Peripheral fragmentation of 8 B nuclei in nuclear emulsion at an energy of 1.2 GeV per nucleon
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MENTARY PARTICLES AND FIELDS Experiment
Peripheral Fragmentation of 8 В Nuclei in Nuclear Emulsion at an Energy of 1.2 GeV per Nucleon ´ 1), 3) , P. I. Zarubin1)* , I. G. Zarubina1), R. Stanoeva1), 2) , V. Bradnova1), S. Vokal 1) 1) N. A. Kachalova , A. D. Kovalenko , A. I. Malakhov1), G. I. Orlova4), N. G. Peresadko4) , P. A. Rukoyatkin1), V. V. Rusakova1), E. Stan5) , M. Haiduc5) , S. P. Kharlamov4), I. Tsakov2), and T. V. Shchedrina1) Received April 13, 2006; in final form, August 7, 2006
Abstract—The results obtained by studying the charge topology of fragments produced in the peripheral dissociation of relativistic 8 B nuclei in emulsion are presented. Fifty-five events of the peripheral dissociation of a 8 B nucleus in events where there was no production of target-nucleus fragments and mesons (“white stars”) were selected. A leading contribution of the 8 B → 7 Be + p mode, which has the lowest energy threshold, was revealed on the basis of these events. Information about the branching ratios for dissociation modes characterized by a higher multiplicity was obtained. The dissociation of the 7 Be core in 8 B bears resemblance to the dissociation of a free 7 Be nucleus. The transverse-momentum distributions of fragments originating from the 8 B → 7 Be + p dissociation mode were obtained. For these distributions, a small mean value of PT∗ = 52 ± 5 MeV/c in the c.m. frame suggests a low binding energy of the outer proton in the 8 B nucleus. An indication of a strong azimuthal correlation of the fragments 7 Be and p was found. PACS numbers: 21.45.+v, 23.60.+e, 25.10.+s DOI: 10.1134/S1063778807070113
INTRODUCTION A low energy of proton separation from 8 B is a feature peculiar to this nucleus. This is indicative of the possible existence in 8 B of a proton halo separated in space from the core in the form of a 7 B nucleus. In 8 B → 7 Bе relativistic-fragmentation reactions, so weak a binding leads to a rather narrow momentum distribution of 7 B nuclei [1, 2]. In just the same way as in the case of exotic nuclei, the possible increase in the radius of the 8 B nucleus because of the proton halo could lead to a relative enhancement of its interaction cross section. However, available experimental data show no enhancement of this type. In view of this circumstance, it is highly desirable to study in 1)
Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia. 2) Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Blvd. Tsarigradsko chausse 72, BG-1784 Sofia, Bulgaria. 3) ˘ ´ ˘ Safarik University, Kosice, Slovak Republic. 4) Lebedev Institute of Physics, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 117924 Russia. 5) Institute of Space Sciences, P.O. Box MG-23, 76-900, Bucharest-Maguerele, Romania. * E-mail: [email protected]
more detail the 8 B nucleus, especially characteristic features of its cluster structure. By way of example, a proton halo may arise from the deuteron cluster formed by an unpaired neutron and the outer proton. This possibility is suggest
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