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RHIC: the “Polarized” Collider

POLARIZATION MEASUREMENTS AND ABSOLUTE POLARIZATION VALUES EVOLUTION DURING PROTON BEAM ACCELERATION IN THE RHIC ACCELERATOR COMPLEX A.Zelenski, T.Roser, BNL. POLARIZATION MEASUREMENTS AND ABSOLUTE POLARIZATION VALUES EVOLUTION DURING PROTON BEAM ACCELERATION IN THE RHIC ACCELERATOR COMPLEX

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RHIC: the “Polarized” Collider

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  1. POLARIZATION MEASUREMENTS AND ABSOLUTE POLARIZATION VALUES EVOLUTION DURING PROTON BEAM ACCELERATION IN THE RHIC ACCELERATOR COMPLEXA.Zelenski, T.Roser, BNL

  2. POLARIZATION MEASUREMENTS AND ABSOLUTE POLARIZATION VALUES EVOLUTION DURING PROTON BEAM ACCELERATION IN THE RHIC ACCELERATOR COMPLEX A.Zelenski, T.Roser Absolute polarization measurements at different beam energies are very important for the understanding of the polarization evolution and polarization losses during acceleration and transport in the RHIC accelerator chain: Source-Linac-Booster-AGS-RHIC. In the RHIC complex there are two absolute proton polarimeters: the elastic proton-Carbon polarimeter at 200 MeV beam energy and theCNI H-jet polarimeter at 24-255 GeV in the RHIC ring. The polarization transport simulations show that depolarization occurs a the edge of the beam and that the polarization of the beam core at the center of the 2-dimensional beam intensity profile should be preserved during acceleration. Polarization profile measurements by the scanning p-Carbon CNI polarimeters in the AGS and RHIC provide experimental data that support these expectations. In addition, an estimate for the upper limit of depolarization at the edge of the beam distribution was deduced from the absolute polarization measurements at 200 MeV and at 100 and 255 GeV.

  3. RHIC: the “Polarized” Collider Polarization facilities at RHIC. Design goal - 70% Polarization L max = 1.6  1032 s-1cm-2 50 < √s < 500 GeV RHIC pC “CNI” polarimeters Absolute H-jet polarimeter RHIC PHENIX STAR Siberian Snakes Spin Rotators 5% Snake Pol. H- ion source LINAC AGS, 24GeV AGS pC “CNI” polarimeter 200 MeV polarimeter 20% Snake BOOSTER, 2.5 GeV

  4. Layout of the 200 MeV proton polarimeter, (2010) 16.2 deg

  5. H -jet polarimeter. Record 12.6∙1016 atoms/s Atomic Beam intensity. H-jet thickness at the collision point-1.2 ∙1012 atoms /cm2

  6. P-carbon polarimeter upgrade for Run 2009, two polarimerers in each ring for polarization profiles neasurements in both planes.

  7. Hydrogen Gas Jet and Carbon Wire Targets Carbon Wire Target Gas Jet Target Beam Cross Section  FWHM~1.8mm Average Pave Peak Ppeak

  8. The target ladder.

  9. Polarization Profiles • Polarization loss from intrinsic resonances: polarization lost at edge of beam → polarization profile. • Impact of polarization profile on beam polarization at collisions: <P>=Pjet-average polarization measured by H-jet or p-Carbon polarimeter in a sweep mode. P0-maximum polarization in the beam center. For RH ≈ RV = R and small: P0 = Pjet (1+R)2 ; Pcoll. = Pjet (1+ ½R) Bazilevskiy, Roser, Fisher

  10. R, Yellow-2

  11. R, Blue-2

  12. “Golden fills” 17416-440

  13. Run 13, P0 –maximum polarization, Pcoll-polarization for colliding beams. Fills-17396-17440 About +/-3-5% errors, mostly systematic on all above numbers.

  14. Run-12, P0 –maximum polarization, Pcoll-polarization for colliding beams. About 3-5% errors, mostly systematic on all above numbers.

  15. Carbon strip target deformation due to electrostatic interaction with the beam at 255 GeV.

  16. Carbon strip target deformation due to electrostatic interaction with the beam at injection energy 24GeV.

  17. Polarization profile R might be underestimated due to rate effects (AGS) and target deformation (largest effects at 255 GeV). • Therefore P0 value can be larger. • Ideally for Yellow P0 should be the Source Polarization: 80 × 0.99 = 79% For RH ≈ RV = R , P0= 0.80, <P> =Pjet= 60% R ~ 0.15 - upper limit on R. Pcoll ~ 64.5%-upper limit For R=0.1→ PpC~ 63% PpC~ 63% < Pcoll < 64.5% • Of course, there are systematic errors (~ 1-2%) in H-jet numbers too.

  18. Polarization (single spin asymmetry) in collisions Pcoll vs. Pjet Maximum P0 ~ 80%-source polarization (81% X 0.99 ~ 80%-for Yellow, 81% X 0.96 ~78% for Blue). For R<<1 corrections for double spin asymmetry are small ~ (RV2 +RH2)/8.

  19. Upper limit for polarization in collisions (single spin asymmetry) vs. H-jet polarization. P0=80% - Red line P0=70% - Blue line Pjet- black line low limit on Pcoll For P0=55 %, maximum Pcoll~ 60% R=0.1, Pcoll.pC~ 58%

  20. Summary • Upper limit on beam polarization in collisions was estimated, in assumption, that the polarization of the beam core at the center of the 2-dimensional beam intensity profile is preserved during acceleration. • This gives a quite narrow range for polarization in collisions 55-60% (for presently achieved average beam polarization of about 55% at 255 GeV). • The correction for polarization profile measured with p-Carbon CNI polarimeter is right in the middle of this range and the actual beam polarization in collisions is limited within the range: Pjet=58%< PpC.coll~61%≤ Pexp.coll < 63%

  21. Bazilevskiy

  22. AGS to RHIC polarization Transfer: <P> ~ 71 × (1- ½ 0.08) ~ 68 % AGS to RHIC Transfer: Blue: <P> × 0.96 ~ 65.4%, P0 =76.8 % Yellow: <P> × 0.99 ~ 67.5%, P0 =79%

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