Application of Nuclear Track Emulsion in Search for the Hoyle State in Dissociation of Relativistic 12 C Nuclei
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NOLOGY OF NUCLEAR MATERIALS
Application of Nuclear Track Emulsion in Search for the Hoyle State in Dissociation of Relativistic 12C Nuclei1 A. A. Zaitseva,b and P. I. Zarubina,b,* a
Veksler and Baldin Laboratory of High Energy Physics, Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia bLebedev Physical Institute, Russian Academy of Sciences, Moscow, Russia *e-mail: [email protected] Received June 6, 2018; revised June 6, 2018; accepted July 6, 2018
Abstract—In dissociation in nuclear track emulsion of 4.5 and 1 A GeV/c 12C nuclei, the formation of triplets of α particles in the Hoyle state (the second excited state 0+) is observed. This state is identified by the invariant mass, calculated from pair angles in the α triples in approximation of conservation of momentum per nucleon of the parent nucleus. An estimate of the contribution of the Hoyle state to the dissociation of 12C → 3α is 10–15%. Keywords: nuclear emulsion, dissociation, invariant mass, relativistic fragments, 12C nucleus, Hoyle’s state, alpha particles DOI: 10.1134/S106377881809020X
INTRODUCTION Exposures of nuclear track emulsion (NTE) to newly formed beams of relativistic nuclei, which began in the 1970s at the JINR Synchrophasotron of and LBL Bevalac (Berkeley, USA), since the early 2000s have found a continuation at the JINR Nuclotron in the BECQUEREL Experiment [1]. A topical application of the NTE technique consists in studying the structure of light nuclei, including radioactive ones, on the basis of advantages of the relativistic approach [2, 3]. Distributions of peripheral interactions of studied nuclei over channels of dissociation into relativistic charged fragments convey features of their structure. This possibility is lacking in electronic experiments. The NTE makes it possible to observe the breakdown of relativistic nuclei up to a coherent dissociation, in which the target nuclei are not visibly destroyed in an obvious way (the example in Fig. 1). Events of this kind, called “white” stars, account for several percent of the total number of interactions. They are the most valuable for interpreting the structure, since in them distortion of an initial state of a nucleus that experiences dissociation can be considered minimal. Among the key results of the BECQUEREL experiment is determination of contribution of unstable 8Be and 9B nuclei in dissociation of relativistic nuclei 10,11C and 10B. The meaning of this fact is as follows. As is known, 1 The article was translated by the authors.
nucleosynthesis involving 8Be and 9B is suppressed because of absence of bound ground states. Nevertheless, this circumstance does not prevent the substantial contribution of 8Be and 9B. The obtained experience of reconstruction of 8Be and 9B is applicable to the search for relativistic decays of the Hoyle state (HS). The status of the experimental and theoretical study of the second excited state of the 12C nucleus is presented in the review [4]. This excitation is named after the astrophysicist F. Hoyle, who postulated its
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