Sensitivity of one-neutron knockout to the nuclear structure of halo nuclei

Background: Information about the structure of halo nuclei are often inferred from one-neutron knockout reactions. Typically the parallel-momentum distribution of the remaining core is measured after a high-energy collision of the exotic projectile with a light target. Purpose: We study how the structure of halo nuclei affects knockout observables considering an eikonal model of reaction. Method: To evaluate the sensitivity of both the diffractive and stripping parallel-momentum distributions to the structure of halo nuclei, we consider several descriptions of the projectile within a halo effective field theory. We consider the case of 11Be, the archetypical one-neutron halo nucleus, impinging on 12C at 68 MeV/nucleon, which are usual experimental conditions for such measurements. The low-energy constants of the description of 11Be are fitted to experimental data as well as to predictions of an ab initio nuclear-structure model. Results: One-neutron knockout reaction is confirmed to be purely peripheral, the parallel-momentum distribution of the remaining core is only sensitive to the asymptotics of the ground-state wavefunction and not to its norm. The presence of an excited state in the projectile spectrum reduces the amplitude of the breakup cross section; the corresponding probability flux is transferred to the inelastic-scattering channel. Although the presence of a resonance in the core-neutron continuum significantly affects the energy distribution, it has no impact on the parallel-momentum distribution. Conclusions: One-neutron knockout cross section can be used to infer information about the tail of the ground-state wavefunction, viz. its asymptotic normalization coefficient (ANC). The independence of the parallel-momentum distribution on the continuum description makes the extraction of the ANC from this observable very reliable.Comment: 10 pages, 4 figures, 4 tables. Accepted for publication in Phys. Rev. C. Compared to the first version, two tests in Sec. IIIC are removed and an appendix is adde

Sensitivity of one-neutron knockout of halo nuclei to their nuclear structure

Halo nuclei are located far from stability and exhibit a very peculiar structure. Due to their very short lifetime, they are often studied through reactions. Breakup reactions are of particular interest since their cross sections are large for these loosely-bound nuclei. Inclusive measurements of breakup--also called knockout reactions--have even higher statistics. In this proceeding, we study which nuclear-structure information can be inferred from the parallel-momentum distribution of the core of one-neutron halo nuclei after the knockout of its halo neutron. In particular, we analyse the influence of the ground-state wavefunction, the presence of excited states within the halo-nucleus spectrum and resonances in the core-neutron continuum. Our analysis shows that such observables are sensitive to the tail of the ground-state wavefunction. The presence of excited state decreases the breakup strength, and this flux is transferred to the inelastic-scattering channel. This indicates a conservation of the flux within each partial wave. We also show that the parallel-momentum distributions are insensitive to the existence of resonances within the continuum, they can thus be ignored in practice. This independence on the continuum argues that the parallel-momentum distributions are ideal observables to extract very precisely the ANCs of halo nuclei.Comment: 6 pages, 3 figures, INPC 2019 proceeding

Sensitivity of one-neutron knockout observables of loosely- to more deeply-bound nuclei

For the last few decades, one-nucleon knockout reactions on light composite targets -- $^9$Be or $^{12}$C -- have been extensively used to study the single-particle (s.p.) structure of nuclei far from stability. To determine which information can be accurately inferred from knockout cross sections, we conduct a sensitivity analysis of these observables considering various s.p. descriptions within the usual eikonal description of the reaction. This work shows that total one-neutron knockout cross sections are not sensitive to the short-range part of the s.p. wave function. Rather, they scale with the mean square radius of the overlap function. Using a perturbative expression of the cross section, we can easily explain our numerical predictions analytically. This analysis suggests that (i) spectroscopic factors extracted from knockout data suffer from sizeable model uncertainties associated with the choice of s.p. wave functions and (ii) knockout reactions constitute an excellent probe of the radius of the nucleus and therefore offer an alternative technique to infer the neutron-skin thickness of exotic nuclei.Comment: 10 pages, 2 figure

Low-energy corrections to the eikonal description of elastic scattering and breakup of one-neutron halo nuclei in nuclear-dominated reactions

