## Abstract

The axial charge in the weak nucleon axial vector current has been precisely determined by measuring the alignment correlation terms in the β-ray angular distributions of the purely spin aligned mirror pair nuclei ^{12}B(I^{π}= 1^{+},T_{1/2}=20.2 ms) and ^{12}N(I^{π}= 1^{+},T_{1/2}=11.0 ms). The axial charge was determined to be y=4.96 ±0.09 (stat.)±0.05 (syst.) at a 90% confidence level. The previously obtained data in the year 1996 was reanalyzed to be added to the present result. The combined result is y=4.90±0.10 at a 90% confidence level. The axial charge is enhanced as much as (72±4)% from the impulse approximation model calculated value y_{IA}=2.85. Calculations using the impulse approximation with the soft-π contribution y_{th}=4.15 explain the data quite well but not completely. If we introduce the in-medium mass renormalization the unexplained part of the experimental result corresponds to an in nuclear-medium nucleon mass reduction of (16±4)% at a 90% confidence level relative to the free nucleon mass, at the place where the decaying nucleon resides.

Original language | English |
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Pages (from-to) | 152091-1520915 |

Number of pages | 1368825 |

Journal | Physical Review C - Nuclear Physics |

Volume | 65 |

Issue number | 1 |

Publication status | Published - 2002 Jan 1 |

## ASJC Scopus subject areas

- Nuclear and High Energy Physics