Hadronic Parity Violation at the SNS

Christopher CrawfordUniversity of Kentucky

2011-01-31

• symmetries and interactions

• properties of the neutron

• NPDGamma & n-3He exp.

• designing coils with ϕm

Madison Spencer

Weak Interaction

Strong Interaction

Hadronic Interaction(residual nuclear force)

Standard Model of Particles

E&M InteractionSPACE

TIM

E

Degenerate Fermi Gas

Particle Decay

Higgs?

Annihilation

Standard Model of Automobiles

Symmetries• Continuous Symmetries

– space-time translation– rotational invariance– Lorentz boosts– gauge invariance

• Noether’s Theorem continuous symmetries correspond to conserved quantities

– energy-momentum– angular momentum– center-of-momentum– electric charge

• Discrete Symmetries– parity P : x -x– time T : t -t– charge C : q -q– particle P12: x1 x2

exchange

• Discrete Theorems– CPT theorem– spin-statistics theorem

position symmetry

conserved momentum

CPT theorem: ALL laws are invariant under CPT

Car Symmetries

L RR

CP (charge, parity)

100km/h

100km/h

99.7km/h

T (time)

I’m coming home …

Be careful, some idiot’sgoing the wrong way

on the freeway.

Only one? They’re all over the place!

Parity-violation in weak interaction

October 1, 1956 issue of the Physical Review

Parity-transformation (P) :

Madame C.S. Wu

Hadronic Weak Interaction• Desplanques, Donahue, & Holstein (DDH) formalism:

– 6 meson-nucleon coupling constants: range + isospin structure– pion channel dominated by neutral current (Z0)– PV effects: interference between strong and weak vertex

• other treatments:– partial waves, chiral perturbation theory, lattice QCD

N N

N N

Meson exchange

STRONG(PC)

WEAK(PV)

Why Study Hadronic PV?• probe of atomic, nuclear,

and hadronic systems– map out coupling constants– resolve 18F, 133Cs discrepancy– probe nuclear structure effects– anapole and qq contributions

to PV electron scattering

• probe of QCD in low energy non-perturbative regime– confinement, many-body

problem– sensitive to qq correlations– measure QCD modification

of qqZ coupling

n + p d +

A = -0.11 f

+ -0.001 hρ1

+ -0.003 h1

n-capture elastic scatteringspin rotation

np A nD A n3He Ap np n pp Az p Az

f -0.11 0.92 -0.19 -3.12 -0.97 -0.34

hρ0 -0.50 -0.036 -0. 23 -0.32 0.08 0.14

hρ1 -0.001 0.10 0.019 0.11 0.08 0.05

hρ2 0.05 0.0006 -0.25 0.03

h0 -0.16 -0.033 -0. 23 -0.22 -0.07 0.06

h1 -0.003 -0.002 0.041 0.22 0.07 0.06

p-p and nuclei

Existing Measurements

Anapole

Nuclear anapole moment(from laser spectroscopy)

Polarized proton scattering asymmetries

Light nuclei gamma transitions(circular polarized gammas)

Properties of the Neutronmn = mp + me + 782 keV

n = 885.7 ± 0.8 s

qn < 2 x 10-21 e

dn < 3 x 10-26 e cm

n = -1.91 N

rm = 0.889 fm

re2 = -0.116 fm2

– 3 valence quarks + sea– exponential magnetization

distribution– pion cloud:

spin 1/2 isospin 1/2

p n

uud uddup down

data from BLAST

Neutron sources - ReactorsILL, Grenoble, France

Spallation Neutron Source (SNS)

• spallation sources: LANL, SNS– pulsed -> TOF -> energy

• LH2 moderator: cold neutrons– thermal equilibrium in ~30 interactions

Oak Ridge National Laboratory, Tennessee

Spallation Neutron Source (SNS)

