analysis of acorn data j. e. adelman*, m. s. dewey†, f. wietfeldt‡, g. darius‡, g.l. jones*,...
TRANSCRIPT
Analysis of aCORN Data
J. E. Adelman*, M. S. Dewey†, F. Wietfeldt‡, G. Darius‡, G.L. Jones*, B.
Collett*, and R. Kosar*August 2012
* Hamilton College, Clinton NY† The National Institute of Standards and Technology, Gaithersburg, MD‡ Tulane University, New Orleans, LA.
Background: Neutron Decays
• Free neutrons undergo beta decay
• Standard Model: Two constants characterize this decay– gA: axial coupling – gV: vector coupling
• Neutron decay has several correlation coefficients– Know any two, get gV, gA.– Know any three – test standard model
• a is the electron-antineutrino correlation coefficient– Current value: -0.103 ± 0.004
EE
ppD
E
pB
E
pA
EE
ppaEQpEN
e
e
e
e
e
eeee
n
1)(1 2
ve
Background II: The aCORN Project
• To get a, measure antineutrino and electron momentum– Proton used to infer νē
• Experiment designed to give two groups– “Fast” and “Slow”
protons
p+vee- e-
p +
Electron Detector
Proton Detector
Group 1 “Fast”
Group 2 “Slow”
• Group Separation depends on electron energy– Result: “Wishbone” data shape
“Slow” Group
“Fast” Group
The aCORN Apparatus
• Analysis focused on four apparatus parameters1. Electrostatic mirror voltage2. Electron detector trim coil current3. Proton detector size and focusing grid4. Electron detector gain
Current State of aCORN
• Apparatus assembled on NCNR’s NG-6 beamline
• January – March 2011: Data collection– Raw data distilled and reduced prior to analysis
• Another round with the beam – February 2012
Goals:1. Introduce a new calibration paradigm2. Perform series by series analysis on
outstanding data3. Note the effects of parameter changes on
calculated asymmetries4. Offer suggestions for next round of data
collection
Part I: Calibration• Bi and Sn sources• Points of Analysis:– Resolutions– Are three Gaussians
better than one?– Effect of apparatus
parameters on resolutions Channel Number
Coun
ts
Results• Resolutions still below
expectations– Need ~ 20%
• Three Gaussian:– 1% better on Sn– 2% better on Bi 975
• Curve correlated to run parameters
• New Bi source shows promise of improved
Part II: Series AnalysisGoal: extract values for “pseudo-a”, wishbone rate, and background
rate for all outstanding data.
Part III: Analysis
• Original Goal: Algebraic isolation of individual effects by pairwise examination– Problem: Splitting series in half gives values
beyond the calculated error bars• Fallback: Single-factor Analysis of Variance
(ANOVA)– f-test to find correlations– Difficult to discern contributions from multiple
effects
ANOVA Results
• Algebraic analysis indicated effects on the order of pseudo a• Evidence is consistent with a problem detecting protons
Series Summary
Part IV: Unanswered Questions• Missing Rate• Shape to Rate vs. Time
Graph
Acknowledgement
I would like to thank NIST, the SURF advisors, my mentor Scott Dewey, the members of the aCORN consortium, PML’s Neutron Research group, and everyone else who helped foster an enjoyable and productive summer