The branching ratio for the A weak radiative decay LAMBDA --> ngamma has been measured. Three statistically independent results from the same experiment (Brookhaven E811) are reported here. They are combined with a previously published measurement, also from Brookhaven E811, to yield a result of (LAMBDA --> ngamma)/(LAMBDA --> anything) = (1.75+/-0.15) X 10(-3), based on 1800 events after background subtraction. This represents a factor of 75 increase in statistics over the previous world total. A comparison with recent theoretical papers shows that no existing model provides a completely satisfactory description of all data on weak radiative decays. A search is also reported for the radiative capture process K-p --> SIGMA(1385)gamma at rest. No signal was observed and an upper limit on the branching ratio of [K-p --> SIGMA(1385)gamma]/[K-p --> anything] < 4 X 10(-4) (90% C.L.) was determined.

The branching ratio for the A weak radiative decay has been measured to be B(LAMBDA --> n + gamma)/(LAMBDA --> anything) = [1.78 +/- 0.24(stat) +/- 0.16(0.14)(syst)] x 10(-3). A low-energy kaon beam was used to produce the LAMBDA hyperons via the reaction K- + p --> LAMBDA + pi-0 at rest. Photons from the signal channel and pi-0 decay were detected with a NaI(Tl) array. The final spectrum contains 287 events after background subtraction, an order of magnitude more events than from the only previous measurement.

The branching ratio for the \ensuremath{\Lambda} weak radiative decay has been measured to be B(\ensuremath{\Lambda}\ensuremath{\rightarrow}n+\ensuremath{\gamma})/(\ensuremath{\Lambda}\ensuremath{\rightarrow}anything) =[1.78\ifmmode\pm\else\textpm\fi{}0.24(stat)${\ifmmode\pm\else\textpm\fi{}}_{0.16}^{0.14}$(syst)]\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$. A low-energy kaon beam was used to produce the \ensuremath{\Lambda} hyperons via the reaction ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$+p\ensuremath{\rightarrow}\ensuremath{\Lambda}+${\mathrm{\ensuremath{\pi}}}^{0}$ at rest. Photons from the signal channel and ${\mathrm{\ensuremath{\pi}}}^{0}$ decay were detected with a NaI(Tl) array. The final spectrum contains 287 events after background subtraction, an order of magnitude more events than from the only previous measurement.

The photon spectrum from ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$d\ensuremath{\rightarrow}\ensuremath{\Lambda}n\ensuremath{\gamma} at rest has been measured for the first time. We obtained the branching ratio, in the end-point region, of (1.89\ifmmode\pm\else\textpm\fi{}0.12\ifmmode\pm\else\textpm\fi{}0.28)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ where the first error is statistical and the second is systematic. We have found that the shape of the photon energy spectrum is consistent with the distribution calculated by Workman and Fearing with \ensuremath{\Lambda}n scattering lengths and effective ranges predicted by the Nijmegen group.

We have measured the weak radiative decay branching ratio (∑+ →pγ)/(∑+ →pπ0). The experiment was carried out at Brookhaven National Laboratory using a low-energy separatedK− beam stopping in liquid hydrogen. The∑+ was tagged by observing the pion fromK−K+p→∑+π− in a range telescope, and the gamma was detected in a segmented NaI detector. The result is (2.81±0.39 −0.43 +0.21 )×10−3, which is consistent with previous measurements. This corresponds to a branching ratio for (∑+ →pγ)/(∑+ → all) of (1.45±0.20 −0.22 +0.11 )×10−3, where the quoted errors are statistical and systematic, respectively. A total of 408 signal events were observed, doubling the previous world total.

Weak as well as pure electromagnetic radiative decays of hyperons are discussed. The radiative decays of excited hyperon states can provide information on the quark wave functions inside the hyperons. The weak (strangeness-changing) decays represent the last low-q2 frontier of weak-interaction physics. The theoretical motivation of these studies is reviewed, as well as the existing experiments. Special emphasis is placed on recent experiments at the Brookhaven AGS and at Fermilab. Radiative K− at rest on the deuteron is also discussed, and new results from Brookhaven are presented.

