In single A hypernuclei, a A hyperon can occupy any orbital in the hypernucleus since it is free from the Pauli exclusion principle due to its additional quantum number strangeness. Due to the Pauli blocking effect, which suppresses the mesonic decay mode A ->N(pi) in the nuclear medium, hypernuclei larger than (5/A)He decay mainly through the nonmesonic channel, AN-> NN, where the A mass excess of 176 MeV is converted into kinetic energy of a final state of nucleons emerging above the Fermi see. This nonmesonic decay mode is assumed to proceed via the exchange of virtual mesons, and the large momentum transfer involved in the reaction leads to a mechanism that is sensitive to the short-distance behaviour of the amplitude and thus raises the possibility that the exchange of mesons heavier than the pion may play an important role. The fairly large momentum transfer also raises the hope that this reaction turns out to be insensitive to nuclear structure details and thus creates a suitable channel to investigate the weak decay mechanism.

Orientador: Carlos Ourivio Escobar / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-05T00:48:53Z (GMT). No. of bitstreams: 1 Gomes_RicardoAvelino_D.pdf: 22856845 bytes, checksum: ff49da476ee952e261dde1c21ce27f56 (MD5) Previous issue date: 2005 / Resumo: Apresentamos uma investigação sobre o decaimento semileptônico ?0??+µ - ?µ. Observamos este decaimento pela primeira vez com nove eventos identificados, utilizando para tal a linha de feixe e os detectores do experimento KTeV no Fermilab. O decaimento é normalizado pelo modo ?0??+e- ?e, resultando em uma razão das taxas de decaimento G(?0??+µ - ?µ)/G(?0??+e- ?e) igual a ( 1,8+0,7-0,5(estat.) ± 0,2(sist.) ) x 10-2 com 68,27% C.L., que se tomou a medida oficial da colaboração KTeV: Em uma análise independente, também utilizamos o decaimento dominante ?0? ?p0(???p-) como modo de normalização, o que corroborou o resultado principal. Realizamos ainda, uma nova medida da razão de ramificação do modo ?0??+e- ?e com base em 1139 eventos e normalizada pelo decaimento ?0??p0(???p-). Os resultados estão em pleno acordo com o modelo a quarks com simetria SU(3) de sabor / Abstract: We report an investigation of the semileptonic decay ?0??+µ - ?µ. This decay was observed for the first time with nine identified events using the KTeV beam line and detector at Fermilab. The decay is normalized to the ?0 beta decay mode and yields a value for the ratio of decayrates G(?0??+µ - ?µ)/G(?0??+e- ?e) igual a ( 1,8+0,7-0,5(stat.) ± 0,2(syst.) ) x 10-2 at the 68,27% confidence level, being the official measurement of KTeV Collaboration. We also used the dominant decay ?0? ?p0(???p-) as normalization mode in an independent analysis which corroborated with the main result. In addition, a new measurement of the ?0??+e- ?e branching ratio is presented, based on 1139 events and normalized to the ?0??p0(???p-) decay mode. The results are in agreement with the SU(3) flavor symmetric quark model / Doutorado / Física das Particulas Elementares e Campos / Doutor em Ciências