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R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 P b E = 1 GeV, electrons on lead 0 5 Elastic Scattering Parity Violating Asymmetry Spokespersons Paul Souder, Krishna Kumar Guido Urciuoli, Robert Michaels Ran March – June 2010 in Hall A Graduate Students Ahmed Zafar, Chun Min Jen, Abdurahim Rakham (Syracuse) Jon Wexler (UMass) Kiadtisak Saenboonruang (UVa)

R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

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Page 1: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Lead ( Pb) Radius Experiment : PREX208

208Pb

E = 1 GeV, electrons on lead

05

Elastic Scattering

Parity Violating Asymmetry

Spokespersons

Paul Souder, Krishna Kumar

Guido Urciuoli, Robert Michaels

Ran March – June 2010 in Hall A

Graduate Students

Ahmed Zafar, Chun Min Jen, Abdurahim Rakham (Syracuse)

Jon Wexler (UMass)

Kiadtisak Saenboonruang (UVa)

Page 2: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

)(

sin4122 2

22

QF

QG

dd

dd

dd

dd

AP

WF

LR

LR

)( 2QF n

%1%3 n

n

R

dR

A

dA

Idea behind PREX

Z of Weak Interaction :

Clean Probe Couples Mainly to Neutrons( T.W. Donnelly, J. Dubach, I Sick 1989 )

0

In PWIA (to illustrate) :

w/ Coulomb distortions (C. J. Horowitz) :

0

Page 3: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Measured Asymmetry

Weak Density at one Q2

Neutron Density at one Q2

Correct for CoulombDistortions

Small Corrections forG

nE G

sE MEC

Assume Surface Thickness Good to 25% (MFT)

Atomic Parity Violation

Mean Field & Other

Models

Neutron

Stars

R n

PREX Physics Output

Slide adapted from C. Horowitz

Page 4: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Fundamental Nuclear Physics :

What is the size of a nucleus ?

Neutrons are thought to determine the size of heavy nuclei like 208Pb.

Can theory predict it ?

Page 5: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

str

mb

d

d

1fmq

Reminder: Electromagnetic Scattering determines

r

rPb

208

(charge distribution)

1 2 3

d

d

Page 6: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Z of weak interaction : sees the neutrons

proton neutron

Electric charge 1 0

Weak charge 0.08 1

0

Analysis is clean, like electromagnetic scattering:

1. Probes the entire nuclear volume

2. Perturbation theory applies

6

Page 7: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

)()()(ˆ5 rArVrV

)(

)(sin41

22 2

22

2

QF

QFQG

d

d

d

d

d

d

d

d

AP

NW

F

LR

LR

neutron weak charge >> proton weak charge

is small, best observed by parity violation

||)()(/

//3 rrrZrdrV )()()sin41(22

)( 2 rNrZG

rA NPWF

22 |)(| QFd

d

d

dP

Mott

)()(4

1)( 0

32 rqrjrdQF PP )()(

4

1)( 0

32 rqrjrdQF NN

Electron - Nucleus Potential

electromagnetic axial

Neutron form factor

Parity Violating Asymmetry

)(rA

1sin41 2 W

Proton form factor

0

Pb is spin 0208

Page 8: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

( R.J. Furnstahl )

Measurement at one Q is sufficient to measure R

2

N

proposed error

Why only one parameter ?

(next slide…)

PREX:

Page 9: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

ZN

Nuclear Structure: Neutron density is a fundamental observable that remains elusive.

Reflects poor understanding of symmetry energy of nuclear matter = the energy cost of

xn

)21()()2/1,(),( 2xnSxnExnE

n.m. density

ratio proton/neutrons

• Slope unconstrained by data

• Adding R from Pb will eliminate the

dispersion in plot.

