Transcript Hadronic PV and latest results – Neutron capture reactions

The n-3He
Parity Violation Experiment
Christopher Crawford
University of Kentucky
for the n-3He Collaboration
NSAC Review Meeting
Chicago, IL, 2011-04-16
Outline
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Scientific Motivation
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Experimental setup
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Transverse RF spin rotator
3He target / ion chamber
Sensitivity
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Reaction and PV observable
Theoretical calculations
Previous experiment
Statistical sensitivity, simulations
Systematic errors
Alignment scheme
Management plan
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Work packages, level of effort
Installation at FnPB
Projected schedule
n-3He PV Asymmetry
Tilley, Weller, Hale, Nucl. Phys. A541, 1 (1992)
S(I):
p
θ
3He
n
3H
PV observables:
~ kn very small for
low-energy neutrons
- the same asymmetry
- must discriminate between
back-to-back proton-triton
20.578
19.815
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sensitive to I=0 and I=1 couplings
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PV A ~ 1.1 x 10-7 (Viviani)
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PC A ~ 1.7 x 10-6 (Hale)
GOAL: dA = 1.3 x 10-8
Theoretical calculations
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Gerry Hale (LANL)
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PC
Ay(90) = -1.7 +/- 0.3 x 10-6
R matrix calculation of PC asymmetry,
nuclear structure, and resonance properties
Vladimir Gudkov (USC)
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PV reaction theory
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Gudkov, PRC 82, 065502 (2010)
Michele Viviani et al. (INFN Pisa)
PV
PV
A = -(1 – 4) x 10-7
A = -1.14 x 10-7
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Full 4-body calc. of strong scattering wave functions Jπ = 0+, 0-, 1+, 1Eval. of weak <J-|VPV|J+> matrix elements in terms of DDH potential
Work in progress on calculation of EFT low energy coefficients
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Viviani, Schiavilla, Girlanda, Kievsky, Marcucci, PRC 82, 044001 (2010)
n-3He PV experiment in 1981
JETP Lett, 33, 411 (1981)
Neutron flux: 6 x 107 n/s
Polarization: 97% (transverse)
PV: Ap = 0.38 ± 0.49 x 10-6
PC: Ap = -0.34 ± 0.57 x 10-6
Experimental setup
FnPB cold
neutron guide
supermirror
bender polarizer
(transverse)
3He
Beam
Monitor
transition field
(not shown)
10 Gauss
solenoid
shim coils
(not shown)
RF spin
rotator
FNPB (already exists)
3He
target /
ion chamber
n-3He (new equipment)
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longitudinal holding field – suppressed PC asymmetry
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RF spin flipper – negligible spin-dependent neutron velocity
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3He
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record ionization signal in each wire; spin asymmetry -> Ap
ion chamber – both target and detector
Transverse RF spin rotator
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Resonant RF spin rotator
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Properties suitable for n-3He expt.
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P-N Seo et al., Phys. Rev. S.T.
Accel. Beam 11, 084701 (2008)
Transverse horizontal RF B-field
Longitudinal or transverse flipping
No fringe field - 100% efficiency
Doesn’t affect neutron velocity
Compact geometry
Matched to the driver electronics
of the NPDGamma spin flipper
Construction
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Development in parallel with similar
design for nEDM neutron guide field
Few-winding prototype built at Uky
currently being tested
Full size RFSF to be built this year
field lines
end cap windings
Detector / Ion Chamber
The chamber design
was finished in 2010
and the completed
chamber was delivered
to U. of Manitoba in the
Fall of 2010.
The chamber has:
4 data ports for up to
200 readout channels.
2 HV ports
2 gas line ports
12 inch Conflat
aluminum windows
(0.9 mm thick).
The chamber is made completely from aluminum except for the knife edges.
Preliminary wire frame and readout design
The chamber is large
enough to completely
cover the SNS beam
profile, even without
collimation.
We are currently
optimizing the
competing issues of
frame size and wire
spacing vs. frame
rigidity and material
cost.
Macor would be best,
but very expensive.
Other possibilities
include Peek (pure too soft),
carbon or glass filled peek.
Preliminary wire frame and readout design
Current options being
explored:
1) 6.4 mm thick frames with
18 HV and 17 signal wires
(alternating).
8 wires per signal frame
9 wires per HV frame
~ 2 cm wire spacing
136 signal wires
2) 4.8 mm thick frames with
23 HV and 22 signal wires.
10 wires per signal frame
~1.5 cm wire spacing
220 signal wires total
(omit the last two frames).
Also shown are initial ideas for readout and HV
distribution boards above and below to frames.
MC Simulations
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Two independent simulations:
1.
2.
