Springer Nature is making SARS-CoV-2 and COVID-19 research free. View research | View latest news | Sign up for updates

Measurements of hyperon semileptonic decays at the CERN Super Proton Synchrotron

III. The\(\sum ^ - \to ne^ - \bar v\) decay mode

  • 32 Accesses

  • 30 Citations


The charged hyperon beam at the CERN Super Proton Synchrotron (SPS) has been used to collect data on semileptonic decays of Σ, Ξ, and Λ. In this article we report results on the\(\sum \to ne\bar v\) decay mode. A magnetic channel selected 100 GeV/c (130 GeV/c) negatively charged particles produced in the forward direction by interaction of the 210 GeV/c (240 GeV/c) SPS proton beam on a BeO target. The Σ hyperons were identified in a DISC Čerenkov counter, and the negatively charged decay particle was analysed by a magnetic spectrometer. The neutron direction was obtained from the Σ decay vertex and from the impact point measured in a neutron detector. Electron-hadron discrimination was achieved by the combined use of lead-glass and transition radiation detectors. The\(\sum \to ne\bar v\) branching ratio measurement gave a value of (0.96±0.05) ×10−3. Measurements of the centre-of-mass distributions (baryon kinetic energy, electron-antineutrino correlation, and Dalitz plot distributions) yield the axial-vector to vector form factor ratio |g 1/f 1|=0.34 ±0.05. From the study of the electron momentum spectrum, the negative sign ofg 1/f 1, which is expected within the Cabibbo theory framework, is favoured by at least 2.6 standard deviations. The effects ofq 2-dependence off 1 andg 1 and of radiative corrections, the measurement of the weak magnetism form factorf 2, and the effect of possible second-class current terms are discussed. Results on the other Ξ, Σ, and Λ semileptonic decays are reported in separate articles.

This is a preview of subscription content, log in to check access.


  1. 1.

    M. Bourquin et al. (I): Z. Phys. C — Particles and Fields12, 307 (1982)

  2. 2.

    M. Bourquin et al. (II): Z. Phys. C — Particles and Fields21, 1 (1983)

  3. 3.

    M. Bourquin et al.: Nucl. Phys.B153, 13 (1979)

  4. 4.

    P.W. Jeffreys: Ph.D. Thesis, University of Bristol (1980)

  5. 5.

    M. Bourquin et al.: Nucl. Instrum. Methods204, 311 (1983)

  6. 6.

    B. Sechi-Zorn, G. Snow: Phys. Rev.D8, 12 (1973)

  7. 7.

    H. Ebenhöh et al.: Z. Phys.266, 367 (1974)

  8. 8.

    A.P. Colleraine et al.: Phys. Rev. Lett.23, 198 (1969)

  9. 9.

    F. Eisele et al.: Z. Phys.223, 487 (1969)

  10. 10.

    C. Baltay et al.: Phys. Rev.D5, 1569 (1972)

  11. 11.

    W. Tanenbaum et al.: Phys. Rev.D12, 1871 (1975)

  12. 12.

    D. Decamp et al.: Phys. Lett.66B, 295 (1977)

  13. 13.

    K. Tóth, T. Margaritisz, K. Szegö: CERN preprint TH-3169 (1981) and private communication

  14. 14.

    A. Baltas et al.: Nuovo Cimento66A, 399 (1981)

  15. 15.

    P. Keller et al.: Phys. Rev. Lett.48, 971 (1982)

Download references

Author information

Additional information

Work supported by the Bundesministerium für Forschung und Technologie, FRG

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Bourquin, M., Brown, R.M., Chatelus, Y. et al. Measurements of hyperon semileptonic decays at the CERN Super Proton Synchrotron. Z. Phys. C - Particles and Fields 21, 17–26 (1983). https://doi.org/10.1007/BF01648772

Download citation


  • Dalitz Plot
  • Semileptonic Decay
  • Weak Magnetism
  • Decay Vertex
  • Vector Form Factor