The magnetic moment of the $\Lambda$ hyperon has been measured at the Brookhaven cosmotron. Polarized $\Lambda$ hyperons were produced by (1.02 ± 0.015)-GeV/c ${\pi }^{+}$ mesons incident on a Be target in the reaction ${\pi }^{+}+n\to K^{+}+\Lambda$. After passing through a strong pulsed longitudinal magnetic field, the $\Lambda$ decay and the $K^{+}$ were observed in parallel-plate spark chambers in which the decay proton and/or the decay ${\pi }^{-}$ could stop to facilitate momentum measurement. The spark chamber was triggered by an electronic counter system where the $K^{+}$ mesons were identified by velocity, specific ionization, and decay. The precession of the $\Lambda$ polarization was detected by observing the rotation of its asymmetric decay distribution projected onto a plane perpendicular to the $\Lambda$ trajectory. Measurement of the direction and magnitude of the angle of rotation about the magnetic field direction gave the moment and its sign. Based on 3868 field-on events with an average value of the ratio $\int \frac{\overrightarrow{\mathrm{H}}·d\overrightarrow{1}}{p_{\Lambda }}$ of about 800 kG cm / (GeV/c), the magnetic moment of the $\Lambda$ hyperon was found to be -0.73 ± 0.18 nuclear magneton.

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