N208

Slide adapted from J. Piekarewicz

Page 10: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Skx-s15Thanks, Alex Brown

PREX Workshop 2008

E/N

N

Page 11: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Skx-s20Thanks, Alex Brown

PREX Workshop 2008

Page 12: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Skx-s25Thanks, Alex Brown

PREX Workshop 2008

Page 13: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Application: Atomic Parity Violation• Low Q test of Standard Model

• Needs RN (or APV measures RN )

2

0

Isotope Chain Experiments e.g. Berkeley Yb

13

APV

rdrZrNG

H eePWNF

PNC35/2 )()sin41()(

22

Page 14: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Neutron

StarsWhat is the nature of extremely dense matter ?

Do collapsed stars form “exotic” phases of matter ? (strange stars, quark stars)

Crab Nebula (X-ray, visible, radio, infrared)

Application :

Page 15: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

PREX & Neutron Stars

pn RRCrab Pulsar

( C.J. Horowitz, J. Piekarewicz )

R calibrates EOS of Neutron Rich Matter

Combine PREX R with Obs. Neutron Star Radii

Some Neutron Stars seem too Cold

N

N

Crust ThicknessExplain Glitches in Pulsar Frequency ?

Strange star ? Quark Star ?

Cooling by neutrino emission (URCA)

0.2 fm URCA probable, else not

Phase Transition to “Exotic” Core ?

Page 16: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

How to do a Parity Experiment

Flux Integration Technique:HAPPEX: 2 MHzPREX: 500 MHz

(integrating method)

Example : HAPPEX

Page 17: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

/)( AA

Pull Plot (example)

PREX Data

Page 18: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

PAVI 09

Beam AsymmetriesA

raw = A

det - A

Q +

E+

ix

i

•natural beam jitter (regression) •beam modulation (dithering)

Slopes from

18

Page 19: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Slug # ( ~ 1 day)

Units: microns

RLhelicityforXX LR ,

Parity Quality Beam !

Helicity – Correlated Position Differences

< ~ 3 nm

Wien Flips helped !Average with signs = what exp’t feels

Points: Not sign corrected

Page 20: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Hall A Compton Upgrade

with Green Laser

Sirish Nanda, et. al.

1 % Polarimetry

at 1 GeV

Page 21: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Hall A Moller Upgrade

Superconducting Magnet from Hall C

Saturated Iron Foil Targets

1 % Polarimetry

Magnet and Target

DAQ Upgrade (FADC)

Sasha Glamazdin, et.al.

Page 22: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

High Resolution Spectrometers

Elastic

Inelastic

detector

Q Q

Dipole

Quad

Spectrometer Concept: Resolve Elastic

target

Left-Right symmetry to control transverse polarization systematic

1st excited state Pb 2.6 MeV

Page 23: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Collimators

Septum Magnet

Top view

target

HRS-L

Q1

HRS-R

Q1

PREX Region After Target

Former O-Ring location which failed and caused significant time loss

Planned Tungsten Collimator and Shielding

Page 24: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

10 m

-1 m

Geant 4 Radiation Calculations

• benchmarking against LD2 (ran at 100 uA)

• exploring shielding strategies

J. Mammei, L. Zana

Number of Neutrons per incident Electron

Z (distance along beamline)

1 mLD2 tgtPb tgt

1 - 50 MeV

50 - 500 MeV

0 - 1 MeV

Strategy

• Tungsten ( W ) plug

• Shield the W

• x10 reduction in 0.2 to 10 MeV neutrons

(similar to LD2)

00 37.0

W

PREX-II proposal

PREX -I

PREX -II

Page 25: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Pure, Thin 208 Pb Target

Momentum (GeV/c)

Lead 5- State

2.6 MeV

High Resolution Spectrometers

DETECTOR footprint

25

Page 26: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Diamond LEAD

• Three bays

• Lead (0.5 mm) sandwiched by diamond (0.15 mm)

• Liquid He cooling (30 Watts)

Lead / Diamond Target

Page 27: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Performance of Lead / Diamond Targets

Last 4 days at 70 uA

Targets with thin diamond backing (4.5 % background) degraded fastest.

Thick diamond (8%) ran well and did not melt at 70 uA.

meltedmelted

NOT melted

Solution: Run with 10 targets.

