PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

)(sin41

22 22

2

QF

QGA

PW

F

)( 2QF n

%1%3 n

n

R

dR

A

dA

Parity Violating Neutron DensitiesZ of Weak Interaction :

Clean Probe Couples Mainly to Neutrons

Low Q elastic nucleus scattering

( T.W. Donnelly, J. Dubach, I Sick )

2

0

In PWIA -- but must account for Coulomb

distortions (C. J. Horowitz)

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

Parity Violating AsymmetryLR

LRPVA

0Z

e e

+

2

Applications :

• Nucleon Structure (strangeness)

• Nuclear Structure (neutron density)

• Standard Model tests ( )W2sin

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

Z sees the neutrons0

proton neutron

Electric charge 1 0

Weak charge 0.08 1

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

PREX in Hall A at JLab

Hall A

Polarized e-

Source

CEBAF

Hall A

Pol. Source

Lead Foil Target

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

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

Lead Parity

Physics Impact of

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

Lead Parity: pins down the symmetry energy (1 parameter)

( R.J. Furnstahl )energy cost for unequal # protons & neutrons

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

Pb Parity : Neutron Stars

Crab Pulsar( from hubblesite.org )

( C.J. Horowitz, J. Piekarweicz )

R calibrates EOS of Neutron Rich Matter

Combine R with Neutron Star Radius

Some Neutron Stars too Cold

n

n

Crust ThicknessExplain Obs. Glitches in Pulsar Frequency ?

Exotic Core ? (strange matter, quark star)

Cooling by neutrino emission (URCA)

0.2 fm URCA probable, else not pn RR

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

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

1 month run

1% in Rn

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

High Resolution Spectrometers

Elastic

Inelastic

detector

Q Q

Dipole

Quad

Spectrometer Concept:

Resolve Elastic

target

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

Septum Magnets (INFN)

Electrons scatteredat 6 deg sent to theHRS at 12.5 deg.

•Superconducting magnets

•Commissioned 2003-4

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

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

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

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

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

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

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

Beam Asymmetries

Araw

= Adet

- AQ +

E+

ix

i

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

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

“Energy” BPM

BPM Y2

BPM Y1

BPM X1

BPM X2

Scale +/- 100 nm

Position Diffs avg

~ 10 nm

Negligible

Systematic Error

Helicity Correlated Differences: Position, Angle, Energy

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

Polarimetry

Electron onlyPhoton only

Preliminary: 2.5% syst ( only)

Møller: Pe/Pe ~ 3 % (foil polarization)

Compton: 2% syst. At present

2 analyses based on either electron

or photon detection

Superlattice:

Pe=86% !

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

Upgrade of Compton Polarimeter (Nanda, Lhuillier)

To reach 1% accuracy:

• Green Laser

• Integrating Method

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

Summary -- Neutron Skin

• R is Fundamental to Nuclear Physics

• HAPPEX program to demonstrate most technical aspects

• Polarimetry Upgrade needed

• Planned 2-day test run in 2005

n

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

extra slides --

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

Moller Polarimetry with Atomic Hydrogen Target

315103 cm

( E. Chudakov, V. Luppov)

H atoms

Solenoid 8T

Trapbeam

Ultra Cold Traps

• Polarization ~ 100%

• Density

• Lifetime > 10 min

Polarimetry

• 1% stat. err. in 30 min at 30 A

• Low background

• High beam currents allowed (100 A)

• Goal: ~ 0.5 % systematic error

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

controls

effective

analyzing

power

Tune residual

linear pol.

Slow helicityreversal

Intensity Attenuator

Polarized Source

High Pe

High Q.E.

Low Apower

•Optical pumping of solid-state photocathode

•High Polarization

• Pockels cell allows rapid helicity flip

•Careful configuration to reduce beam asymmetries.

•Slow helicity reversal to further cancel beam asymmetries

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

Beam Modulation to Calibrate Sensitivity to Beam Systematics

PN12 WorkshopJLab, Nov 2004

R. Michaels

Jefferson Lab

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