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RHIC Spin and Collider. Mei Bai. Outline. Introduction: why polarized protons spin “crisis” accelerate polarized protons to high energy RHIC: the first polarized proton collider brief history of RHIC spin program achieved performance of RHIC pp Conclusion plan for RHIC improvements. - PowerPoint PPT Presentation
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RHIC Spin and ColliderRHIC Spin and Collider
Mei Bai
Outline
Introduction: why polarized protons spin “crisis” accelerate polarized protons to high energy
RHIC: the first polarized proton collider brief history of RHIC spin program achieved performance of RHIC pp
Conclusion plan for RHIC improvements
What is Spin? From Google…
revolve quickly and repeatedly around one's own axis, "The dervishes whirl around and around without getting dizzy"
twist and turn so as to give an intended interpretation, "The President's spokesmen had to spin the story to make it less embarrassing"
a distinctive interpretation (especially as used by politicians to sway public opinion), "the campaign put a favorable spin on the story"
What is Spin?Classical definition
the body rotation around its own axis
Particle spin: an intrinsic property, like mass and chargea quantum degree freedom associated with the intrinsic magnetic moment.
Smq
G)(1s μ
G: anomalous gyromagnetic factor, describes the particle internal structure. For particles:
point-like: G=0 electron: G=0.00115965219 muon: G=0.001165923 proton: G=1.7928474
m: particle mass
q: electrical charge of particle
Spin: single particle pure spin state align along a quantization axis
Spin vector S: a collection of particles the average of each particle spin expectation value along a given direction
spin vector and spin-orbit interaction
BμdtSd
s
S
N
Spin orbit interaction
SN
I IAμ
S
BμdtJd
Discovery of Spin: 1925
“This is a good idea. Your idea may be wrong, but since both of you are so young without any reputation, you would not lose anything by making a stupid mistake.” --- Prof. Ehrenfest
G.E. Uhlenbeck and S. Goudsmit, Naturwissenschaften 47 (1925) 953. A subsequent publication by the same authors, Nature 117 (1926) 264,
Spin Crisis: what makes up the proton spin?
ΔΣ21
21
S
P
u
d
u
Sum of spins of all quarks
CERN EMC and SLAC SMC: ~ 20%!
Current model: Proton spin sum-
rule
gq LLg21
21
S ΔΔΣ
Orbital angular momentum ofquarks and gluons?
Spin contribution from all the gluons?
gg
q
gluon spin contribution
quark/antiquark spin contribution
g
High energy proton proton collisions: gluon gluon collision and gluon quark collision
Quest to unveil the proton spin structure:
STAR
RHIC: world’s first polarized proton collider
RHIC spin physics
STAR
• Excellent calorimeter granularity and muon detection • electrons, muons, photons and leading hadrons
measure gluon spin contribution g measure quark and anti quark spin contribution
• Large acceptance with Time Projection Chamber and calorimeters• Jets and photons and electrons
Design parameters for RHIC pp
Parameter Unit p-p
relativistic , injection … 25.9
relativistic , store … 266.5
no of bunches, nb … 112
ions per bunch, Nb 1011 2.0
emittance eN x,y 95% mm-mrad 20
average luminosity 1030 cm-2s-1 150
polarization,store % 70
Figure of merit of polarized proton collider
Luminosity: number of particles per unit area per unit time. The
higher the luminosity, the higher the collision rates
beam polarizationStatistical average of all the spin vectors.
zero polarization: spin vectors point to all directions. 100% polarization: beam is fully polarized if all spin vectors
point to the same directions.
