger • Spectrum shows transmission peaks of the combined ABS and BRP sextupole system

  15. Summary • Highly efficient and stable polarization (P=0.958±0.001) • Very accurate measurement with BRP (DP/P < 0.1% ) • No bunch field depolarization detectable with 60 bunches • Next run probably with 120 bunches, but uniformity of the target holding field assumed to be sufficient for a working point with no depolarization • Target density of (1.10 ± 0.02)ּ1012 atoms/cm2 • Looking forward to run 2005 (120 bunches) Alexander Nass, Brookhaven National Laboratory SPIN 2004, Oct 14 2004

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