Transcript RHIC

Lecture I&II
RHIC
The Relativistic Heavy Ion Collider
Particle accelerators
Large scientific instruments that produce and
accelerate subatomic particles and ‘smashes them’
 Fixed target
 Collider
Particles: electrons, positrons, protons,
anti-protons, ions…..
(atoms stripped of electrons: nuclei)
Nuclei  protons + neutrons
 quarks + gluons
E.C. Aschenauer
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RHIC @ Brookhaven National Lab
1st Collisions: 13/06/2000
Jet/C-Polarimeters
12:00 o’clock
RHIC
PHENIX
8:00 o’clock
LINAC
NSRL
EBIS
Booster
AGS
ANDY
2:00 o’clock
RF
4:00 o’clock
What do we collide ?
STAR
6:00 o’clock
Polarized protons
24-250 GeV
ERL p
Test Facility
Tandems
Light ions (d,Si,Cu)
Heavy ions (Au,U)
5-100 GeV/u
Polarized light ions
He3 16 - 166 GeV/u
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The RHIC Complex
Absolute Polarimeter (H jet)
RHIC pC Polarimeters
ANDY
100 GeV/u
79+
PHENIX
STAR
Siberian Snakes
Spin Rotators
Pol. Proton Source
500 mA, 300 ms
Partial Siberian Snake
Strong AGS Snake
LINAC
BOOSTER
200 MeV Polarimeter
1 MeV/u
32+
AGS
Stripping Au 77+ to 79+
9 GeV/u
77+
AGS Internal Polarimeter
AGS pC Polarimeters
Rf Dipoles
MP7
MP6
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E.C. Aschenauer
Tandem Van der Graaf
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The RHIC Accelerator System
AGS
Booster
Ring
Switchyard
Tandem
Van de Graaff
Yellow Ring
RHIC
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Blue Ring
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What does RHIC do?
RHIC accelerates gold nuclei in two
beams to about 100 GeV/nucleon each
(i.e., to kinetic energies that are over
100 times their rest mass-energy)
and brings these beams into a
200 GeV/nucleon collision.
RHIC accelerates polarized protons
up to 250 GeV and brings them into
up to 500 GeV collision
Three experiments, STAR,PHENIX,
and ANDY study these collisions.
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The RHIC project chronology
 1989
RHIC design
 1991
construction starts
 1996
commissioning AtR injection lines
 1997
sextant test (1/6 of the ring)
 1999
RHIC engineering/test run
 2000
first collisions
 2001-02 Au-Au run, polarized p run
 2003
deuteron-Au run, pp
 2004
Au-Au physics run and 5 weeks pp development
 2005 …..
RHIC is also a giant engineering challenge:
magnets (3000+ industry and lab built superconducting magnets)
cryogenics (2 weeks to cool down to 4.2K) ,instrumentation, etc.
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RHIC operations
The operation of RHIC and its injectors is a rather challenging
endeavor….
RHIC operates for ~5-6 months/year – 24h/day 7 days/week
RHIC Shutdown 6-7 months, for machine improvements (other
programs are run by the injectors, Tandem delivering ions for
industrial R&D, Booster delivering ions for NASA experiments, etc.)
 CONTROL ROOM : remote access to instrumentations and controls
 Accelerator physicists, shift leaders (machine initial set-up, new
developments, beam experiments)
 Operations group: operation coordinator, operators (“routine’
operations, shifts 1 OC + 2 operators)
 Technical support (engineers and technicians on call and/or site for
system diagnosis and trouble-shooting)
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inject, accelerate, collide......!
Beam
intensities
Beta*
squeeze
transition
Pilot
bunch
cogging
