EVIDENCE FOR A T = 0 RESONANCE IN THE V * SYSTEM [electronic resource].
- Washington, D.C. : U.S. Atomic Energy Commission, 1961.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
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- U.S. Atomic Energy Commission
United States. Department of Energy. Office of Scientific and Technical Information
- In previous letters the authors have reported a Σπ resonance observed through the study of the interaction of 1.15-Bev/c K⁻ meons in hydrogen in the Lawrence Radiation Laboratory 15-in. bubble chamber. They now wish to report the results of the study of the three reactions: (1) K⁻ + p → Σ⁺ + π⁻ + π⁻ + π⁺; (2) K⁻ + p → Σ⁻ + π⁺ + π⁺ + π⁻; and (3) K⁻ + p → Σ° + π° + π⁺ + π⁻. Although reactions (1) and (2) are readily identified and measured, reaction (3) cannot be identified unambiguously. Accordingly, they discuss first the results pertaining to reactions (1) and (2). Nineteen events of type (1) and 13 events of type (2) were observed, corresponding to cross sections of 0.19 ± .06 and 0.12 ± .05 mb, respectively. In a search for possible Σπ resonances, they have plotted in Figure 1 histograms of the invariant masses of the Σ and each of the three pions in reactions (1) and (2). Figure 1b refers to the Σ and pion of like charge; Figure 1a to the Σ and each of the pions of unlike charge. Since there are two unlike-charged pions in each event, twice as many points appear in Figure 1a as in Figure 1b. The plotted curves are mass distributions expected on the basis of a uniform phase-space population. The histogram of Figure 1b agrees with the phase-space curve, but the Σ and unlike-charged pion distribution appears to exhibit an anomaly, suggesting a concentration of events with a (Σπ) mass of about 1405 Mev. To explore this anomaly in more detail, they use the following representation of the data. Since, according to Figure 1b, the doubly charged Σπ systems do not depart significantly from the expected phase-space distribution, they eliminate the like-charged pion from further consideration. They then transform the Σ and the remaining two pions (both of charge opposite to that of the Σ) into the center-of-mass (c.m.) system of these three particles and determine the total energy available in this particular coordinate system. For each event they can then calculate a Dalitz plot of the available phase space. However, to permit the comparison of events that involve different amounts of c.m. energy, they can conveniently relabel the axes of the Dalitz plot to correspond to the invariant Σπ mass squared, which is linearly related to the kinetic energy of the other pion. The phase-space ellipses obtained from individual events are then added to obtain a composite phase-space probability contour map in the mass-squared space. The result of this procedure is shown in Figure 2a. Only half of the plot is shown, since it is symmetrics about the 45-deg line because the two pions considered are indistinguishable.
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Eberhard, Philippe; Ticho, Harold K.; Good,Myron L.; Alvarez, Luis W.; Wojcicki, Stanley G.; Alston, Margaret H.; Graziano, William.
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
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