Quantum Correlations Between Two Giant Dipole Resonances in Ultra-Peripheral Collisions

by Ashik Ikbal (Hiroshima University)

Friday 27 Nov 2026, 10:00 → 11:00 Europe/Budapest

Médiaterem (2. épület)

Giant dipole resonances (GDRs) are among the most prominent collective excitations of atomic nuclei, yet angular correlations between neutrons emitted from GDR-excited nuclei have not been experimentally explored. In ultra-peripheral Au+Au collisions (UPCs), both nuclei can undergo GDR excitation and subsequently separate before decaying into forward neutrons, forming a natural system of two spatially separated nuclear dipole oscillations. This provides a unique opportunity to investigate whether the two GDR excitations evolve independently or exhibit coherent correlations.

We report the first measurement of the angular correlation between GDR neutron emission from the two nuclei in Au+Au UPCs at $\sqrt{s_{NN}} =$ $200$ GeV with STAR. The position-sensitive ZDC-SMD detectors measure the transverse distribution of forward neutrons independently on the East and West sides, from which we reconstruct the first-order neutron-emission directions, $\Psi_1^E$ and $\Psi_1^W$. In mutual electromagnetic dissociation XnXn events, we observe a highly significant nonzero angular correlation, $\langle\cos(\Psi_1^E\Psi_1^W)\rangle$, between the two GDR neutron-emission directions.

To investigate the origin of the observed neutron angular correlation, we compare it with expectations from independent GDR decay, electromagnetic recoil, and a phase-locking scenario connecting the measured neutron directions to the two spatially separated GDR oscillations. This measurement introduces a new experimental approach to studying quantum correlations between collective nuclear excitations and provides a testbed for probing possible entanglement between spatially separated nuclear systems.

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