re-bucketing
collimation
steering
collisions
Start
acceleration
time
injection
preparation
E.C. Aschenauer
acceleration
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Store
(collisions)
collisions
Set-up
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A day in the life of RHIC…
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A week in the life of RHIC…
[66% of calendar time in store]
60x109Au
intensity
Beam experiments
Week 9 Feb to 17 Feb
E.C. Aschenauer
enhanced
luminosity
design
luminosity
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A few years in the life of RHIC…
Polarized proton runs
Operated modes (beam energies):
Au–Au 3.8/4.6/5.8/10/14/32/65/100 GeV/n
Achieved peak luminosities (100 GeV, nucl.-pair):
d–Au* 100 GeV/n
Au–Au
1951030 cm-2 s -1
Cu–Cu
11/31/100 GeV/n
p–p
601030 cm-2 s -1
p–p
11/31/100, 250 GeV
Other large hadron colliders (scaled to 100 GeV):
Planned or possible future modes:
Tevatron (p – pbar)
431030 cm-2 s -1
Au – Au 2.5 GeV/n (~ SPS cm energy)
LHC (p – p)
371030 cm-2 s -1
U–U
100 GeV/n
p – Au* 100 GeV/n
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E.C. Aschenauer
Cu – Au* 100 GeV/n (*asymmetric rigidity)
AnDY in Run-11 (250 GeV pp)
 Beam envelope function b* = 3.0 m at IP2
 Reduced IP2 crossing angle from initially 2.0 mrad to zero
 Added 3rd collision with following criteria (last instruction):
1. Nb ≤ 1.5x1011
2. Beam loss rate <15%/h in both beams
3. Not before first polarization measurement 3h into store
x/IP = 0.005
visible impact,
small impact
x/IP = 0.004
PHENIX
few percent loss to STAR/PHENIX
STAR
loss rates
AnDY
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ANDY an getting Lumi
ANDY got ~ 6.5/pb
systematically
increased thresholds
for IP2 collisions
in run11 with b*=3m
~0mr crossing angle
~1.6mr crossing angle
~2mr crossing angle
14 Aschenauer
E.C.
Varenna, July 2011
Future operation of AnDY
 Can reduce b* at IP2
have run with b* = 2.0 m previously for BRAHMS
b* = 1.5 m probably ok, needs to be tested
 Longer stores
10h instead of 8h in Run-11 (depends on luminosity lifetime and store-to-store
time)
 Collide earlier in store when conditions are met
needs coordination with polarization measurement, PHENIX and STAR
 Electron lenses (see later) if AnDY runs beyond Run-13
increases max beam-beam tune spread, currently DQmax,bb ≈ 0.015
can be used for to increase x~Nb/e and/or number of collisions
Run-11 luminosity at AnDY:
max ~0.5 pb-1/store
With improvements:
~3x increase,
~10 pb-1/week (max)
pp in Run-4 (100 GeV)
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E.C. Aschenauer
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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"
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What is Spin?
 Classical definition
 the body rotation around its own axis
 Particle spin:
 an intrinsic property, like mass and charge
 a quantum degree freedom associated with the intrinsic magnetic
moment.
q: electrical charge
of particle
q
m s  (1  G ) S
m
m: particle mass
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
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spin vector and spin-orbit interaction
 Spin: single particle
 pure spin state aligned along a quantization axis
 Spin vector S: a collection of particles
 the average of each particles spin expectation value
along a given direction
 Spin orbit interaction
S

