lead ( pb) radius experiment : prexweb.mit.edu/pavi09/talks/michaels_prex.pdflead ( 208pb) radius...
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Lead ( Pb) Radius Experiment : PREX208Lead ( Pb) Radius Experiment : PREXElastic Scattering
Parity Violating Asymmetry
E = 1 GeV,electrons on lead
05=θ
Parity Violating Asymmetry
electrons on lead
Spokespersons
• Paul Souder
208Pb
• Krishna Kumar
• Guido Urciuoli
• Robert Michaels208Pb
Run in March 2010 !
R. MichaelsPREX atPAVI 09
Idea behind PREXIdea behind PREXZ of Weak Interaction :0
Clean Probe Couples Mainly to Neutrons( T.W. Donnelly, J. Dubach, I Sick )
⎥⎦
⎤⎢⎣
⎡−−=
⎞⎛⎞⎛
⎟⎠⎞
⎜⎝⎛Ω
−⎟⎠⎞
⎜⎝⎛Ω
=)(
sin4122 2
22
QFQG
dddd
dd
A WFLR θ
πασσ
σσ)( 2QF n
In PWIA (to illustrate) :
⎦⎣⎟⎠⎞
⎜⎝⎛Ω
+⎟⎠⎞
⎜⎝⎛Ω
)(22 QFdd
dd P
LR
πασσ
dw/ Coulomb distortions (C. J. Horowitz) :
0≈
%1%3 =→=n
n
RdR
AdA
R. MichaelsPREX atPAVI 09
Measured AsymmetryPREXCorrect for Coulomb
DistortionsPhysics Output
Weak Density at one Q2
Small Corrections forn s
Mean Field & Other
Neutron Density at one Q2
GnE G
sE MECAtomic
Parity Violation
& Other Models
Assume Surface Thickness Good to 25% (MFT) Neutron
Stars
RSlide adapted from C. Horowitz
R. MichaelsPREX atPAVI 09
R n
Fundamental Nuclear Physics :
What is the size of a nucleus ?nucleus ?
Neutrons are thought to determine Neutrons are thought to determine the size of heavy nuclei like 208Pb.
Can theory predict it ?
R. MichaelsPREX atPAVI 09
Reminder: Electromagnetic Scattering determines ( )rρ(charge distribution)
⎞⎛ bd ( )
Pb208
(charge distribution)
⎟⎠⎞
⎜⎝⎛
Ω strmb
ddσ ( )rρ
R. MichaelsPREX atPAVI 09
( ) 1−fmq1 2 3
Z of weak interaction : sees the0Z of weak interaction : sees the neutrons
Analysis is clean, like electromagnetic scattering:
1. Probes the entire nuclear volume
t t
2. Perturbation theory applies
proton neutron
Electric charge 1 0
Weak charge 0.08 1
R. MichaelsPREX atPAVI 09
)()()(ˆ AVV +Electron - Nucleus Potential
)()()( 5 rArVrV γ+=
||)()(///3d∫ [ ])()()i41()( 2 NZGA F θ
electromagnetic axial
is small, best observed by parity violation
||)()( //3 rrrZrdrV −= ∫ ρ [ ])()()sin41(22
)( 2 rNrZGrA NPWF ρρθ −−=
dd
)( rAPb is spin 0
208
neutron weak charge >> proton weak charge
22 |)(| QFdd
dd
PMottΩ
=Ω
σσ
Neutron form factor
1sin41 2 <<− Wθ
Proton form factor
∫= )()(41)( 0
32 rqrjrdQF PP ρπ ∫= )()(
41)( 0
32 rqrjrdQF NN ρπ
Neutron form factor
Parity Violating Asymmetry
Proton form factor
⎥⎦
⎤⎢⎣
⎡−−=
⎟⎞
⎜⎛+⎟
⎞⎜⎛
⎟⎠⎞
⎜⎝⎛Ω
−⎟⎠⎞
⎜⎝⎛Ω
=)()(
sin4122 2
22
2
QFQFQG
dddd
dd
AP
NW
FLR θπασσ
σσParity Violating Asymmetry
R. MichaelsPREX atPAVI 09
⎟⎠
⎜⎝ Ω
+⎟⎠
⎜⎝ Ω dd LR 0≈
Measurement at one Q is sufficient to measure R2
PREX:
( R.J. Furnstahl )
easu e e t at o e Q s su c e t to easu e N
0.3
Skyrmecovariant mesoncovariant point coupling
0.28
0.29
/Ncovariant mesoncovariant point coupling
Wh l
0.27
0.28
F n(Q2 )/
N Why only one parameter ?
