Beta Decay Data Research Articles

Neutrino reaction in 13C

The authors obtain cross sections for the reaction nu e+13C to 13N(gs)+e- and nu mu +13C to 13N(gs)+ mu - from threshold to several hundred MeV. They obtain the vector current form factors from electron scattering data and the axial current form factors from beta decay data and arguments based on an impulse approximation result. The behaviour of the form factors is discussed in detail.

Tests of the standard model with free neutron beta decay

I review recent measurements of neutron beta decay data. Implications of these measurements for CVC, the unitarity of the KM matrix, SU(3) flavour symmetry, right-handed currents, solar physics and big bang cosmology are investigated.

Gv, KM and mt

Analysis of superallowed Fermi beta decay using a new approach to the nuclear mismatch factor and evaluation of the radiative corrections using renormalization group methods and including nuclear-structure-dependent terms in the “inner” radiative correction leads to | V ud| 2+| V us| 2+| V ub| 2 = 0.9999 ± 0.0012 for the first row of the Kobayashi-Maskawa matrix using a mass of 130 GeV for the top quark. We may, alternatively, assuming unitarity of the KM matrix, infer a top quark mass of (1.40±80) GeV from beta-decay data alone.

Empirically optimum M1 operator for sd-shell nuclei

Abstract M1 matrix elements deduced from experimental data on M1 transitions and magnetic moments in the sd-shell nuclei are analysed with calculations based on the full-basis sd-shell wave functions of Wildenthal to extract the parameters for an effective M1 operator. These empirical parameters are analogous to the predicted corrections for the free-nucleon M1 operator which arise from the effects of higher-order configuration mixing and mesonic-exchange currents. From the differences between the effective operators associated with isoscalar M1 matrix elements, isovector M1 matrix elements, and Gamow-Teller (GT) matrix elements (as deduced previously from GT beta decay data) we are able to evaluate the relative importance of higher-order configuration mixing, mesonic exchange currents involving the Δ-isobar, and other mesonic exchange currents.

Monte Carlo, hypothesis-tests for rare events superimposed on a background

We describe two techniques to search for small numbers of counts under a peak of known shape and superimposed on a background with statistical fluctuations. Many comparisons of a single experimental spectrum with computer simulations of the peak and background are made. From these we calculate the probability that y hypothesized counts in the peaks of the simulations, will result in a number larger than that observed in a given energy interval (bin) in the experimental spectrum. This is done for many values of the hypothesized number y. One procedure is very similar to testing a statistical hypothesis and can be analytically applied. Another is presented which is related to pattern recognition techniques and is less sensitive to the uncertainty in the mean. Sample applications to double beta decay data are presented.

Neutrinoless double beta decay and the limits to the right-handed currents

We consider the neutrinoless double beta decay within two extended electroweak gauge models with right-handed weak interactions, the left-right symmetric model and the mirror fermion model. We show that if the two electron-like neutrinos with opposite chiralities appearing in these models are lighter than a few MeV, the double beta decay data do not restrict the magnitude of right-handed currents.

