Β-ray Angular Distribution Research Articles

Search for the G-parity irregular term in weak nucleon currents extracted from mirror beta decays in the mass 8 system

The alignment correlation terms in the β-ray angular distributions from purely spin aligned 8Li and 8B have been measured to search for the G-parity violating induced tensor term gII in the weak nucleon currents. The gII was extracted from the present alignment correlation terms, combined with the known β–α angular correlation terms and weak magnetism. This analysis permits an experimental determination of all the matrix elements necessary to extract gII. As a result, the induced tensor term was extracted as gII/gA=−0.28±0.28(stat.)±0.15(syst.) at a 1σ (68%) level. The present data and the data in the mass A=12 and 20 systems were analyzed under the KDR model in which medium effects including the off-shell effect and meson exchange current were taken into account. We determined the 1-body contribution to be ζ=−(0.13±0.13)×10−3MeV−1 and the 2-body contribution to be λ=+(0.27±0.97)×10−3 at a 1σ level.

β-Ray angular distribution from purely nuclear spin aligned 20F

The alignment correlation term in the β-ray angular distribution from purely nuclear spin aligned 20F has been measured to test the G-parity conservation law which is one of the fundamental symmetries in the weak nucleon current. We utilized the hyperfine interaction of 20F in an MgF2 single crystal and successfully created the pure alignment from the polarization by means of the spin manipulation technique based on the β-NMR method.

Nuclear Spin Alignment and Alignment Correlation Terms in Mass A = 8 System

The pure nuclear spin alignments of 8Li and 8B were produced from the nuclear spin polarization applying the β-NMR method. The alignment correlation terms in the β-ray angular distribution were observed to test the G parity conservation in the nuclear β decay.

β-ray Angular Distribution from Purely Nuclear Spin Aligned 20Na

β-ray Angular Distribution from Purely Nuclear Spin Aligned 20Na

Alignment correlation term in mass A = 8 system and G-parity irregular term

The pure nuclear spin alignments of 8Li and 8B were produced from the nuclear spin polarization applying the β-NMR method. The alignment correlation terms in the β-ray angular distribution of the mirror pair 8Li and 8B were observed to limit the G parity irregular term in the weak nuclear current. The significant deviation due to the forbidden matrix elements between the alignment correlation terms and the β-α correlation terms was observed. The determination of the alignment correlation terms was essential to extract the G-parity violating induced tensor term without the influence of the forbidden term in the vector current.

Alignment correlation term in the β-ray angular distribution from spin aligned 20Na

The alignment correlation term in the β -ray angular distribution from nuclear-spin aligned 20 Na( I π = 2 + , T 1/2 = 449.7 ms) has been measured for the first time. A large enhancement of the time component d in the main axial vector current was preliminarily obtained and the higher order matrices j 2 and j 3 were also evaluated. In order to extract very small G -parity violating induced tensor term, the alignment correlation term of the mirror partner 20 F have to be measured.

Precise nuclear moments of 13B and the β-ray angular distribution

The nuclear moments of 13B(Iπ = 3/2−, T1/2 = 17.36ms) have been re-measured precisely in order to establish the spin manipulation technique for the study of the alignment correlation term in mass system A = 13. From the β-NMR on 13B in Pt, the magnetic moment was determined as |μ(13B)| = 3.1778(5)μN. From the β-NQR on 13B in TiO2, the Q moment has been determined as |Q(13B)| = 36.6(8)mb. We have measured the alignment correlation term α_E for 13B β decay for the first time and obtained a preliminary result as α−(13B) = 0.15(12)%/MeV.

G-parity irregular current in the β decays of the mass A = 12 system - with the refined empirical value of the weak magnetism -

The β-ray angular distribution from the purely spin aligned mirror pair of 12B and 12N were precisely remeasured and the G-parity irregular induced tensor coefficient in the weak nucleon axial vector current was determined to be 2M f T f A = 0.15±0.12±0.05 (theory) at a 90% confidence level. In the extraction of the result, the refined empirical value of the weak magnetism a = (4.04±0.03)/2 M and the theoretical calculation of the charge asymmetry in the axial charge Δ y = 0.10 ± 0.05(theory) were used.

