Multistep Coulomb & Nuclear Breakup of Halo Nuclei

Multistep Coulomb & Nuclear Breakup of Halo Nuclei Ian Thompson, Surrey University, United Kingdom; with Surrey: Jeff Tostevin, John Mortimer, Brian Cross Porto: Filomena Nunes

Breakup Dynamics • Recoil & Finite Range of projectile vertex. • Final-state (partial wave) interference • Nuclear and Coulomb mechanisms • Core excitation (initial and/or dynamic) • Final-state interactions: • between halo fragments (needed if resonances) • between fragments and target (needed if close in) • Multistep Processes(higher order effects)

Previous Reaction Theories • Semiclassical Theory (1st order eikonal) • DWBA: • Prior DWBA, DWIA (FSI between fragments to all orders) • Post DWBA (FSI fragment-target to all orders) • Time-dependent Schrödinger Eqn. solutions • Adiabatic (high energy) • e.g. Glauber (eikonal); Bremstrahlung. • Coupled Channels • CRC: expand on bound states • CDCC: expand on continuum bin states

Adiabatic Few-body Model • Projectile excitation energy << beam energy • so scattering parametric for projectile inner coordinates [with eikonal dynamics, this gives Few-Body Glauber] • Neglect halo-nucleon target interaction • eg for neutron halo in Coulomb breakup • Gives soluble 3-body  (RC Johnson et al, PRL 79 (1997) 2771) • Use adiabatic  in post T-matrix integral • Gives Bremstrahlung integral for Coulomb breakup

Deuteron breakup via Coulomb Bremstrahlung Forward-angle proton energy distributions from J.A. Tostevin et al, Phys. Letts. B424 (1998) 219; Phys. Rev. C57 (1998) 3225. Agreement is best for heavier targets: dominated by Coulomb. Now need to include nuclear breakup mechanisms equally well!

Improving on Bremstrahlung • Need: • Nuclear mechanisms • Non-adiabatic effects • Proton halo breakup e.g. 8B • Try CDCC: Coupled Discretised Continuum Channels • Proposed by Rawitscher, developed by Kamimura group. • Treat Coulomb and Nuclear mechanisms • Need to check convergence of long-range Coulomb process! • All higher-order effects with a (r,R,L) reaction volume • Can calculate fragment coincident angular distributions

Discretised Continuum bins • The breakup continuum is integrated in `bins’, so the continuum is represented by an orthonormal basis set: Continuum bins for 8B (`up arrows’ for DWBA are shown)

Couplings between Bins Not: Surface peaked. Semiclassical methods assume these Coulomb form factors too. But: The Nuclear couplings extend as far as the ground state 0(r), as do the deviations of the Coulomb couplings from 1/R+1 . Continuum-continuum couplings have yet longer range.

Compare, in Adiabatic Few-Body Model, with Bremstrahlung integral Compare, in first-order PWBA model, with semiclassical theory Testing CDCC Convergence

Multistep Coulomb only Multistep Nuclear Only SubCoulomb 8B + 58Ni @ ND from F.M. Nunes and I.J. Thompson, Phys. Rev. C59 (1999) 2652

Coulomb+nuclear Effect of continuum-continuum couplings Coulomb+Nuclear Multistep Green lines: no continuum-continuum couplings

8B angular distribution 7Be angular distributions Convergence: max bin Erel

lab(7Be) = 20 + 21 deg lab(7Be) = 30 deg Breakup energy distributions Preliminary!!

Conclusions • CDCC method is useful for two-cluster halo nuclei: • Finite-range & recoil included • Coulomb and nuclear both approach convergence • Large radii and partial-wave limits needed, but feasible now • Non-adiabatic treatment of Coulomb breakup • Multistep effects manifest from all final-state interactions • Still need equivalent method for three-cluster projectiles (e.g. two neutron halo nuclei)

Multistep Coulomb & Nuclear Breakup of Halo Nuclei