Elementary particle lifetimes: An untapped goldmine of information
Part of the Lecture Notes in Physics book series (LNP, volume 81)
Part II. Angular momentum quantization: Spin and orbital angular momenta
KeywordsDecay Mode Resonance Region Experimental Lifetime Lifetime Systematic Meson Resonance
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References for Chapter 10.
- 1.article Data Group, “Review of Particle Properties”, Rev. Mod. Phys. 48, No. 2, Part II, April (1976).Google Scholar
- 2.The Σo lifetime is from F. Dyak et al., Nucl. Phys. B118, 1 (1977). The Ξo and Λ lifetimes are from G. Zech et al., Nucl. Phys. B124, 413 (1977).Google Scholar
- 3.A Duane et al., Phys. Rev. Lett. 32, 425 (1974). The η′ lifetime shown in Table 10.1 was obtained by fitting parabolas to the two sets of data in Table I of Duane et al. and averaging the results; the error limit quoted here is an average of the Δχ2 = +1 values obtained from these two parabolas.Google Scholar
- 4.See B. T. Feld, Models of Elementary Particles, Blaisdell, Waltham (1969), Sec. 7.4.Google Scholar
- 5.M. H. Mac Gregor, in Fundamental Interactions at High Energies, proceedings of the 1971 Coral Gables Conference, edited by M. Dal Cin, G. J. Iverson, and A. Perlmutter (Gordon and Breach, New York, 1971), Vol. 3, p. 75; Nuovo Cimento 8A, 235 (1972) and 20A, 471 (1974); Phys. Rev. D9, 1259 (1974), Sec. XII.Google Scholar
- 6.The short-lived resonances include all resonances in RPP76, Ref. 1, except those of Table 10.1 in the present paper, which have quoted lifetime or width values. In cases where a spread of values is given, the RPP76 quoted average was used where available.In some cases where different charge states of a resonance have separately quoted lifetimes, both of these lifetimes were included. In Figs. 10.5 and 10.6, the abscissa corresponds to the lifetime logarithms X as obtained from Eq. 10.3, and the ordinate gives an equally spaced distribution of the logarithms X after they have been sorted out into ΔX = 0.1 bins.Google Scholar
- 7.We ordinarily expect a resonance to exhibit the same mass and the same observed, total width in all of its decay modes. However, both the observed mass and the observed width for a particular decay mode can be shifted if there is a severe phase-space constraint which occurs for just this specific decay mode. The meson is the only example known to the author in which this condition occurs. The φ → KK decay mode, which has been used for most experimental determinations of the φ-meson parameters, is highly unusual in that it is a spin-1 decay with a very small Q value.From the Q value of 30 MeV, each final-state kaon has a kinetic energy of only 15 MeV, or a linear momentum of 123 MeV/c.Thus, in order to carry away the spin-1 angular momentum of the φ, the two kaons must have a noncollinear separation distance of 2.3 fermis.If we assume that the 1020-MeV φ meson has about the same “size” as the measured size of the 939-MeV nucleon, this large separation distance required for the final-state kaons constitutes a severe kinematic constraint, and it limits the available phase space for the decay by cutting off the low-momentum portion, thus increasing the observed mass of the in this decay channel and decreasing its observed width.The φ in its φ->πππ decay mode does not have this severe kinematic constraint, and it appears in some experiments at a lower mass and with an apparently broader width [see M. AguilarBenitez et al., Phys. Rev. D9, 29 (1971), Fig. 61 and the accompanying discussion; J.-E. Augustin et al., Phys. Lett. 28B, 517 (1969); G. R. Kalbfleisch et al., Phys. Rev. D13, 22 (1976)], which would place it closer to the “resonance region” of Fig. 10.5 in the present paper. However, in Orsay Storage Ring experiments [G. Cosme et al., Phys. Lett. 48B, 155 (1974); G. Parrour et al., Orsay Report No. LAL 1280 (1975), (unpublished)], the e+e-→ 3π and e+e-> → KLOKSO measurements of the φ mass and width give very similar results.Google Scholar
- 8.A review of SU(3) classification schemes is given in Ref. 1. Also see Chapter 14 in Ref. 4.Google Scholar
- 9.See M. H. Mac Gregor, Lett. Nuovo Cimento 1, 759 (1971). The factor a18 is approximately equal to the square of the ratio of the proton mass to the Planck mass (m* = V √ℏ/g); see J. A. Wheeler, Analytical Methods in Mathematical Physics, edited by R. P. Gilbert and R. G. Newton, Gordon and Breach, New York (1970), p. 335.Google Scholar
- 10.J. Bernstein, Elementary Particles and Their Currents, Freeman, San Francisco (1968), p. 128.Google Scholar
- 11.M. L. Perl et al., Phys. Rev. Lett. 35,1489 (1975); also see a theoretical paper by A. De Rújula et al., Phys. Rev. Lett. 35, 628 (1975).Google Scholar
- 12.The ratio of the lifetimes of the J/Ψ and Ψ′ particles (see Table 10.1) is currently given in Ref. 1 as 3.3 ± 1.1, which may or may not be in agreement with the factor-of-two lifetime ratios shown in Fig. 10.9.Google Scholar
- 13.Amsterdam-CERN-Nijmegen-Oxford Collaboration, CERN/EP/PHYS 76–19, June (1976); a total of 32 Ω− events at 4.2 GeV/c gave a lifetime T = 0.75 ± 0.15 x 10–10 sec. Also, in a recent compilation of Ω− events [R. J. Hemingway, CERN/ EP/PHYS 76–50, Aug. 10 (1976) (unpublished)], 50 low-momentum events (4–6 GeV/c) gave a lifetime τΩ − = 0.79 ± 0.11 x 10−10 sec.Google Scholar
- 14.M. Deutschmann et al., Phys. Lett. 73B, 96 (1978).A total of 101 high-momentum Ω− events at 10-16 GeV/c gave a lifetime Γ = 1.41 + 0.15,-0.24 x 10−10 sec.Google Scholar
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