Neutron-neutron scattering length from the $^6$He$(p,pα)nn$ reaction
Matthias Göbel, Thomas Aumann, Carlos A. Bertulani, Tobias Frederico, Hans-Werner Hammer, Daniel R. Phillips
备注：
Paper + supplemental material: 20+11 pages, 7+4 figures. Paper restructured, further explanations and discussions added, results unchanged. Accepted for publication in Phys. Rev. C
We propose a novel method to measure the neutron-neutron scattering length using the $^{6}$He$(p,pα)nn$ reaction in inverse kinematics at high energies. The method is based on the final state interaction (FSI) between the neutrons after the sudden knockout of the $α$ particle. We show that the details of the neutron-neutron relative energy distribution allow for a precise extraction of the $s$-wave scattering length. We present the state-of-the-art in regard to the theory of this distribution. The distribution is calculated in two steps. First, we calculate the ground-state wave function of $^6$He as a $αn n$ three-body system. For this purpose we use Halo effective field theory (Halo EFT), which also provides uncertainty estimates for the results. We compare our results at this stage to model calculations done with the computer code FaCE. In a second step we determine the effects of the $nn$ FSI using the $nn$ t-matrix. We compare these FSI results to approximate FSI approaches based on standard FSI enhancement factors. While the final distribution is sensitive to the $nn$ scattering length, it depends only weakly on the effective range. Throughout we emphasize the impact of theoretical uncertainties on the neutron-neutron relative energy distribution, and discuss the extent to which those uncertainties limit the extraction of the neutron-neutron scattering length from the reaction $^{6}$He$(p,pα)nn$.
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以32S+90Zr和32S+96Zr为基准反应，研究了库仑势垒以下聚变过程中中子转移的作用.一个完整的耦合通道计算的聚变激发函数已进行了两个系统，通过使用多中子转移耦合的中子更丰富的反应。通过NTFus程序计算，包括Zagrebaev半经典模型下的中子转移通道的耦合，在亚势垒能量下很好地再现了32 S +96 Zr的熔合截面的增强。我们发现40Ca+90Zr和40Ca+96Zr熔合激发函数的效应相似。