(next slide…)
0.26 proposed error *
5.6 5.65 5.7 5.75 5.8
rn in
208Pb (fm)
0.25
R. MichaelsPREX atPAVI 09
rn in Pb (fm)
* 2/3 this error if 100 uA, dPe/Pe = 1%
Nuclear Structure: Neutron density is a fundamental
Slide adapted from J. Piekarewicz
observable that remains elusive.
Reflects poor understanding of symmetry energy of nuclear
ZN ≠symmetry energy of nuclear matter = the energy cost of
)21()()2/1()( 2xnSxnExnE −+==
== xn
)21()()2/1,(),( xnSxnExnE +== υ
n.m. density ratio proton/neutrons
• Slope unconstrained by data
• Adding R from Pb 208
• Adding R from Pb will eliminate the dispersion in plot.
N
R. MichaelsPREX atPAVI 09
Skx-s15Thanks, Alex Brown
PREX Workshop 2008
E/NE/N
Nρ
R. MichaelsPREX atPAVI 09
Skx-s20Thanks, Alex Brown
PREX Workshop 2008
R. MichaelsPREX atPAVI 09
Skx-s25Thanks, Alex Brown
PREX Workshop 2008
R. MichaelsPREX atPAVI 09
Interpretation p
of PREX
Acceptance
R. MichaelsPREX atPAVI 09
Application: Atomic Parity Violation• Low Q test of Standard Model2• Low Q test of Standard Model
• Needs RN (or APV measures RN )
[ ]GF 35/2∫
Isotope Chain Experiments e.g. Berkeley Yb
[ ] rdrZrNG
H eePWNF
PNC35/2 )()sin41()(
22ψγψρθρ∫ −+−≈
rr
0≈
APV
R. MichaelsPREX atPAVI 09
Neutron Application :
Neutron Stars
What is the nature of extremely dense of extremely dense matter ?
Do collapsed stars form “exotic” phases of matter ? (strange stars, ( g ,quark stars)
R. MichaelsPREX atPAVI 09
Crab Nebula (X-ray, visible, radio, infrared)
)(ρPInputs:
Eq. of state (EOS)
PREX h l h
Hydrostatics (Gen. Rel.)
Astrophysics Observations
PREX helps here
Astrophysics Observations
Luminosity LTemp. TMass M from pulsar timing
424 TRL Bπσ=(with corrections … )
di l i hi
Fig from: Dany Page.
Mass - Radius relationship
R. MichaelsPREX atPAVI 09
J.M. Lattimer & M. Prakash, Science 304 (2004) 536.
PREX & Neutron Stars( C.J. Horowitz, J. Piekarewicz )
R calibrates EOS ofNR calibrates EOS of Neutron Rich Matter
N
Crust ThicknessExplain Glitches in Pulsar Frequency ?
Combine PREX R with Obs. Neutron Star Radii
N
Ph T iti t “E ti ” C ?
Some Neutron Stars
Strange star ? Quark Star ?Phase Transition to “Exotic” Core ?
Crab Pulsar
seem too Cold Cooling by neutrino emission (URCA)
0.2 fm URCA probable, else not>− pn RR
R. MichaelsPREX atPAVI 09
PREX DesignSpectometers
Lead Foil Target
Hall APol. Source
CEBAF
R. MichaelsPREX atPAVI 09
Hall A at Jefferson Lab
Polarized e-
SourceHall A
R. MichaelsPREX atPAVI 09
High Resolution SpectrometersSpectrometer Concept: Resolve Elastic
Elastic detector
1st excited state Pb 2.6 MeV
Inelastic
QuadLeft-Right symmetry to control transverse
Dipoletarget
control transverse polarization systematic
R. MichaelsPREX atPAVI 09
Q Q
HRS-L50 Septum magnet augments the
High Resolution Spectrometers
HRS-Rcollimator
Increased Figure of Merit
collimator
target
L / R HRS control vertical A_T.
