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 JETDesign of the High Frequency Transitions (HFT)Accuracy of Breit-Rabi-polarimeter (BRP) measurementEfficiencies of the HFT’s and atomic polarizationDepolarizing effectsVelocity at the Interaction Point and target densitySummary

Alexander Nass, Brookhaven National Laboratory SPIN 2004, Oct 14 2004

Setup of the JET

Atomic beam produced by expansion of a dissociated H beam through a cold nozzle into vacuum chamberNuclear polarization achieved by HFT’s (SFT, WFT) after focusing with sextupole magnetsAfter passing RHIC beam BRP sextupoles focus the atomic beam into the detectorDetermination 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

High Frequency Transitions

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

HFT’s located in a shielding box to reduce large z-field of main target magnet and avoid non adiabatic regionsWater cooling to reduce resonance drifting effects of cavity due to thermal expansion

Solving the problem

Creation of plasma depends on surrounding magnetic field, gas density and RF-powerNot convenient to change magnetic fields and necessary RF-power.Solution: Pulsing of dissociator power to reduce density for a short period (~10 ms)

Accuracy of the BRP measurement

1/3 of the full jet beam analyzed in BRP2 beam blockers to remove atoms in states |3> and |4> and molecules from beamChopped beam signal to subtract backgroundHigh signal to noise ratio due to improved signal processing (noise reduction, signal amplification, proper grounding)Determination of HFT efficiencies to a relative error of S/S < 0.1% in t < 1 min

Efficiencies and nuclear polarization

Due to beam blockers only atoms in state |1> and |2> reaching the BRP detectorUsing 4 HFT’s in ABS and BRP to create and analyze the nuclear polarizationParameters are the efficiencies (1- 1-3), (1-), (1-’1-3), (1-’2-4) and the transmission ratio N2/N1 of state |2> to |1> through sextupolesPolarization: (=arctan BC/BJET, BC=50.7 mT, BJET=120 mT)

Efficiencies and nuclear polarization

Stable behavior over the whole 2004 run, mean values for nuclear polarization of the atoms:

P+ = 0.9570.001 and Pˉ = -0.9590.001

Stability of nuclear polarization

Depolarizing effectsMajorana depolarization if change of direction of magnetic fields in rest frame of the atoms along atomic beam path is too rapidNo depolarization if field changes are adiabatic, i.e. slow compared to Larmor time tL ~ 1/B

Depolarizing EffectsBeam induced depolarization due to bunched structure of p-beam transient magnetic fields transverse to the beam directionClosely spaced depolarizing resonances in the usable range of the surrounding target holding field

High uniformity of the target holding field necessary

Required at JET:B/B=6ּ10-3

achieved 5ּ10-3

No depolarizationwith 60 bunches inRHIC

Toms theoretical values to be added

Velocity at the IP with RHIC

Measurements done using a fast chopper and a QMATOF signal influenced by opening function of the chopper windowInfluence decreases as speed of chopper increases Measurements at different chopper speedsResult: v=1562±20 m/sVariation 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

Areal density of the Jet

FWHM of the JET (comp. tube measurement): 5.5mmMeasured intensity: (12.4±0.2)ּ1016 atoms/sUsing measured velocity: z=(7.94±0.13)ּ1010 atoms/mmAssuming Gaussian distribution:

Density for RHIC interaction (square of 1 mm2):

= (1.33 ± 0.02) 1012 atoms/cm2

Velocity distribution at the BRP

Measurement done using the ABS-SFT and a QMA in BRP chamberTOF spectrum measured using SFT pickup amplitude as triggerSpectrum shows transmission peaks of the combined ABS and BRP sextupole system

Summary

Highly efficient and stable polarization (P=0.958±0.001)Very accurate measurement with BRP (P/P < 0.1% )No bunch field depolarization detectable with 60 bunchesNext run probably with 120 bunches, but uniformity of the target holding field assumed to be sufficient for a working point with no depolarizationTarget 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