Rapid fluctuation of the tensor polarization of deuteron beams behind carbon foils and their relation to the resonances in the isospin-breaking $^{12}{\rm C}(d,\alpha_{2})^{10}{\rm B}^{*}$ reaction

TL;DR

This study investigates rapid fluctuations in the tensor polarization of deuteron beams transmitted through carbon targets, linking these fluctuations to resonances in an isospin-breaking nuclear reaction and modeling them with Gaussian cross-sections.

Contribution

It introduces a novel analysis connecting polarization fluctuations to specific nuclear resonances and provides a model for predicting polarization outcomes based on target properties.

Findings

Fluctuations in tensor polarization correspond to narrow nuclear resonances.

Removal of deuterons in specific spin states relates to the formation of particular nitrogen states.

Predicted polarization ranges for carbon targets suggest potential for polarization control.

Abstract

Rapid fluctuations are observed in the tensor-polarization $p_{zz}$ of deuteron beams forward-transmitted through graphite targets. Unpolarized 9.50 to 18.60\,MeV beams from the K\"oln tandem accelerator were utilized, and the polarization behind seven 36 to 188\,mg/cm$^{2}$ targets was measured with a polarimeter based on the $^{3}{\rm He}(\vec{d},p)^{4}{\rm He}$ reaction. Due to the chosen relation between the areal target densities and the initial beam energies $E_{\rm in}$, the seven sets of $p_{zz}(E_{\rm in})$ can be combined in a common plot as a function of $E_{\rm in}$. This allows one to understand $p_{zz}$, measured behind the 188\,mg/cm$^{2}$ target at $E_{\rm in}$=18.6\,MeV, as resulting from the sequence of differential polarization production $\Delta p_{zz}(E)/\Delta E$ during energy degradation in the target from $E$=18.60 to 9.50\,MeV. The rapid fluctuations of $\Delta p_{zz}(E)/\Delta E$$p_{zz}$ are described by 51 Gaussian-distributed cross-sections removing deuterons either in the $m=0$ or in the $m=\pm 1$ state from the beam. The 51 fitted central energies $E_{0}$ with a single exception agree with the energies of the narrow peaks in the excitation functions of the weak, isospin-breaking $^{12}{\rm C}(d,\alpha_{2})^{10}{\rm B}^{*}(1.74\,{\rm MeV},J^{\pi}=0^{+},T=1)$ reaction with population of the second excited $^{10}{\rm B}$ state via intermediate excited $^{14}$N states. Strong evidence is found that removal of deuterons in the $m=0$ ($m=\pm 1$) state from the beam leads to the formation of $^{14}$N states of established positive (negative) parity. As an application, the removal cross-section functions allow to calculate $p_{zz}$ achievable with carbon targets for initial beam energies $E_{\rm in}$ between 18.60 and 9.50\,MeV and $E_{\rm out}$ given by the areal target density. Carbon layers in a sandwich technique would enable $p_{zz}$ between -0.4 and +0.3.