)(
)(
4
1)(
2
2
0 t
tnNftL
rms
Transverse beam size
# of particles in one bunch
# of bunches
Basics of circular accelerator
bending dipole Constant magnetic field Keeps particles circulating around the ring
quadrupole Magnetic field proportional to the distance from the
center of the magnet. Keeps particles focused
radio frequency cavities Electric field for acceleration and keeping beam
bunched longitudinally
Closed orbit in a circular accelerator
Closed orbit in a machine with dipole errors
Closed orbit ina perfect machine:center of quadrupoles
Courtesy of Lingyun Yang
Closed orbit: particle comes back to the same position after one orbital revolution
Betatron oscillation in a circular accelerator
))(2cos(2)( yyy sQJsy Beta function
Betatron tune: number of oscillations in one orbital revolution
Courtesy of Lingyun Yang
Spin motion in circular accelerator: Thomas BMT Equation
In a perfect accelerator, spin vector precesses around the bending dipole field direction: vertical
Spin tune Qs: number of precessions in one orbital revolution. In general,
SBGBGm
eS
dt
Sd
])1([ //
Spin vector in particle’s rest frame
B
beam
GγQs
polarized proton acceleration challenges: preserve beam polarization Depolarization(polarization loss) mechanism
Come from the horizontal magnetic field which kicks the spin vector away from its vertical direction
Spin depolarizing resonance : coherent build-up of perturbations on the spin vector when the spin vector gets kicked at the same frequency as its precession frequency
xB
x
y
z
beam
Initial
xB
x
y
z
beam
1st full betatron Oscillation period
xB
x
y
z
beam
2nd full betatron Oscillation period
spin depolarizing resonance
Imperfection resonance Source: dipole errors,
quadrupole mis-alignments
Resonance location:
G = k k is an integer
Intrinsic resonance Source: horizontal
focusing field from betatron oscillation
Resonance location:
G = kP±Qy,P is the periodicity of the
accelerator, Qy is the vertical
betatron tune
Intr
insi
c sp
in r
eso
nance
Qx=
28.7
3,
Qy=
29.7
2,
em
it=
10
Spin depolarization resonance in RHIC
• For protons, imperfection spin resonances are spaced by 523 MeV
• the higher energy, the stronger the depolarizing resonance
First invented by Derbenev and Kondratenko from Novosibirsk in 1970s
A group of dipole magnets with alternating horizontal and vertical dipole fields
rotates spin vector by 180o
Innovative polarized proton acceleration techniques: Siberian snake
Particle trajectory in a snake:
Use one or a group of snakes to make the spin tune to be at ½
How to preserve polarization using Siberian snake(s)
xB
y
z
beam
xB
y
z
beam
Break the coherent build-up of the perturbations on the spin vector
Accelerate polarized protons in RHIC
PHENIX (p)
AGS
LINACBOOSTER
Pol. H- Source
Solenoid Partial Siberian Snake
200 MeV Polarimeter
Helical Partial Siberian Snake
Spin Rotators(longitudinal polarization)
Siberian Snakes
Spin Rotators(longitudinal polarization)
Strong AGS Snake
RHIC pC PolarimetersAbsolute Polarimeter (H jet)
STAR (p)
BRAHMS(p)
AGS Polarimeters
Spin flipper
Polarized proton in the AGS
AGS (Alternating Gradient Synchrotron) Energy: 2.3 GeV ~ 23.8 GeV
A total of 41 imperfection resonances and 7 intrinsic resonances from injection to extraction
AGS polarized proton development
1988 Harmonic
correction
Fast tune jump Months 21.7 0.108 42
imperfection intrinsic Setup time Energy
GeV
Int
[1011]
Pol
[%]
1994 5%solenoid
partial snake
Fast tune jump 2 weeks 23.0 0.05 31
1998 5%solenoid
partial snake
AC dipole @ 3 strong intrinsic resonance
2 weeks 23.0 0.05 37
2005 5%helical
partial snake
AC dipole @ 4 strong intrinsic resonance
2 weeks 23.8 1.0 50
2000 New polarized H- source with high current high polarization
2005 5% helical partial snake +10% super-conducting helical partial snake
2 weeks 23.8 1.5 65
Polarized proton acceleration setup in RHIC
Energy: 23.8 GeV ~ 250 GeV (maximum store energy) A total of 146 imperfection resonances and about
10 strong intrinsic resonances from injection to 100 GeV.Two full Siberian snakes
2
1 Qs
21s φφπ
1Q
Polarized proton acceleration in RHIC
snake depolarization resonance
Condition
even order resonance When m is an even
number Disappears in the two
snake case like RHIC if the closed orbit is perfect
odd order resonance When m is an odd number Driven by the intrinsic
spin resonances
Ram
p w
orki
ng p
t.
Sto
re w
orki
ng p
t.
