R. Michaels PREX at HE06 July 2006 Lead ( Pb) Radius Experiment : PREX Z of Weak Interaction : Clean...

HE06 July 2006 R. Michaels PREX

at

)(

sin4122 2

22

QF

QG

d

d

d

d

d

d

d

d

AP

WF

LR

LR

)( 2QF n

%1%3 n

n

R

dR

A

dA

Lead ( Pb) Radius Experiment : PREX

Z of Weak Interaction :

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

0

In PWIA (to illustrate) :

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

208

208Pb

E = 850 MeV, electrons on lead

06 Elastic Scattering Parity Violating Asymmetry

0


at

Parity Violating Asymmetry 610~

LR

LRPVA

0Z

e e

+

2

Applications of PV at Jefferson Lab

• Nucleon Structure (strangeness) -- HAPPEX / G0

• Standard Model Tests ( ) -- e.g. Qweak

• Nuclear Structure (neutron density) : PREX

W2sin

Applications of PV at Jefferson Lab


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Z of weak interaction : sees the neutrons

0

proton neutron

Electric charge 1 0

Weak charge 0.08 1

Analysis is clean, like electromagnetic scattering:

1. Probes the entire nuclear volume

2. Perturbation theory applies


at

str

mb

d

d

1fmq

Reminder: Electromagnetic Scattering determines

r

r

Pb208

(charge distribution)

1 2 3


at

neutron weak charge >> proton weak charge

is small, best observed by parity violation

)()()(ˆ5 rArVrV

||)()(/

//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

)(

)(sin41

22 2

22

2

QF

QFQG

d

d

d

d

d

d

d

d

AP

NW

F

LR

LR

Electron - Nucleus Potential

electromagnetic axial

Neutron form factor

Parity Violating Asymmetry

)(rA

1sin41 2 W

Proton form factor

0

Pb is spin 0208


at

( R.J. Furnstahl )

Measurement at one Q is sufficient to measure R

2

N

PREX error bar

Why only one parameter ?

(next slide…)

PREX:

)1(


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PREX: pins down the symmetry energy (1 parameter)

( R.J. Furnstahl )

energy cost for unequal # protons & neutrons.../ 3/1

2

4

AaA

ZNaa

A

Esv

PREX

PREX error bar

Pb208

)1(


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

ZN

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


at

PREX & Neutron Stars

Crab Pulsar

( C.J. Horowitz, J. Piekarweicz )

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 pn RR

Phase Transition to “Exotic” Core ?


at

FP

TM1Solid

Liquid

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.

Neutron EOS and Neutron Star Crust

Fig. from J.M. Lattimer & M. Prakash, Science 304 (2004) 536.



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Pb Radius vs Neutron Star Radius

• The 208Pb radius constrains the pressure of neutron matter at subnuclear densities.

• The NS radius depends on the pressure at nuclear density and above.

• Most interested in density dependence of equation of state (EOS) from a possible phase transition.

• Important to have both low density and high density measurements 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…



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PREX Constrains Rapid Direct URCA Cooling of Neutron Stars

• Proton fraction Yp for matter in beta equilibrium depends on symmetry energy S(n).

• Rn in Pb determines density dependence of S(n).

• The larger Rn in Pb the lower the threshold mass for direct URCA cooling.

• If Rn-Rp<0.2 fm all EOS models do not have direct URCA in 1.4 M¯ stars.

• If Rn-Rp>0.25 fm all models do have URCA in 1.4 M¯ stars.

Rn-Rp in 208Pb

If Yp > red line NS cools quickly via direct URCA reaction n p+e+



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Impact on Atomic Parity Violation• Low Q test of Standard Model

• Needs R to make further progress.

