Nuclear and Particle Physics Colloquium 18

The development of radioactive-ion beams in the mid 80s has enabled us to explore the nuclear landscape far from stability. This led to the discovery of exotic nuclear structures such as halo nuclei [1]. These neutron-rich nuclei exhibit a large matter radius in comparison to their isobars. This peculiarity is due to the strongly clusterised structure of halo nuclei: they can be seen as a dense core to which one or two valence neutrons are loosely bound. By tunnel eff

ect, these neutrons exhibit a high probability of presence at a large distance from the other nucleons and hence form a sort of halo around the core.

Being far away from stability, halo nuclei cannot be studied through usual spectroscopic techniques and we must rely on indirect methods, such as reactions, to infer information about their structure [2]. Breakup reaction is probably the most used tool to study halo nuclei. In this reaction, the halo neutrons dissociate from the core through the interaction with a target. In order to get valuable information from breakup observables, a good understanding of the reaction process is required and its sensitivity to the properties of the projectile structure must be assessed.

In this presentation, I will review the basics of the theoretical description of breakup reactions involving halo nuclei and present results obtained within the Dynamical Eikonal Approximation (DEA) for the breakup of 11Be, the archetypical one-neutron halo nucleus, and explain what kind of information can be inferred from usual breakup observables [3,4].

Based on these results, I will present a new way to extract information about the structure of halo nuclei through reactions. The basic idea of this new method is to perform the ratio of angular distributions for breakup and scattering [5]. These two mechanisms exhibit very similar features that depend mostly on the projectile-target interaction [6]. Taking the ratio of these two cross sections hence removes most of the dependence on the reaction mechanism, leading to an observable much more sensitive to the projectile internal structure than usual reaction cross sections [5,7]. The ratio method should thus help us better understand the structure of nuclear matter far from stability.

References:

[1] I. Tanihata et al., Phys. Lett. B (1985).

[2] I. Tanihata, J. Phys. G 22, 157 (1996).

[3] D. Baye, P. Capel, and G. Goldstein, Phys. Rev. Lett. 95, 082502 (2005).

[4] G. Goldstein, D. Baye, and P. Capel, Phys. Rev. C 73, 014615 (2006).

[5] P. Capel, R. C. Johnson, F. M. Nunes, Phys. Lett. B 705, 112 (2012).

[6] P. Capel, M. S. Hussein, D. Baye, Phys. Lett. B 693, 448 (2010).

[7] P. Capel, R. C. Johnson, F. M. Nunes, Phys. Rev. C 88, 044602 (2013).