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 pCarbon 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.
Polarization facilities at RHIC.
32 s-1cm-2 50 < √s < 500 GeV
Design goal - 70% Polarization
RHIC: theL “Polarized”
max = 1.6  10 Collider
RHIC pC “CNI”
polarimeters
Absolute H-jet
polarimeter
RHIC
PHENIX
STAR
Siberian Snakes
Spin Rotators
Pol. H- ion source
5% Snake
LINAC
AGS, 24GeV
200 MeV polarimeter
BOOSTER, 2.5 GeV
AGS pC “CNI” polarimeter
20% Snake
Layout of the 200 MeV proton polarimeter, (2010)
16.2 deg
H -jet polarimeter.
Record 12.6∙1016 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
p
Beam Cross Section


FWHM~1.8mm
Average Pave
Peak Ppeak
The target ladder.
I ( x)  I max
 I2
R 2
P
P( x)  Pmax
 x2 
 exp   2 
 2 I 
 x2 
 exp   2 
 2 P 
Polarization Profiles
• Polarization loss from intrinsic resonances: polarization lost at edge of beam
→ polarization profile.
• Impact of polarization profile on beam polarization at collisions:
Pjet 
P0
(1  RH )(1  RV )
<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, Blue-2
“Golden fills” 17416-440
Run 13, P0 –maximum polarization, Pcoll-polarization
for colliding beams. Fills-17396-17440
24 GeV
B
<P>
255 GeV
Y
65%, AGS 66%, AGS
B
Y
58%
57%
R
0.08
0.08
0.10
0.11
P0
76%
79%
71%
70%
61%
60 %
Pcoll
About +/-3-5% errors, mostly systematic on all above numbers.
Run-12, P0 –maximum polarization, Pcollpolarization for colliding beams.
<P> Hjet
R
P0
Pcoll
24
GeV
24
GeV
100
GeV
100
GeV
255
GeV
255
GeV
B
Y
B
Y
B
Y
57.0
51.7
53.7
0.10
0.16
0.17
0.15
72%
76 %
71 %
71 %
64%
61%
56%
58 %
63±3.5 61.1
0.05 0.06
71 %
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%
 P 
P0
(1  RH )(1  RV )
For RH ≈ RV = R , P0= 0.80, <P> =Pjet= 60%
R ~ 0.15 - upper limit on R.
Pcoll
RV  RH
~  P  (1 
)
4
For R=0.1→ PpC~ 63%
Pcoll ~ 64.5%-upper limit
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
P0
Pjet 
(1  RH )(1  RV )
Pcoll
 Pjet
P0
Pjet
For  RV  RH  R  1  R 
(1  RV )(1  RH )
1 R
2 Pjet
2 Pjet
 Pjet


1
1
1
1
Pjet
(1  RV )(1  RH )
1 R 1
2
2
2
1 R 1 P
0
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.
Pcoll 
2 Pjet
Pjet
1
P0
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
• 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 5560% (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 polarization Transfer:
V
fix
P
V
fix
P
P0

(1  RV ) 1  RH
1
 P 
~ P (1  RH )
2
1  RH
V
fix
 P 
V
Pfix
1  RH

P0
(1  RH )(1  RV )
<P> ~ 71 × (1- ½ 0.08) ~ 68 %
AGS to RHIC Transfer:
Blue: <P> × 0.96 ~ 65.4%,
Yellow: <P> × 0.99 ~ 67.5%,
P0 =76.8 %
P0 =79%