Speaker
Valery Lyuboshitz
(Joint Institute for Nuclear Research ( Dubna ))
Description
Spin correlations for the $\Lambda \Lambda$ and $\Lambda \bar{\Lambda}$ pairs, generated in relativistic heavy-ion collisions, and related angular correlations at the joint registration of space-parity nonconserving hadronic decays of two hyperons are theoretically analyzed. These correlations give important information about the character and mechanism of multiple processes, and the advantage of the $\Lambda \Lambda$ and $\Lambda \bar{\Lambda}$ systems over other ones is conditioned by the fact that the P-odd decays $\Lambda \rightarrow p + \pi^-$ and $\bar{\Lambda} \rightarrow \bar{p} + \pi^+$ serve as effective analyzers of spin states of the $\Lambda$ and $\bar{\Lambda}$ particles. The correlation tensor components can be derived by the method of "moments" -- as a result of averaging the combinations of trigonometric functions of proton ( antiproton ) flight angles over the double angular distribution of flight directions for products of two decays. The properties of the "trace" $T$ of the correlation tensor ( a sum of three diagonal components ), which determines the angular correlations as well as the relative fractions of the triplet states and singlet state of respective pairs, are discussed . In the present talk, spin correlations for two identical particles ($\Lambda \Lambda$) and two non-identical particles ($\Lambda \bar{\Lambda}$) are generally considered from the viewpoint of the conventional model of one-particle sources. In the framework of this model, correlations vanish at enough large relative momenta. However, under these conditions -- especially at ultrarelativistic energies -- in the case of two non-identical particles ( $\Lambda \bar{\Lambda}$ ) the two-particle annihilation sources ( two-quark, i.e. quark--antiquark, and two-gluon ones ) start playing a noticeable role and lead to the difference of the correlation tensor from zero. In particular, such a situation may arise, when the system passes through the "mixed phase" and -- due to the multiple production of free quarks and gluons in the process of deconfinement of hadronic matter -- the number of two-particle sources strongly increases.