dS  
μ
B
s
dt
S

dJ   I
μB
dt
m
μIA
N
N
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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
2
1
n
(
t) # of particles in one bunch
L
(
t) f
N
2
4
0 
(
t)
rms
# of bunches
Transverse beam size
 beam polarization
 Statistical 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.
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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
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Closed orbit in a circular accelerator
Closed orbit: particle comes back to the same position after
one orbital revolution
Closed orbit in
a perfect machine:
center of quadrupoles
E.C. Aschenauer
Closed orbit in
a machine with
dipole errors
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Betatron oscillation in a circular accelerator
Betatron tune: number
of oscillations in one
orbital revolution
b

y
(
s
)

2
J
cos(
2
Q
(
s
)

)
y
y
y
Beta function
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Varenna, July 2011
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Spin motion in circular accelerator:
Thomas BMT Equation

 e


d
S



S


[
G
B

(
1

G
)
B
]

S

//
dt
m


Spin vector in particle’s rest frame
B
 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,
beam
Qs  G
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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
y
y
beam
beam
x
z

Bx
Initial
E.C. Aschenauer
y

Bx
beam
z
x1st full betatron
Oscillation period
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x

Bx
z
2nd full betatron
Oscillation period
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spin depolarizing resonance
 Imperfection resonance
 Source: dipole errors,
quadrupole misalignments
 Resonance location:
G = k
k is an integer
E.C. Aschenauer
 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
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Intrinsic spin resonance
Qx=28.73, Qy=29.72, emit= 10
Spin depolarization resonance in RHIC
 For protons, imperfection spin resonances are spaced
by 523 MeV
 the higher energy, the stronger the depolarizing resonance
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Innovative polarized proton acceleration
techniques: Siberian snake
 First invented by Derbenev and Kondratenko from Novosibirsk
in 1970s
 A group of dipole magnets with alternating horizontal and
vertical dipole fields
o
 rotates spin vector by 180
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Particle trajectory in a snake:
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How to preserve polarization using
Siberian snake(s)
 Use one or a group of snakes
to make the spin tune to be
1/2
 Break the coherent build-up
of the perturbations on the
spin vector
y
y
beam
beam

Bx
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z

Bx
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z
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ANDY(p)
Absolute Polarimeter (H jet) RHIC pC Polarimeters
Siberian Snakes
Spin flipper
PHENIX (p)
STAR (p)
Spin Rotators
(longitudinal polarization)
Spin Rotators
Solenoid Partial Siberian Snake (longitudinal polarization)
LINAC
Pol. H Source
BOOSTER
200 MeV Polarimeter
AGS
Alternating Gradient Synchrotron
Helical Partial
Siberian Snake
AGS Polarimeters
Strong AGS Snake
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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
1
Q
φ
s φ
1
2
π
1
Qs 
2
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Varenna, July 2011
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E.C. Aschenauer
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What is beam polarization?
Simple example: spin-1/2 particles (proton, electron)
Can have only two spin states relative to certain axis Z: Sz=+1/2 and Sz =-1/2
N

N
S


1
/2
S


1
/2
Z
Z
P

N

N
S


1
/2
S


1
/2
Z
Z
|P|<1
40
P
1
40
3

1
P


0
.5
3

1
22
P
0
22
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Varenna, July 2011
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How to measure proton beam polarization
There are several established physics processes sensitive
to the spin direction of the transversely polarized protons
Scattering
to the left
e 
Scattering
to the right
N left  N right
N left  N right
 AN P
AN – the Analyzing Power (|AN|<1)
(left-right asymmetry for 100% polarized protons)
Once AN is known: P 
E.C. Aschenauer
e
AN
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Polarization Measurements
N
e
1N
P
 
LefRight
t
pC elastic scattering
A

N
N A
NN
Lef
Right
t
AN depends on the process
and kinematic range of the
measurements
-t=2MCEkin
Precision of the
measurements
1 1
(P
) 
A
N
N
N=NLeft+NRight
For (P)=0.01 and AN~0.01  N~108
!
Requirements:
Large AN or/and high rate (N)
Good control of kinematic range
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RHIC and Polarimetry
Absolute Polarimeter (H jet)
RHIC pC Polarimeters
Siberian Snakes
ANDY (p)
PHENIX (p)
RHIC
STAR (p)
Siberian Snakes
Spin Rotators
Solenoid Snake
LINAC
Pol. Proton Source
500 mA, 400 ms
200 MeV Polarimeter
BOOSTER
AGS
Warm Snake
AC Dipole
AGS pC CNI Polarimeter
Cold Snake Varenna, July 2011
E.C. Aschenauer
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RHIC Polarimetry
Polarized hydrogen Jet Polarimeter (HJet)
Source of absolute polarization (normalization to other polarimeters)
Slow (low rates  needs lo-o-ong time to get precise measurements)
Proton-Carbon Polarimeter (pC)
Very fast  main polarization monitoring tool
Measures polarization profile (polarization is higher in beam center)
Needs to be normalized to HJet
Local Polarimeters (in PHENIX and STAR experiments)
Defines spin direction in experimental area
Needs to be normalized to HJet
All of these systems are necessary for the proton
beam polarization measurements and monitoring
E.C. Aschenauer
Varenna, July 2011
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Polarized H-Jet Polarimeter
AN 
Left-right asymmetry in elastic scattering due to
spin-orbit interaction:
interaction between (electric or strong) field of
one proton and magnetic moment associated with
the spin of the other proton
NL  NR
NL  NR

