The n-3He  Parity Violation Experiment

Christopher CrawfordUniversity of Kentucky

for the n-3He Collaboration

NSAC Review MeetingChicago, IL, 2011-04-16

Outline

Scientific Motivation• Reaction and PV observable• Theoretical calculations• Previous experiment

Experimental setup• Transverse RF spin rotator• 3He target / ion chamber

Sensitivity• Statistical sensitivity, simulations• Systematic errors• Alignment scheme

Management plan• Work packages, level of effort• Installation at FnPB• Projected schedule

n-3He PV Asymmetry

S(I):

sensitive to I=0 and I=1 couplings PV A ~ 1.1 x 10-7 (Viviani) PC A ~ 1.7 x 10-6 (Hale)

19.81520.578

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

n 3He

p

3H

θ

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

PV observables:

GOAL: A = 1.3 x 10-8

Theoretical calculations

Gerry Hale (LANL) PC Ay(90) = -1.7 +/- 0.3 x 10-6

• R matrix calculation of PC asymmetry,nuclear structure , and resonance properties

Vladimir Gudkov (USC) PV A = -(1 – 4) x 10-7

• PV reaction theory • Gudkov, PRC 82, 065502 (2010)

Michele Viviani et al. (INFN Pisa) PV A = -1.14 x 10-7

• Full 4-body calc. of strong scattering wave functions Jπ = 0+, 0-, 1+, 1-

• Eval. of weak <J-|VPV|J+> matrix elements in terms of DDH potential• Work in progress on calculation of EFT low energy coefficients• Viviani, Schiavilla, Girlanda, Kievsky, Marcucci, PRC 82, 044001 (2010)

n-3He PV experiment in 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

JETP Lett, 33, 411 (1981)

10 Gausssolenoid

RF spinrotator

3He target /ion chamber

supermirrorbender polarizer

(transverse)

FnPB coldneutron guide

3He BeamMonitor transition field

(not shown)

FNPB (already exists) n-3He (new equipment)

Experimental setup

longitudinal holding field – suppressed PC asymmetry

RF spin flipper – negligible spin-dependent neutron velocity

3He ion chamber – both target and detector

record ionization signal in each wire; spin asymmetry -> Ap

shim coils(not shown)

Transverse RF spin rotator

Resonant RF spin rotator• P-N Seo et al., Phys. Rev. S.T.

Accel. Beam 11, 084701 (2008)

Properties suitable for n-3He expt.• 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• 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 linesend cap windings

The chamber is made completely from aluminum except for the knife edges.

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).

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.

Also shown are initial ideas for readout and HV distribution boards above and below to frames.

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 frame9 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).

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:• 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

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• Self-normalization of beam

fluctuations• Reduction in sensitivity to A

Backgrounds

Wraparound neutronsBACKGROUND: < 0.02%,

Compton electrons from Gammas• 10% gammas/neutron from SNS

- Conservative, assuming E=.5 MeV• 2.4% probability of Compton scattering

from Al window• 10% ionization current from e- vs. p+

BACKGROUND: < 0.02%, NO false asymmetry

Betas from Al decay – 2.4 min lifetime• 0.231 b thermal neutron cross section• 0.9 mm thick Al window• 0.25% capture probability;

half of decays go through chamber• 10% ionization current from e- vs. p+

BACKGROUND: < 0.015%• Al asymmetry measured for NPDGamma

Rob Mahurin, technical note 2009-08-19

Primary window

Wrap-around neutrons

Neutron flux vs. Wavelength

neutrons

gammas x 18

Neutron & Gamma flux vs. Position

Systematics

Beam fluctuations, polarization, RFSF efficiency• Only systematic beam fluctuations contribute (A<<1)• Self-normalizing detector – forward wires sensitive to flux only

Parity allowed asymmetries minimized with longitudinal polarization• Alignment of field, beam, and chamber: 1 mrad achievable

knr ~ 10-5 small for cold neutrons

Alignment procedure

Suppression of 1.7 x 10-6 nuclear PC asymmetry• longitudinal polarization

doubly suppresses sn . kn x kp

1. Symmetric detector• Rotate 180 deg about kn

during data taking

2. Align B field to detector within 1 mrad• Vant-Hull and Henrickson

windblown generator• Minimize Bx, By by observing

eddy currents in generator

§ Align detector and neutrons to 1 mrad1. Perform xy-scans of beam

at 2 z-positions before/after target2. B4C target in beam with CsI detector,

6Li chopper

B4C targetCsI crystal

6Li Shutter

Work Packages 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

(Percentage of research time)

Institution Researcher Category 2011 2012 2013            Duke University, Triangle Universities Nuclear Laboratory    Pil-Neo Seo Research Staff 10 10 10 Istituto Nazionale di Fisica Nucleare, Sezione di Pisa      Michele Viviani Research Staff 15 15 15 Oak Ridge National Laboratory        Seppo Pentillä Research Staff 20 30 50  David Bowman Research Staff 30 40 20  TBD Postdoc 30 40 20 University of Kentucky          Chris Crawford Faculty 30 35 35  TBD Grad Student 50 100 100 Western Kentucky University        Alex Barzilov Faculty 5 5 70  Ivan Novikov Faculty 5 5 70  TBD * 2 Undergraduate 100 100 100 University of Manitoba          Michael Gericke Faculty 30 40 30  Shelley Page Faculty 20 20 10  WTH. Van Oers Faculty   20 10  Rob Mahurin Postdoc 20 30 20  V. Tvaskis Postdoc   20 10  Mark McCrea Grad Student 70 80 100  D. Harrison Grad Student 80 100 100 Universidad Nacional Autónoma de México        Libertad Baron Faculty 25 30 30  TBD Grad Student   100 100 University of New Hampshire          Calarco Faculty 50 50 50 University of South Carolina        Vladimir Gudkov Faculty 10 10 5  Young-Ho Song Postdoc 10 10 5  TBD Grad Student 10 20 10 Univeristy of Tennessee        ` Geoff Greene Faculty 10 10 10  S. Kucuker Postdoc 20 20 20 University of Virginia          S. Baessler Faculty 5 15 20

Installation at FnPB

Existing equipment:• 3He beam monitor• SM polarizer• Beam position monitor• Radiation shielding• Pb shield walls• Beam Stop

New equipment:• 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

Existing electronics:• B-field power supply• RFSF electronics• Trigger electronics• SNS / chopper readout• Fluxgate magnetometers• Computer network

Projected schedule

July 2012• Stage stand, solenoid,

RFSF, Target/Ion Chamberin nEDM building

Dec 2012• Installation at FnPB• Field map at FnPB

Feb 2013• Beam axis scans • 3He Polarimetry

Apr – Dec 2013• 3He data-taking

Jan – Dec 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

Jan – May 2012• test RFSF, 3He chamber,

and DAQ at HFIR

SNS Offsite

Beam time request: 5000 hrs.

Conclusion

Theoretical progress• Full 4-body calculation published, EFT calculation under way• Test of consistency of DDH or EFT within few-body systems

Experimental progress• Prototype RFSF resonator designed and built• Target chamber delivered, instrumentation under way

Sensitivity• 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