R. MichaelsPREX atPAVI 09
What about horizontal ?
Collimator at entrance to spectrometerSuppressing A_T systematics
Paul Souder
Aligned in spectrometers to define identical Left / RightA T hole
Be degraderscattering angles as well as good up / down symmetry
A_T hole
Insertable blockerInsertable blockerto block Be
R. MichaelsPREX atPAVI 09
Events from A_T hole (Be plug)
Main detector
A_T detector
Measures horizontal A_Tsystematic.
(Vertical is (Vertical is measured from Left/Right spectrometers)
Thanks:
Dustin McNulty
Krishna Kumar
P l S d
R. MichaelsPREX atPAVI 09
Paul Souder
Measure θ from Nuclear RecoilδE=Energy lossE BE=Beam energyMA=Nuclear massθ=Scattering angle
EE 2θδ=
θ=Scattering angle
AME 2=
Scattered Electron Energy (GeV)
Recoil is large for H, small for nuclei(3X better accuracy than survey)
Scattered Electron Energy (GeV)
R. MichaelsPREX atPAVI 09
(3X better accuracy than survey)
P I T A EffectImportant Systematic :
)sin(θε Δ=IA Laser at
Polarization Induced Transport Asymmetry
Intensity Asymmetry
y
Initial Linear Polarization
Pockels Cell
)(I Laser at Pol. Source
yx
yx
TTTT
+−
=εwhere
Transport Asymmetry
y y y
45o
x
Pockels Cell(Imperfect λ/4 Plate)
Fast/SlowAxes
Δ = 0
PolarizationEllipses
Transport Asymmetry
RL
Δ 0
θ
x'y'
AsymmetricTransport System
θ
z
Δ
drifts, but slope is ~ stable.
Feedback on
Δ
R. MichaelsPREX atPAVI 09
See talk by Gordon Cates
Double Wien FilterCrossed E & B fields to rotate the spin
(NEW for PREX)
• Two Wien Spin Manipulators in series• Solenoid rotates spin +/‐90 degrees (spin rotation as B but focus as B2).
Flips spin without moving the beam !Flips spin without moving the beam !
Electron Beam
SPIN
R. MichaelsPREX atPAVI 09
See talk by Riad Suleiman
Beam AsymmetriesA A A Δ Σβ ΔAraw = Adet - AQ + αΔE+ ΣβiΔxi
•natural beam jitter (regression) Slopes from•beam modulation (dithering)
p
R. MichaelsPREX atPAVI 09
The Corrections Work !Sh i d f d t d i HAPPEX (4H ) h b h d
X Angle BPM
Shown : period of data during HAPPEX (4He) when beam had a helicity-correlated position due to a mistake * in electronics.
dif
f With corrections
on pm. P
osit
ion
micro p
elic
ity-
corr
.
R ALL A t
He
* The mistake: Helicity signal deflecting the beam through electronics “pickup”
Helicity signal to driver reversed Helicity signal to
driver removed
Raw ALL Asymetry
R. MichaelsPREX atPAVI 09
The mistake: Helicity signal deflecting the beam through electronics pickup
Final Beam Position Corrections (HAPPEX-H)X Angle BPMX Angle BPM
Energy: -0.25 ppb
X Target: 1 nm
Beam Asymmetry Results
on X Target: 1 nm
X Angle: 2 nm
Y Target : 1 nm
micro
Y Angle: <1 nm
Corrected and Raw, Left spectrometer arm alone, Superimposed!
m
Total correction for beam position asymmetry on Left, Right, or ALL detector: 10 ppb
pp Spectacular results from HAPPEX-H show we can do PREX.