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Ionization at each wire plane
averaged over:
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a code based on GEANT4
a stand-alone code
including wire correlations
neutron beam phase space
capture distribution
ionization distribution (z)
uniform distribution of proton angles
cos n¢kp/kp
Used to calculate detector efficiency
(effective statistics / neutron flux)
MC Simulations – Results
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N = 2.2x1010 n/s flux (chopped)
x 107 s (4 full months @ 1.4 MW)
P = 96.2%
neutron polarization
d = 6
detector efficiency
Majority of neutron captures occur
at the very front of chamber
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Self-normalization of beam
fluctuations
Reduction in sensitivity to A
Backgrounds
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Wraparound neutrons
Neutron flux vs. Wavelength
BACKGROUND: < 0.02%,
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Compton electrons from Gammas
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10% gammas/neutron from SNS
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Conservative, assuming E=.5 MeV
Primary
window
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2.4% probability of Compton scattering
from Al window
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10% ionization current from e- vs. p+
BACKGROUND: < 0.02%,
NO false asymmetry
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Betas from Al decay – 2.4 min lifetime
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0.231 b thermal neutron cross section
0.9 mm thick Al window
0.25% capture probability;
half of decays go through chamber
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10% ionization current from e- vs. p+
BACKGROUND: < 0.015%
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Al asymmetry measured for NPDGamma
Rob Mahurin, technical note 2009-08-19
Wrap-around
neutrons
Neutron & Gamma flux vs. Position
gammas
x 18
neutrons
Systematics
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Beam fluctuations, polarization, RFSF efficiency
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Parity allowed asymmetries minimized with longitudinal polarization
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Only systematic beam fluctuations contribute (A<<1)
Self-normalizing detector – forward wires sensitive to flux only
Alignment of field, beam, and chamber: 1 mrad achievable
knr ~ 10-5 small for cold neutrons
Alignment procedure
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10-6
Suppression of 1.7 x
nuclear PC asymmetry
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1.
Symmetric detector
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2.
Rotate 180 deg about kn
during data taking
Align B field to detector within 1 mrad
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longitudinal polarization
doubly suppresses sn . kn x kp
Vant-Hull and Henrickson
windblown generator
Minimize Bx, By by observing
eddy currents in generator
Align detector and neutrons to 1 mrad
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Perform xy-scans of beam
at 2 z-positions before/after target
B4C target in beam with CsI detector,
6Li
chopper
6Li
Shutter
CsI crystal
B4C target
Work Packages
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Theory
- Michele Viviani
MC Simulations
- Michael Gericke
Polarimetry
- Geoff Greene
Beam Monitor
- Rob Mahurin
Alignment
- David Bowman
Field Calculation
- Septimiu Balascuta
Solenoid / field map
- Libertad Baron Palos
Transition, trim coil
- Pil-Neyo Seo
RFSF
- Chris Crawford
Target / detector
- Michael Gericke
Preamps
- Michael Gericke
DAQ
- Chris Crawford
Analysis
- Nadia Fomin
System integration/CAD - Seppo Pentilla
Rad. Shielding / Tritium - John Calarco
Effort Estimate for n-3He Collaborators
Institution Researcher
Category
2011
2012
2013
10
10
10
Research Staff
15
15
15
Research Staff
Research Staff
Postdoc
20
30
30
30
40
40
50
20
20
Faculty
Grad Student
30
50
35
100
35
100
5
5
100
5
5
100
70
70
100
30
20
40
20
20
30
20
80
100
30
10
10
20
10
100
100
Duke University, Triangle Universities Nuclear Laboratory
Pil-Neo Seo
Research Staff
Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
Michele Viviani
Oak Ridge National Laboratory
Seppo Pentillä
David Bowman
TBD
University of Kentucky
Chris Crawford
TBD
Western Kentucky University
Alex Barzilov
Ivan Novikov
TBD * 2
Faculty
Faculty
Undergraduate
University of Manitoba
Michael Gericke
Shelley Page
WTH. Van Oers
Rob Mahurin
V. Tvaskis
Mark McCrea
D. Harrison
Faculty
Faculty
Faculty
Postdoc
Postdoc
Grad Student
Grad Student
20
70
80
Universidad Nacional Autónoma de México
Libertad Baron
TBD
Faculty
Grad Student
25
30
100
30
100
Faculty
50
50
50
Faculty
Postdoc
Grad Student
10
10
10
10
10
20
5
5
10
Faculty
Postdoc
10
20
10
20
10
20
Faculty
5
15
20
University of New Hampshire
Calarco
University of South Carolina
Vladimir Gudkov
Young-Ho Song
TBD
Univeristy of Tennessee
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Geoff Greene
S. Kucuker
University of Virginia
S. Baessler
(Percentage of research time)
Installation at FnPB
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Existing equipment:
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3He
beam monitor
SM polarizer
Beam position monitor
Radiation shielding
Pb shield walls
Beam Stop
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Existing electronics:
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B-field power supply
RFSF electronics
Trigger electronics
SNS / chopper readout
Fluxgate magnetometers
Computer network
New equipment:
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Transition guide field
flight path from SMpol to RFSF (reuse 6Li shielding)
Longitudinal field solenoid mounted on stand
Longitudinal RFSF resonator mounted in solenoid
3He target/ion chamber mounted in solenoid
Preamps mounted on target
Windblown generator
DAQ: single-board computers + ADC modules + RAID array
Projected schedule
Offsite
SNS
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Jan – Dec 2011
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July 2012
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Installation at FnPB
Field map at FnPB
Feb 2013
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Dec 2012
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Stage stand, solenoid,
RFSF, Target/Ion Chamber
in nEDM building
Beam axis scans
3He Polarimetry
Apr – Dec 2013
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3He
data-taking
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Beam time
request:
5000 hrs.
Construction and field mapping
of solenoid at UNAM
Construction and testing of
RFSF resonator at UKy
Assembly of 3He ion chamber
at Univ. Manitoba
DAQ electronics and software
at UKy / UTK / ORNL
Jan – May 2012
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test RFSF, 3He chamber,
and DAQ at HFIR
Conclusion
 Theoretical progress
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Full 4-body calculation published, EFT calculation under way
Test of consistency of DDH or EFT within few-body systems
 Experimental progress
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Prototype RFSF resonator designed and built
Target chamber delivered, instrumentation under way
 Sensitivity
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Statistics: ±A = 1.3 x 10-8, low background levels
Systematic effects suppressed with longitudinal polarization
 Will be ready to commission and run after NPDGamma