3/4
5/6
7/8
5/8
kQmQ sy
z
beam
xB
y
-xxB
-x
y
z
beam
z
beam
xB
y
-x
z
beam
xB
y
-x
z
beam
xB
y
-x
z
beam
xB
y
-x
kQQ sy 6
Snake resonance observed in RHIC
7/10 snake resonance
How to avoid a snake resonance
Keep the spin tune as close to ½ as possible
-10
0
10
20
30
40
50
300 305 310 315 320 325 330 335
snake Inner Current [Amp]
po
lari
zati
on
Blue FY04 flatten orbit Yellow FY04 zero orbit Yellow FY05 Zero orbit
Blue FY05 flatten orbit Yellow FY05 flatten orbit
• set the vertical tune to 0.745
• measure the beam polarization with different snake current
• expect no depolarization if the corresponding spin tune is very close to 0.5
snake current setting
How to avoid a snake resonance Keep the vertical closed orbit as flat as possible
rms: 0.45mm
How to avoid a snake resonance
Keep the spin tune as close to ½ as possible snake current setting
Keep the vertical closed orbit as flat as possible orbit control
Keep the betatron tunes away from snake resonance locations Precise tune control
Betatron tune along the ramp
flattop*=2m
10 seconds after flattop beta1*=2m
¾ snake resonance
7/10 snake resonance
Milestones of RHIC pp development
2000
New polarized proton source One snake installed in Blue ring of RHIC New fast polarimeter in Blue
2002 All 4 snakes for both rings and CNI polarimeter in Yellow
2003 Spin rotators
2004 RHIC absolute polarimeter using H Jet target AGS 5% helical warm snake
2005
New super-conducting solenoid for the polarized H- source 205 GeV polarized protons with ~ 30% polarization AGS strong super-conducting helical snake
2006
Dual snake configuration for the AGS and reached a polarization of 65% at the AGS extraction with 1.5x1011 protons per bunch 250 GeV polarized protons in RHIC with a polarization of 45%
0.1
1
10
100
2001 2002 2003 2004 2005 2006 2007
Calendar year
Inte
grat
ed lu
min
osit
y
[
pb-1
]
0
10
20
30
40
50
60
70
Bea
m P
ola
riza
tio
n [
%]
RHIC pp performance
Courtesy of W. Fischer
RHIC pp performance: polarization transmission efficiency
Intr
insi
c sp
in r
eso
nance
Qx=
28.7
3,
Qy=
29.7
2,
em
it=
10
AchievedPhysics Run
RHIC intrinsic spin resonance strength
Design goal
45% !
First look of beam polarization at 250 GeV
0
0.002
0.004
0.006
0.008
0.01
0.012
20 40 60 80 100 120 140 160 180 200 220 240
Beam Energy [GeV]
Asy
mm
etry
d
Resonance around 138 GeV
Polarization 250 GeV ramp measurement
Plan for RHIC polarized protons
Improve luminosity performance
Increase the average luminosity at 100 GeV from 6.0x1030 cm-2s-1 to 20x1030 cm-2s-1 (x3) Luminosity limit beam-beam effect Accelerator developments to mitigate the beam-
beam effect increase bunch intensity eliminate emittance grow
At 250 GeV: 150x1030 cm-2s-1
Reach polarization of 70% or higher
AGS: operating the AGS with both betatron tunes
in the spin tune gap to avoid additional polarization loss due to horizontal betatron oscillation as observed in RHIC 2006 Run
RHIC: preserve beam polarization to 250 GeV
Improve the tune control technique Improve the orbit control system to control the
orbit distortion within 0.3mm or less.
Conclusion
Over the past 5 years, all the essential hardware and diagnostic apparatus for
polarized beam were put in place and successfully commissioned.
successfully accelerated polarized protons to 100 GeV with no polarization loss.
The performance of RHIC pp in Run 2006 was greatly improved due to the great success of the AGS dual snake setup as well as the improvement of RHIC systems.
The 500 GeV development demonstrated a beam polarization of 45% at 250 GeV and also identified the location of depolarizing resonances.
With the success in the AGS and improvements in RHIC, we expect RHIC to achieve the design goal in the near future.
Great physics is ahead of us, stay tuned in …
Acknowledgement
L. Ahrens, I.G. Alekseev, J. Alessi, J. Beebe-Wang,M. Blaskiewicz, A. Bravar, J.M. Brennan, D. Bruno,G. Bunce, J. Butler, P. Cameron, R. Connolly, J. Delong,T. D’Ottavio, A. Drees, W. Fischer, G. Ganetis, C. Gardner, J. Glenn, T. Hayes, H-C. Hseuh. H. Huang, P. Ingrassia,U. Iriso-Ariz, O. Jinnouchi, J. Laster, R. Lee, A. Luccio,Y. Luo, W.W. MacKay, Y. Makdisi, G. Marr, A. Marusic,G. McIntyre, R. Michnoff, C. Montag, J. Morris, A. Nicoletti, P. Oddo, B. Oerter, J. Piacentino, F. Pilat, V. Ptitsyn,T. Roser, T. Satogata, K. Smith, D.N. Svirida, S. Tepikian,R. Tomas, D. Trbojevic, N. Tsoupas, J. Tuozzolo, K. Vetter, M. Milinski. A. Zaltsman, A. Zelinski, K. Zeno, S.Y. Zhang.
Acknowledgement
Special Thanks to my mentors
Prof. S. Y. Lee, Indiana University
Dr. Thomas Roser, C-A Department
Dr. Mike Syphers, Fermi Lab.
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