• spallation sources: LANL, SNS– pulsed -> TOF -> energy

• LH2 moderator: cold neutrons– thermal equilibrium in ~30 interactions

Guides - neutron optical potential

slide courtesy A. Young

1B - Disordered Mat’lsCommission 2010

2 - Backscattering Spectrometer Commission 2006

3 - High Pressure Diffractometer Commission 2008

4A - Magnetism Reflectometer Commission 2006

4B - Liquids ReflectometerCommission 2006

5 - Cold Neutron Chopper Spectrometer Commission 2007

18 - Wide Angle Chopper Spectrometer Commission 2007

17 - High Resolution Chopper SpectrometerCommission 2008

13 - Fundamental Physics Beamline Commission 2007

11A - Powder Diffractometer Commission 2007

12 - Single Crystal Diffractometer Commission 2009

7 - Engineering Diffractometer IDT CFI Funded Commission 2008

6 - SANS Commission 2007

14B - Hybrid Spectrometer Commission 2011

15 – Spin Echo

9 – VISION

Flight Paths at the SNS

What can we do with neutrons?• scattering / diffraction

– complementary to X-ray Bragg diffraction

– large penetration– large H,D cross section

• life sciences• fuel cell research• oil exploration

• fundamental tests ofquantum mechanics– neutron interferometry

• scattering lengths• neutron charge radius• spinor 4 periodicity• gravitational phase shift

– quantum states in a gravitational potential

p (or d)

d (or t)

n γ

What can we do with neutrons?• fundamental symmetry tests

of the standard model– neutron decay lifetime and correlations– PV: NPDGamma, 4He spin rotation– T reversal: electric dipole moment

Electron

Proton

Neutrino

Neutron SpinA

B

C

nEDM

Neutron Trapsultra cold neutrons:

slow enough to be completely reflected by 58Ni optical potential

kinetic: 8 m/sthermal: 4 mKwavelength: 50 nm

nuclear: 335 neV (58Ni)magnetic: 60 neV (1 T)gravity: 102 neV (1 m)

3mg

Car Traps

R. Alarcon, L. Barron, S. BalascutaArizona State University

S.J. Freedman, B. LaussUniv. of California at Berkeley

S. SantraBhabbha Atomic Research Center

Todd SmithUniv. of Dayton

G.L. JonesHamilton College

W. Chen, R.C. Gillis, J. Mei, H. Nann, W.M. Snow, M. Leuschner, B. Losowki

Indiana University

R.D. CarliniThomas Jefferson National Accel.Facility

E. SharapovJoint Institute of Nuclear Research

T. Ino, Y. Masuda, S. MutoHigh Energy Accel. Research Org. (KEK)

C. B. Crawford, E. MartinUniv. of Kentucky

J.D. Bowman (spokesman), N. Fomin, G.S. Mitchell, S. Penttila, A. Salas-Bacci,

W.S. Wilburn, V. YuanLos Alamos National Laboratory

M.T. Gericke, S. Page, D. RamsayUniv. of Manitoba

L. BarronUniversity National Autonomica de Mexico

T.E. Chupp, M. SharmaUniv. of Michigan

T.R. GentileNational Institute of Standards and Tech.

S. Covrig, M. Dabaghyan, F.W. HersmanUniv. of New Hampshire

P.N. SeoNorth Carolina State University

G.L. Greene, R. Mahurin, M. MusgravesUniv. of Tennessee

S. Baessler, D. PocanicUniv. of Virginia

NPDGamma Collaboration

PV Gamma Asymmetry

3He Polarizer

Overview of NPDGamma Setup

Gamma DetectorsLH2 TargetRF Spin RotatorBeam Monitors

3He neutron polarizer• n + 3He 3H + p cross section is highly spin-dependent

J=0 = 5333 b /0

J=1 ¼ 0

• 10 G holding field determines the polarization anglerG < 1 mG/cm to avoid Stern-Gerlach steering

Steps to polarize neutrons:

1. Optically pump Rb vaporwith circular polarized laser

2. Polarize 3He atoms viaspin-exchange collisions

3. Polarize 3He nuclei viathe hyperfine interaction

4. Polarize neutrons by spin-dependent transmission

n + n p pn pn +p

P3 = 57 %

Neutron Beam Monitors • 3He ion chambers• measure transmission

through 3He polarizer

RF Spin Rotator– essential to reduce instrumental systematics

• spin sequence: cancels drift to 2nd order• danger: must isolate fields from detector• false asymmetries: additive & multiplicave

