Abstract
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.
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M. Bourquin et al. (I): Z. Phys. C — Particles and Fields12, 307 (1982)
M. Bourquin et al. (II): Z. Phys. C — Particles and Fields21, 1 (1983)
M. Bourquin et al.: Nucl. Phys.B153, 13 (1979)
P.W. Jeffreys: Ph.D. Thesis, University of Bristol (1980)
M. Bourquin et al.: Nucl. Instrum. Methods204, 311 (1983)
B. Sechi-Zorn, G. Snow: Phys. Rev.D8, 12 (1973)
H. Ebenhöh et al.: Z. Phys.266, 367 (1974)
A.P. Colleraine et al.: Phys. Rev. Lett.23, 198 (1969)
F. Eisele et al.: Z. Phys.223, 487 (1969)
C. Baltay et al.: Phys. Rev.D5, 1569 (1972)
W. Tanenbaum et al.: Phys. Rev.D12, 1871 (1975)
D. Decamp et al.: Phys. Lett.66B, 295 (1977)
K. Tóth, T. Margaritisz, K. Szegö: CERN preprint TH-3169 (1981) and private communication
A. Baltas et al.: Nuovo Cimento66A, 399 (1981)
P. Keller et al.: Phys. Rev. Lett.48, 971 (1982)
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Work supported by the Bundesministerium für Forschung und Technologie, FRG
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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
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DOI: https://doi.org/10.1007/BF01648772