Breakup of ${}^6\mathrm{Li}+p$ at near-barrier energies and the effect on elastic scattering

Exclusive breakup measurements have been performed for the ${}^6\mathrm{Li}+p$ system in inverse kinematics at ${}^6\mathrm{Li}$ incident energies of 25 and 29 MeV. The results are considered in the Continuum Discretized Coupled-Channels framework, together with elastic scattering data at 16, 20, 25, and 29 MeV, obtained simultaneously in the same experiment and reported previously. Good agreement between data and theory is observed, interpreted as evidence for strong coupling to the continuum. The direct and sequential (via the ${}^6\mathrm{Li}{3}_1{}^{+}$ resonance) breakup cross sections are found to be equally large at the higher incident energies but the dominant effect on the elastic scattering is due to coupling to the sequential breakup. This effect remains dominant even at the lowest energy of 16 MeV, despite the negligible cross section for excitation of the resonance at this low incident energy.

Figure 1

Upper figure: Two-dimensional plot at 25 MeV (4.17 MeV/u) representing coincident events of the two ${}^6\mathrm{Li}$ breakup fragments. Energy of $\alpha$ particles (energy $\alpha$) vs energy of deuterons or recoiling protons (energy $d\left(p\right)$). The $\alpha$ particles were detected in the MAGNEX spectrometer over the angular range ${\theta }_{\mathrm{lab}}=0$ to ${10}^{\circ }$, while the deuterons and the recoiling protons were detected in a silicon detector fixed at ${\theta }_{\mathrm{lab}}=5^{\circ }$. The observed loci for $\alpha -p$ coincidences and $\alpha -d$ coincidences due to breakup of ${}^6\mathrm{Li}$ on protons and $\alpha -d$ coincidences due to breakup on carbon are indicated on the figure. Lower figure: Superimposed on the experimental spectrum, denoted by the black dots, are simulated events for the first kinematic solution of the resonant and direct breakup, denoted by the red and green dots, respectively.

Figure 2

Same as in Fig. 1 but for 29 MeV (4.83 MeV/u).

Figure 3

Exclusive breakup spectrum, acquired in the $5^{\circ }$ silicon detector with a ${\mathrm{CH}}_2$ target at 25 MeV ($\alpha -d$ or $p$ coincidences). The results of simulations of the first kinematic solution for $\alpha -d$ coincidences are denoted by the dot-dashed red line. The peak at the left corresponds to $\alpha$ coincidences with the recoiling protons. The spectrum in green represents an exclusive spectrum acquired with a carbon target, appropriately normalized. The dashed blue line represents a simulation of the ${}^6\mathrm{Li}+p\to {}^5\mathrm{Li}+d\to \alpha +p+d$ reaction, arbitrarily normalized (see text).

Figure 4

Same as in Fig. 3 but for 29 MeV (4.83 MeV/u).

Figure 5

Experimental and theoretical angular distributions in the center of mass for the breakup of ${}^6\mathrm{Li}$ on a proton target at 25 MeV (4.17 MeV/u). The experimental data, referring to the first kinematic solution, are shown by the filled red stars. The solid black line represents the full CDCC calculation. The dot-dashed red line denotes the result of a CDCC calculation taking into account coupling to the $3_1{}^{+}$ resonant state only.

Figure 6

Same as in Fig. 5 but for 29 MeV (4.83 MeV/u).

Figure 7

Elastic scattering of ${}^6\mathrm{Li}$ + p at 16 MeV (2.67 MeV/u). The data are compared with full CDCC calculations (solid black line), one-channel calculations (dot-dashed blue line), and calculations with coupling to direct breakup only (dashed green line). The uncertainty of the experimental data is included in the size of the stars.

Figure 8

Same as in Fig. 7 but for 20 MeV (3.33 MeV/u).

Figure 9

Same as in Fig. 7 but for 25 MeV (4.17 MeV/u).

Figure 10

Same as in Fig. 7 but for 29 MeV (4.83 MeV/u).