Manipulation of Giant Multipole Resonances via Vortex $\gamma$ Photons

TL;DR

This paper explores how vortex $b3$ photons can selectively excite and manipulate giant multipole resonances in nuclei, enabling new nuclear physics experiments and applications.

Contribution

It develops a calculation method for photonuclear cross sections with vortex $b3$ photons and demonstrates their ability to selectively excite specific nuclear resonances.

Findings

Forbidden transitions with $J<m_b3$ due to angular momentum conservation.

Selective excitation of isovector giant quadrupole resonance without dipole interference.

Suppression of transitions with $J>m_b3$ at specific angles.

Abstract

Traditional photonuclear reactions primarily excite giant dipole resonances, making the measurement of isovector giant resonances with higher multipolarties a great challenge. In this work, the manipulation of collective excitations of different multipole transitions in nuclei via vortex $\gamma$ photons has been investigated. We develop the calculation method for photonuclear cross sections induced by the vortex $\gamma$ photon beam using the fully self-consistent random-phase approximation plus particle-vibration coupling (RPA+PVC) model based on Skyrme density functional. We find that the electromagnetic transitions with multipolarity $J< m_\gamma$ are forbidden for vortex $\gamma$ photons due to the angular momentum conservation, with $m_\gamma$ being the projection of total angular momentum of $\gamma$ photon on its propagation direction. For instance, this allows for probing the isovector giant quadrupole resonance without interference from dipole transitions using vortex $\gamma$ photons with $m_\gamma=2$. The electromagnetic transitions with $J>m_\gamma$ are strongly suppressed compared with the plane-wave-$\gamma$-photon case, and even vanish at specific polar angles. Therefore, the giant resonances with specific multipolarity can be extracted via vortex $\gamma$ photons. Moreover, the vortex properties of $\gamma$ photons can be meticulously diagnosed by measuring the nuclear photon-absorption cross section. Our method opens new avenues for photonuclear excitations, generation of coherent $\gamma$ photon laser and precise detection of vortex particles, and consequently, has significant impact on nuclear physics, nuclear astrophysics and strong laser physics.