Dynamics of hypernuclear nonmesonic weak decay

Abstract

Abstract. Simple and coincidence spectra of the NM weak decay of light hypernuclei have been evaluated in a systematic way for the first time. We have only considered 1N induced processes, neglecting entirely the events induced by 2N emission, as well as the effects of the FSIt's. As the theoretical framework we have used the IPSM with three different parametrizations for the transition potential. The comparison with data strongly suggests that the soft π + K exchange model could be a good starting point to describe the dynamics in the NM weak decays of s-and p-shell hypernuclei.Keywords: nonmesonic weak decay; one-meson-exchange: independent-particle shell model PACS: 21.80.+a, 13.75.Ev, 27.10.+hThe Λ-hypernuclei are mainly produced by the (K − , p − ) and the (p + , K + ) strong reactions, and disintegrate by the weak decay with the ratewhere Γ M is decay rate for the mesonic (M) decay Λ → πN, and Γ NM is the rate for the nonmesonic (NM) decay, which can be induced either by one bound nucleon (1N), Γ 1 (ΛN → nN), or by two bound nucleons (2N), Γ 2 (ΛNN → nNN), where N = p, n i.e.,In both cases the mass is changed by 176 MeV, and the strangeness by ΔS = −1, which makes the NM weak process to be the most radical modification of an elementary particle within the nuclear envarment, and offers the best opportunity to scrutinize the strangeness-changing force between hadrons. On the other hand, the hypernuclear physics leads to the extension of the radioactivity domain to three dimensions (N, Z, S), which, because of the additional binding due to the Λ-hyperon, modifies the neutron drip line, and is even richer in elements than the ordinary (N, Z) domain. (For instance, while the one-neutron separation energy in 20 C is 1.01 MeV, it is 1.63 MeV in 21 Λ C, and 6 Λ He is bound while 5 He is unbound.) Because of this glue attribute of hypernuclei the ΛN interaction is closely related to the inquiry on the existence of strange quark matter and its fragments, and strange stars (analogues of neutron stars), which makes the NM decay also relevant for astrophysics and cosmology. The schematic representation of the two decay channels, when the pertinent dynamics is described by OME potentials, is shown in Fig. 1. This is the most frequently used Nuclear Structure and Dynamics 2012

Nonmesonic Weak Decay Spectra of Light Hypernuclei

“…The dominant role is being played by the exchange of pion and kaon mesons (PKE). We have recently shown that the π + K meson exchange potential with soft dipole form factors (SPKE) reproduces fairly well both s-shell [10], and p-shell [11] NMWD.…”

“…In the evaluation of Γ N M , and the corresponding spectra, are used the Shell Model (SM) and the Fermi Gas Model (FGM) for Γ 1 (within the two-particle phase space) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][20][21][22][23], while for Γ 2 (within the three-particle phase space) only the later model has been employed so far [20][21][22][23].…”

Superasymmetric fission of heavy nuclei induced by intermediate-energy protons

“…It is important to emphasize that the CRISP code has been used to simulate nuclear reactions of several kinds, such as those induced by protons [33][34][35], photons [19,27,[36][37][38], electrons [39,40], or hypernuclei [21,41,42], with energies from 50 MeV up to 3.5 GeV, and on nuclei with masses going from A = 12 up to A = 240 and with several observables: spallation products, strange particles, fission products, hyperon-decay particles, fragment mass, and atomic number distributions. The code has been applied in the study for development of nuclear reactors [43][44][45].…”

Estudo de processos a energias médias e altas pelo método Monte Carlo

“…Nas altas energias, o fóton apresenta uma componente hadrônica na sua função de onda que aumenta a seção de choque de interação com os nucleons. De acordo com o modelo de dominância vetorial (VMD) [18][19][20][21], no meio nuclear, a seção de choque totalé dominada pela produção de O código CRISP tem obtido bons resultados no estudo de reações induzidas por prótons [45,46,66,67], fótons [17,44,55,68], elétrons [69,70] e processos que dependem da cascata intranuclear, como a produção de káon [71] e o decaimento de hypernúcleos [72][73][74]. Os processos de evaporação/fissão estudados com o código obtiveram pela primeira Chapter 1.…”