Background: The eikonal approximation is a high-energy reaction model which is very computationally efficient and provides a simple interpretation of the collision. Unfortunately, it is not valid at energies around 10 MeV/nucleon, the range of energy of HIE-ISOLDE at CERN and the future ReA12 at MSU. Fukui etal. [Phys. Rev. C 90, 034617 (2014)] have shown that a simple semiclassical correction of the projectile-target deflection could improve the description of breakup of halo nuclei on heavy targets down to 20 MeV/nucleon. Purpose: We study two similar corrections, which aim at improving the projectile-target relative motion within the eikonal approximation, with the goal to extend its range of validity down to 10 MeV/nucleon in nuclear-dominated collisions, viz. on light targets. The semiclassical correction substitutes the impact parameter by the distance of closest approach of the corresponding classical trajectory. The exact continued $S$-matrix correction replaces the eikonal phase by the exact phase shift. Both corrections successfully describe the elastic scattering of one-neutron halo nuclei. Method: We extend these corrections and study their efficiency in describing the breakup channel. We evaluate them in the case of $^{11}\mathrm{Be}$ impinging on $^{12}\mathrm{C}$ at 20 and 10 MeV/nucleon. Results: Albeit efficient to reproduce the elastic channel, these corrections do not improve the description of the breakup of halo nuclei within the eikonal approximation down to 20 MeV/nucleon. Conclusions: Our analysis of these corrections shows that improving the projectile-target relative motion is not the ultimate answer to extend the eikonal approximation down to low energies. We suggest another avenue to reach this goal.Comment: 7 pages, 4 figures, accepted for publication in Phys. Rev.

The communities and their schools. A plea for an involved and active school administration

Der Autor wendet sich gegen die (von Manfred Neumann in Heft 4/03) geäußerten "Überlegungen, Schulträgerschaft in herkömmlicher Form abzuschaffen und auf der Länderebene zu zentralisieren. Bei einem Verlust der Schulträgerschaft würde den Städten und Gemeinden ein immer bedeutsamer werdender Gestaltungsbereich kommunaler Selbstverwaltung verloren gehen. Kommunale Schulträgerschaft ist somit nicht abzuschaffen, sondern vielmehr zu stärken. Mit Blick auf die Qualitätsverbesserung der Schulen sind ortsnahe und nicht ortsferne Entscheidungsstrukturen und -abläufe notwendig. ... Das kommunale Engagement sollte zukünftig vor allem darauf ausgerichtet sein, aktiv-gestaltend auf die Schulentwicklung vor Ort einzuwirken und die handelnden Akteure, das sind vor allem Schulaufsicht, Schulen, Schulträger und Eltern, auf der örtlichen Ebene zu vernetzen. Den Ländern kommt die Aufgabe zu, die rechtlichen und finanziellen Voraussetzungen hierfür zu schaffen. (DIPF/Orig.)Against the demand of abolishing community-controlled school administration (cf Manfred Neumann in Issue 4/03), perspectives are developed concerning the extended community participation. In the sense of an "action network", the extended independence of the schools would be consistently supplemented. (DIPF/Orig.

New perspectives on spectroscopic factor quenching from reactions

The evolution of single-particle strengths as the neutron-to-proton asymmetry changes informs us of the importance of short- and long-range correlations in nuclei and has therefore been extensively studied for the last two decades. Surprisingly, the strong asymmetry dependence of these strengths and their extreme values for highly-asymmetric nuclei inferred from knockout reaction measurements on a target nucleus are not consistent with what is extracted from electron-induced, transfer, and quasi-free reaction data, constituting a two-decade old puzzle. This work presents the first consistent analysis of one-nucleon transfer and one-nucleon knockout data, in which theoretical uncertainties associated with the nucleon-nucleus effective interactions considered in the reaction models are quantified using a Bayesian analysis. Our results demonstrate that, taking into account these uncertainties, the spectroscopic strengths of loosely-bound nucleons extracted from both probes agree with each other and, although there are still discrepancies for deeply-bound nucleons, the slope of the asymmetry dependence of the single-particle strengths inferred from transfer and knockout reactions are consistent within $1\sigma$. Both probes are consistent with a small asymmetry dependence of these strengths. The uncertainties obtained in this work represent a lower bound and are already significantly larger than the original estimates.Comment: 14 pages: 7 pages of the main text (including one and a half of reference) and 7 pages of supplemental material. Accepted for publication in Phys. Rev. Let

