1. The n-3He Experiment Christopher Crawford for the n-3He Collaboration
University of Kentucky
for the n-3He Collaboration
FnPB PRAC
ORNL, TN

2. Outline Introduction Components Simulations Physics analysis
Experimental setup
Long. vs. trans. asym
Timeline & beam time
Statistics & sensitivity
Components
Chopper – window tune
RFSF – polarimetry
Ion Chamber – scans
DAQ – instrumental asym.
Simulations
Status of simulations
MC Validation
Physics analysis
L/R wire pair asym.
U/D singles asym.
Conclusion

3. Experimental setup y x z FNPB n-3He 10 Gauss Holding field
RF spin rotator
3He target /
ion chamber
FnPB cold
neutron guide
3He Beam
Monitor
FNPB
n-3He
Super-mirror
polarizer
Collimator y z x
----- Meeting Notes ( :38) -----
Here is a schematic of the experiment. 3

4. Longitudinal vs. transverse PV asymmetry
Initial design: measure a longitudinal PV asymmetry
Insensitive to misalignment: L/R – U/D mixing
Problem: chamber not self-normalizing
Solution: flip spin half-way during TOF of pulse
Reconsideration: measure transverse PV asymmetry
Factor of 2x better sensitivity to PV asymmetry:
No dilution due to the opposite sign of asymmetry coming from upstream vs. downstream of sense wire
Can decrease pressure so ions make it out of beam
We decided to run both PC and PV in transverse mode

5. Timeline – Installation & Commissioning: 2014
Spring – construction: Solenoid, RFSF, Ion Chamber, Preamp, DAQ
June – removed NPDG from FnPB
July – construction: barrier wall, mounting hardware tuned solenoid, tested major components
Aug – installation of solenoid / frame in FnPB
Sept – transverse fieldmap; ISSR tritium safety meeting
Nov – commissioning without beam; IRR 1 review filled Ion Chamber with 3He, tested
Dec – beam profile scans; RFSF tune / polarimetry
Accomplished installation and commissioning (except for IRR 2 and L/R asymmetry) on schedule during Fall 2014.

6. Timeline – Data collection: 2015
Jan 21 – IRR 2 approval; tune RFSF / polarimetry; initial PV data
Feb 10–Feb 16 – PC data collection : kW δA= 6.8x10-8
Feb 16 – tuned chopper, began PV collection in final configuration
June 26–Aug 13 – summer shutdown MW hr RUN 1
Sept 26–Oct 14 – SNS target failure MW hr RUN 2
Oct 14– Dec 22 – production expect~1300 MW hr RUN 3 δA=1.1x10-8
JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC
Jan 21 – IRR2 approval
Feb tuned choppers
4520 hr = 1.07 MW ave

7. Optimization of Chopper, RFSF, DAQ window
Unchopped single-pulse neutron spectrum
Neutron Flux [arb. units]
Dropped pulse every 10 s
Chopped
spectrum
TOF x 60 Hz
Chopper efficiency
Chopper efficiency
Chopped 60 Hz beam
Ion chamber TOF signal

8. Solenoid Definition of σndirection
Adiabatic rotation from transverse to longitudinal spin
10 mG, 0.1% uniformity
Univ. Nacional Autónoma de México

9. Transverse RF Spin Rotator
Double-cosine-theta coil
Fringeless transverse RF field
Longitudinal OR transverse
Designed using scalar potential
Univ. Tennessee / Univ. Kentucky

10. 3He transmission polarimetry
Larmor
Resonance
Rabi
Oscillation
Polarization of 3He Cell
Beam Polarization
Spin Flip Efficiency

11. Target / Ion Chamber 3He for both target and ionization gas
Macor frames with 9 x 16 sense wires, 8 x 17 HV wires
All aluminum chamber except for knife edges, 0.9 mm Al windows
7 psi pure 3He
16 mCi tritium over life of experiment
University of Manitoba

12. Measured ion yield in target chamber

13. Garfield / gmsh / Elmer simulation of ion drift
Ion collection across diagonal

14. Readout electronics Ionization read out in current mode
144 channels read out simultaneously
Low-noise I-V preamplifiers mounted on chamber
24-bit, 100 kS/s, 48 channel Δ-Σ ADC FMC modules
Oak Ridge National Lab, Univ. Kentucky, Univ. Tennessee
Electronic Tests:
Instrumental
false asymmetry
measurements