2

N

rdrZrNG

H eePWNF

PNC35/2 )()sin41()(

22

0

APV

Isotope Chain Experiments e.g. Berkeley Yb


at

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


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PREX: Experimental Issues

Spokespersons:

P.A. Souder, G.M. Urciuoli, R. Michaels

Hall A Collaboration Experiment


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PREX in Hall A at JLab

CEBAF

Hall A

Pol. Source

Lead Foil Target

Spectometers


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Hall A at Jefferson Lab

Polarized e-

SourceHall A


at

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


at

Halfwave plate (retractable, reverses helicity)

Laser

Pockel Cell flips helicity

Gun

GaAs Crystal

e beam-

• Rapid, random helicity reversal

• Electrical isolation from rest of lab

• Feedback on Intensity Asymmetry

Polarized Electron Source


at

P I T A Effect

)sin( IA Laser at Pol. Source

Polarization Induced Transport Asymmetry

yx

yx

TT

TT

where

Transport Asymmetry

Intensity Asymmetry

drifts, but slope is ~ stable. Feedback on

Important Systematic :


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Intensity FeedbackAdjustmentsfor small phase shiftsto make close tocircular polarization

Low jitter and high accuracy allows sub-ppmCumulative charge asymmetry in ~ 1 hour

In practice, aim for 0.1 ppm overduration of data-taking.

~ 2 hours

HAPPEX


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Beam Position Corrections (HAPPEX)X Angle BPM

Energy: -0.25 ppb

X Target: 1 nm

X Angle: 2 nm

Y Target : 1 nm

Y Angle: <1 nm

Beam Asymmetry Results

Corrected and Raw, Left spectrometer arm alone, Superimposed!

pp

mm

icro

n

Total correction for beam position asymmetry on Left, Right, or ALL detector: 10 ppbSpectacular results from HAPPEX-H show we can do PREX.


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Integrating Detection

PMT

Calorimeter (for lead, fits in palm of hand)

ADC

Integrator

electrons

• Integrate in 30 msec helicity period.

• Deadtime free.

• 18 bit ADC with < 10 nonlinearity.

• But must separate backgrounds & inelastics ( HRS).

- 4


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The Raw Asymmetry

Flux Integration Technique:HAPPEX: 2 MHzPREX: 850 MHz


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Application of Parity Violating Electron Scattering :

sME

dME

uME

pME GGGG ,,,, 3

1

3

1

3

2

sME

dMEW

uMEW

pME GGGG ,,

2,

2, sin

3

1

4

1sin

4

1

0Z

Isolating the u, d, s quark structure in protons (and He)

sME

uME

dME

nME GGGG ,,,, 3

1

3

1

3

2

Electromagnetic Scattering:

Parity Violation can Access:

HAPPEX & Strange Quarks Hall A Proton Parity Experiment 4


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1H Preliminary 2006 Results

Q2 = 0.1089 ± 0.0011GeV2

Araw = -1.418 ppm 0.105 ppm (stat)

Araw correction ~11 ppb

Raw Parity Violating Asymmetry

Helicity Window Pair Asymmetry

Asym

metr

y

(pp

m)

Slug


at

Strange FF near ~0.1 GeV2

Preliminary

GMs = 0.28 +/- 0.20

GEs = -0.006 +/- 0.016

~3% +/- 2.3% of proton magnetic moment

~0.2 +/- 0.5% of electric distribution


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Polarimetry Accuracy : 2 % required, 1% desiredHydrogen: 86.7% ± 2%

Helium: 84.0% ± 2.5%

Preliminary

Prelim. HAPPEX Results

Møller : Pe/Pe ~ 3 % (limit: foil polarization)(a high field target ala Hall C being considered)

Compton : 2% syst. at present

e


at

Upgrade of Compton Polarimeter

To reach 1% accuracy:• Green Laser (increased sensitivity at low E)

laser on-hand, being tested

• Integrating Method (removes some systematics of analyzing power)

developed during HAPPEX & in 2006

• New Photon Detector

electron

s


at

Optimum Kinematics for Lead Parity: E = 850 MeV, <A> = 0.5 ppm. Accuracy in Asy 3%

n

Fig. of merit

Min. error in R

maximize:

