Polarimetry of Proton Beams at RHIC A.Bazilevsky Summer Students Lectures June 17, 2010.
-
Upload
wendy-ramsey -
Category
Documents
-
view
222 -
download
1
Transcript of Polarimetry of Proton Beams at RHIC A.Bazilevsky Summer Students Lectures June 17, 2010.
Polarimetry of Proton Beams at RHIC
A.Bazilevsky
Summer Students LecturesJune 17, 2010
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
2/12/1
2/12/1
ZZ
ZZ
SS
SS
NN
NNP
022
22
P
5.013
13
P
104
04
P
|P|<1
Why polarized protons?See lecture by A.Vossen
Longitudinally polarized protonsProton helicity structure: (anti-)quark and gluon polarization inside proton
Transversely polarized protons(Anti-)quark transversityParton orbital momentum
Polarimetry goals: Measure and monitor beam polarizationDefine and monitor spin direction in experimental area
BPA
1Single
21Double
1
BB PPA
Double spin asymmetrySingle spin asymmetry
“+” spin aligned with beam direction (long. spin) or spin up (transverse spin)“” spin anti-aligned with beam direction (long. spin) or spin down (transverse spin)
p
p
How to measure proton beam polarizationThere are several established physics processes sensitive to the spin direction of the transversely polarized protons
Scattering to the right
Scattering to the left
AN – the Analyzing Power (|AN|<1)(left-right asymmetry for 100% polarized protons)
NAP
Once AN is known:
PANN
NNN
RightLeft
RightLeft
Polarization MeasurementsRightLeft
RightLeft
NN NN
NN
AAP
1
AN depends on the process and kinematic range of the measurements
pC elastic scattering
NAP
N
11)( Precision of the
measurements 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
-t=2MCEkin
RHIC and Polarimetry
BRAHMS & PP2PP (p)
STAR (p)PHENIX (p)
AGS
LINAC BOOSTER
Pol. Proton Source500 A, 400 s
Spin RotatorsSolenoid Snake
Siberian Snakes
200 MeV Polarimeter
AGS pC CNI PolarimeterAC Dipole
RHIC pC Polarimeters
Absolute Polarimeter (H jet)
RHIC
Siberian Snakes
Cold Snake
Warm Snake
6
RHIC PolarimetryPolarized 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 toolMeasures 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 areaNeeds to be normalized to HJet
All of these systems are necessary for the proton beam polarization measurements and monitoring
Beam and target are both protons
beam
beam
target
target
PPtAN
RHIC proton beam
Forward scatteredproton
H-jet target
recoil proton
target
target beam
beam PP
02 inout ppt
Ptarget is provided by Breit Rabi Polarimeter
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
8
PNN
NN
PA N
RL
RLN
1
Polarized H-Jet Polarimeter
1 day
Breit-Rabi Polarimeter:
Separation of particles with different spin states in the inhomogeneous magnetic field (ala Stern-Gerlach experiment)
Nuclear polarization
Very stable for entire run period !Polarization cycle (+/ 0/ ) = (500/50/500) seconds
HJet: PtargetSource of normalization for polarization measurements at RHIC
Nuclear polarization of the atoms:
95.8% 0.1%
After background correction:
Ptarget = 92.4% 1.8%
HJet:
Provides statistical precision (P)/P~0.10 in a store (6-8 hours)
target
target beam
beam PP Example from Run-2006
εbeam
εtarget
t=-2MpEkin
Use the same statistics (with exactly the same experimental cuts) to measure beam and target
(selecting proper spin states either for beam or for target)
Many systematic effect cancel out in the ratio Ekin (MeV)Ekin (MeV)
target
beam
HJet Provides very clean and stable polarization measurements but with limited stat. precison
Need faster polarimeter!
