Speaker
Description
The BECQUEREL experiment is aimed at solving topical problems in nuclear cluster physics [1]. Due to its unique sensitivity and spatial resolution the used method of nuclear track emulsion (NTE) makes it possible, to study in a unified approach multiple final states arising in the dissociation of relativistic nuclei. The focus is a concept of α-particle Bose-Einstein condensate ($\alpha$BEC) - the extremely cold state of several S-wave $\alpha$-particles near the coupling threshold. The unstable $^8$Be nucleus is described as 2$\alpha$BEC, and the $^{12}$C(0$^+_2$) excitation or Hoyle state (HS) as 3$\alpha$BEC. The state $^{16}$O(0$^+_6$) above the 4$\alpha$ threshold, considered as 4$\alpha$BEC, can sequentially decay $^{16}$O(0$^+_6$) → $\alpha$$^{12}$C(0$^+_2$) or $^{16}$O(0$^+_6$) → 2$^8$Be(0$^+$).
In NTE layers longitudinally exposed to relativistic nuclei the invariant mass of ensembles of He and H fragments can be determined from the emission angles in the approximation of conservation of initial momentum per nucleon. $^8$Be and HS decays, as well as $^9$B → $^8$Be$p$ decays, are identified in fragmentation of light nuclei by an upper constraint on the invariant mass [2]. Photos and videos of characteristic interactions are available on the site http://becquerel.jinr.ru/. This approach has been used to identify $^8$Be and HS and search for more complex states of $\alpha$BEC in fragmentation of medium and heavy nuclei. Recently, based on the statistics of dozens of $^8$Be decays, an enhancement in the probability of detecting $^8$Be in an event with an increase in the number of relativistic $\alpha$-particles in it was found [3]. A preliminary conclusion is drawn that the contributions from $^9$B and HS decays also increase. The exotically large sizes and lifetimes of $^8$Be and HS suggest the possibility of synthesizing $\alpha$BEC by successively connecting the emerging $\alpha$-particles 2$\alpha$ → $^8$Be, $^8$Be$\alpha$ → $^{12}$C(0$^+_2$), $^{12}$C(0$^+_2$)$\alpha$ → $^{16}$O(0$^+_6$), 2$^8$Be → $^{16}$O(0$^+_6$) and further with a decreasing probability at each step, when $\gamma$-quanta or recoil particles are emitted. Nowadays, the main task is to clarify the relation between the appearance of $^8$Be and HS and the multiplicity of $\alpha$-ensembles and to search on this basis for decays of the $^{16}$O(0$^+_6$) state. In this regard, the BECQUEREL experiment aims to measure multiple channels of $^{84}$Kr fragmentation at energies up to 950 MeV per nucleon. There are a sufficient number of NTE layers, the transverse scanning of which on a motorized microscope makes it possible to achieve the required statistics. A status of the ongoing research is presented.
- P.I. Zarubin, Lect. Notes in Phys. 875, Clusters in Nuclei, Volume 3. Springer Int. Publ., 51 (2013); DOI: 10.1007/978-3-319-01077-9_3, arXiv: 1309.4881.
- D.A. Artemenkov et al., Eur. Phys. J. A 56 (2020) 250; DOI: 10.1140/epja/s10050-020-00252-3, arXiv: 2004.10277.
- A.A. Zaitsev et al., Phys. Lett. B 820 (2021) 136460; DOI 10.1016/j.physletb.2021.136460, arXiv: 2102.09541.
| Section | 1. Nuclear structure: theory and experiment |
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