POLARIZATION MEASUREMENTS AND ABSOLUTE POLARIZATION VALUES EVOLUTION DURING PROTON BEAM ACCELERATION...
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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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Rhic the polarized collider

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


Rhic the polarized collider

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.


Rhic the polarized collider

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


Rhic the polarized collider

Layout of the 200 MeV proton polarimeter, (2010)

16.2 deg


H jet polarimeter

H -jet polarimeter.

Record 12.6∙1016 atoms/s

Atomic Beam intensity.

H-jet thickness at the collision point-1.2 ∙1012 atoms /cm2


Rhic the polarized collider

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

Hydrogen Gas Jet and Carbon Wire Targets

Carbon Wire Target

Gas Jet Target

Beam Cross Section

FWHM~1.8mm

Average Pave

Peak Ppeak


Rhic the polarized collider

The target ladder.


Polarization profiles

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


R yellow 2

R, Yellow-2


R blue 2

R, Blue-2


Golden fills 17416 440

“Golden fills” 17416-440


Run 13 p 0 maximum polarization p coll polarization for colliding beams fills 17396 17440

Run 13, P0 –maximum polarization, Pcoll-polarization for colliding beams. Fills-17396-17440

About +/-3-5% errors, mostly systematic on all above numbers.


Run 12 p 0 maximum polarization p coll polarization for colliding beams

Run-12, P0 –maximum polarization, Pcoll-polarization for colliding beams.

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 255 GeV.


Rhic the polarized collider

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


Rhic the polarized collider

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.


Polarization single spin asymmetry in collisions pcoll vs pjet

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.


Upper limit for polarization in collisions single spin asymmetry vs h jet polarization

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%


Summary

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%


Rhic the polarized collider

Bazilevskiy


Ags to rhic polarization transfer

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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