R. MichaelsPREX atPAVI 09
Redundant position measurements at the ~1 nm level
(i) Stripline monitors (2 pairs of wires)
80
Helicity Correlated Position Differences --
80m)
(ii) Resonant microwave cavities
(Helicity – correlated differences averaged over ~1 day) HAPPEX 2005
(i) Stripline monitors (2 pairs of wires)
40
60
80
avit
y D
iff
(n
m)
40
60
80
Y C
avit
y D
iff
(nm
)
nm
n
m
-20
0
20X C
av
-20
0
20
Y
X
(ca
vit
y)
(c
av
ity)
-60
-40
-20
-60
-40
-20X Y
-80 -60 -40 -20 0 20 40 60 80
-80
X Stripline Diff (nm)-80 -60 -40 -20 0 20 40 60 80
-80
Y Stripline Diff (nm)
X (stripline) nm Y (stripline) nm
R. MichaelsPREX atPAVI 09
X (stripline) nm Y (stripline) nm
PREX Integrating Detectors
DETECTORS
UMass / Smith
R. MichaelsPREX atPAVI 09
Lead TargetgPb208 !!A 100at ly testedSuccessful μ (2 x I in proposal)
Liquid Helium Coolant
C12
Diamond Backing:
beam
Diamond Backing:• High Thermal Conductivity• Negligible Systematics
R. MichaelsPREX atPAVI 09
Target Assembly
R. MichaelsPREX atPAVI 09
5000
6000Momentum of Electron Scattering from Lead
ElasticPb Elastic
208 Lead Target Tests
3000
4000
5000
DetectorDetector
m.
even
ts Low Rate
at E = 1.1 GeV
-30 -25 -20 -15 -10 -5 0 5 100
1000
2000
MeV
First excited state2.6 MeV (~0.1% rate)
06=θ1st Excited State (2.6 MeV)
• Check rates
Nu
m
-30 -25 -20 -15 -10 -5 0 5 10MeV
IA1∝σ
4000
X-Y Tracks for Lead Momentum (MeV) • Backgrounds (HRS is clean)
• Sensitivity to beam parameters
100015002000250030003500 • Width of asymmetry
• HRS resolution
Nu
m.
even
ts
IA1∝σ
-0.6 -0.4 -0.2 -0 0.2 0.4
-0.15-0.1
-0.05-0
0.050.1
0.150.2
0500
1000 HRS resolution
• Detector resolution
N
R. MichaelsPREX atPAVI 09
-1 -0.8 -0.6 -0.4-0.2
-0.15-0.1
Noise (integrating at 30 Hz)
• PREX: ~120 ppm Want only counting y gstatistics noise, all others << 120 ppm
• New 18-bit ADCsimprove beam noise. (HAPPEX data)p
• Careful about cable runs, PMTs, grounds loops.
(HAPPEX data)
.Test: Use the “Luminosity Monitor” to demonstrate noise
(next slide)
R. MichaelsPREX atPAVI 09
Luminosity Monitor Luminosity Monitor
A source of extremely high y grate
Established noise floor of 50 ppm
R. MichaelsPREX atPAVI 09
PREX : SummaryPREX : Summary • Fundamental Nuclear Physics with
many applications
&• HAPPEX & test runs have demonstrated technical aspects
• Polarimetry Upgrade critical
• 2 month run starting March 2010
R. MichaelsPREX atPAVI 09
Extra Slides
R. MichaelsPREX atPAVI 09
“What if ’’ ScenariosWhat if ScenariosAssuming other systematics are negligible
dPe/Pe
= 1%dPe/Pe
= 2%
50 uA30 days
dRN/RN
1 % 1 2 %30 days 1 % 1.2 %
100 uA dRN/RN
60 days - 0.6 % 0.8 %
R. MichaelsPREX atPAVI 09
Optimum Kinematics for Lead Parity: E = 1 GeV if<A> = 0 5 ppm Accuracy in Asy 3%<A> = 0.5 ppm. Accuracy in Asy 3%
Fig. of merit
Min. error in Rnmaximize:
n
1 month run1% in R
(2 months x 100 uA
0.5% if no systematics)
R. MichaelsPREX atPAVI 09
y )
Polarimetry Accuracy : 1% from 2 methodsHydrogen: 86.7% ± 2%y g
Møller (New High-field design )
Compton
Helium: 84.0% ± 2.5%
γ−e
HAPPEX
Compton P l i Polarimety Measuremens
R. MichaelsPREX atPAVI 09
Pb Radius vs Neutron Star Radius(slide from C. Horowitz)
Pb Radius vs Neutron Star Radius• The 208Pb radius constrains the pressure of neutron
matter at subnuclear densitiesmatter at subnuclear densities.• The NS radius depends on the pressure at nuclear
density and above.M t i t t d i d it d d f ti f• Most interested in density dependence of equation of state (EOS) from a possible phase transition.
