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)