15. False electronic asymmetries

16. MC Simulations Three independent simulations:
GEANT4 with white source – Manitoba
C-code with McStas ntuple source – UKy
C-code with FnPB measured source – UTK
Ionization weighted averages:
Used to calculate detector efficiency (effective statistics / neutron flux)
ionization yield
yield covariance
geometry factor
Two independent simulations have been done of the wire chambers and detection efficiency of the asymmetry to estimate delta A and were consistent with each other. I will describe the second one. It simulated neutrons event by event, to find the average number of ions (beta_i) in each wire plane, and also the correlation between wires (beta_i,j) since the same neutron leaves a track through multiple wires. Since the physical asymmetry is small it was not simulated, only the sensitivity to the asymmetry (alpha_I or cos theta). From this we get the effective statistics of the asymmetry which goes as 1/sqrt(N) times the detection efficiency sigma_d, which is about 6 for the optimal neutron wavelength range.

17. Test of MC simulation – ionization deposit
Three independent simulations:
GEANT4 with white source
C-code with McStas ntuple source
C-code with FnPB measured source
Event - weighted averages:
ionization correlation geometry
Used to calculate detector efficiency (effective statistics / neutron flux)
PRELIMINARY – work in progress
Two independent simulations have been done of the wire chambers and detection efficiency of the asymmetry to estimate delta A and were consistent with each other. I will describe the second one. It simulated neutrons event by event, to find the average number of ions (beta_i) in each wire plane, and also the correlation between wires (beta_i,j) since the same neutron leaves a track through multiple wires. Since the physical asymmetry is small it was not simulated, only the sensitivity to the asymmetry (alpha_I or cos theta). From this we get the effective statistics of the asymmetry which goes as 1/sqrt(N) times the detection efficiency sigma_d, which is about 6 for the optimal neutron wavelength range.

18. Test of MC simulation – correlations
Difference of correlation: MC - experiment
PRELIMINARY – work in progress

19. PC Asymmetry analysis
Single-wire asymmetry, 30 hr. data subset

20. PC Asymmetry analysis
Single wire asymmetries – offset due to beam asymmetry

21. PC Asymmetry analysis
Wire pair asymmetry – does not include correlations

22. Covariant – weighted analysis
Histogrammed extracted physics PC asymmetry from each good run (746 total = 86 hr)
used full covariant weighting of each wire pair to extract the PC asymmetry
PRELIMINARY – work in progress
(43.6 ± 6.8) x 10-8
G. Hales, R-matrix theory

23. PV asymmetry – wire 2

24. Conclusion Sensitivity of data collected by December
Expect 1.1 x10-8 statistical uncertainty in PV asymmetry
Preliminary analysis of PC asymmetry
7 x10-8 statistical uncertainty in 5 days of data taking
Data appear statistically consistent
Analysis of PV asymmetry underway
Investigating some inconsistencies
Preliminary MC validation
Still needs work

25. n3He Collaboration
Duke University, TUNL • Pil-Neo Seo INFN, Sezione di Pisa • Michele Viviani University of Kentucky • Chris Crawford • Latiful Kabir • Aaron Sprow Western Kentucky University • Ivan Novikov University of Manitoba • Michael Gericke • Mark McCrea • Carlos Olguin University of New Hampshire • John Calarco Universidad Nacional Autónoma de México • Libertad Barrón • José Favel • Andrés Ramírez Oak Ridge National Laboratory • David Bowman • Vince Cianciolo • Paul Mueller • Seppo Penttilä • Jack Thomison University of South Carolina • Vladimir Gudkov • Matthias Schindler • Young-Ho Song Middle Tennessee State University • Rob Mahurin University of Tennessee • Noah Birge • Chris Coppola • Nadia Fomin • Irakli Garishvili • Connor Gautham • Geoff Greene • Chris Hayes • Serpil Kucuker • Eric Plemons • Mae Scott University of Tennessee at Chattanooga • Josh Hamblen • Jeremy Watts • Caleb Wickersham University of Virginia • Stefan Baessler