arXiv subjects

E. Harris

Publications and source records attributed to E. Harris.

7 recordsLinked to original sources

arXiv2025

Quantifying alpha clustering in the ground states of 16-O and 20-Ne

Understanding the role of multi-nucleon correlations in the structure of light nuclei is at the forefront of modern nuclear science. In this letter, we present a quantitative benchmark study of alpha-cluster correlations in the ground states of 16-O and 20-Ne. Experimental data provide direct evidence that the wave functions of the ground states of 16-O and 20-Ne are dominated by alpha-cluster correlations, in agreement with the predictions of sophisticated nuclear structure models. We also provide a new model-independent constraint for the alpha asymptotic normalization coefficient of the 16-O ground state and discuss the implications of these findings on the 12-C(alpha,gamma)16-O reaction, which is of critical importance for nuclear astrophysics.

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arXiv2024

First Experimental Test of the Ratio Method

The ratio is a new reaction observable suggested to extract accurately structure information on halo nuclei. It corresponds to the ratio of differential cross sections for scattering and breakup, which is predicted to remove the uncertainty related to the reaction dynamics. We present here the first experimental test of the method for the 11Be + 12C collision at ELab = 20A MeV performed at Texas A&M University. Differential cross sections for scattering and inclusive one-neutron breakup have been measured with the new detector array BlueSTEAl. The ratio of cross sections is very smooth and independent of the projectile-target interaction, which demonstrates the validity of the ratio method. We extend our analysis to existing 11Be + 208Pb data, confirming that the method works well on any target.

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arXiv2024

First experimental test of the ratio method for nuclear-reaction analysis

Nuclear halos are very exotic quantal structures observed far from stability. Because of their short lifetime, they are mostly studied through reactions. The ratio method offers a new observable: the ratio of angular differential cross sections for breakup and scattering. It is predicted to be much more sensitive to the projectile structure than individual cross sections thanks to its independence of the reaction process. We test this new observable experimentally for the first time considering the collision of 11Be on C at 22.8 MeV/nucleon. We extend this analysis to similar data recently measured on Pb at 19.1 MeV/nucleon. Both analyses confirm the theoretical predictions, which opens the door to a new era in the study of nuclear structure near the neutron dripline. This should prove invaluable in conjunction with the start of FRIB. The ratio method could also be extended to other fields of quantum physics beyond nuclear reactions.

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arXiv2024

Cluster structure of 3$\alpha$+p states in $^{13}$N

Background: Cluster states in $^{13}$N are extremely difficult to measure due to the unavailability of $^{9}$B+$\alpha$ elastic scattering data. Purpose: Using $\beta$-delayed charged-particle spectroscopy of $^{13}$O, clustered states in $^{13}$N can be populated and measured in the 3$\alpha$+p decay channel. Method: One-at-a-time implantation/decay of $^{13}$O was performed with the Texas Active Target Time Projection Chamber (TexAT TPC). 149 $\beta 3\alpha p$ decay events were observed and the excitation function in $^{13}$N reconstructed. Results: Four previously unknown $\alpha$-decaying excited states were observed in $^{13}$N at an excitation energy of 11.3 MeV, 12.4 MeV, 13.1 MeV and 13.7 MeV decaying via the 3$\alpha$+p channel. Conclusion: These states are seen to have a [$^{9}\mathrm{B}(\mathrm{g.s}) \bigotimes \alpha$/ $p+^{12}\mathrm{C}(0_{2}^{+})$], [$^{9}\mathrm{B}(\frac{1}{2}^{+}) \bigotimes \alpha$], [$^{9}\mathrm{B}(\frac{5}{2}^{+}) \bigotimes \alpha$] and [$^{9}\mathrm{B}(\frac{5}{2}^{+}) \bigotimes \alpha$] structure respectively. A previously-seen state at 11.8 MeV was also determined to have a [$p+^{12}\mathrm{C}(\mathrm{g.s.})$/ $p+^{12}\mathrm{C}(0_{2}^{+})$] structure. The overall magnitude of the clustering is not able to be extracted however due to the lack of a total width measurement. Clustered states in $^{13}$N (with unknown magnitude) seem to persist from the addition of a proton to the highly $\alpha$-clustered $^{12}$C. Evidence of the $\frac{1}{2}^{+}$ state in $^{9}$B was also seen to be populated by decays from $^{13}$N$^{\star}$.