Impact of the 6^6Li asymptotic normalization constant onto α\alpha-induced reactions of astrophysical interest

Indirect methods have become the predominant approach in experimental nuclear astrophysics for studying several low-energy nuclear reactions occurring in stars, as direct measurements of many of these relevant reactions are rendered infeasible due to their low reaction probability. Such indirect methods, however, require theoretical input that in turn can have significant poorly-quantified uncertainties, which can then be propagated to the reaction rates and have a large effect on our quantitative understanding of stellar evolution and nucleosynthesis processes. We present two such examples involving $\alpha$-induced reactions, $^{13}$C($\alpha,n)^{16}$O and $^{12}$C$(\alpha,\gamma)^{16}$O, for which the low-energy cross sections have been constrained with $(^6$Li$,d)$ transfer data. In this Letter, we discuss how a first-principle calculation of $^6$Li leads to a 21% reduction of the $^{12}$C$(\alpha,\gamma)^{16}$O cross sections with respect to a previous estimation. This calculation further resolves the discrepancy between recent measurements of the $^{13}$C$(\alpha,n)^{16}$O reaction and points to the need for improved theoretical formulations of nuclear reactions.Comment: 6 pages (including references) and 3 figure

Quantifying uncertainties due to optical potentials in one-neutron knockout reactions

One-neutron knockout reactions have been widely used to extract information about the single-particle structure of nuclei from the valley of stability to the driplines. The interpretation of knockout data relies on reaction models, where the uncertainties are typically not accounted for. In this work we quantify uncertainties of optical potentials used in these reaction models and propagate them, for the first time, to knockout observables using a Bayesian analysis. We study two reactions in the present paper, the first of which involves a loosely-bound halo projectile, $^{11}$Be, and the second a tightly-bound projectile, $^{12}$C. We first quantify the parametric uncertainties associated with phenomenological optical potentials. Complementing to this approach, we also quantify the model uncertainties associated with the chiral forces that can be used to construct microscopic optical potentials. For the phenomenological study, we investigate the impact of the imaginary terms of the optical potential on the breakup and stripping components of the knockout cross sections as well as the impact of the angular range. For the $^{11}$Be case, the theoretical uncertainty from the phenomenological method is on the order of the experiment uncertainty on the knockout observables; however, for the $^{12}$C case, the theoretical uncertainty is significantly larger. The widths of the confidence intervals for the knockout observables obtained for the microscopic study and the phenomenological approach are of similar order of magnitude. Based on this work we conclude that structure information inferred from the ratio of the knockout cross sections, will carry a theoretical uncertainty of at least $20\%$ for halo nuclei and at least $40\%$ for tightly-bound nuclei.Comment: 12 pages (including 2 of supplemental material and 1 of reference), 5 figures, 2 table

Strong and Tight Security Guarantees against Integral Distinguishers

Integral attacks belong to the classical attack vectors against any given block ciphers. However, providing arguments that a given cipher is resistant against those attacks is notoriously difficult. In this paper, based solely on the assumption of independent round keys, we develop significantly stronger arguments than what was possible before: our main result is that we show how to argue that the sum of ciphertexts over any possible subset of plaintext is key-dependent, i.e., the non existence of integral distinguishers

Magnetic susceptibility of insulators from first principles

We present an {\it ab initio} approach for the computation of the magnetic susceptibility $\chi$ of insulators. The approach is applied to compute $\chi$ in diamond and in solid neon using density functional theory in the local density approximation, obtaining good agreement with experimental data. In solid neon, we predict an observable dependence of $\chi$ upon pressure.Comment: Revtex, to appear in Physical Review Lette