A study has been made of the $K-p$ interactions in a hydrogen bubble chamber. Cross sections have been determined at 25-MeV/c intervals in the range 75 to 275 MeV/c $K^{-}$ lab momentum. About 90% of the hyperons were produced by $K^{-}-p$ interactions at rest, and these events were used to calculate at-rest production ratios and hyperon lifetimes.

The observed hyperon decay rates from this experiment yield the following hyperon mean lifetimes: ${\tau }_{{\Sigma }^{-}}=(1.58\mathrm{}\pm 0.06)\times {10}^{-10\mathrm{}}$ sec, ${\tau }_{{\Sigma }^{+}}=(0.765\mathrm{}\pm 0.04)\times {10}^{-10\mathrm{}}$ sec, and ${\tau }_{\Lambda }=(2.69\mathrm{}\pm 0.11)\times {10}^{-10\mathrm{}}$ sec. The observed branching ratios for ${\Sigma }^{+}$ and $\Lambda$ decay are $\frac{({\Sigma }^{+}\to {\pi }^{+}+n)}{\left[\right({\Sigma }^{+}\to {\pi }^{+}+n)+({\Sigma }^{+}\to {\pi }^0+p\left)\right]}=0.490\mathrm{}\pm 0.024$, and $\frac{(\Lambda \to {\pi }^{-}+p)}{\left[\right(\Lambda \to {\pi }^{-}+p)+(\Lambda \to {\pi }^0+n\left)\right]}=0.643\mathrm{}\pm 0.016$.

The $K^{-}-p$ interactions occurring at rest yield hyperon production rates in the ratio ${\Sigma }^{-}:{\Sigma }^{+}:{\Sigma }^0:\Lambda =0.447:0.208:0.281:0.064\mathrm{}$.

The in-flight $K^{-}-p$ interactions are dominated by the hyperon production process. Analysis of the elastic-scattering angular distribution shows that the nuclear part of the amplitude has a large imaginary part and a real part consistent with zero. The absorption cross section is nearly geometric for $s$-wave interactions throughout the observed laboratory momentum range. Angular distributions for all the $K^{-}-p$ interactions are quite consistent with isotropy.

An $s$-wave zero-effective-range analysis of the $K^{-}-p$ interactions has been carried out. Two sets of parameters were found that give acceptable fits to all the data. The ${\chi }^2$ test gives probability of 48% for solution 1, and 8% for solution 2. The scattering lengths which best fit the data of this experiment are $A_0=-0.220+2.742i$ for the isotopic spin-0 channel, and $A_1=0.019+0.384i$ for the isotopic spin-1 channel.

• Received 30 March 1962

DOI:https://doi.org/10.1103/PhysRev.127.1305