1. Thomas Jefferson National Accelerator Facility
Parity Violation at Jefferson Lab
PREX, MOLLER, & PVDIS Experiments
Robert Michaels Hall A
1/16
Thomas Jefferson National Accelerator Facility

2. Parity Violating Asymmetry2 +
APV from interference
208Pb
208Pb
Applications of APV at Jefferson Lab
Nucleon Structure
Test of Standard Model of Electroweak
Nuclear Structure (neutron density)
Strangeness s s in proton (HAPPEX, G0 expts)
e – e (MOLLER) , e – q (PVDIS)
elastic e – p at low Q2 (QWEAK)
This talk
PREX
e Pb
2/16

3. How to do a Parity Experiment
(integrating method)
Flux Integration Technique:
HAPPEX: 2 MHz
PREX: MHz
Example : HAPPEX
3/16

4. Small beam-related Systematics -- thanks to Jlab beam quality
Parity Violating Asymmetry
Offline asymmetries nearly identical to online.
Corrections tiny (here, 3 ppb)
Errors are statistical only
Asymmetry (ppm)
Slug
HAPPEX-II data
D. Lhuillier, K. Kumar spokespersons
(~1 day)
Araw = ppm  (stat)  0.04 (syst)
HAPPEX-II data
(HWP = optical element used to flip beam helicity, helps suppress some systematics)
4/16

5. Araw = Adet - AQ +  E+ i xi
Parity Quality Beam : Unique Strength of JLab
Helicity – Correlated Position Differences
Plotted below
Araw = Adet - AQ +  E+ i xi
Measured separately
Points: Not sign-corrected nm diffs. with pol. source setup & feedback
Sign flips using ½ wave plate & Wien filter
This BPM, Average = nm
Sign flips provide further suppression : Average with signs = what experiment feels
achieved
< 5 nm
Units: microns
PREX data
Slug # ( ~ 1 day)
5/16

6. PREX : Z0 of weak interaction : sees the neutrons
T.W. Donnelly, J. Dubach, I. Sick
proton
neutron
Electric charge 1
Weak charge
0.08
Nucl. Phys. A 503, 589, 1989
C. J. Horowitz, S. J. Pollock, P. A. Souder, R. Michaels
Phys. Rev. C 63, , 2001
Neutron form factor
C.J. Horowitz
Parity Violating Asymmetry
6/16

7. PREX & Neutron Stars
C.J. Horowitz, J. Piekarewicz
RN calibrates equation of state (pressure vs density) of Neutron Rich Matter
Combine PREX RN with Observed Neutron Star Radii
Phase Transition to “Exotic” Core ?
Strange star ? Quark Star ?
Some Neutron Stars seem too cold
Explained by Cooling by neutrino emission (URCA process) ?
0.2 fm URCA probable, else not
7/16
Crab Pulsar

8. PREX Hall A JLAB CEBAF Pol. Source Results Statistics limited ( 9% )
PRL 108 (2012)
HRS + septum
Physics Asymmetry
Pb target
Statistics limited ( 9% )
Systematic error goal achieved ! (2%)
HRS
Septum Magnet
Pb target 50
8/16

9. Asymmetry leads to RN Neutron Skin = RN - RP = 0.33 + 0.16 - 0.18 fm
Establishing a neutron skin at ~95 % CL
Neutron Skin = RN - RP = fm
published
proposed
Spokespersons
K. Kumar
R. Michaels
K. Paschke
P. A. Souder
G. Urciuoli
Also considering a new 48Ca proposal
9/16

10. GeV Parity Program MOLLER (e-e scattering) PVDIS (e-q scattering)
Fundamental tests of electroweak theory
10/16

11. MOLLER
Credit: Krishna Kumar
Moller (e-e) Scattering: Search for New Physics at the TeV Scale +
11 GeV Beam
LH2
5-10 mrad
APV = 35.6 ppb
best contact interaction reach for leptons at
low OR high energy
δ(QeW) = ± 2.1 % (stat.) ± 1.0 % (syst.)
Luminosity: 3x1039 cm2/s!
To do better for a 4-lepton contact interaction would require:
Giga-Z factory, linear collider, neutrino factory or muon collider
Ebeam = 11 GeV
75 μA
80% polarized
δ(APV) = 0.73 parts per billion
11/16

12. SOLID Spectrometer for PVDIS
Credit: Paul Souder
Standard Model test in the e – quark couplings.
Novel window on QCD using a broad kinematic scan to unfold hadronic effects (CSV, higher twist)
Project is still at an early planning stage
Error bar σA/A (%) at bins in Q2, x
Q2 (GeV2)
12/16

