Parity Violation at Jefferson Lab

1
Parity Violation at Jefferson Lab
PREX, MOLLER, PVDIS Experiments

Robert Michaels Hall A
1/16
2

• Parity Violating Asymmetry

2

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 - 208Pb
2/16
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How to do a Parity Experiment
(integrating method)
Example HAPPEX
3/16
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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

HAPPEX-II data
D. Lhuillier, K. Kumar spokespersons
(1 day)
Araw -1.58 ppm ? 0.12 (stat) ? 0.04 (syst)
HAPPEX-II data
(HWP optical element used to flip beam
helicity, helps suppress some systematics)
4/16
5
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. 20-50 nm diffs.
with pol. source setup feedback
Sign flips using ½ wave plate Wien
filter - - --
This BPM, Average 2.4 3.1 nm
Sign flips provide further suppression
Average with signs what experiment
feels achieved lt 5 nm
Units microns
PREX data
Slug ( 1 day)
5/16
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PREX Z0 of weak interaction sees
the neutrons
T.W. Donnelly, J. Dubach, I. Sick
proton neutron
Electric charge 1 0
Weak charge 0.08 1
Nucl. Phys. A 503, 589, 1989
C. J. Horowitz, S. J. Pollock, P. A.
Souder, R. Michaels
Phys. Rev. C 63, 025501, 2001
Neutron form factor
C.J. Horowitz
Parity Violating Asymmetry
6/16
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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
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PREX
Results
PRL 108 (2012) 112502
HRS septum
Physics Asymmetry
Pb target

• Statistics limited ( 9 )
• Systematic error goal achieved ! (2)

HRS
Septum Magnet
50
Pb target
8/16
9
Asymmetry leads to RN
Establishing a neutron skin at 95 CL
Neutron Skin RN - RP 0.33 0.16 -
0.18 fm
published
proposed
Spokespersons K. Kumar R. Michaels K.
Paschke P. A. Souder G. Urciuoli
Also considering a new 48Ca proposal
9/16
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• GeV Parity Program
• MOLLER (e-e scattering)
• PVDIS (e-q scattering)
• Fundamental tests of electroweak theory

10/16
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MOLLER
Credit Krishna Kumar
Moller (e-e) Scattering Search for New
Physics at the TeV Scale

11 GeV Beam
5-10 mrad
LH2
APV 35.6 ppb
best contact interaction reach for leptons
at low OR high energy
d(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
d(APV) 0.73 parts per billion
11/16
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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 sA/A () at bins in Q2, x
Q2 (GeV2)
12/16
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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)
/
TeV-Scale Z
13/16
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Interplay with LHC EW Physics
mW and sin2?W are powerful indirect probes
of the mH
use standard model electroweak radiative
corrections to evolve best measurements to Q MZ
MOLLER projected d(sin2?W) 0.00026 (stat.)
0.00012 (syst.)
precise enough to affect the central value of the
world average
14/16
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MOLLER Status
Directors 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
• gt 10 gm/cm2 liquid hydrogen target
• 1.5 m 5 kW _at_ 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
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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
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appendix
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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) 0.229x0.229 (0.128) 2.3x1.5 (0.8)
Weight of a coil (lbs) 44 555 7600
Magnetic Forces (lbs) 100 3000 27000
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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 RD 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 Directors Review in Fall 2012

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PREX
2
Measurement at one Q is sufficient to
measure R
N
( R.J. Furnstahl )
Why only one parameter ? (next slide)
proposed error
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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
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Thanks, Alex Brown PREX Workshop 2008
Skx-s15
E/N
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Thanks, Alex Brown PREX Workshop 2008
Skx-s20
E/N
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Thanks, Alex Brown PREX Workshop 2008
Skx-s25
E/N
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Lead / Diamond Target
Diamond
LEAD

• Three bays
• Lead (0.5 mm) sandwiched by diamond (0.15
  mm)
• Liquid He cooling (30 Watts)

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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.
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PREX-I Result
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 0
Transverse Polarization 0.0012 0.2
Q2 (1) 0.0028 0.4
Target Thickness 0.0005 0.1
12C Asymmetry (2) 0.0025 0.4
Inelastic States 0 0
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) 112502
(2) Nonzero correction (the rest assumed zero)
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Improvements for PREX-II
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
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Geant 4 Radiation Calculations PREX-II
shielding strategies
scattering chamber
shielding
Number of Neutrons per incident Electron
0 - 1 MeV
beamline
Energy (MeV)
--- PREX-I --- PREX-II, no shield ---
PREX-II, shielded
1 - 10 MeV

• Strategy
• Tungsten ( W ) plug
• Shield the W
• x 10 reduction in
• 0.2 to 10 MeV neutrons

Energy (MeV)
10 - 1200 MeV
Energy (MeV)
49
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Polarized Electron Source
Laser
GaAs Crystal
Pockel Cell flips helicity
Halfwave plate (retractable, reverses
helicity)
Gun
-
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

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P I T A Effect
Important Systematic
Polarization Induced Transport Asymmetry
Intensity Asymmetry
Laser at Pol. Source
where
Transport Asymmetry
drifts, but slope is stable. Feedback
on
28/53
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Methods to Reduce Systematics
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
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Pull Plot (example)
PREX Data
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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