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Momentum distributions and spatial signatures of proton halos in the sd shell

Taslima S. C. Diba1,*, Carlos A. Bertulani1,2,†, and Ronaldo V. Lobato3,‡

  • *Contact author: tdiba@leomail.tamuc.edu
  • †Contact author: carlos.bertulani@etamu.edu
  • ‡Contact author: lobato@cbpf.br
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Phys. Rev. C 114, 044607 – Published 6 October, 2026

DOI: https://doi.org/10.1103/b9lc-dkp9

Abstract

We perform a theoretical study of intermediate-energy quasifree one-proton knockout reactions on proton targets. Single-particle wave functions constrained by the experimental proton separation energies are employed to calculate longitudinal momentum distributions, one-proton removal cross sections, and full momentum-space profiles for P26, S27, and Ar31 nuclei. To establish robust criteria to identify proton halos, the analysis is extended beyond the traditional momentum-width approach by investigating the spatial extension of the valence proton through root-mean-square radii and the probability that the proton resides outside the core nucleus, P(r>Rcore). We also examine Coulomb-barrier systematics, mirror-nucleus comparisons, realistic spectroscopic mixtures, finite experimental momentum resolution, and uncertainties associated with the proton separation energy. Our calculations indicate that proton-halo structure cannot be identified reliably from a single observable. A consistent interpretation emerges only when momentum distributions, spatial observables, Coulomb effects, and many-body structure are considered simultaneously. Within the present model, P26 exhibits the strongest proton-halo signatures, while S27 retains pronounced halolike features despite its larger Coulomb barrier. The more strongly confined Ar31 provides a useful comparison and illustrates the progressive suppression of halo observables with increasing binding and core charge.

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Phys. Rev. C 114, 044607– Published 6 October, 2026
  • Received 6 August 2026
  • Accepted 22 September 2026
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