Elsevier

Nuclear Physics B

Volume 66, 17 December 1973, Pages 253-292
Nuclear Physics B

The second-class current problem in nuclear beta decay

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Abstract

Taking into account in a simple but non-trivial way both off-mass-shell and meson-exchange effects, we calculate the second-class current (scc) contribution to asymmetries in nuclear mirror Gamow-Teller decays. No assumptions on the divergence of the scc are made but the previous result obtained for a divergenceless current is recovered straightforwardly from our formula. Of the plethora of parameters that can be brought in for a current with non-vanishing divergence, we confine ourselves to the minimum number (two) which still renders our calculation sufficiently realistic while retaining its predictive power. The two parameters - one associated with the off-shell phenomenon and the other with meson-exchange current - are determined from two pieces of experimental data on the A = 8 system (the averaged asymmetry δ obtainable from the total decay rates and the slope in the plot of δ versus the energy release) and predictions are made for the scc effects in other mirror transitions. On the average the expected scc contribution to mirror asymmetry δ is 2 to 5%, for both even- and odd-A nuclei. We reach the same conclusion as Wilkinson that the large residual asymmetry (≳10%) left unaccounted in odd-A nuclei must be nuclear in origin. The fundamental nucleon pseudotensor coupling constant implied by this result is still of the same order (∼1/M, where M is nucleon mass) as that of the weak magnetism or pseudoscalar terms. In the absence of kinematic suppression, this could induce large effects. Thus the ω-decay into π±e−+ν is expected to be as fast as any allowed first-class decay of a meson with comparable mass. The asymmetries in various correlation experiments (i.e. eη correlation and up-down asymmetry with respect to nuclear spin polarization) are predicted to be large enough to be measurable. We make a detailed analysis on whether, as conjectured by Lipkin, the meson-exchange current can build up coherently for large nuclei. The conclusion drawn therefrom is that such an enhancement does not materialize.

References (37)

  • P.L. Pritchett et al.

    Phys. Letters

    (1972)
  • R. Blin-Stoyle et al.

    Nucl. Phys.

    (1965)
  • D.H. Wilkinson

    Phys. Rev. Letters

    (1971)
  • Stanford preprint...J. Delorme et al.

    Nucl. Phys.

    (1971)
    J. Delorme et al.

    Nucl. Phys.

    (1972)
    H.J. Lipkin

    Phys. Letters

    (1971)
    H.J. Lipkin

    Phys. Rev. Letters

    (1971)
  • J.N. Huffaker et al.

    Phys. Rev.

    (1963)
  • N. Cabibbo
    (1966)
  • A. Arima, G.E. Brown, H. Hyuga and M. Ichimura, Phys. Letters, in...
  • M. Moshinsky et al.

    Tables of transformation brackets

    (1960)
  • J. Elliott et al.

    Proc. Roy. Soc. (London)

    (1955)
  • T. Lauritsen et al.

    Nucl. Phys.

    (1966)
  • T. Minamisono and K. Sugimoto, private...
  • M. Steels et al.

    Contribution to Osaka Conf.

    (1972)
  • N. Cabibbo et al.

    Weak interactions

    CERN Report 65-30

    (1965)
  • K. Kubodera et al.

    DPh-T/72-35, CEN Saclay

    (1972)
  • D.H. Wilkinson

    Few-particle problems in nuclear interaction

  • J. Lindquist

    Phys. Rev. Letters

    (1971)
    K.H. Althoff

    Phys. Letters

    (1971)
    A. Garcia

    Phys. Rev.

    (1971)
  • T.W. Donnelly et al.

    Phys. Letters

    (1972)
    S.M. Brown

    Test of second class currents in Δ(1236) production by neutrinos

    CTS-HE-72-2

    (1972)
  • J.D. Walecka, Semi-leptonic weak interactions in nuclei, in Muon physics, eds. V.W. Hughes and C.S. Wu (Academic Press,...
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    Permanent address: Institut de Physique Nucléaire de Lyon, Université Claude Bernard, Villeurbanne, France.

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