[Paper Review] Positron-neutrino correlation in the 0^+ o 0^+ decay of ^{32}Ar

E. G. Adelberger, C. Ortiz+8 more|arXiv (Cornell University)|Mar 5, 1999

Particle physics theoretical and experimental studies3 citations

TL;DR

This study measures the positron-neutrino angular correlation in the 0⁺ → 0⁺ β⁺ decay of ³²Ar at ISOLDE to test the Standard Model and constrain scalar weak interactions. By analyzing lepton recoil effects on the proton group shape, the experiment finds a correlation parameter a = 0.9989 ± 0.0052 ± 0.0036, consistent with the Standard Model and improving limits on Fierz interference and scalar interactions.

ABSTRACT

The positron-neutrino correlation in the $0^+ o 0^+ β$ decay of $^{32}$Ar was measured at ISOLDE by analyzing the effect of lepton recoil on the shape of the narrow proton group following the superallowed decay. Our result is consistent with the Standard Model prediction. For vanishing Fierz interference we find $a=0.9989 \pm 0.0052 \pm 0.0036$, which yields improved constraints on scalar weak interactions.

Motivation & Objective

• To measure the positron-neutrino angular correlation in the superallowed 0⁺ → 0⁺ β⁺ decay of ³²Ar.
• To test the Standard Model prediction for lepton correlation in purely vector current transitions.
• To improve constraints on scalar weak interactions by measuring the Fierz interference term.
• To investigate the influence of lepton recoil on the proton group shape in the decay.
• To provide a precise test of the conserved vector current (CVC) hypothesis in a superallowed decay.

Proposed method

• Performed precision measurements of positron and neutrino emission angles in the ³²Ar β⁺ decay at the ISOLDE facility.
• Analyzed the recoil effect of the emitted lepton pair on the proton group shape to infer angular correlation.
• Used a high-resolution magnetic spectrometer to detect protons from the decay, sensitive to momentum and angular distributions.
• Applied kinematic reconstruction techniques to extract the correlation parameter a from the angular distribution of positrons and neutrinos.
• Fitted the observed proton group shape to a model incorporating the lepton recoil effect and the correlation parameter a.
• Compared results with theoretical predictions assuming vector current dominance and zero Fierz interference.

Experimental results

Research questions

• RQ1 What is the value of the positron-neutrino correlation parameter a in the 0⁺ → 0⁺ decay of ³²Ar?
• RQ2 How does the measured correlation parameter compare to the Standard Model prediction of a = 1.0?
• RQ3 To what extent is the Fierz interference term consistent with zero, as predicted by the Standard Model?
• RQ4 What constraints do the results place on scalar weak interactions in this decay?
• RQ5 How well does the recoil effect on the proton group shape agree with theoretical expectations?

Key findings

• The measured correlation parameter is a = 0.9989 ± 0.0052 (statistical) ± 0.0036 (systematic), consistent with the Standard Model prediction of a = 1.0.
• The result excludes significant deviations from pure vector current interaction, supporting the conserved vector current (CVC) hypothesis.
• For vanishing Fierz interference, the data yield improved upper limits on scalar weak interactions.
• The observed proton group shape is well described by a model including lepton recoil effects, validating the analysis technique.
• The precision of the measurement improves constraints on non-standard scalar interactions in β decay.
• The result is in agreement with the Standard Model and provides a stringent test of the vector current nature of the weak interaction in superallowed decays.