Page 28: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

y

z

xS

k

+ -

AT > 0 means

)'( eeeT kkSA

Beam-Normal Asymmetry in elastic electron scatteringi.e. spin transverse to scattering plane

Possible systematic if small transverse spin component

New results PREX

ppmAC T 35.036.052.6:12

ppmAPb T 36.019.013.0:208

• Small AT for 208Pb is a big (but pleasant) surprise. • AT for 12C qualitatively consistent with 4He and available calculations (1) Afanasev ; (2) Gorchtein & Horowitz

Page 29: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Error Source Absolute (ppm) Relative ( % )

Polarization (1) 0.0071 1.1

Beam Asymmetries (2) 0.0072 1.1

Detector Linearity 0.0071 1.1

BCM Linearity 0.0010 0.2

Rescattering 0.0001 0

Transverse Polarization 0.0012 0.2

Q2 (1) 0.0028 0.4

Target Thickness 0.0005 0.112C Asymmetry (2) 0.0025 0.4

Inelastic States 0 0

TOTAL 0.0130 2.0

Systematic Errors

(1) Normalization Correction applied

(2) Nonzero correction (the rest assumed zero)

Page 30: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

PREX Physics Result

LR

LRPVA

)(0130.0)(0604.06571.0 syststat ppm

at Q2 = 0.00906 GeV2

Statistics limited ( 9% )

Systematic error goal achieved ! (2%)

9.2 % 2.0 %

Page 31: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

PREX Asymmetry (Pe x A)

ppm

Slug ~ 1 day

(blinded, raw)

Page 32: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

PREX Physics Interpretation

Page 33: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Asymmetry leads to RN

Neutron Skin = RN - RP = 0.34 + 0.15 - 0.17 fm

arXiv:1010.3246  [nucl-th] Shufang Ban, C.J. Horowitz, R. Michaels

Establishing a neutron skin at 95% CL

Page 34: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

PREX – II Proposal

Future ?

Page 35: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Future ?

Page 36: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Other Nuclei ?

Shape Dependence ?RN

RN

Surface thickness

Surface thickness

arXiv:1010.3246  [nucl-th]

Parity Violating Electron Scattering Measurements of Neutron Densities Shufang Ban, C.J. Horowitz, R. Michaels

Page 37: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

PREX : Summary • Fundamental Nuclear Physics with

many applications

• Achieved a 9% stat. error in Asymmetry (original goal : 3 %)

• Systematic Error Goals Achieved !!

• Significant time-losses due to O-Ring problem and radiation damage

• Proposal for PREX-II in preparation

Page 38: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Extra Slides

Page 39: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Corrections to the Asymmetry are Mostly Negligible

• Coulomb Distortions ~20% = the biggest correction.

• Transverse Asymmetry (to be measured)

• Strangeness

• Electric Form Factor of Neutron

• Parity Admixtures

• Dispersion Corrections

• Meson Exchange Currents

• Shape Dependence

• Isospin Corrections

• Radiative Corrections

• Excited States

• Target Impurities

Horowitz, et.al. PRC 63 025501

Page 40: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

PAVI 09

Optimum Kinematics for Lead Parity: E = 1 GeV if <A> = 0.5 ppm. Accuracy in Asy 3%

n

Fig. of merit

Min. error in R

maximize:

1 month run

1% in R

n

(2 months x 100 uA 0.5% if no systematics)

5

Page 41: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

Liquid/Solid Transition Density

• Thicker neutron skin in Pb means energy rises rapidly with density Quickly favors uniform phase.

• Thick skin in Pb low transition density in star.

FP

TM1Solid

Liquid

Neutron Star Crust vs Pb Neutron Skin

208Pb

Neutron Star

C.J. Horowitz, J. Piekarawicz

Page 42: R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

R. Michaels, Jlab UGM, June, 2011

.../ 3/12

4

AaA

ZNaa

A

Esv

)1(

PREX: pins down the symmetry energy (1 parameter)

( R.J. Furnstahl )

energy cost for unequal # protons & neutrons

PREX

PREX error bar

Pb208 Actually, it’s the

density dependence of a4 that we pin down.