Within the self-consistent nuclear many-body theory and the Green function method, the task of calculation probabilities of the E1- transition between the first $2^+ and 3^-$  -excited levels in nuclei with pairing is considered. For the first time, calculations were performed for a long chain of even-even tin isotopes. For the characteristics of both phonons and E1- transitions between excited states, the well-known Fayans energy density functional was used. A good description of the available experimental data has been obtained for the reduced probabilities of E1 transitions between the first one-phonon states for isotopes ^116-124Sn, rather than for isotopes ¹¹²Sn and ¹¹⁴Sn. Possible causes of this discrepancy are discussed, the most probable of which is the appearance of deformation in the ground or excited states. It is shown that for the explanation of E1-transition experiments in ^116−124Sn it is necessary  to take into account new (i.e. dynamic three-quasiparticle) ground state correlations (GSC), Fig.1. Therefore, a self-consistent theoretical analysis of transitions between excited states is very promising for low-energy physics.

Fig.1. The reduced probabilities of E1-transition between one-phonon states B(E1)($3^-_1 \rightarrow 2^+_1$), e²fm².
           The results of the calculation with and without dynamic ground state correlations are given. Experimental data [1, 2]

[1] R. Wirowski, M. Shimmer, L. Eser, S. Alberos, K.O. Zell and P. von Brentano, Nucl. Phys. A 586, 427 (1995).
       [2] L. I. Govor, A. M. Demidov, O. K. Zhuravlev, I. V. Mikhajlov and E. Y. Shkuratova, Sov. J. Nucl. Phys. 54, 196 (1991).

M. I. Shitov, S. P. Kamerdzhiev, S. V. Tolokonnikov
JETP Letters 117, issue 1 (2023)