1 month run

1% in R

n


at

Lead Target

Liquid Helium Coolant

Pb

C

208

12

Diamond Backing:

• High Thermal Conductivity• Negligible Systematics

Beam, rastered 4 x 4 mm

A 80at ly testedSuccessful

beam


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PREX : Summary

• Fundamental Nuclear Physics with many applications

• HAPPEX & test runs have demonstrated technical aspects

• Polarimetry Upgrade needed

• Will run 1 month in 2008


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Extra Slides


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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 Impact

Heavy Ions


at

4He Preliminary 2006 Results

Q2 = 0.07725 ± 0.0007 GeV2

Araw = 5.253 ppm 0.191 ppm (stat)

Raw Parity Violating Asymmetry

Helicity Window Pair Asymmetry

Araw correction ~ 0.12 ppm

Slug

Asym

metr

y

(pp

m)


at

Optimization for Barium -- of possible direct use for Atomic PV

1 GeV optimum


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X (dispersive coord)

(m)

Y (m)

Momentum (MeV)

Detector

Pb Elastic

208

1st Excited State (2.6 MeV)

Lead Target Tests

• Check rates

• Backgrounds (HRS is clean)

• Sensitivity to beam parameters

• Width of asymmetry

• HRS resolution

• Detector resolution

IA1

Nu

m.

eve

nts

Nu

m.

eve

nts

Data taken Nov 2005


at

Neutron Skin and Heavy – Ion Collisions

Danielewicz, Lacey, and Lynch, Science 298 (2002) 1592.

• Impact on Heavy - Ion physics: constraints and predictions

• Imprint of the EOS left in the flow and fragmentation distribution.


at

B. Krusche arXiv:nucl-ex/0509003 Sept 2005

Example : Recent Pion Photoproduction

This paper obtains

PN RR

Mean Field Theory fmRR PN 35.005.0

PREX accuracy

fmRN 05.0

!!

fmRR PN 111.0083.0 Proton – Nucleus Elastic:


at

Transverse Polarization

TTTTT PAAPAA 00 sin

oT PP 3sin

ppmAT 150

HRS-Left HRS-Right

Transverse Asymmetry

Systematic Error for Parity

“Error in”

TP

Left-right apparatus asymmetry

Need 33 1010 <

ppmAT 10 measure in ~ 1 hr (+ 8 hr setup)

Theory est. (Afanasev)

P

Transverse polarization

Part I: Left/Right Asymmetry

correction syst. err.

<

Control w/ slow feedback on polarized source

solenoids.


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Transverse Polarization

cos0cos 0TT PAA

HRS-Left HRS-

Right

Vertical misalignment

Systematic Error for Parity

P

Horizontal polarization e.g. from (g-2)

Part II: Up/Down Asymmetry

( Note, beam width is very tiny

m100~

up/down misalignment

• Measured in situ using 2-piece

detector.

• Study alignment with tracking & M.C.

• Wien angle feedback ( )

33 1010cos TP

Need

)

<<

sinPPT


at

Noise • Need 100 ppm per window pair

• Position noise already good enough

• New 18-bit ADCs Will improve BCM noise.

• Careful about cable runs, PMTs, grounds. Will improve detector noise.

• Plan: Tests with Luminosity Monitor

to demonstrate capability.


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Warm Septum

Existing superconducting septum won’t work at high L

Warm low energy (1 GeV) magnet designed.

Grant proposal in preparation (~100 k$) [Syracuse / Smith College]

TOSCA design

P resolution ok


at

( R.J. Furnstahl )

Measurement at one Q is sufficient to measure R

2

N

Pins down the symmetry energy (1 parameter)

PREX accuracy

PREX accuracy

R. Michaels PREX at HE06 July 2006 Lead ( Pb) Radius Experiment : PREX Z of Weak Interaction : Clean...

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Transcript of R. Michaels PREX at HE06 July 2006 Lead ( Pb) Radius Experiment : PREX Z of Weak Interaction : Clean...