eN
P
Beam and target are both protons
etarget
e

A
t
beam
N
P
P
target
beam
e
beam
P

P
beamtarget
etarget
RHIC proton
beam
Forward scattered
proton
H-jet target
2


t

p

p

0
out
in
recoil proton
Ptarget is provided by Breit Rabi Polarimeter
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H-jet system
target
 Height: 3.5 m
 Weight: 3000 kg
Recoil proton
 Entire system moves along
x-axis 10 ~ +10 mm to
adjust collision point with
RHIC beam.
RHIC proton
beam
y
IP12
z
x
E.C. Aschenauer
Varenna, July 2011
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H = p+ + e
|1> |2> |3> |4>
Hyperfine
structure
HJet target system
H2 desociater
Separating Magnet
(Sextuples)
|1>
|2>
P+ OR
|1> |3>
P
RF transitions
(WFT or SFT)
Ion gauge E.C.
Scattering
chamber
Holding
magnet
|2> |4>
|1> |2>
Atomic
Beam
Source
Breit-Rabi
Polarimeter
2nd RFtransitions for
calibration
Separating
magnet
Aschenauer
Varenna,
Ion gauge
July 2011
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HJet: Identification of Elastic Events
ToF vs Energy
Forward scattered
proton
proton beam
proton
target
recoil proton
Energy vs Channel #
YELLOW
mode
BLUE
mode
Array of Si detectors measures TR & ToF of recoil proton.
Channel # corresponds to recoil angle R.
Correlations
(TR & ToF ) and
(TR &July
R2011
)  the elastic
process
Varenna,
43
E.C. Aschenauer
HJet: Ptarget
Source of normalization for polarization measurements at RHIC
Breit-Rabi Polarimeter:
Nuclear polarization
Separation of particles with
different spin states in the
inhomogeneous magnetic field (ala
Stern-Gerlach experiment)
Nuclear polarization of the atoms:
95.8%  0.1%
After background correction:
Ptarget = 92.4%  1.8%
1 day
Very stable for entire run period !
Polarization cycle
(+/ 0/  ) = (500/50/500) s
E.C. Aschenauer
Varenna, July 2011
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HJet:
Example from Run-2006
e
beam
P

P
beamtarget
etarget
εtarget
Use the same statistics
(with exactly the same
experimental cuts) to
measure ebeam and etarget
(selecting proper spin
states either for beam
or for target)
e beam
e target
εbeam
t=-2MpEkin
 Many systematic
effects cancel out in the
ratio
Ekin (MeV)
Ekin (MeV)
Provides statistical precision (P)/P ~ 0.10 in a store (6-8 hours)
HJet Provides very clean and stable polarization measurements but
with limited stat. precision
 Need faster polarimeter!
E.C. Aschenauer
Varenna, July 2011
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P-Carbon Polarimeter:
Left-right asymmetry in elastic scattering due to spin-orbit interaction:
interaction between (electric or strong) field of Carbon and magnetic
moment associated with the spin of the proton
Pbeam  


N
N
Lor
L
eN
ANpC
NL  NR
eN 
NL  NR

or

Carbon
target
Polarized
proton
6

5
18cm
4
1
Recoil
carbon
Ultra thin Carbon
ribbon Target
(5 mg/cm2)
Target Scan mode (20-30 sec per measurement)
Stat. precision 2-3%
2
3


N
N
Ror
R
Si strip detectors Polarization profile, both vertical and horizontal
(TOF, EC)
E.C. Aschenauer
Normalized to H-Jet measurements over many fills
(with precision <3%)
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pC: AN
Elastic scattering: interference between electromagnetic and hadronic
amplitudes in the Coulomb-Nuclear Interference (CNI) region

 
*
*
em
had
em
had
N
1
flip
non

flip
2
non

flip
flip
A

C 
C
pC Analyzing Power
Run04
Phys.Rev.Lett.,89,052302(2002)
unpublished
zero hadronic
spin-flip
With hadronic
spin-flip (E950)
Ebeam = 21.7GeV
E.C. Aschenauer
Ebeam = 100 GeV
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Polarization Profile
If polarization changes across the beam, the average
polarization seen by Polarimeters and Experiments (in beam
collision) is different
H-Jet

p
pC
Collider
Experiments
~1 mm
6-7 mm
x=x0

P
(
x
,
y
)

