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The percentages of state Nos. 1,3, and the D states are also given in the tables. These numbers should not be taken literally, of course, since wave functions which have not even converged for purposes of the ground-state energy have very doubtful validity for finding quantities other than the energy. But the trend is clearly towards larger admixtures of state No. 3, albeit not as large as the 4% which Schiff would like for fitting the electron scattering data; we feel that discussion of the significance of any such discrepancy should await the inclusion of the D states into Schiff s calculations.We are grateful to the Courant Institute, New York University, for a very generous allocation of IBM-7094 machine time, and to the staff of the Courant Institute for much appreciated help and advice. We thank Professor Schiff for communicating his results prior to publication, andIn this note we present evidence for the existence 1 of a new meson of strangeness-zero, which we temporarily call the "X 0 ." 2 Its mass and full width are M*960 MeV and T<25 MeV; its isospin is either 0 or 1. Data relevant to determination of its other quantum numbers are now being analyzed and the results will be reported in a subsequent paper.The data discussed here come from a bubble chamber study of the K'-p interactions at 2.3 BeV/c. The general features of this study have been described elsewhere. 3 The evidence for the existence of X° comes primarily from effective-mass studies in the following reaction channels:K~ +/>-A+77 + +77"+7r + + 7T +7T°,K~ +p* A + 7r + + 7r" + (neutrals with mass>w n ). (3) The number of events in each 4 channel are 1277, 43, and 415, respectively, all coming from a for useful discussions. Breit, Phys. Rev. 126, 881 (1962).complete sample occurring within a suitable fiducial region. We discuss each of these channels in sequence below. A histogram of the squared missing mass of the neutrals emitted in Reaction (1), denoted by M 2 (neutrals), is shown in Fig. 1. As indicated in the figure, there are peaks of varied size corresponding to the known two-body production of a A 0 and a 7r°, 77°, u>°, and (f°. From an ideogram of the data of Fig. 1, we find that these peaks occur at 130 ±30 MeV, 550±20MeV, 780±15MeV, and 1020±15 MeV, respectively, in excellent agreement with the accepted masses of these mesons. In addition, one sees a new peak at 960 ± 15 MeV of width »40 MeV corresponding to the reaction K'+p-A+X 0 .We have investigated other possible production mechanisms such as Y* + rf, F* + u)°, I^ + u; 0 , etc., and find that none of them is capable of giving rise to a peak of width as narrow as that observed.

YamamotoIn two recent Letters,^'^ evidence was presented for the existence of the "^," a meson of strangeness 0, mass 960 MeV, and narrow width. In this note we discuss the evidence pertinent to the detailed nature of the X^ decay modes and quantum number assignments including G-parity, isospin, spin, and parity.In reference 1 we reported observation of three final states of J^ decay, namely (A) X^-neutrals, (B)X^-7r'^4-7r"^ + 77"+7T"+7r°, (C)-X^-Tr^ + Tr" + neutrals, which occur^'^ in the ratio --4:1:4. The detailed nature of these final states is discussed below.The mode (B) can be ascribed to either of two decay chains: js^ •* 57r (direct) or x^^-n' + 7r^Direct evidence against X^-^bn comes from con-siderations based on the distribution of the four possible (n'^TT'Tr^) mass combinations for each 5-pion final state. The outstanding feature of the distribution is that every one of the 45 X^ events^ contains at least one Miir'^n'Tr^) combination consistent with the rf mass (taken to be 550 ± 25 MeV for these well-measured events). It is easy to see that this circumstance is inconsistent with the assumption X^-*57T. Firstly we estimate from the appropriate STT phase space the probability P that three pions from 960 -STT have M(3TT) = 550± 25 MeV. Including resolution broadening, we find P = 0.2 ± 0.05. Then, ignoring correlations'* among the four possible mass choices, the expected number of events with at least one "successful" mass combination is only 45[l-(1-0.2 ± 0.05)^]« 27 ±3 events which is (45-27)/3«6 standard deviations from the observed value.

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