Spectroscopy of 28Al(Lambda), 12B(Lambda), 7He(Lambda) by the (e,e'K+) Reaction

Abstract

Hypernuclear spectroscopy by the (e, e ′ K +) reaction is one of the powerful tools to investigate precise structures of hypernuclei and to study ΛN interaction. The second generation hypernuclear experiment at Jefferson Laboratory Hall C, E01-011 experiment, was successfully performed in 2005, introducing the following two novel experimental improvements based on the first pilot experiment performed in 2000. 1) The High resolution and large acceptance Kaon Spectrometer (HKS) which was specialized for the hypernuclear experiment was newly constructed and installed. The HKS was designed to obtain the momentum resolution of 2 × 10 −4 (∆p/p) for a central momentum of 1.2 GeV/c and to have a large acceptance of 16 msr with the splitter magnet which deflects a kaon and a scattered electron at very forward angles to the opposite directions. 2) The detection angle of scattered electrons was optimized to suppress a huge electron background from Bremsstrahlung and Møller scattering which had been main background for the electron spectrometer in the first generation experiment. The scattered electron spectrometer was vertically tilted by 8 degree (Tilt method). Thanks to these new configurations, both the energy resolution and the hypernuclear yield were significantly improved and spectroscopic studies were performed for various hypernuclei. The achieved energy resolution of ∼ 500 keV (FWHM) is the best resolution among hypernuclear reaction spectroscopy. The missing mass scale was calibrated with the well-known masses of Λ/Σ 0 hyperons with a CH 2 target. Systematic errors of the absolute mass scale and its linearity were carefully evaluated from the detailed Monte Carlo simulation. Missing mass spectrum of a typical p-shell hypernucleus, 12 Λ B, was obtained and two major peaks were interpreted as the states with a Λ hyperon bound in s and p orbits. Obtained binding energies and cross sections for these states agree with the results of the first pioneering experiment, E89-009, and the shell model predictions. By the (e, e ′ K +) reaction, the first sd-shell hypernucleus, 28 Λ Al, was successfully measured thanks to the HKS and the Tilt method. Two prominent peaks were interpreted as corresponding to states that a Λ hyperon bound in s and p orbits, respectively. It was found that the obtained binding energy of −17.57 ± 0.02 (stat.) ± 0.24 (sys.) MeV for the ground state was bound deeper than that of the mirror symmetric hypernucleus, 28 Λ Si, and shell model calculation. The success of 28 Λ Al spectroscopy is a gateway to heavier mass hypernuclear spectroscopy with electron beam. A neutron-rich hypernucleus, 7 Λ He, was also studied with sufficient statistics. The binding energy of the ground state was determined as −5.68 ± 0.03 (stat.) ± 0.22 (sys.) MeV reliably for the first time. This result provides new information on charge symmetry breaking effect in the ΛN interaction.

Criação de Valor e Assemblage: Conexões do Universo Nerd

“…Por exemplo, crianças consideradas nerds, que demonstravam interesse por determinada disciplina no âmbito escolar e tiravam boas notas, poderiam, por isso, ser ridicularizadas por seus colegas (KENDALL, 1999). Matos (2013) explica que a difusão mundial da cultura norte-americana contribuiu para configurar um estereótipo ligado à imagem do nerd: um indivíduo que usa roupas fora de moda, de jeito atrapalhado e envergonhado, óculos e aparelhos dentários. Adicionalmente, a ideia de que o nerd seria alguém com dificuldade de lidar com a responsabilidade que a vida adulta exige e de se inserir no padrão imposto pela sociedade explicaria certo preconceito e rejeição direcionados a este indivíduo (ANDEREGG, 2008).…”