Yields of hydrogen isotopes in stopped-pion absorption by light nuclei
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CLEI Experiment
Yields of Hydrogen Isotopes in Stopped-Pion Absorption by Light Nuclei Yu. B. Gurov, V. S. Karpukhin, L. Yu. Korotkova, S. V. Lapushkin, T. I. Leonova, R. V. Pritula, B. A. Chernyshev* , and T. D. Schurenkova National Research Nuclear University MEPhI, Kashirskoe sh. 31, Moscow, 115409 Russia Received January 18, 2017
Abstract—The spectra of p, d, and t charged particles produced in stopped-pion absorption by nuclei are analyzed. Respective measurements were performed for 17 nuclei by means of a semiconductor spectrometer. A phenomenological model developed previously for medium-heavy and heavy nuclei was applied to describing the spectra and yields of charged particles originating from light nuclei (6,7 Li, 9 Be, 10,11 B, and 12 C). The contribution of intranuclear clusters (such as pp and 3,4 He) to pion absorption was estimated. DOI: 10.1134/S106377881705009X
1. INTRODUCTION The nature of charged-particle production in the absorption of stopped π − mesons by nuclei has yet to be clarified conclusively. For negatively charged pions, a dominant mechanism of absorption on an intranuclear quasideuteron nucleon pair does not lead to the production of charged particles. Therefore, it is necessary to consider rarer processes, such as absorption by intranuclear proton–proton (pp) pairs and heavier clusters and secondary interactions. Stopped-pion absorption by pp pairs is almost one order of magnitude less probable than absorption by proton–neutron (pn) pairs [1, 2]. In stopped-pion absorption by the helium isotopes 3 He and 4 He, the contribution of the π − +3 He → n + d (13%) and π − +4 He → n + t (19%) two-particle reaction channels is substantially smaller than the contribution of two-nucleon processes [1–3]. For heavier nuclei, the situation is less clear because of the enhancement of the contribution of secondary processes proceeding after pion absorption by intranuclear clusters. From the experimental point of view, the reaction mechanism manifests itself most clearly in correlation data. However, the probability for the emission of primary particles without secondary interactions is low for all target nuclei, with the exception of extremely light ones; therefore, it is difficult to extend the results obtained in correlation measurements to the whole reaction. Inclusive measurements make it possible to obtain information about the whole process, but their *
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interpretation requires invoking theoretical models in order to take into account secondary interactions. However, these models provide only a qualitative description of experimental data—in many cases, distinctions may reach several tens percent [2, 4, 5]. At the same time, some qualitative conclusions on the absorption process can be drawn from a phenomenological analysis of experimental data. In [6–10], our group developed a phenomenological model that describes satisfactorily the yields of p, d, and t particles and 3,4 He nuclei on mediumheavy and heavy nuclei [11]. The model is based on experimental information
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