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 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 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.

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

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

H -jet polarimeter. Record 12.6∙10 16 atoms/s Atomic Beam intensity. H-jet thickness at the collision point- 1.2 ∙10 12 atoms /cm 2

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

Hydrogen Gas Jet and Carbon Wire Targets Gas Jet Target Carbon Wire Target Beam Cross Section  FWHM~1.8mm Average P ave Peak P peak

The target ladder.

Polarization Profiles Polarization loss from intrinsic resonances: polarization lost at edge of beam → polarization profile. Impact of polarization profile on beam polarization at collisions: For R H ≈ R V = R and small: P 0 = Pjet (1+R) 2 ; P coll. = Pjet (1+ ½R) Bazilevskiy, Roser, Fisher =Pjet-average polarization measured by H-jet or p-Carbon polarimeter in a sweep mode. P 0 -maximum polarization in the beam center.

R, Yellow-2

R, Blue-2

“Golden fills”

Run 13, P 0 –maximum polarization, P coll -polarization for colliding beams. Fills GeV255 GeV BYBY 65%, AGS66%, AGS58%57% R P0P0 76% 79%71%70% P coll 61%60 % About +/-3-5% errors, mostly systematic on all above numbers.

Run-12, P 0 –maximum polarization, P coll - polarization for colliding beams. 24 GeV 24 GeV 100 GeV 100 GeV 255 GeV 255 GeV BYBYBY Hjet63± R P0P0 71 %72%76 %71 % P coll 64%61%56%58 % About 3-5% errors, mostly systematic on all above numbers.

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

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

Polarization profile R might be underestimated due to rate effects (AGS) and target deformation (largest effects at 255 GeV). Therefore P 0 value can be larger. Ideally for Yellow P 0 should be the Source Polarization: 80 × 0.99 = 79% Of course, there are systematic errors (~ 1-2%) in H-jet numbers too. For R H ≈ R V = R, P 0 = 0.80, =Pjet= 60% R ~ upper limit on R. P coll ~ 64.5%-upper limit P pC ~ 63% < P coll < 64.5% For R=0.1→ P pC ~ 63 %

Polarization (single spin asymmetry) in collisions Pcoll vs. Pjet Maximum P 0 ~ 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 ~ (R V 2 +R H 2 )/8.

Upper limit for polarization in collisions (single spin asymmetry) vs. H-jet polarization. P 0 =80% - Red line P 0 =70% - Blue line P jet - black line low limit on P coll For P 0 =55 %, maximum Pcoll~ 60% R=0.1, P coll.pC ~ 58%

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 % (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%< P pC.coll ~61%≤ P exp.coll < 63%

Bazilevskiy

AGS to RHIC Transfer: Blue: × 0.96 ~ 65.4%, P 0 =76.8 % Yellow: × 0.99 ~ 67.5%, P 0 =79% ~ 71 × (1- ½ 0.08) ~ 68 % AGS to RHIC polarization Transfer: