### Speaker

### Description

The electromagnetic processes of annihilation of $(e^+ e^-)$ pairs, produced

in high-energy nucleus-nucleus collisions, into heavy lepton pairs are

theoretically studied in the one-photon approximation, using the technique of

helicity amplitudes . For the process $e^+e^- \rightarrow \mu^+\mu^-$, it is

shown that -- in the case of the unpolarized electron and positron -- the final

muons are also unpolarized but their spins are strongly correlated. For the

final $(\mu^+ \mu^-)$ system, the structure of triplet states is analyzed and

explicit expressions for the components of the spin density matrix and

correlation tensor are derived. It is demonstrated that here the spin correlations

of muons have the purely quantum character, since one of the Bell-type

incoherence inequalities for the correlation tensor components is always violated.

In doing so, it is established that the qualitative character of the muon spin

correlations does not change when involving the additional contribution of the

weak interaction of lepton neutral currents through the virtual $Z^0$ boson.

On the other hand, the theoretical investigation of spin structure for the two-photon

process $\gamma \gamma \rightarrow e^+e^-$ ( where the photon pairs, in

particular, may be emitted in relativistic heavy-ion and hadron-nucleus collisions )

is performed as well. Here -- quite similarly to the process

$e^+e^- \rightarrow \mu^+\mu^-$ -- in the case of unpolarized photons the final

electron and positron remain unpolarized, but their spins prove to be strongly

correlated. Explicit expressions for the components of the correlation tensor

and for the relative fractions of singlet and triplet states of the final $(e^+ e^-)$

system are derived. Again, one of the Bell-type incoherence inequalities for the

correlation tensor components is always violated and, thus, spin correlations of

the electron and positron have the strongly pronounced quantum character.

Analogous considerations can be wholly applied as well, respectively, to the

annihilation process $e^+ e^- \rightarrow \tau^+ \tau^-$ and to the two-photon

processes $\gamma \gamma \rightarrow \mu^+ \mu^-$, $\gamma \gamma
\rightarrow \tau^+ \tau^-$, which become possible at considerably higher energies.

Centralised submission by Collaboration | Presenter name already specified |
---|---|

Content type | Theory |