3600 two-pronged events, obtained in p-p interactions at 2 Bev in the BNL 20-in. hydrogen bubble chamber, have been analyzed. Cross sections have been measured for elastic scattering, for the two modes of single-pion production, p-\-p -» p-3 rn-\-ir + , p+p -> p-\-p-\-n°, and for strange-particle production. The branching ratio for the two one-pion production reactions is c-(£wr + )/a-(^7r°)=4.l7=fc:0.25. Momentum distributions and Q values indicate that single-pion production proceeds almost entirely through the (f,f) resonant state. The data have been considered in terms of the extended isobar model and also a one-pion exchange model for production. The branching ratio and momentum distributions can be explained by including a small effect from the /=£ resonant state in addition to the dominant I-\ resonance. The cm. angular distribution of the nucleons in single-pion production shows very marked backward-forward peaking indicating a one-pion exchange mechanism. Absolute differential cross sections as a function of laboratory kinetic energy have been calculated from Selleri's equation for the pmr + reaction. There is good agreement with the data for low four-momentum transfers [# 2 <0.15(Bev/c) 2 ], but for higher momentum transfers the theoretical cross sections are larger than the experimental cross sections.

Analyses have been made for 871 four-prong events and 463 two-prong events corresponding to multiple pion production, resulting from p-p interactions at 2 Bev in the BNL 20-in. hydrogen bubble chamber. Cross sections have been obtained for all the observable double and triple pion production processes; the branching ratios predicted by the extended isobar model are shown to be in fair agreement with the data, but there are significant differences. The cm. momentum distributions are also in fair agreement with the predictions of the model, although there are ambiguities in the interpretation. The pion-nucleon Q values give clear evidence for the importance of the ( §, §) resonant state in multiple pion production, but consideration of this state alone does not provide an explanation of the features of double pion production. Some contribution from another state, possibly the / = \ nucleon isobar, is necessary. In double production, the cm. angular distributions of the nucleons show backward-forward peaking suggestive of a one-pion exchange process. The angular distributions of the nucleons from triple production are almost isotropic

A study has been completed of three-body final states, hyperon+K +TI, in pion-nucleon collisions at an incident pion momentum of 1.68 BeV/c. The purpose of this investigation was to obtain information on the spin of the 7 0 * (1405) resonance by observing angular correlations in its decay. Our results, by use of a moments analysis, 1 are consistent with spin I, but our statistics at present are too poor for a parity determination. We have also examined the decay of the F 1 *(1385) resonance and find, in agreement with other authors, 2 that spin ^ is ruled out, spin | is acceptable, and spin § is not required by these data.The data were obtained from approximately Phys. Rev. Letters 12, 527 (1964);We must point out two minor qualifications to these results: (a) The cut on lM 2 (all neutrals) I =s 0.01 results in the loss of a small fraction of 77 (959) events due to resolution. Thus, we would expect this effect with approximately the same magnitude to occur in the case of the cp\ (b) our data at this time do not rule out the possibility of a weak alternate decay mode, cp -+p + ir (branching ratio = 18± 8%). Again due to resolution we may be including a small amount of pV in our p°y and 7T ir~~y determinations. The effect of (a) is to underestimate and (b) to overestimate the limits on py and 7r + 7r~"7. However, the net effect can alter our conclusions on the branching ratios by no more than ±1 to 2%. 13 We have assumed an all-neutrals branching ratio of 69% for the 17 (548) and 10% for the to in arriving at these branching ratios. We have introduced a slight bias in the wy and 77 (548)7 determinations because of the removal of events with M 2 (all neutrals )< 4 ra^o 2 , inasmuch as the lower bound for these cases would be m^2 [w or 77(548)-^7T + + 7r""+7T 0 ] or zero [r\ (548) -7r + + 7r~ + y]. Therefore, the branching ratios for these modes should be somewhat larger, but probably by no more than 1 to 2%. 2xl0 5 ?T"~/> and 1.2 xlO 5 ii + d pictures in the Brookhaven National Laboratory 20-in. bubble chamber exposed at the AGS. The incident beam momentum corresponds to a cm. energy 50 MeV below the threshold for the reaction K*(890) + 2. Table I gives the number of events in the various final states. For the reaction ir + +d-+ hy-peron+K+71 + nucleon, only events with a nucleon momentum of ^200 MeV/c are included. 3 In these events the nucleon is considered to be a "spectator" not affected by the primary 7r-nucleon interaction, except for energy-momentum conservation. The Dalitz plot and its mass-squared projections for 220 events in