Spin flip transitions inC13andF19probed with the (π−, γ) reaction

Photon spectra from radiative capture of stopped negative pions captured by $^{13}\mathrm{C}$ and $^{19}\mathrm{F}$ nuclei have been measured with a high resolution pair spectrometer. In the bound region transitions have been observed to $^{13}\mathrm{B}$(g.s.), $^{13}\mathrm{B}$(3.5 MeV), $^{19}\mathrm{O}$(g.s.), $^{19}\mathrm{O}$(4.9 MeV), and $^{19}\mathrm{O}$(6.3 MeV). In addition, strong transitions to narrow states above the neutron separation threshold were observed in both cases. The results for $^{13}\mathrm{C}$ are in agreement with detailed shell model calculations of this process. Major strength is observed for states formed by coupling extra nucleons or holes to the spin-quadrupole ${d}_{\frac{5}{2}}$ and ${d}_{\frac{3}{2}}$, ${J}^{\ensuremath{\pi}}={2}^{\ensuremath{-}}$ states in $^{16}\mathrm{O}$. The $^{13}\mathrm{C}({\ensuremath{\pi}}^{\ensuremath{-}}, \ensuremath{\gamma})^{13}\mathrm{B}_{\mathrm{g}.\mathrm{s}.}$ branching ratio is shown to be consistent with beta decay and electroexcitation data, through a combined phenomenological analysis. The observed transition strengths are accounted for by matrix elements of the spin-density operators ${[\ensuremath{\sigma}\ifmmode\times\else\texttimes\fi{}{Y}_{0}]}^{1}{t}^{+}$ and ${[\ensuremath{\sigma}\ifmmode\times\else\texttimes\fi{}{Y}_{1}]}^{2}{t}^{+}$.NUCLEAR REACTIONS $^{13}\mathrm{C}({\ensuremath{\pi}}^{\ensuremath{-}}, \ensuremath{\gamma})$, $^{19}\mathrm{F}({\ensuremath{\pi}}^{\ensuremath{-}}, \ensuremath{\gamma})$; measured normalized $I({E}_{\ensuremath{\gamma}})$; deduced upper limit on $\ensuremath{\delta}(\frac{E2}{M1})$ for $^{13}\mathrm{C}$\ensuremath{\rightarrow}$^{13}\mathrm{B}$(g.s.) at $q=125$ MeV/c, systematics of SIGDR in $12\ensuremath{\le}A\ensuremath{\le}20$. Stopped ${\ensuremath{\pi}}^{\ensuremath{-}}$; pair spectrometer; 850 keV at 129.4 MeV.

Coupling constants and electromagnetic radiative corrections in beta-decay and the mass of the intermediate vector boson

Effective beta-decay coupling constants G′ v and G′ A are defined which include renomalizing effects due to the electromagnetic interaction. Analysis of recent beta-decay data then gives G′ v = 1.4150 ± 0.0011 × 10 −49 erg · cm 3 and |G′ A G′ v| = 1.226 ± 0.011 . It is concluded that only those theories of electromagnetic radiative corrections which take account of a very heavy intermediate vector boson are able to reconcile the values of G′ v , G μ and the Cabibbo angle determined from polar vector strangeness changing semi-leptonie decays.

Beta Decay ofLi8

The beta decay of ${\mathrm{Li}}^{8}$, formed in the ${\mathrm{Li}}^{7}(d, p){\mathrm{Li}}^{8}$ reaction, has been studied by measuring the energy distribution of the alpha particles that come from the subsequent breakup of ${\mathrm{Be}}^{8}$. The effects of the penetration into backing foils of the ${\mathrm{Li}}^{8}$ recoils have been corrected for by comparing, for several deuteron bombarding energies, the alpha-particle spectra seen using a very thin foil target and the same target backed by a thick foil. The resulting "correct" alpha-particle spectrum is adjusted for various small effects including that due to electron-neutrino recoil and then compared with a prediction based on the empirical alpha-alpha scattering phase shifts, themselves adjusted by the subtraction of a hard-sphere phase shift. It is shown that the prediction is rather insensitive to the choice of hard-sphere radius. The agreement between the beta-decay data and the alpha-alpha phase shifts in the peak position (the "2.9-MeV state" of ${\mathrm{Be}}^{8}$) is excellent as it is also in the shape of the transition probability distribution on the low- (alpha-particle) energy side of the peak where the falloff of intensity is here experimentally followed over two orders of magnitude. On the high-energy side of the peak, the familiar discrepancy is found in the sense that the transition probability is much too high to be explained by the first excited state alone. The present results, in addition to constituting an accurate comparison between ${\mathrm{Li}}^{8}$ beta decay and alpha-alpha scattering, strengthen the interpretation of the reaction ${\mathrm{Be}}^{9}(p, d){\mathrm{Be}}^{8}$ in terms of the "ghost" of the ground state of ${\mathrm{Be}}^{8}$ and provide necessary data for discussing ${\mathrm{Li}}^{8}$ and ${\mathrm{B}}^{8}$ decay to regions of higher excitation in ${\mathrm{Be}}^{8}$ where the effects of transitions to the tail of the first $T=1$ state of ${\mathrm{Be}}^{8}$ are probably important.