Spin Entanglement for \((p⃗,n⃗)\) Quasi-elastic Scattering

We present the first experimental extraction of nucleon–nucleon spin entanglement in the quasi-elastic \((p, n)\) reactions. Entanglement was quantified using von Neumann entropy \( E\) and concurrence \( C\). The latter was derived from the experimentally measured spin polarization transfer coefficients (PTC, \(Dⱼᵢ\)). Data obtained in 1996 at RCNP using the NTOF and NPOL facilities were used in Bai’s method framework. The \(pn\) entanglements for QES induced by the \(^2\)H\((p,n)\) and \(¹²\)C\((p,n)\) reactions showed a high degree of entanglement, with values of \(~ 0.7 ≤ E ≤ 0.99\), and they had an almost identical value. These findings provide novel experimental insight into nuclear correlations and open up new avenues for investigating nuclear forces and structure through quantum entanglement. Abstract Published by the Jagiellonian University 2026 authors