Hadronic Parity Violation at the SNS
Christopher Crawford
University of Kentucky
2011-01-31
• symmetries and interactions
• properties of the neutron
• NPDGamma & n-3He exp.
• designing coils with ϕm
Madison
Spencer
TIME
Standard Model of Particles
SPACE
E&M Interaction
Weak Interaction
Strong Interaction
Hadronic Interaction
(residual nuclear force)
Standard Model of Automobiles
Annihilation
Higgs?
Degenerate Fermi Gas
Particle Decay
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
time
charge
particle
exchange
P : x  -x
T : t  -t
C : q  -q
P12: x1 x2
Discrete Theorems
– CPT theorem
– spin-statistics theorem
position
symmetry
conserved
momentum
Car Symmetries
T (time)
R
100
100
km/h
km/h
km/h
99.7
L
R
Be careful, some idiot’s
CP (charge,
parity)
going the wrong way
I’m coming
home …
Only one? They’re
all over the place!
on the freeway.
CPT theorem: ALL laws are invariant under CPT
Parity-violation in weak interaction
Parity-transformation (P) :
October 1, 1956 issue of the Physical Review
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
STRONG
(PC)
N
N
Meson
exchange
WEAK
(PV)
N
Why Study Hadronic PV?
• probe of atomic, nuclear,
and hadronic systems
–
–
–
–
• probe of QCD in low energy
non-perturbative regime
map out coupling constants
resolve 18F, 133Cs discrepancy
probe nuclear structure effects
anapole and qq contributions
to PV electron scattering
– confinement, many-body
problem
– sensitive to qq correlations
– measure QCD modification
of qqZ coupling
np A
nD A
n3He Ap
np 
n 
-0.11
0.92
-0.19
-3.12
-0.97
-0.50
-0.036
-0. 23
-0.32
0.08
0.14
0.10
0.019
0.11
0.08
0.05
hr2
0.05
0.0006
-0.25
h0
-0.16
-0.033
-0. 23
fp
h 0
h 1
h 1
-0.001
-0.003 -0.002
n-capture
0.041
pp Az
p Az
-0.34
0.03
-0.22
-0.07
0.06
0.22
0.07
0.06
spin rotation
elastic scattering
n+pd+
A = -0.11 fp
+ -0.001 h 1
+ -0.003 h1
Existing Measurements
Polarized proton scattering asymmetries
Light nuclei gamma transitions
(circular polarized gammas)
p-p and nuclei
Nuclear anapole moment
(from laser spectroscopy)
Anapole
Properties of the Neutron
mn = 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
spin 1/2
up
down
isospin 1/2
p
n
uud
udd
rm = 0.889 fm
re2 = -0.116 fm2
– 3 valence quarks + sea
– exponential magnetization
distribution
– pion cloud:
data from BLAST
Neutron sources - Reactors
ILL, Grenoble, France
Spallation Neutron Source (SNS)
Oak Ridge National Laboratory, Tennessee
• spallation sources: LANL, SNS
– pulsed -> TOF -> energy
• LH2 moderator: cold neutrons
– thermal equilibrium in ~30 interactions
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
Flight Paths at the SNS
11A - Powder
Diffractometer
Commission 2007
9 – VISION
7 - Engineering
Diffractometer
IDT CFI Funded
Commission 2008
6 - SANS
Commission 2007
12 - Single Crystal
Diffractometer
Commission 2009
5 - Cold Neutron
Chopper
Spectrometer
Commission 2007
13 - Fundamental
Physics Beamline
Commission 2007
4B - Liquids
Reflectometer
Commission 2006
14B - Hybrid
Spectrometer
Commission 2011
4A - Magnetism
Reflectometer
Commission 2006
15 – Spin Echo
17 - High Resolution
Chopper Spectrometer
Commission 2008
18 - Wide Angle
Chopper Spectrometer
Commission 2007
3 - High Pressure
Diffractometer
Commission 2008
1B - Disordered Mat’ls
Commission 2010
2 - Backscattering
Spectrometer
Commission 2006
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 of
quantum mechanics
– neutron interferometry
•
•
•
•
scattering lengths
neutron charge radius
spinor 4p periodicity
gravitational phase shift
– quantum states in a
gravitational potential
What can we do with neutrons?
• fundamental symmetry tests
of the standard model
A
Electron
– neutron decay lifetime and correlations
– PV: NPDGamma, 4He spin rotation
C
– T reversal: electric dipole moment
Proton
nEDM
d (or t)
n
p (or d)
γ
Neutron Spin
B
Neutrino
Neutron Traps
ultra cold neutrons:
slow enough to be completely
reflected by 58Ni optical potential
kinetic:
8 m/s
thermal:
4 mK
