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

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

STARPHENIX

AGS, 24GeVLINAC

BOOSTER, 2.5 GeV

Pol. H- ion source

Spin Rotators

20% Snake

Siberian Snakes

200 MeV polarimeter

RHIC pC “CNI” polarimeters

RHIC

Absolute H-jetpolarimeter

Design goal - 70% Polarization L max = 1.6 1032 s-1cm-2 50 < √s < 500 GeV

AGS pC “CNI” polarimeter

5% Snake

Polarization facilities at RHIC.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 ∙1012 atoms /cm2

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

p

FWHM~1.8mmFWHM~1.8mm

Average Pave Peak Ppeak

The target ladder.

2

2

max 2exp)(

I

xIxI

2

2

P

IR

2

2

max 2exp)(

P

xPxP

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 RH ≈ RV = R and small: P0 = Pjet (1+R)2 ;

Pcoll. = Pjet (1+ ½R)

Bazilevskiy, Roser, Fisher

<P>=Pjet-average polarization measured by H-jet or p-Carbon polarimeter in a sweep mode. P0-maximum polarization in the beam center.

)1)(1(0

VHjet RR

PP

R, Yellow-2

R, Blue-2

“Golden fills” 17416-440

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

17440

24 GeV 255 GeV

B Y B Y

<P> 65%, AGS 66%, AGS 58% 57%

R 0.08 0.08 0.10 0.11

P0 76% 79% 71% 70%

Pcoll 61% 60 %

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

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

24 GeV

24

GeV

100 GeV

100

GeV

255 GeV

255

GeV

B Y B Y B Y

<P> Hjet 63±3.5 61.1 57.0 51.7 53.7

R 0.05 0.06 0.10 0.16 0.17 0.15

P0 71 % 72% 76 % 71 % 71 %

Pcoll 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 P0 value can be larger.• Ideally for Yellow P0 should be the Source Polarization: 80 × 0.99 = 79%

)1)(1(0

VH RR

PP

•Of course, there are systematic errors (~ 1-2%) in H-jet numbers too.

For RH ≈ RV = R , P0= 0.80, <P> =Pjet= 60%R ~ 0.15 - upper limit on R.

)4

1(~ HVcoll

RRPP

Pcoll ~ 64.5%-upper limit

PpC~ 63% < Pcoll < 64.5%For R=0.1→ PpC~ 63%

Polarization (single spin asymmetry) in collisions Pcoll vs. Pjet

0

1

2

11

1

2

21

1

1

)21

1)(21

1(

)1)(1(

P

P

Pjet

R

Pjet

R

RP

RR

RRPP

jet

jet

HV

HVjetcoll

)1)(1(0

VHjet RR

PP

jetHV P

PRRRRFor 01

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 +RH

2)/8.

Upper limit for polarization in collisions (single spin asymmetry) vs. H-jet

polarization.

0

1

2

P

P

PjetP

jet

coll

P0=80% - Red line

P0=70% - Blue line

Pjet- black linelow limit on Pcoll

For P0=55 %, maximum Pcoll~ 60%

R=0.1, Pcoll.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 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%

Bazilevskiy

AGS to RHIC Transfer:

Blue: <P> × 0.96 ~ 65.4%, P0 =76.8 % Yellow: <P> × 0.99 ~ 67.5%, P0 =79%

<P> ~ 71 × (1- ½ 0.08) ~ 68 %

AGS to RHIC polarization Transfer:

)1)(1(10

VHH

Vfix

RR

P

R

PP

)

2

11(~

1H

Vfix

H

Vfix RPR

PP

HV

Vfix

RR

PP

1)1(0