Effective polarization in proton-induced $\alpha$ knockout reactions

TL;DR

This paper investigates the effective polarization of residual nuclei in proton-induced alpha knockout reactions, revealing a mechanism that enables polarization without controlling the proton's spin, based on the reaction's selectivity and absorption effects.

Contribution

It introduces a novel understanding of polarization mechanisms in alpha knockout reactions, distinct from proton knockout processes, emphasizing the role of absorption and reaction selectivity.

Findings

Strong absorption leads to selectivity based on orbital angular momentum

Effective polarization occurs without involving spin degrees of freedom

Complete kinematics can be used as a polarization technique

Abstract

The effective polarization of the residual nucleus in the proton-induced $\alpha$ knockout reaction is investigated within the distorted wave impulse approximation framework. The strong absorption of the emitted $\alpha$ particle results in strong selectivity on the reaction "position" depending on the third component of the single-particle orbital angular momentum of the $\alpha$ particle inside a nucleus, hence on the spin direction of the reaction residue. This is caused by a mechanism that is similar to the Maris effect, the effective polarization in the proton-induced proton knockout reactions. However, as a distinct feature of the effective polarization in the $\alpha$ knockout process, the spin degrees of freedom of the reacting particles play no role. The $\alpha$ knockout process with complete kinematics can be a useful polarization technique for the residual nucleus, without actively controlling the spin of the proton.