Proposal Update: the n-3He Parity Violation Experiment
Christopher CrawfordUniversity of Kentucky
for the n-3He Collaboration
FnPB PRAC Meeting
ORNL, TN 2010-12-16
Outline
Theoretical advances• Viviani – full 4-body calc.• Gudkov – reaction theory
Experimental update• Transverse RF spin rotator• 3He target / ion chamber• Statistical sensitivity - simulations• Systematic errors• Alignment scheme
Management plan• Installation: changes from NPDG• Operation: run time and sensitivity
n-3He PV Asymmetry
~ kn very small for low-energy neutrons
- essentially the same asym.- must discriminate between back-to-back proton-triton
S(I):
4He J =0+ resonance
sensitive to EFT couplingor DDH couplings
~10% I=1 contribution(Gerry Hale, qualitative)
A ~ -.3–1x10-7 (M. Viviani, PISA)
A ~ -1–4x10-7 (Gudkov)mixing between 0+, 0- resonance
Naïve scaling of p-p scattering at 22.5 MeV: A ~ 5x10-8
PV observables:
19.81520.578
Tilley, Weller, Hale, Nucl. Phys. A541, 1 (1992)
nn + nn pp ppnn ppnn +pp nn pp
nnpp
Theoretical calculations – progress
Gerry Hale (LANL) PC Ay(90) = -1.7 +/- 0.3 x
10-6
• R matrix calculation of PC asymmetry,nuclear structure , and resonance properties
Michele Viviani et al. (INFN Pisa) PV A = -(.248 – .944)£10-
7
• full 4-body calculation of scattering wave function• calculation of asymmetry within DDH framework• progress on calculation of EFT low energy coefficients• Viviani, Schiavilla, Girlanda, Kievsky, Marcucci, PRC 82, 044001 (2010),
Vladimir Gudkov (USC) PV A = -(1 – 4)£10-7
• PV reaction theory • Gudkov, PRC (in press)
http://arXiv.org/abs/1007.2052
Sensitivity to DDH couplings
1. Calculation of strong 4-body wave functions • Kohn variational method with hyperspherical functions• No parity mixing in this step: Jπ = 0+, 0-, 1+, 1-
• Tested against n-3He scattering lengths
§ Evaluation of weak <J-|VPV|J+> matrix elements• In terms of DDH potential• EFT calculation in progress
Sensitivity matrix for few-body reactions
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
Transverse RF spin rotator
extension of NPDGamma design• P-N Seo et al., Phys. Rev. S.T.
Accel. Beam, vol 11, 084701 (2008)• TEM RF waveguide
new resonator for n-3He expt.• transverse horizontal RF B-field• longitudinal / transverse flipping• no fringe field - 100% efficiency• compact geometry - efficient
- smaller diameter for solenoid• matched to driver electronics
for NPDGamma spin flipper
prototype design• parasitic with similar design for
nEDM guide field near cryostat• fabrication, testing at UKy – 2010
NPDGammawindings
n-3Hewindings
field linesend cap windings
Prototype holding field coil
Developed for static nEDM guide field
1% uniformity DC field
Field map of DSCTC
Prototype RFSF coil
3He Target / Ion Chamber – Design
M. Gericke, U. Manitoba
Custom aluminum CF flanges with SS knife-edges
Macor ceramic frame,Cu wires, 200um diameter
Chamber and flanges have been delivered to U. Manitoba
Construction of frame / wires will be completed in 2011.