P-Carbon Polarimeter:
Ultra thin Carbon ribbon Target(5 g/cm2)
11
3344
55
66
22
Si strip detectorsSi strip detectors(TOF, E(TOF, ECC))
18cm18cm
Polarized proton
Recoil carbon
Carbon target
LL NN or
RR NN or
or
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 NAN
pC
N NL NR
NL NR
Target Scan mode (20-30 sec per measurement)
Stat. precision 2-3%
Polarization profile, both vertical and horizontal
Normalized to H-Jet measurements over many fills (with precision <3%)
Poarization Profile
H-Jet
p
~1 mm
6-7 mm
pC ColliderExperiments
P1,2(x,y) – polarization profile, I1,2(x,y) – intensity profile, for beam #1 and #2
x=x0
),(),( 01011 yxIyxPP ),(),(),( 2111 yxIyxIyxPP ),(),( 111 yxIyxPP
If polarization changes across the beam, the average polarization seen by Polarimeters and Experiments (in beam collision) is different
Pol. Profile and Average Polarization
Carbon
Scan C target across the beamIn both X and Y directions
Target Position
Inte
nsity
Pola
rizati
on
I
P
2
2
P
IR
YX
YX
YX
HJet
Exp RR
RR
RR
P
P
4
11
21
121
1
11
Run-2009:
Ebeam=100 GeV: R~0.1 5% correction
Ebeam=250 GeV: R~0.35 15% correction
Ideal case: flat pol. profile (P= R=0)
pC+HJet: Polarization vs FillRun-2009 results (Ebeam=100 GeV)
Normalized to HJet Corrected for polarization profile (by pC)
P/P < 5%
Dominant sources of syst. uncertainties:
~3% - HJet background
~3% - pC stability (rate dependencies, gain drift)
~2% - Pol. profile“Yellow” beam
“Blue” beam
Need for Local Polarimeters
BRAHMS & PP2PP (p)
STAR (p)PHENIX (p)
AGS
LINAC BOOSTER
Pol. Proton Source500 A, 400 s
Spin RotatorsSolenoid Snake
Siberian Snakes
200 MeV Polarimeter
AGS pC CNI PolarimeterAC Dipole
RHIC pC Polarimeters
Absolute Polarimeter (H jet)
RHIC
Siberian Snakes
Cold Snake
Warm SnakeSpin Rotators around experiments may change spin direction in experimental areas
Need to monitor spin direction in experimental areas
Local Polarimeter: PHENIXUtilizes spin dependence of very forward neutron production discovered in RHIC Run-2002 (PLB650, 325)
neutronchargedparticles
Zero Degree Calorimeter
Quite unexpected asymmetryTheory can not yet explain itBut already can be used for polarimetry! PAN
Monitor spin direction
Vertical ~ ±/2Radial ~ 0Longitudinal no asymmetry
Measures transverse polarization PT , Separately PX and PY
Longitudinal component:P – from CNI polarimeters
22TL PPP
Vertical
Radial
Longitudinal
-/2 0 /2
Asymmetry vs
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 fillPolarization profile
PHENIX and STAR Local Polarimeters: Monitor spin direction (through trans. spin component) at collision
Backups
H-jet system
RHIC proton beam
Recoil proton
• Height: 3.5 m
• Weight: 3000 kg
• Entire system moves along x-axis 10 ~ +10 mm to adjust collision point with RHIC beam.
IP12
zyx
target
RF transitions (WFT or SFT)
|1> |2> |3> |4>
Separating Magnet (Sextuples)
H2 desociater
Holding magnet
2nd RF-transitions for calibration
P+ OR P
H = p+ + e
Atomic Beam Source
Scattering chamber
Breit-Rabi Polarimeter
Separating magnet
Ion gauge
|1> |3> |2> |4>
|1> |2>
|1> |2>
Ion gauge
Hyper fine structure
HJet target system
Stern-Gerlach ExperimentSeparation of spin states in the inhomogeneous magnetic field
HJet: Identification of Elastic Events
proton beam
Forward scatteredproton
proton target recoil proton
Array of Si detectors measures TR & ToF of recoil proton. Channel # corresponds to recoil angle R.Correlations (TR & ToF ) and (TR & R ) the elastic process
23
BLUE mode
YELLOW mode
Energy vs Channel #
ToF vs Energy
pC: AN
zero hadronic spin-flip
With hadronic spin-flip (E950)
Phys.Rev.Lett.,89,052302(2002)
pC Analyzing Power
Ebeam = 21.7GeVEbeam = 21.7GeV Ebeam = 100 GeVEbeam = 100 GeV
unpublished
Run04
hadflip
emflipnon
hadflipnon
emflipN CCA *
2
*
1
Elastic scattering: interference between electromagnetic and hadronic amplitudes in the Coulumb-Nuclear Interference (CNI) region
STAR Local Polarimeter
3.3<||< 5.0 (small tiles only)
Utilizes spin dependence of hadron production at high xF:
Bunch-by-bunch (relative) polarization
Monitors spin direction in STAR collision regionCapable to precisely monitor polarization vs time in a fill, and bunch-by-bunch