PNPI was an active participant in the study of rare hyperon decays at the FNAL
hyperon beams. The beginning of the PNPI – FNAL collaboration goes back to the year 1981. The basis of the collaboration was the PNPI suggestion of an experiment for studying the S
-
-hyperon b
-decay in view of a strange situation in investigation of this process. The existing at that time experimental information on the asymmetry in the decay of polarized S
-
-hyperons was in contradiction with the Cabibbo model prediction while the b
-decay of the other baryon octet members were well described by this model. The most difficult task in the study of the reaction S
-
®ne  was the separation from the 103 times more intense reaction S
-
®np-. To overcome this difficulty, the PNPI group proposed to use a Transition Radiation Detector sensitive to electrons and less sensitive to p
mesons. This detector occurred to be a very important part of the E715 experiment dedicated to the study of the S
-
-hyperon b
-decay. The measured electron asymmetry in the b
-decay of polarized S
-
proved to be in good agreement with the Cabibbo model prediction. So, the long time contradiction between experiment and theory was settled in favour of the Cabibbo model.
Following the PNPI initiative, in 1986 a new experiment (E761) was proposed. Existing at that time experimental data revealed a strong asymmetry in the radiative decay S
+®
pg
, and none of the theoretical attempts succeeded in explanation of this fact. In the E761 experiments, the data on the radiative decay of S
+
®
pg
were obtained with high statistical accuracy. A possible admixture of the more intensive background reaction S
+
®
pp
0
®
p2g
was suppressed with a new specially developed Transition Radiation Detector. The E761 data demonstrated that the asymmetry in the S
+-hyperon radiative decay was indeed large and negative, the observed decay rate being in agreement with the world data. In the E761 experiment, the data on the radiative decays X
-
®
S
-
g
and W
-
®
X
-
g
were also obtained and the polarization of S
+
and S
-
produced in the interaction of high energy protons with nuclei was measured.
In addition to the main program of the E715 and E761 experiments, the magnetic moments of S
-, S
+
,  +, and X
-
hyperons were also measured.
(For more detail review see article "Study of rare hyperon decays " in PNPI report of
the High Energy Physics Division "Main Scientific Activities 1971-1996").
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