The breakup dynamics of helium dimer

We demonstrate a significant impact of continuum-continuum couplings in the helium dimer on both elastic and breakup (dissociation) cross sections for the reaction 4 H e 2 + 4 H e → 4 H e + 4 H e + 4 H e , employing the Continuum Discretized Coupled Channels (CDCC) formalism with different model potentials, including Gaussian and exponential interactions. The resulting differential angular distributions elastic and breakup cross sections as well as elastic phase shifts are systematically analyzed and compared with available theoretical results in the literature. We find that the breakup cross section exhibits a threshold at zero energy, approaching zero as the center-of-mass energy tends to zero, while the elastic cross section approaches a finite constant value. The continuum-continuum couplings are shown to significantly modify the elastic phase shifts and to reduce their sensitivity to the specific form of the dimer potential. These findings highlight the essential role of continuum-continuum couplings in accurately describing low-energy three-body scattering and dissociation processes in weakly bound systems such as the helium dimer.