Precision Neutron Polarimetry for Neutron Beta Decay

Area of Science:

• Nuclear Physics
• Particle Physics
• Spectroscopy

Background:

• Neutron beta decay experiments measure fundamental particle interactions.
• Precision measurements of correlation coefficients (a, A, B) and shape parameter (b) are vital.
• Accurate neutron polarization is essential for these measurements.

Purpose of the Study:

• To develop and validate a novel field-expansion spectrometer for neutron beta decay.
• To achieve high-precision measurement of correlation coefficients and neutron polarization.
• To minimize statistical and systematic errors in the determination of neutron polarization.

Main Methods:

• Utilizing a pulsed cold neutron beam from the Spallation Neutron Source (SNS).
• Employing a Helium-3 (³He) neutron spin filter for neutron polarization.
• Implementing time-of-flight (TOF) measurements to determine neutron velocity and polarization.

Main Results:

• Demonstrated that measuring the TOF dependence of coefficients A and B allows simultaneous determination of coefficients and polarization.
• Achieved determination of neutron polarization with a statistical error less than 10⁻⁴.
• Showed that fractional systematic errors in measuring A and B are less than 2 × 10⁻⁴.

Conclusions:

• The developed field-expansion spectrometer enables precise neutron polarimetry for beta decay studies.
• The TOF-based method offers a robust approach to determine neutron polarization with high accuracy.
• This technique significantly reduces systematic uncertainties, enhancing the reliability of fundamental physics measurements.