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