13. Interplay with LHC: New Physics
Assume either SUSY or Z’ discovered at LHC
Does Supersymmetry provide a candidate for dark matter?
MSSM
Not if Nature lies in RPV SUSY space rather than MSSM space
RPV
SUSY
Ramsey-Musolf
and Su, Phys. Rep. 456 (2008)
Virtually all GUT models predict new Z’s
LHC reach ~ 5 TeV, but....
For ‘light’ 1-2 TeV, Z’ properties can be extracted
Suppose a 1 to 2 TeV heavy Z’ is discovered at the LHC
Can we point to an underlying GUT model?
J. Erler and E. Rojas /
TeV-Scale Z
13/16

14. Interplay with LHC: EW Physics
mW and sin2ϴW are powerful indirect probes of the mH
use standard model electroweak radiative corrections to evolve best measurements to Q ~ MZ
MOLLER projected δ(sin2θW)
= ± (stat.) ± (syst.)
precise enough to affect the central value of the world average
14/16

15. MOLLER Status ~ 20M$ project funding sought 3-4 years construction
Director’s Review chaired by C. Prescott: positive endorsement
MOLLER Collaboration
~ 100 authors, ~ 30 institutions
Expertise from SAMPLE A4, HAPPEX, G0, PREX, Qweak, E158
4th generation JLab parity experiment
Technical Challenges
~ 150 GHz scattered electron rate
Idea is to flip Pockels cell ~ 2 kHz
80 ppm pulse-to-pulse statistical fluctuations
1 nm control of beam centroid on target
Improved methods of “slow helicity reversal”
> 10 gm/cm2 liquid hydrogen target
1.5 m: ~ 5 85 μA
Full Azimuthal acceptance with ~ 5 mrad
novel two-toroid spectrometer
radiation hard, highly segmented integrating detectors
Robust and Redundant 0.4% beam polarimetry
Compton and Moller Polarimeters
~ 20M$ project funding sought
3-4 years construction
2-3 years running
15/16
thanks, Krishna Kumar

16. Thomas Jefferson National Accelerator Facility
Conclusions : Parity-Violation at Jefferson Lab
Robert Michaels Hall A
Jefferson Lab is a great place to do parity-violation Leverages the strengths of the
polarized source and superconducting RF accelerator.
Parity experiments provide
Unique information about structure of
nucleon ( strangeness content )
nuclei ( neutrons ) PREX
Precision Frontier of Standard Electroweak Model
complementary to LHC.
not discussed
MOLLER, SOLID-PVDIS
Thomas Jefferson National Accelerator Facility

17. appendix

18. MOLLER Spectrometer Design Progress
Magnet Concepts :
increased the size of the water cooling hole
simplified layout with slightly larger conductor
current density fine with sufficient water flow
water-cooling achievable
weight and magnetic forces modest
still need work on support structure and water/electrical connections
Ongoing studies (students/postdocs) :
optimize the optics
position sensitivity studies
magnetic forces for asymmetric coils
Property
Upstream
Moller
Concept 2
Qweak
Field Integral (Tm)
0.15
1.1
0.89
Total Power (kW) 40
765
1340
Current per wire (A)
298
384
9500
Voltage per coil (V) 19
285 18
Current Density (A/cm2)
1200
1550
500
Wire cross section
(ID: water hole) (in)
0.229x0.229
(0.128)
2.3x1.5
(0.8)
Weight of a coil (lbs) 44
555
7600
Magnetic Forces
(lbs)
100
3000
27000
The spectrometer consists of two resistive toroidal magnets. The upstream magnet provides pre-bending in order to enable the hybrid torus to more effectively separate the Moller electrons from the ep-elastic scattered electrons. The hybrid torus has several features which make it stand out. There are multiple current returns in order to focus a large range of Moller electrons angles and energies (5.5 to 17 mrads and 8.25 down to 2.75 GeV, respectively). There is a negative bend at the downstream end to reduce the amount of integral Bdl seen by the lowest energy (highest angle) Mollers. The magnet is relatively long, which allows it to achieve the necessary integral Bdl while still allowing full azimuthal acceptance. There are an odd number of coils so that the fact of identical particle scattering can be exploited to achieve full azimuthal acceptance, with opposite sectors blocked to avoid double-counting.