• Important to have both low density and high density p y g ymeasurements to constrain density dependence of EOS.– If Pb radius is relatively large: EOS at low density is stiff with
high P. If NS radius is small than high density EOS soft.– This softening of EOS with density could strongly suggest a
transition to an exotic high density phase such as quark matter, strange matter, color superconductor, kaon condensate…
R. MichaelsPREX atPAVI 09
Asymmetries in Lumi Monitors
after beam noise subtraction
~ 50 ppm noise per pulse milestone for
electronics electronics
( need << 120 ppm)
Jan 2008 D t
R. MichaelsPREX atPAVI 09
Data
Liquid/Solid Transition DensityNeutron Star Crust vs Pb N t Ski
FP Liquid
Pb Neutron SkinC.J. Horowitz, J. Piekarawicz
FP q
208 bNeutron Star
TM1Solid
208PbStar
• Thicker neutron skin in Pb means energy risesThicker neutron skin in Pb means energy rises rapidly with density Quickly favors uniform phase.
• Thick skin in Pb low transition density in star.
R. MichaelsPREX atPAVI 09
PREX: pins down the symmetry energy (1 parameter)energy cost for unequal # protons & neutrons.../ 3/1
2
4 ++⎟⎠⎞
⎜⎝⎛ −
+−≈ AaA
ZNaaAE
sv
( R.J. Furnstahl )
PREX error bar
)1( σ
Pb208
)1( σ
Actually, it’s the density dependence ofPb density dependence of a4 that we pin down.
PREX
R. MichaelsPREX atPAVI 09
PREX Constrains Rapid Direct (slide from C. Horowitz)
pURCA Cooling of Neutron Stars
Proton fraction Y for matter in• Proton fraction Yp for matter in beta equilibrium depends on symmetry energy S(n).
• R in Pb determines densityRn in Pb determines density dependence of S(n).
• The larger Rn in Pb the lower the threshold mass for direct
Rn-Rp in 208Pb
URCA cooling.• If Rn-Rp<0.2 fm all EOS models
do not have direct URCA in 1 4 M stars1.4 M¯ stars.
• If Rn-Rp>0.25 fm all models do have URCA in 1.4 M¯ stars. If Yp > red line NS cools quickly via
direct URCA reaction n p+e+R. Michaels
PREX atPAVI 09
direct URCA reaction n p+e+ν
How to MeasureNeutron Distributions, Symmetry Energy
• Proton-Nucleus ElasticPi l h d S i• Pion, alpha, d Scattering
• Pion Photoproduction• Heavy ion collisions
(d l )
Involve strong probes
• Rare Isotopes (dripline)
• Magnetic scattering Most spins couple to zero.
• PREX (weak interaction)
• Theory MFT fit mostly by data other than neutron densities
R. MichaelsPREX atPAVI 09
Hall ACherenkovcones
PMT
Polarimeters Compton Moller
Polarimeters
Target Spectro: SQQDQ
R. MichaelsPREX atPAVI 09
Isospin Diffusion (NSCL)
Probe the symmetry
Heavy Ions(adapted from Betty Tsang, PREX Workshop) Probe the symmetry
energy in 124Sn + 112Sn( p y g, p)
R. MichaelsPREX atPAVI 09
At 50 the new Optimal FOM is at 1.05 GeV (+/- 0.05)(when accounting for collimating small angle, not shown)
1% @ ~1 GeV
R. MichaelsPREX atPAVI 09
Corrections to the Asymmetry are Mostly Negligible
• Coulomb Distortions ~20% = the biggest correction.
