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Entanglement entropy for π+p elastic scattering using a spin-density matrix

Seung-il Nam*

  • *Contact author: sinam@pknu.ac.kr
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Phys. Rev. C 113, 015203 – Published 21 January, 2026

DOI: https://doi.org/10.1103/7vps-vt18

Abstract

The π+p elastic scattering process is studied, using an effective Lagrangian approach that incorporates the s-, u-, and t-channel amplitudes, including Δ++(1232), Δ0(1232), neutron, and ρ0 contributions. By constructing the spin-density matrices from the scattering amplitudes, the von Neumann (entanglement) entropy is derived and associated with the spin degrees of freedom of the initial and final state particles. The entropy is computed by performing a partial trace over the spin subsystems, and its behavior is analyzed as a function of the center-of-mass energy W and scattering angle θ. It is found that entropy exhibits nontrivial angular and energy dependences, reflecting the interplay among resonance contributions and background amplitudes. In particular, the Δ++ region shows relatively low entanglement, suggesting spin coherence dominated by the specific resonant contribution, while the background contributions increase entropy due to mixed spin configurations. These results indicate that entanglement entropy can serve as a novel probe into the quantum structure of hadronic scattering amplitudes, providing complementary insights beyond conventional cross-section analyses.

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Phys. Rev. C 113, 015203– Published 21 January, 2026
  • Received 18 June 2025
  • Revised 1 July 2025
  • Accepted 8 December 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.

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