I
(
x
,
y
)

I
(
x
,
y
)
P

P
(
x
,
y
)

I
(
x
,
y
)P

P
(
x
,
y
)

I
(
x
,
y
)P
1
1
1
2
1
1
1
1
1
0
1
0
P1,2(x,y) – polarization profile, I1,2(x,y) – intensity profile, for beam #1 and #2
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Pol. Profile and Average Polarization
 I2
R 2
P
P



1

R

1

R
1
Exp 
X
Y




1

R

R
X
Y
P
4
 1
 1
HJet
1

R

1

R




X
Y
2
2




I
Ideal case: flat pol. profile (P=  R=0)
Polarization
Carbon
Intensity
Scan C target across the beam
In both X and Y directions
Run-2009:
P
Ebeam=100 GeV: R~0.1
Ebeam=250 GeV: R~0.35  15% correction
Target Position
E.C. Aschenauer
 5% correction
Varenna, July 2011
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pC+HJet: Polarization vs Fill
Run-2009 results (Ebeam=100 GeV)
 Normalized to HJet
 Corrected for polarization profile (by pC)
“Blue” beam
P/P < 5%
Dominant sources of syst. uncertainties:
~3% - HJet background
~3% - pC stability
(rate dependencies, gain drift)
“Yellow” beam
E.C. Aschenauer
~2% - Pol. profile
Varenna, July 2011
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Need for Local Polarimeters
Absolute Polarimeter (H jet)
RHIC pC Polarimeters
Siberian Snakes
ANDY(p)
PHENIX (p)
RHIC
STAR (p)
Siberian Snakes
Spin Rotators
Solenoid Snake
LINAC
BOOSTER
Pol. Proton Source
500 mA, 400 ms
AGS
200 MeV Polarimeter
Spin Rotators around
experiments may change spin
Warm
Snake in experimental areas
direction
AC Dipole
AGS pC CNI Polarimeter
 Need to monitor spin
Cold Snake
direction in experimental areas
E.C. Aschenauer
Varenna, July 2011
51
Local Polarimeter: PHENIX
Utilizes spin dependence of very
forward neutron production discovered
in RHIC Run-2002 (PLB650, 325)
charged
particles
Zero Degree Calorimeter
neutron
Quite unexpected asymmetry
Theory can not yet explain it
But already can be used for polarimetry!
E.C. Aschenauer
e
A
P
N
Varenna, July 2011
52
Monitor spin direction
Asymmetry vs 
Measures transverse polarization PT ,
Separately PX and PY
Longitudinal component:
P – from CNI polarimeters
2
2
P

P

P
L
T
Vertical
Radial
Vertical   ~ ±/2
Radial   ~ 0
Longitudinal  no asymmetry
Longitudinal
-/2
E.C. Aschenauer
Varenna, July 2011
/2
0
53
STAR Local Polarimeter
Utilizes spin dependence of hadron production at high xF:
3.3<|h|< 5.0 (small tiles only)
Bunch-by-bunch (relative) polarization
Monitors spin direction in STAR collision region
Capable to precisely monitor polarization vs time in a fill, and
bunch-by-bunch
Varenna, July 2011
54
E.C. Aschenauer
Now we have the polarised proton beam
and
know what the polarisation is,
what is next
How do we measure things
 Detectors
E.C. Aschenauer
Varenna, July 2011
55
E.C. Aschenauer
Varenna, July 2011
56
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
E.C. Aschenauer
Varenna, July 2011
57
Stern-Gerlach Experiment
Separation of spin states in the inhomogeneous magnetic field
E.C. Aschenauer
Varenna, July 2011
58
Summary
 Polarimetry is a crucial tool in RHIC Spin Program
Provides precise RHIC beam polarization measurements and
monitoring
Provides crucial information for RHIC pol. beam setup, tune and
development
 RHIC Polarimetry consists of several independent subsystems, each
of them playing their own crucial role (and based on different
physics processes)
HJet:
Absolute polarization measurements
pC:
Polarization monitoring vs bunch and vs time in a fill
Polarization profile
PHENIX and STAR Local Polarimeters:
Monitor spin direction (through trans. spin component) at
collision
E.C. Aschenauer
Varenna, July 2011
59