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arXiv2023

Radiative decay branching ratio of the Hoyle state

Background: The triple-alpha process is a vital reaction in nuclear astrophysics, characterized by two consecutive reactions [$2\alpha\leftrightarrows{^{8}\rm{Be}}(\alpha,\gamma){^{12}\rm{C}}$] that drive carbon formation. The second reaction occurs through the Hoyle state, a 7.65 MeV excited state in ${^{12}\rm{C}}$ with $J^{\pi}=0^{+}$. The rate of the process depends on the radiative width, which can be determined by measuring the branching ratio for electromagnetic decay. Recent measurements by Kib\'edi et al. conflicted with the adopted value and resulted in a significant increase of nearly 50\% in this branching ratio, directly affecting the triple-alpha reaction. Purpose: This work aims to utilize charged-particle spectroscopy with magnetic selection as a means to accurately measure the total radiative branching ratio ($\Gamma_{\rm{rad}}/\Gamma$) of the Hoyle state in $^{12}{\rm C}$. Methods: The Hoyle state in $^{12}{\rm C}$ was populated via $^{12}\rm{C}(\alpha, \alpha')^{12}\rm{C^{*}}$ inelastic scattering. The scattered $\alpha$ particles were detected using a $\Delta$E-E telescope, while the recoiled $^{12}{\rm C}$ ions were identified in a magnetic spectrometer. Results: A radiative branching ratio value of $\Gamma_{\rm{rad}}/\Gamma\times10^{4}=4.0\pm0.3({\rm stat.})\pm0.16({\rm syst.})$ was obtained. Conclusions: The radiative branching ratio for the Hoyle state obtained in this work is in agreement with the original adopted value. Our result suggests that the proton-$\gamma$-$\gamma$ spectroscopy result reported by Kib\'edi et al. may be excluded.

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arXiv2023

First observation of the $\beta$3$\alpha$p decay of $^{13}\mathrm{O}$ via $\beta$-delayed charged-particle spectroscopy

Background: The $\beta$-delayed proton-decay of $^{13}\mathrm{O}$ has previously been studied, but the direct observation of $\beta$-delayed $\alpha$+$\alpha$+$\alpha$+p decay has not been reported. Purpose: Observing rare 3$\alpha$+p events from the decay of excited states in $^{13}\mathrm{N}^{\star}$ allows for a sensitive probe of exotic highly-clustered configurations in $^{13}$N. Method: To measure the low-energy products following $\beta$-delayed 3$\alpha$p-decay, the TexAT Time Projection Chamber was employed using the one-at-a-time $\beta$-delayed charged-particle spectroscopy technique at the Cyclotron Institute, Texas A&M University. Results: A total of $1.9 \times 10^{5}$ $^{13}\mathrm{O}$ implantations were made inside the TexAT Time Projection Chamber. 149 3$\alpha$+p events were observed yielding a $\beta$-delayed 3$\alpha+p$ branching ratio of 0.078(6)%. Conclusion: Four previously unknown $\alpha$-decaying states were observed, one with a strong $^{9}\mathrm{B(g.s)}+\alpha$ characteristic at 11.3 MeV, one with a $^{9}\mathrm{B}(\frac{1}{2}^{+})+\alpha$ nature at 12.4 MeV, and another two that are dominated by $^{9}\mathrm{B}({\frac{5}{2}}^{+})+\alpha$ at 13.1 and 13.7 MeV. Population of the $\frac{1}{2}^{+}$ state in $^{9}\mathrm{B}$ has been unambiguously seen, cementing the predicted existence of the mirror-state based on the states observed in $^{9}\mathrm{Be}$.

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arXiv2006

Universal Mixing of Quantum Walk on Graphs

We study the set of probability distributions visited by a continuous-time quantum walk on graphs. An edge-weighted graph G is universal mixing if the instantaneous or average probability distribution of the quantum walk on G ranges over all probability distributions on the vertices as the weights are varied over non-negative reals. The graph is uniform mixing if it visits the uniform distribution. Our results include the following: (a) All weighted complete multipartite graphs are instantaneous universal mixing. This is in contrast to the fact that no unweighted complete multipartite graphs are uniform mixing (except for the four-cycle). (b) The weighted claw or star graph is a minimally connected instantaneous universal mixing graph. In fact, as a corollary, the unweighted claw is instantaneous uniform mixing. This adds a new family of uniform mixing graphs to a list that so far contains only the hypercubes. (c) Any weighted graph is average almost-uniform mixing unless its spectral type is sublinear in the size of the graph. This provides a nearly tight characterization for average uniform mixing on circulant graphs. (d) No weighted graphs are average universal mixing. This shows that weights do not help to achieve average universal mixing, unlike the instantaneous case. Our proofs exploit the spectra of the underlying weighted graphs and path collapsing arguments.

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