– works by the same principle as NMR• RF field resonant with Larmor frequency rotates spin• time dependent amplitude tuned to all energies• compact, no static field gradients

holding field

sn

BRF

NPDGammawindings

n-3Hewindings

16L liquid para-hydrogen target

15 m

eV

ortho

para

capture

En (meV)

(b

)

• 30 cm long 1 interaction length• 99.97% para 1% depolarization• super-cooled to reduce bubbles• SAFETY !!

p p

para-H2

p p

ortho-H2

E = 15 meV

CsI(Tl) Detector Array• 4 rings of 12 detectors each

– 15 x 15 x 15 cm3 each• VPD’s insensitive to B field• detection efficiency: 95%• current-mode operation

– 5 x 107 gammas/pulse– counting statistics limited

• activation of materials, e.g. cryostat windows

• Stern-Gerlach steering in magnetic field gradients

• L-R asymmetries leaking into U-D angular distribution (np elastic, Mott-Schwinger...)

• scattering of circularly polarized gammas from magnetized iron (cave walls, floor...)

estimated and expected to be negligible (expt. design)

Systematics, e.g:A

stat. err.

systematics

(proposal)

Statistical and Systematic Errors

Systematic Uncertainties

slide courtesy Mike Snow

LANSCE Results

2nd phase at the SNS: SM polarizer Fe/Si on boron float glass, no Gd

m = 3.0 critical anglen = 45 channelsr = 9.6 m radius of curvaturel = 40 cm lengthd = 0.3mm vane thickness

T=25.8% transmissionP=96.2% polarizationN=2.2£1010 n/s output flux (chopped)

simulations using McStas / ROOT ntuple

NPDG at the FnPB:50x higher luminosity 4x higher FOM of polarization 6x longer run timeGoal: A = 1 x 10-8

n-3He PV Asymmetry

S(I):

4He J =0+ resonance

sensitive to EFT couplingor DDH couplings

~10% I=1 contribution(Gerry Hale, qualitative)

A ~ -1–3x10-7 (M. Viviani, PISA)

~ kn very small for low-energy neutrons- must discriminate between back-to-back proton-triton

PV observables:

19.81520.578

Tilley, Weller, Hale, Nucl. Phys. A541, 1 (1992)

n + n p pn pn +p n p

np

10 Gausssolenoid

RF spinrotator

3He target /ion chamber

supermirrorbender polarizer

(transverse)

FnPB coldneutron guide

3He BeamMonitor transition field

(not shown)

FNPB n-3He

Experimental setup

• longitudinal holding field – suppressed PC asymmetry• RF spin flipper – negligible spin-dependent neutron velocity• 3He ion chamber – both target and detector

Projected SensitivityStatistical Sensitivity Systematic Sensitivity

Magnetic Scalar Potential

Examplescapacitor solenoid

Boundary Conditions

Designing fields from the inside out• Standard iterative method:

Create coils and simulate field.

• New technique: start with boundary conditions of the desired B-field, and simulate the winding configuration

1. Use scalar magnetic potential (currents only on boundaries)

2. Simulate intermediate region using FEA with Neumann boundary conditions (Hn)

3. Windings are traced along evenly spaced equipotential lines along the boundary

red - transverse field linesblue - end-cap windings

Magnetostatic calculation with COMSOL

Prototype RFSF• Developed for static nEDM guide field• 1% uniformity DC field

Conclusion• The hadronic parity violation is

a unique probe of short distance nuclear interactions and QCD structure

• Cold neutrons valuable for tests of symmetry in particle interactions

– neutron capture is an important key to mapping the structure of the hadronic weak interaction

• We expect results of NPDGamma from the SNS in 2012

• New techniques have been developed for designing magnetic fields – our “handle” on neutrons