The two presently available measurements of the low-energy 3H(a, ~)TLi reaction differ from each other by roughly 30% in total magnitude as well as in their determination of the branching ratios for the transition into the two final 7Li bound states. Studying the 3H(e, 7)7Li reaction in the framework of the microscopic Resonating Group Method we were able to reproduce both experimental total cross sections using different effective nucleon-nucleon interactions. However, none of the effective forces yields branching ratios compatible with the data measured by the Toronto-M/inster-collaboration. PACS: 25.55. -e; 25.70.Jj; 21.60.GxThe 3H(e, 7)7Li reaction is a main source for the 7Li production during the big bang nucleosynthesis [1]. Measurements of this reaction rate in the energy range E= 150-600 keV performed by Griffith et al.[2] are consistent with the assumption of an energy independent astrophysical S-factor for the 3H(c~, 7)7Li reaction at stellar energies with a value of S(0)=0.064keV-b [3]. This energy-independent S(E)-factor has been adopted in standard hot big bang model studies [4,5].Recently several microscopic calculations of the 3H(e, 7)VLi reaction at low energies (E < 1 MeV) have been performed in the framework of the Resonating Group Method [6][7][8] or on the basis of a microscopic potential model [9]. While these studies reproduced the experimental data of [2], they do not support the assumption of an energy-independent 3H(e, 7)7Li S-factor at low energies. In agreement with each other these calculations predict the S-factor to increase noticeably with decreasing energy resulting in S(0)~0.10keV.b [6][7][8][9]. Consequently the microscopic studies recommend a higher thermally averaged 3H(c~, 7)7Li reaction rate at astrophysically important temperatures T< 109K than the rate given by Fowler et al. [-3] resulting in a production of 7Li during the big bang which is noticeably higher than currently believed.Motivated by the theoretical predictions a Mfinster-Toronto collaboration [10] has very recently measured the 3H(~, y)VLi cross sections in the energy range E = 80-500 keV. In fact the new experimental data show the predicted increase of the S-factor towards E =0, however, they exceed the data of [-2] by roughly 30% and are also noticeably larger than the microscopically calculated cross sections [6][7][8][9]. An extrapolation of the new experimental data resulted in S (0) ~ 0.14 + 0.02 keV. b [ 10]. Without knowledge of the data of [10] Kajino investigated the dependence of the microscopically calculated 3H(c~, 7)7Li cross sections and those of its analogue reaction 3He(e, 7)TBe on the effective nucleon-nucleon interaction used in these studies [11]. As a main result he observed that the various calculations predict different energy dependences of the Sfactor in the astrophysically important energy regime. In close relation to the study of Kajino [11] we will show in the following that the experimental data of [10] are compatible with the results of the microscopic calculations if other force...

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We have studied the particle-bound levels in the hypernuclei 3A'4H, ]He, ]Li and 8'9Be in the framework of the full microscopic Resonating Group Method (RGM). In a first step we have solved the respective nuclear many-body problem within the RGM. For each hypernucleus we have then performed a static calculation, in which the nuclear degrees of freedom were kept fixed, and a dynamical calculation in which nuclear degrees of freedom were allowed to vary. The differences between these two studies allowed us to investigate nuclear distortion effects caused by the presence of the A-particle. We find the nuclear distortion effects to be inverse proportional to the binding of the nuclear constituents. Thus, the strongest effects are observed for 3aH and for 9aBe. Our dynamical approach does not show the strong overbinding of 5aHe and 9Be as reported in other cluster model studies. Our results for the p-shell hypernuclei agree reasonably well with those obtained in a semi-microscopic Orthogonal Condition Model (OCM) study which used the same effective AN-interaction as employed in our calculation.

We have calculated the BA value of AHe within the framework of the resonating group method using antisymmetrized a+A cluster wave functions and two different effective AN interactions. Differing from previous studies, we allow the a particle to have a nonvanishing D-state admixture.We find that the presence of a D-state component reduces the BA value. Depending on the strength of the D-state admixture, which we adopt from theoretical predictions or analyses of experimental data, we calculate a reduction of the Bf, value of 150-505 keV for the Minnesota AN interaction and of 80-270 keV for the effective AN force of Yamamoto and Bando. The binding energy of the A particle within the "He hypernucleus has been evaluated in several microscopic calculations. ' It is common to all these studies that they describe the AHe ground state as a bound state of the a+A system approximating the a particle ground state by a configuration with all four nucleons occupying (Os) orbitals. The studies differ, however, in their assumptions about the AN potential. Dalitz et al. , ' employing a phenomenological AN potential which fairly well reproduces the Ap low-energy scattering data as well as the binding energy of the hypernuclei "H and "H, calculated a BA value of 5.46 MeV, which is substantially larger than the experimentally observed binding energy (8"=3.12 MeV, Ref. 4). Motivated by the fact that the inclusion of a Majorana exchange operator in the AN potential improves the agreement between calculated BA values and empirically determined results for nuclear matter involving a A particle, Schimert et al. introduced a Majorapa component into the AN potential of Ref. 1. However, they found that this modification has only a minimal effect on the calculated B"value. Recently Yamamoto and Bando derived an effective AN interaction which has been constructed to simulate the 6 matrix calculated for the Nijmegen model D potential. This interaction is implicitly dependent on the Fermi momentum kF. Yamamoto and Bando used the dependence on kF by adjusting it to the experimental BA value of the hypernucleus to be studied. With this procedure it is possible to reproduce the experimental BA value for the AHe nucleus as well as the low-energy spectrurn of other light hypernuclei.Note that similar to the resonating group calculations of Refs. 1 and 2, an overestimation of the B"value is also encountered in variational studies adopting an Urbanatype AN potential and a rather flexible product trial wave function for the AHe ground state. Thus, Bodmer et aI. suggest the existence of a strongly repulsive ANN force.All previous studies' ' ' assumed the four nucleons in the AHe ground state to be coupled to total spin S =0.However, it has experimentally been shown ' that the He ground state has a noticeable D-state admixture with total spin S =2. Speaking in shell model terms, the four nucleons occupy a (Os) (Op) configuration in this latter component rather than a (Os) configuration as in the dominant (S =0) He ground state component. As the ...

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