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Register a new userStatistical double $Lambda$ hypernuclear formation from $Xi^-$ absorption at rest in light nuclei
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We investigate double $Lambda$ hyperfragment formation from the statistical decay of double $Lambda$ compound nuclei produced in the $Xi^-$ absorption at rest in light nuclei, $^{12}mathrm{C}$, $^{14}mathrm{N}$ and $^{16}mathrm{O}$. We examine the target and the $LambdaLambda$ bond energy dependence of the double $Lambda$ hyperfragment formation probabilities, especially of those double hypernuclei observed in experiments. For the $^{12}mathrm{C}$ ($^{14}mathrm{N}$) target, the formation probabilities of $^{6}_{LambdaLambda}mathrm{He}$ and $^{10}_{LambdaLambda}mathrm{Be}$ ($^{13}_{LambdaLambda}mathrm{B}$) are found to be reasonably large as they are observed in the KEK-E373 (KEK-E176) experiment. By comparison, for $^{16}mathrm{O}$ target, the formation probability of $^{11}_{LambdaLambda}mathrm{Be}$ is calculated to be small with $Delta B_{LambdaLambda}$ consistent with the Nagara event. We also evaluate the formation probability of ${}^{5}_{LambdaLambda}mathrm{H}$ from a $Xi^-$-${}^{6}mathrm{He}$ bound state, ${}^{7}_{Xi}mathrm{H}$.
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Novel data from the $K^{-}_{stop}A$ absorption reaction in light nuclei $^{6,7}$Li and $^{9}$Be are presented. The study aimed at finding $Lambda t$ correlations. Regardless of $A$, the $Lambda t$ pairs are preferentially emitted in opposite directions. Reaction modeling predominantly assigns to the $K^-_{stop}AtoLambda t(N)A$ direct reactions the emission of the $Lambda t$ pairs whose yield is found to range from $10^{-3}$ to $10^{-4}$$/K^-_{stop}$. The experiment was performed with the FINUDA spectrometer at DA$Phi$NE (LNF).
Formation mechanisms of single, twin, and double hypernuclei from Xi^- absorption at rest on 12C are investigated with an refined microscopic transport model, that incorporates the recently developed Quantal Langevin treatment into Antisymmetrized Molecular Dynamics. The quantum fluctuations suppress the formation probability of double hyperfragments to around 10%, which is comparable to the experimental data, and the dynamical formation of twin hyperfragment can be described qualitatively.
$p,Lambda$ emission in coincidence following $K^-$ absorption at rest in nuclei is studied using quantum mechanical scattering theory and nuclear wave functions. $K^-$ absorption is assumed to occur on two protons in the nucleus. In the formalism, emphasis is put on the study of the final state interaction (FSI) effects of $p$ and $Lambda$ with the recoiling nucleus. We include elastic scattering and single nucleon knock-out (KO) channels in the FSI. Calculations are presented for the $^{12}$C nucleus, using shell model wave functions, and without any extra mass modification of the $K^-,pp$ system in the nucleus. Calculated results are presented for the angular correlation distribution between $p$ and $Lambda$, their invariant mass distribution and the momentum spectra of $p$ and $Lambda$. These results are compared with the corresponding experimental measurements cite{agnello}. With only elastic scattering FSI included, the angular correlation distribution and the momentum spectra are found to be in good accord with the corresponding measurements. With full FSI the calculated $p,Lambda$ invariant mass distribution is found to have two peaks, one corresponding to the elastic scattering FSI and another to single nucleon KO FSI. The KO peak agrees fully, in position and shape, with the peak observed in Ref. cite{agnello}. The peak corresponding to elastic scattering FSI does not seem to exist in the measured distribution. Considering that such a two peak structure is always seen in the inclusive ($p$, $p^prime $) and ($e$, $e^prime $) reactions in nuclei at intermediate energies, absence of the elastic scattering peak in the $p,Lambda$ reaction is intriguing.
Fragmentation reactions induced on light target nuclei by protons and light nuclei of energies around 1 GeV/nucleon and below are studied with the latest Los Alamos Monte Carlo transport code MCNP6 and with its cascade-exciton model (CEM) and Los Alamos version of the quark-gluon string model (LAQGSM) event generators, version 03.03, used as stand-alone codes. Such reactions are involved in different applications, like cosmic-ray-induced single event upsets (SEUs), radiation protection, and cancer therapy with proton and ion beams, among others; therefore, it is important that MCNP6 simulates them as well as possible. CEM and LAQGSM assume that intermediate-energy fragmentation reactions on light nuclei occur generally in two stages. The first stage is the intranuclear cascade (INC), followed by the second, Fermi breakup disintegration of light excited residual nuclei produced after INC. Both CEM and LAQGSM account also for coalescence of light fragments (complex particles) up to He4 from energetic nucleons emitted during INC. We investigate the validity and performance of MCNP6, CEM, and LAQGSM in simulating fragmentation reactions at intermediate energies and discuss possible ways of further improving these codes.
Double strangeness $Xi^{-}$ production in Au+Au collisions at 2, 4, and 6 GeV/nucleon incident beam energies is studied with the pure hadron cascade version of a multi-phase transport model. It is found that due to larger nuclear compression, the model with the soft equation of state (EoS) gives larger yields of both single strangeness ($K^{+}$ and $Lambda+Sigma^{0}$) and double strangeness $Xi^{-}$. The sensitivity of the double strangeness $Xi^{-}$ to the EoS is evidently larger than that of $K^{+}$ or $Lambda+Sigma^{0}$ since the phase-space distribution of produced $Xi^{-}$ is more compact compared to those of the single strangeness. The larger sensitivity of the yields ratio of $Xi^{-}$ to the EoS from heavy and light systems is kept compared to that of the single strangeness. The study of $Xi^{-}$ production in relativistic heavy-ion collisions provides an alternative for the ongoing heavy-ion collision program at facilities worldwide for identifying the EoS at high densities, which is relevant to the investigation of the phase boundary and onset of deconfinement of dense nuclear matter.
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