Spin Manipulation by Use of Nuclear Quadrupole Interactions – Quarks and Medium Effects in the Nucleus

The alignment correlation terms in the β-ray angular distributions from the purely spin aligned mirror pair 12B(Iπ= 1+ T1/2 = 20.2ms) and 12N(Iπ = 1+,T1/2 = 11.0ms)were precisely measured to place a new limit on the G-parity conservation law. For the creation of the alignment, the spin manipulation technique was applied, which utilized the nuclear quadrupole interactions. The - parity violating induced tensor coefficient was determined to be 2MfT/fa = -0,15 ± 0,12 ± 0,05 (theor.), which is consistent with the theoretical prediction based on QCD in which 2MfT/fA is proportional to the mass difference between up and down quarks which constitute the nucleon. Also determined the axial charge to be y= 4,90±0,10 (90% CL). From the result, we have found that the nucleon mass inside the nucleus is reduced (16 4)% relative to the free nucleon mass

β Decays of Nucleons and Quarks Embedded in the Nucleus

The β-ray angular distributions from purely spin aligned 1 2 B and 1 2 N nuclei were precisely remeasured to determine a new limit of the G-parity irregular induced tensor form factor in weak nucleon axial vector currentsand to study the in-medium mass renormalization of nucleons through the axial charge. A more reliable result on the induced tensor term was obtained as -0.31 < 2M f T /f A < 0.02 at a 90% confidence level. This result is consistent with the theoretical prediction in the framework of which the form factor is proportional to the mass difference between the up and down quarks. The axial charge of the axial vector current was determined to be y = 4.9 ′ 0.10, which may disclose an in-medium mass reduction of the decaying nucleon of (16 ′ 4)% at a 90% confidence level.

New limit of the G-parity irregular induced tensor current and of the axial charge in the weak nucleon current detected in alignment correlation terms of 12B and 12N β decays

The β-ray angular distributions from purely spin aligned 12 B and 12 N were precisely remeasured using a further refined spin-manipulation technique. We determined the amount of a G -parity violating induced tensor form factor in a weak axial vector current as 2 M f T /f A = + 0.22 ± 0.05 (stat) ± 0.15 (syst) ± 0.05 (theor.). The result is consistent with the theoretical prediction in the framework of which induced tensor form factor is proportional to the u- and d-quark mass difference. We also determined the axial charge of the weak nucleon current to be y = 4.66 ± 0.06 (stat) ± 0.13 (syst), which can be explained mainly in terms of the impulse value y 1A and soft pion exchange effect y EX . There, however, remains 18 % unexplained part of the experimental value relative to the theoretical value y th = y 1A + y EX = 4.12. An in medium mass reduction of 12 ± 4 % may explain the unexplained part if there is such an effect for the decaying nucleon.

Spin control and structure of weak nucleon currents in A= 8, 12, 20 and 41

The β-ray angular distributions from purely spin aligned 12B and 12N were precisely remeasured using a further refined spin-manipulation technique. We determined the amount of a g-parity violating induced tensor form factor in a weak axial vector current as 2M fT/fA= +0.22 ± 0.05\ (stat.) ± 0.15\ (syst.) ± 0.05\ (theor.). The result is consistent with the theoretical prediction in the framework of which induced tensor form factor is proportional to u- and d-quark mass difference. To study the g-parity violation in weak nucleon current systematically, we have started to measure the alignment correlation terms of 8Li, 8B, 20F and 41Sc.

SPIN CONTROL OF 12B AND 12N AND THE AXIAL CHARGE FROM THEIR BETA -RAY SPIN-ALIGNMENT CORRELATIONS

The spin manipulation technique by use of the β-NMR is further refined, based on the recent thorough studies of hyperfine interactions of 12B and 12N in Mg. By using this technique, the alignment correlation terms in the β-ray angular distribution of the A = 12 system are precisely measured, so that the axial charge is singled out to be y = 4.66 ± 0.06 (stat.) ± 0.13 (syst.) which shows clear mesonic enhancement over the impulse value.

Creation of the nuclear alignment and theG-parity conservation law in weak nucleon currents

β-ray angular distributions from nuclear spin aligned12B and12N were detected and the correlation coefficients were determined. From the comparison of these with the experimental weak magnetism term, it was concluded that the parity of the weak nucleon currents in the iso-spin space was strictly conserved.

On the β-γ Angular Correlations of Tm170and Sb124

We have calculated the β-ray angular distribution functions FLL’M(θ) for the interference between different types of the Fermi interactions in the second forbidden transition, taking into account the effect of the nuclear charge to the emitted electron. The investigation of the β-γ angular correlation is performed in the case of Tm170, assuming the linear combination of vector and tensor interactions. With this combination, we have also given the formulae of β-γ angular correlation for Sb124.