• Transverse Asymmetry (to be measured)
• Strangeness
• Electric Form Factor of Neutron• Electric Form Factor of Neutron
• Parity Admixtures
• Dispersion Corrections
• Meson Exchange Currents
• Shape Dependence
• Isospin Corrections
Horowitz, et.al. PRC 63 025501
• Radiative Corrections
• Excited States
• Target Impurities
R. MichaelsPREX atPAVI 09
• Target Impurities
Successful Results of beam tests Jan 2008 2
1 ⎟⎞
⎜⎛ Δ+=
EσσGood energy resolution 0 1 ⎟⎠
⎜⎝
+=E
σσ
R. MichaelsPREX atPAVI 09
Intensity FeedbackyAdjustmentsfor small phase shiftsto make close tocircular polarization
HAPPEX
Low jitter and high accuracy allows sub-ppmcumulative charge asymmetry in ~ 1 hourcumulative charge asymmetry in 1 hour
In practice, aim for 0.1 ppm over~ 2 hours
R. MichaelsPREX atPAVI 09
duration of data-taking.
q (fm -1)
dσ/d
Ω (
mba
rn) Cross Section
at E=1.0 GeV
q (fm -1)
A (
ppm
)
Asymmetry
q (fm -1)
ε =
dA/A Sensitivity
to R_n
E (GeV)0.5
1
610Θ
FOM x ε2
Ba138
Optimization for Barium -- of possible direct use for Atomic PV
q (fm -1)
dσ/d
Ω (
mba
rn) Cross Section
at E=1.0 GeV
q (fm -1)
A (
ppm
)
Asymmetry
q (fm -1)
ε =
dA/A Sensitivity
to R_n
E (GeV)0.5
1
610Θ
FOM x ε2
Ba138
q (fm -1)
dσ/d
Ω (
mba
rn) Cross Section
at E=1.0 GeV
q (fm -1)
A (
ppm
)
Asymmetry
q (fm -1)
ε =
dA/A Sensitivity
to R_n
E (GeV)0.5
1
610Θ
FOM x ε2
Ba138
q (fm -1)
dσ/d
Ω (
mba
rn) Cross Section
at E=1.0 GeV
q (fm -1)
A (
ppm
)
Asymmetry
q (fm -1)
ε =
dA/A Sensitivity
to R_n
E (GeV)0.5
1
610Θ
FOM x ε2
Ba138
G V i
q (fm -1)
dσ/d
Ω (
mba
rn) Cross Section
at E=1.0 GeV
q (fm -1)
A (
ppm
)
Asymmetry
q (fm -1)
ε =
dA/A Sensitivity
to R_n
E (GeV)0.5
1
610Θ
FOM x ε2
Ba138
1 GeV optimum
q (fm -1)
dσ/d
Ω (
mba
rn) Cross Section
at E=1.0 GeV
q (fm -1)
A (
ppm
)
Asymmetry
q (fm -1)
ε =
dA/A Sensitivity
to R_n
E (GeV)0.5
1
610Θ
FOM x ε2
Ba138
R. MichaelsPREX atPAVI 09
q (fm -1)
dσ/d
Ω (
mba
rn) Cross Section
at E=1.0 GeV
q (fm -1)
A (
ppm
)
Asymmetry
q (fm -1)
ε =
dA/A Sensitivity
to R_n
E (GeV)0.5
1
610Θ
FOM x ε2
Ba138
Warm Septum p
Existing superconducting septum won’t work at high L
Warm low energy (1 GeV) magnet designed.
Delta = 0 (Elastic)Delta = 0.0035 (3 MeV / 850 MeV)
gy g g
Grant proposal in preparation (~100 k$) [Syracuse / Smith College]
0.03
rect
ion
(m
)
0.03
TOSCA design
0.0
Tra
nsve
rse
Dir
ec TOSCA design
P resolution ok
−0.03 −0.03
R. MichaelsPREX atPAVI 09
0.02 0.0 0.04 Dispersive Direction (Meters)