ИСТИНА

Superfluid He-4 can serve as a tool for neutrino [1] and dark matter detection [2]. Low-energy neutrino interaction with superfluid He-4 can take place in the form of coherent elastic neutrino-atom scattering (CEvAS) [3] - a process that has not been observed so far. The first experimental study of CEvAS is under preparation in the National Center for Physics and Mathematics in Sarov [4]. Using a high-intensity tritium neutrino source and a superfluid He-4 detector, it will have a rich potential to test the neutrino physics of Standard Model and beyond it at unprecedentedly low energies. For example, one of the observable effects of beyond-Standard-Model physics in CEvAS can be neutrino millicharge and magnetic moment [5]. In this study, we have applied the formalism of open quantum systems [6] to describe the evolution of the recoil helium atom after neutrino scattering on superfluid helium. In particular, we have obtained the Lindblad equation for a helium atom with an initial recoil energy of higher than 2 meV — the energy enough to knock the atom out from the condensate.  [1] R.E. Lanou, H.J. Maris, and G.M. Seidel, Detection of solar neutrinos in superfluid helium, Phys. Rev. Lett. 58 (1987) 2498. [2] You, Y., Smolinsky, J., Xue, W., Matchev, K., Saab, T., Gunther, K., and Lee, Y. Signatures and detection prospects for sub-GeV dark matter with superfluid helium. JHEP 2023(7) (2023)  1-31. [3] M. Cadeddu, F. Dordei, C. Giunti, K. Kouzakov, E. Picciau and A. Studenikin, Potentialities of a low-energy detector based on 4He evaporation to observe atomic effects in coherent neutrino scattering and physics perspectives, Phys. Rev. D 100 (2019) no.7, 073014 [arXiv:1907.03302 [hep-ph]]. [4] А.А. Yukhimchuk, А.N. Golubkov, I.P. Maximkin, et al., Physics of hydrogen isotopes, FIZMAT 1 (2023) 5 (in Russian). [5] G. Donchenko, K. Kouzakov, and A. Studenikin, Elastic neutrino-atom scattering as a probe of neutrino millicharge and magnetic moment, JETP Lett. 117 (2023) 879. [6] H.-P. Breuer, F. Petruccione, The Theory of Open Quantum Systems, Oxford University Press, 2002.