wavelength: 50 nm
nuclear:
magnetic:
gravity:
335 neV (58Ni)
60 neV (1 T)
102 neV (1 m)
g
3m
Car Traps
NPDGamma Collaboration
R. Alarcon, L. Barron, S. Balascuta
Arizona State University
S.J. Freedman, B. Lauss
Univ. of California at Berkeley
S. Santra
Bhabbha Atomic Research Center
Todd Smith
Univ. of Dayton
G.L. Jones
Hamilton College
W. Chen, R.C. Gillis, J. Mei, H. Nann,
W.M. Snow, M. Leuschner, B. Losowki
Indiana University
R.D. Carlini
Thomas Jefferson National Accel.Facility
E. Sharapov
Joint Institute of Nuclear Research
T. Ino, Y. Masuda, S. Muto
High Energy Accel. Research Org. (KEK)
C. B. Crawford, E. Martin
Univ. of Kentucky
J.D. Bowman (spokesman), N. Fomin,
G.S. Mitchell, S. Penttila, A. Salas-Bacci,
W.S. Wilburn, V. Yuan
Los Alamos National Laboratory
M.T. Gericke, S. Page, D. Ramsay
Univ. of Manitoba
L. Barron
University National Autonomica de Mexico
T.E. Chupp, M. Sharma
Univ. of Michigan
T.R. Gentile
National Institute of Standards and Tech.
S. Covrig, M. Dabaghyan, F.W. Hersman
Univ. of New Hampshire
P.N. Seo
North Carolina State University
G.L. Greene, R. Mahurin, M. Musgraves
Univ. of Tennessee
S. Baessler, D. Pocanic
Univ. of Virginia
PV Gamma Asymmetry
Overview of NPDGamma Setup
3He
Polarizer
Beam Monitors
RF Spin Rotator
LH2 Target
Gamma Detectors
3He
neutron polarizer
• n + 3He  3H + p cross section is highly spin-dependent
n
+
p
n
p
n
n
p
+
p
J=0 = 5333 b /0
J=1 ¼ 0
• 10 G holding field determines the polarization angle
rG < 1 mG/cm to avoid Stern-Gerlach steering
Steps to polarize neutrons:
1.
Optically pump Rb vapor
with circular polarized laser
2.
Polarize 3He atoms via
spin-exchange collisions
3.
Polarize 3He nuclei via
the hyperfine interaction
4.
Polarize neutrons by spindependent transmission
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
• danger: must isolate fields from detector
• false asymmetries: additive & multiplicave
2nd
holding field
order
sn
– 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
NPDGamma
windings
BRF
n-3He
windings
16L liquid para-hydrogen target
•
•
•
•
30 cm long  1 interaction length
99.97% para  1% depolarization
super-cooled to reduce bubbles
SAFETY !!
p
E =
15 meV
p
para-H2
p
p
ortho-H2
15 meV
ortho
 (b)
para
capture
En (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
Systematic Uncertainties
Statistical and Systematic Errors
A
stat. err.
(proposal)
systematics
Systematics, e.g:
• 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)
slide courtesy Mike Snow
LANSCE Results
2nd phase at the SNS: SM polarizer
Fe/Si on boron float glass, no Gd
m = 3.0
n = 45
r = 9.6 m
l = 40 cm
d = 0.3mm
critical angle
channels
radius of curvature
length
vane thickness
T=25.8%
P=96.2%
N=2.2£1010 n/s
transmission
polarization
output flux (chopped)
simulations using
McStas / ROOT ntuple
NPDG at the FnPB:
50x higher luminosity
4x higher FOM of polarization
6x longer run time
Goal: A = 1 x 10-8
n-3He PV Asymmetry
n
p
np
+
n
n pp
p
+
n
np
PV observables:
~ kn very small for
low-energy neutrons
S(I):
- must discriminate between
back-to-back proton-triton
20.578
19.815
Tilley, Weller, Hale, Nucl. Phys. A541, 1 (1992)

4He

sensitive to EFT coupling
or DDH couplings

~10% I=1 contribution
(Gerry Hale, qualitative)

A ~ -1–3x10-7 (M. Viviani, PISA)
Jp =0+ resonance
Experimental setup
FnPB cold
neutron guide
supermirror
bender polarizer
(transverse)
10 Gauss
solenoid
3He
Beam
Monitor
FNPB
•
•
•
transition field
(not shown)
3He
RF spin
rotator
target /
ion chamber
n-3He
longitudinal holding field – suppressed PC asymmetry
RF spin flipper – negligible spin-dependent neutron velocity
3He ion chamber – both target and detector
Projected Sensitivity
Statistical Sensitivity
Systematic Sensitivity
Magnetic Scalar Potential
Examples
capacitor
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
Magnetostatic calculation with
COMSOL
red - transverse field lines
blue - end-cap windings
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