The reactions pp -» iV* ++ (1238)rc and pn-*N*~~(1238)p at 2.8 GeV/c incident laboratory momentum are analyzed with the Brookhaven National Laboratory 20-in. bubble chamber. Isobar and anti-isobar production differential cross sections and decay angular distributions are compared with the predictions of an absorptive single-pion-exchange model. The absolute values, shapes, and ratios of the cross sections are in good agreement with the theory when the absorptive parameters 71 and 72 are 0.033 and 0.016 for the pn reaction, and 0.057 and 0.019, respectively, for the pp reaction.T HE observed peripherally of reactions producing quasi-two-body final states in particle collisions at high energies indicates the importance of singleparticle-exchange mechanisms. Experimental results for a variety of reactions are in general agreement with the predictions of a single-pion-exchange model in which effects of absorption due to competing interaction channels in the initial and final states are included. 1 A comparison of isobar and anti-isobar production in pp and pn collisions provides a further test of this model in that it includes the added absorptive effects of the annihilation channels in the pn reaction. For, while the absorption reduces cross sections of both pp and pn reactions leading to quasi-two-body final states, the model predicts a stronger absorption of low partial waves for the pn than for the pp interactions; in consequence, anti-isobar production shows a more collimated forward differential cross section and an additional reduction of total cross section over that for isobar production. Since the isospins of the two reactions reported here differ only in the sign of the third component, the two channels can be compared directly.In this paper we present an analysis of 1302 events of the type pp->pw + n and 944 events of the type pn^-^p^pip),where (p) represents the spectator proton of the deuteron. An account of the pp reaction at 2.8 GeV/c has been published 2 ; the data are presented here in a form suitable for comparison with the predictions of the absorptive one-pion-exchange model. The pn sample was obtained from approximately 15 000 three-and four-prong events observed in the deuteriumfilled 20-in. bubble chamber exposed to 2.8-GeV/c antiprotons at the Brookhaven alternating gradient synchrotron. We shall discuss only those events with at [Phys. Rev. 139, B428 (1965)] in which experimental results on several different quasi-two-body reactions are compared with the predictions of an absorptive single-particle-exchange model. 2 W. J. Fickinger, E. Pickup, D. K. Robinson, and E, O. Salant, Phys. Rev. 125, 2082 (1962). 162 least one proton of momentum less than 200 MeV/c, a range in which the impulse approximation appears valid by comparison of the proton momentum distribution with that predicted by the Hulthen wave function. 3 For the purpose of analysis the proton with lower momentum was chosen as the "spectator." Total cross sections have been computed using all events. In Figs. 1 (a) and 1 (b) are sho...

Evidence has been reported for two resonances in the 7T + 7r~7r° system at about 770 Mev (co) 1 " 3 and 550 Mev (TJ). 2 ' 4 In an investigation of pion production in p-p collisions at 2 Bev in the BNL 20inch hydrogen bubble chamber we observed 5 indications of the r\ in the triple pion production reactionTo confirm this, the remainder of the total sample of 1951 four-pronged events in the fiducial volume was measured and analyzed, using the GUTS fitting program and bubble density measurements. 135 pp + -0 events, 256 of the type p+p -*-/>+n + 7r + + 7r + + 7r", (pn++~) and 1560 of the type p+p -*/>+/>+ 7r + + 7r", (/>/>+-) were obtained. We report here observation of the charged decay mode of the r\ (T]-*+-0) in the pp+-0 reaction. A search for the 7r + 7r"y decay mode (ri-++-y) has shown that, if it occurs, the decay rate is very small. Evidence has also been obtained for the decay of rj into neutrals. There are indications of the a, and a possible new resonance.Q values for the 377 systems, +-0 and ++-, are shown in Fig. 1. The 7] can be seen in the +-0 system at an effective mass of 546 ± 4 Mev and a width of the order of the experimental resolution. Using known cross sections for p-p interactions, 5 we obtain the cross section a(T?-»-+-0) for p+p-»p+p + rfto be 57 ± 10 jub. This corresponds to 35 events FIG. 1, Histograms of 37r Q values in 20-Mev intervals: (a) Q + _ 0 from the reaction p+p-~p+p + it + +7r~ + 7i°, (b) Q++_ from the reaction£+£-~/>+W + 7T + + 7T + + 7T~. Effective mass scales are also given. The masses of the r\ and cu are indicated by vertical lines. The insert above (a) shows Q+_o about the i? peak, plotted in 4-Mev intervals.Q + -0 ABOUT t) PEAK JX. ^ rEb_ 80 IOO 120 140 160 180 0 + -o r y _ru~i I"