Data Acquisition
Requirements similar to NPDGamma• 16 bit resolution, 100 kHz sample rate• Simultaneous external triggering (precise timing)
High channel density: ~144 channels• Driven by the size of the chamber and proton range• Data rate ~3x higher than NPDGamma
VME-based system• Groups of 4 IP modules mounted on CPU processors
for data reduction with direct access to RAID disk
Alphi Technologies: $36k for 192 channels DAQ + storage
New Detection Scheme under consideration
Strategy: detect higher ion density of triton, not longer range of proton
Both proton and triton range out at Si wafer cell walls
Form asymmetry from ions near each side of cell
Less ions per event, but not differential measurement
σd = 2 (left/right planes) vs. σd = 6 (proton range / absorption length)
Can measure 6Li asymmetry to same level with this technique
-HV -HV -HV -HV -HV -HV
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3He gas < 1 cm
baffles
MC Simulations
Two independent simulations:1. a code based on GEANT42. a stand-alone code
including wire correlations
• Ionization at each wire plane averaged over:1. neutron beam phase space2. capture distribution3. ionization distribution (z)4. uniform distribution of proton angles
cos n¢kp/kp
• Used to calculate detector efficiency (effective statistics / neutron flux)
MC Simulations – Results
Majority of neutron captures occur at the very front of chamber• Self-normalization of beam fluctuations• Reduction in sensitivity to A
Measurement of LANSCE FP12 absolute flux
Measurement of LANSCE FP12 absolute flux
Comparison of statistics at LANSCE FP12
based on: • D. Bowman, technical note, 2010-09-24,• A. Salas-Bacci, technical note, 2010-10-14• Gericke, NIMA 611 239 (2009)
2.68 x 107 n/s cm2 neutron flux at 100 μA, measured with FC
3.5” collimator, 87.6 μA proton current
4966 runs (after cut) x 104/20 Hz
0.88 (air) x 0.90 (Al) x 0.88 (glass) x 0.346 (3He) transmission
0.60 capture in LH2 x 0.3017 geom. factor
0.53 pol. 3He x 0.989 SF eff. / (1+0.25) bkg. Dilution
δA = 1.9 x 10-7 from calc. vs. 2.1 x 10-7 RMS width in Aγ
Runtime estimate for n-3He at FnPB
N = 2.2£1010 n/s flux (chopped) x 107 s (4 full months @ 1.4 MW)
P = 96.2% neutron polarization
d = 6 detector efficiency
Systematics
Beam fluctuations, polarization, RFSF efficiency:
knr ~ 10-5 small for cold neutrons
PC asymmetries minimized with longitudinal polarization
Alignment of field, beam, and chamber: 10 mrad achievable
Unlike NPDG, NDTG: insensitive to gammas (only Compton electrons)
Alignment procedure
Suppression of 1.7 x 10-6 nuclear PC asymmetry• longitudinal polarization: sn . kn x kp doubly suppressed
1. Symmetric detector• Rotate 180 deg about kn during data taking
2. Align B field with detector axis to 1 mrad• Vant-Hull and Henrickson windblown generator• Minimize Bx, By by observing eddy currents in generator
§ Align detector/field with neutron beam to 1 mrad• Perform xy-scans of beam at 2 z-positions before/after target• NPDG: B4C target in beam with CsI detector, 6Li chopper
Scanning beam monitor
B4C target
CsI crystal
6Li Shutter
Work Packages
Theory - Michele Viviani
MC Simulations - Michael Gericke
Polarimetry - Stefan Baessler / Matthew Musgrave
Beam Monitor - Rob Mahurin
Alignment - David Bowman / Geoff Greene
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 - Nadia Fomin / Chris Crawford
Analysis - Nadia Fomin / Chris Crawford
System integration/CAD - Seppo
Rad. Shielding / Tritium - John Calarco
Installation at FnPB
NPDG equipment:• 3He beam monitor• SM polarizer• Beam position monitor• Radiation shielding• Pb shield walls• Beam Stop
New equipment:• Transition guide field• 4He 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• DAQ: single-board computers + ADC modules + RAID array
NPDG electronics:• B-field power supply• RFSF electronics• Trigger electronics• SNS / chopper readout• Fluxgate magnetometers• Computer network
Projected schedule
Jan 2011 – Jul 2012 (beam)• NPDGamma data-taking
July 2012• Stage of stand, solenoid,
RFSF, Ion Chamberin nEDM building
Aug 2012• Installation at FnPB• Field map at FnPB
Sept 2012 (request: 1000 hrs)• Beam axis scans • 3He Polarimetry
Jan 2013 (request: 5000 hrs)• 3He data-taking
Jan 2011 – July 2011• 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
Aug 2011, May 2012• test RFSF, 3He chamber, and
DAQ at LANSCE FP12
ORNL Offsite
Conclusion
Published 4-body calculation• EFT calculation under way
Experimental progress• Prototype RFSF resonator• Target chamber delivered• Systematics under control
Scheduled to immediately follow NPDG