19. SoLID PVDIS Progress
CLEO-II magnet fulfills requirements of SoLID PVDIS and SoLID SIDIS. Preliminary discussions about procuring magnet from Cornell have been started.
Baffles: workable concept has been developed for the baffle assembly.
GEM prototyping on going at UVa and several Chinese institutions (USTC, CIAE, Tsinghua U, Lanzhou U,IMP).
Cherenkov conceptual design with two readout options (PMT/GEM).
Shashlyk type EM Calorimeter R&D ongoing by user institutions, collaboration with IHEP from Russia.
A Geant4 simulation framework, GEMC, is successfully applied.
Analysis Software: Tracking framework and calibration methods being developed
Aiming for a Director’s Review in Fall 2012

20. PREX: Measurement at one Q is sufficient to measure R2
Measurement at one Q is sufficient to measure R N
( R.J. Furnstahl )
Why only one parameter ?
(next slide…)
proposed error

21. Slide adapted from J. Piekarewicz
Nuclear Structure: Neutron density is a fundamental observable that remains elusive.
Reflects poor understanding of symmetry energy of nuclear matter = the energy cost of
ratio proton/neutrons
n.m. density
Slope unconstrained by data
Adding R from Pb will significantly reduce the dispersion in plot.
208 N

22. Thanks, Alex Brown
PREX Workshop 2008
Skx-s15
E/N

23. Thanks, Alex Brown
PREX Workshop 2008
Skx-s20
E/N

24. Thanks, Alex Brown
PREX Workshop 2008
Skx-s25
E/N

25. Lead / Diamond Target Diamond LEAD Three bays
Lead (0.5 mm) sandwiched by diamond (0.15 mm)
Liquid He cooling (30 Watts)

26. Performance of Lead / Diamond Targets
melted
melted
Targets with thin diamond backing (4.5 % background) degraded fastest.
Thick diamond (8%) ran well and did not melt at 70 uA.
NOT melted
Last 4 days at 70 uA
Solution: Run with 10 targets.

27. PREX-I Result Statistics limited ( 9% )
Systematic Errors
Error Source
Absolute (ppm)
Relative ( % )
Polarization (1)
0.0083
1.3
Beam Asymmetries (2)
0.0072
1.1
Detector Linearity
0.0076
1.2
BCM Linearity
0.0010
0.2
Rescattering
0.0001
Transverse Polarization
0.0012
Q2 (1)
0.0028
0.4
Target Thickness
0.0005
0.1
12C Asymmetry (2)
0.0025
Inelastic States
TOTAL
0.0140
2.1
Physics Asymmetry
Statistics limited ( 9% )
Systematic error goal achieved ! (2%)
A physics letter was recently accepted by PRL.
(1) Normalization Correction applied
PRL 108 (2012)
(2) Nonzero correction (the rest assumed zero)

28. Septum Magnet Improvements for PREX-II Tungsten Collimator & Shielding
Region downstream of target
Tungsten Collimator & Shielding
HRS-L Q1
Septum Magnet
target
HRS-R Q1
Location of ill-fated O-Ring
which failed & caused significant
time loss during PREX-I
 PREX-II to use all-metal seals
Collimators

29. Geant 4 Radiation Calculations PREX-II shielding strategies
scattering chamber
shielding
Number of Neutrons per incident Electron
MeV
beamline
Energy (MeV)
PREX-I
PREX-II, no shield
PREX-II, shielded
MeV
Strategy
Tungsten ( W ) plug
Shield the W
x 10 reduction in
0.2 to 10 MeV neutrons
Energy (MeV)
MeV
Energy (MeV) 49

30. Polarized Electron Source
Laser
GaAs Crystal
Pockel Cell flips helicity
Gun
Halfwave plate
(retractable, reverses helicity) -
e beam
Based on Photoemission from GaAs Crystal
Polarized electrons from polarized laser
Need :
Rapid, random helicity reversal
Electrical isolation from the rest of the lab
Feedback on Intensity Asymmetry

31. P I T A Effect Intensity Asymmetry
Important Systematic :
Polarization Induced Transport Asymmetry
Intensity Asymmetry
Laser at Pol. Source
where
Transport Asymmetry
drifts, but slope is ~ stable Feedback on
28/53

32. Methods to Reduce Systematics
A simplified picture: asymmetry=0 corresponds to minimized DoLP at analyzer
Perfect DoCP
Intensity Asymmetry (ppm)
Pockels cell voltage D offset (V)
Scanning the Pockels Cell voltage = scanning the residual linear polarization (DoLP)
A rotatable l/2 waveplate downstream of the P.C. allows arbitrary orientation of the ellipse from DoLP

33. Pull Plot (example)
PREX Data

34. 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