The photon spectrum from ${K}^{\mathrm{\ensuremath{-}}}$ stopping in liquid hydrogen has been measured with a high-resolution (1.5% FWHM at 300 MeV) NaI(Tl) detector. The branching ratios for ${K}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}\ensuremath{\Lambda}\ensuremath{\gamma} (${E}_{\ensuremath{\gamma}}$=281.4 MeV) and ${K}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}${\ensuremath{\Sigma}}^{0}$\ensuremath{\gamma} (${E}_{\ensuremath{\gamma}}$=219.5 MEV) were obtained. The results are ${\mathit{R}}_{\mathrm{\ensuremath{\Lambda}}\ensuremath{\gamma}}$=(0.86\ifmmode\pm\else\textpm\fi{}0.${07}_{\mathrm{\ensuremath{-}}0.08}^{+0.1}$)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ and ${\mathit{R}}_{\mathrm{\ensuremath{\Sigma}}0\ensuremath{\gamma}}$=(1.44\ifmmode\pm\else\textpm\fi{}0.${20}_{\mathrm{\ensuremath{-}}0.10}^{\ifmmode\pm\else\textpm\fi{}0.12}$)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ where the first error is statistical and the second systematic. These results are not in good agreement with published predictions or with previous \ensuremath{\Lambda}\ensuremath{\gamma} measurements.

A novel method of analysis which eliminates the combinatorial background in searches for states produced in p-barn annihilations and in association with a recoil ..pi../sup -/ is presented. The difference between ..pi../sup -/ and ..pi../sup +/ spectra on p-barn annihilations is the spectrum of the recoiling ..pi../sup -/ or difference spectrum. We applied this analysis to the exclusive channels p-barn..-->..2..pi../sup -/..pi../sup +/, 2..pi../sup -/..pi../sup +/..pi../sup 0/, 3..pi../sup -/2..pi../sup +/. A new prominent state of mass and width approx. =1480 and 100 MeV/c/sup 2/ is present in the first and dominates the third channel. These three channels are interpreted in terms of two-body intermediate states only. The suppression or absence of ''direct'' annihilation is consistent with theoretical models which view the annihilation as a short-range (0.1 fm) phenomenon.

The charged pion spectra in pd→π−π0ps, π−π+ns have been measured. The Doppler broadening of the pion mom entum due to the spectator neutron recoil is at least a factor of two larger than that due to the proton and in disagreement with that expected from the deuteron wave function. This effect and earlier observations on spectators are well described by assuming narrow NN bound states near threshold.

Annihilations of antiprotons from atomic pp and pd states have been extensively examined in search of resonant states in a mass region where the low-lying levels for several anticipated spectroscopies are expect­ ed to be. Spectroscopies based on NN potentials! (quasinuclear states), four-quark composites 2 (bary­ onium), and two-gluon states 3 (glueballs) are some of them. The NN annihilation which is rich in "N-N," quarks, and gluons is expected to couple to these spec­ troscopies. Many searches have been made in the past and more recently at the CERN Low Energy Antipro­ ton Ring (LEAR). 4 All of them have been done in hydrogen and have been sensitive to narrow states, and the results have been negative, or at best incon­ clusive.

We have studied the absorption cross section of antiprotons on Al, Cu, and Pb for T=131.6 and 193.6 MeV. These results are compared with predictions of an optical model fitted to antiproton elastic scattering data on these nuclei and are in agreement with these predictions. The cross sections have an exponential dependence on the mass number A with an exponent of approximately 0.61.

We have measured the ratio of the real to the imaginary parts of the $\overline{p}p$ forward-scattering amplitude in the incident-momentum range 360 to 650 MeV/c. These results are in good agreement with predictions of the Paris nucleon-antinucleon potential model which include spin-flip effects.

Resonant structure is studied in the 1.5-to-1.9-GeV mass region of the neutral four-pion system in the reaction ${\ensuremath{\pi}}^{+}n\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}$ at 6 GeV/c incident momentum. The ${\ensuremath{\rho}}^{0}$ and ${{A}_{2}}^{\ifmmode\pm\else\textpm\fi{}}$ content are determined as a function of the four-pion mass. The $4\ensuremath{\pi}$ mass spectrum is best fitted by two resonances, both of which decay predominantly into ${\ensuremath{\rho}}^{0}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$, each with evidence for an appreciable ${A}_{2}\ensuremath{\pi}$ component.

Data are presented on the reactions π+n → ϱ0 + X and K−p → K∗0 + X at 6.0 and 7.3 GeV/c, respectively. Comparisons are made between these two reactions and with other reactions involving inclusive vector meson production at different energies.

Results on K0 and Λ production in p↑p interactions at 6 GeV are presented. The data are from an exposure of the Argonne 12 ft bubble chamber to a 60% transversely polarized proton beam. Results include data on Λ and K0 inclusive production, and on the reactions p↑p → pΛK+(pΣ0K+). The beam asymmetry parameter for p↑p → K0(K0) + X is determined to be (−0.52 ± 0.12).