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Background: One-nucleon knockout reactions provide insightful information on the single-particle structure of nuclei. When applied to one-neutron halo nuclei, they are purely peripheral, suggesting that they could be properly modeled by describing the projectile within a halo effective field theory (halo-EFT).Purpose: We reanalyze the one-neutron knockout measurements of $^{11}\mathrm{Be}$ and $^{15}\mathrm{C}$---both one-neutron halo nuclei---on beryllium at about 60 MeV/nucleon. We consider halo-EFT descriptions of these nuclei which already provide excellent agreement with breakup and transfer data.Method: We include a halo-EFT description of the projectile within an eikonal-based model of the reaction and compare its outcome to existing data.Results: Excellent agreement with experiment is found for both nuclei. The asymptotic normalization coefficients inferred from this comparison confirm predictions from ab initio nuclear-structure calculations and values deduced from transfer data.Conclusions: Halo-EFT can be reliably used to analyze one-neutron knockout reactions measured for halo nuclei and test predictions from state-of-the-art nuclear structure models on these experimental data.

Background: One-neutron removal reactions are used to study the single-particle structure of unstable nuclei, and in particular the exotic halo nuclei. The eikonal reaction theory (ERT) has been developed by Yahiro, Ogata, and Minomo [Prog. Theor. Phys. 126, 167 (2011)10.1143/PTP.126.167] to include dynamical effects, which are missing in the usual eikonal description of these reactions. Encouraging results have been obtained for total breakup cross sections in comparison to more elaborate reaction models. Purpose: We extend these comparisons to more differential breakup cross sections expressed as functions of the relative energy or parallel momentum between the core and halo neutron. Method: ERT predictions of these cross sections are compared to state-of-the-art calculations. Results: The hypotheses upon which the ERT is based are confirmed and their range of validity is made clearer. The actual ordering of the evolution operators affects ERT differential cross sections and a specific choice leads to excellent agreement with the reference calculation. Dynamical effects in the treatment of the neutron-target interaction can be significant in the parallel-momentum observable. Conclusions: The role of the different interactions in the dynamics of breakup reactions of one-neutron halo nuclei are better understood and improvements to the ERT are suggested., SCOPUS: ar.j, info:eu-repo/semantics/published

The clear separation of scales observed in halo nuclei between the extended halo and the compact core makes these exotic nuclei a perfect subject for Effective Field Theory (EFT). Such description leads to a systematic expansion of the core-halo Hamiltonian, which naturally orders the nuclear-structure observables. In this short review, I show the advantage there is to include Halo-EFT descriptions within precise models of reactions. It helps identifying the nuclear-structure observables that matter in the description of the reactions, and enables us to easily bridge predictions of nuclear-structure calculations to reaction observables. I illustrate this on breakup, transfer and knockout reactions with 11Be, the archetypical one-neutron halo nucleus., Comment: Reviewed version accepted for publication

We present a determination of optical potentials using the double-folding method based on chiral effective field theory nucleon-nucleon interactions at next-to-next-to-leading order combined with dispersion relations to constrain the imaginary part. This approach is benchmarked on O16-O16 collisions, and extended to the C12-C12 and C12-O16 cases. Predictions derived from these potentials are compared to data for elastic scattering at energies up to 1000 MeV, as well as for fusion at low energy. Without adjusting parameters, excellent agreement with experiment is found. In addition, we study the sensitivity of the corresponding cross sections to the nucleon-nucleon interactions and nuclear densities used., SCOPUS: ar.j, info:eu-repo/semantics/published

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For one-neutron halo nuclei, the cross sections for elastic scattering and breakup at intermediate energy exhibit similar angular dependences. The Recoil Excitation and Breakup (REB) model of reactions elegantly explains this feature. It also leads to the idea of a new reaction observable to study the structure of loosely-bound nuclear systems: the Ratio. This observable consists of the ratio of angular distributions for different reaction channels, viz. elastic scattering and breakup, which cancels most of the dependence on the reaction mechanism; in particular it is insensitive to the choice of optical potentials that simulate the projectile-target interaction. This new observable is very sensitive to the structure of the projectile. In this article, we review a series of previous papers, which have introduced the Ratio Method and its extension to low beam energies and proton-halo nuclei., SCOPUS: ar.j, info:eu-repo/semantics/published

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., 6 pages, 3 figures, INPC 2019 proceedings

Background: Aside from being a one-neutron halo nucleus, $^{15}\mathrm{C}$ is interesting because it is involved in reactions of relevance for several nucleosynthesis scenarios.Purpose: The aim of this work is to analyze various reactions involving $^{15}\mathrm{C}$, using a single structure model based on halo effective field theory (halo EFT) following the excellent results obtained in [P. Capel et al., Phys. Rev. C 98, 034610 (2018)].Method: To develop a halo-EFT model of $^{15}\mathrm{C}$ at next to leading order (NLO), we first extract the asymptotic normalization coefficient (ANC) of its ground state by analyzing $^{14}\mathrm{C}(d,p)^{15}\mathrm{C}$ transfer data at low energy using the method developed in [J. Yang and P. Capel, Phys. Rev. C 98, 054602 (2018)]. Using the halo-EFT description of $^{15}\mathrm{C}$ constrained with this ANC, we study the $^{15}\mathrm{C}$ Coulomb breakup at high (605 MeV/nucleon) and intermediate (68 MeV/nucleon) energies using eikonal-based models with a consistent treatment of nuclear and Coulomb interactions at all orders, and which take into account proper relativistic corrections. Finally, we study the $^{14}\mathrm{C}(n,\ensuremath{\gamma})^{15}\mathrm{C}$ radiative capture.Results: Our theoretical cross sections are in good agreement with experimental data for all reactions, thereby assessing the robustness of the halo-EFT model of this nucleus. Since a simple NLO description is enough to reproduce all data, the only nuclear-structure observables that matter are the $^{15}\mathrm{C}$ binding energy and its ANC, showing that all the reactions considered are purely peripheral. In particular, it confirms the value we have obtained for the ANC of the $^{15}\mathrm{C}$ ground state: ${\mathcal{C}}_{1/{2}^{+}}^{2}=1.59\ifmmode\pm\else\textpm\fi{}0.06\phantom{\rule{4pt}{0ex}}{\mathrm{fm}}^{\ensuremath{-}1}$. Our model of $^{15}\mathrm{C}$ provides also a new estimate of the radiative-capture cross section at astrophysical energy: ${\ensuremath{\sigma}}_{n,\ensuremath{\gamma}}(23.3\phantom{\rule{0.16em}{0ex}}\mathrm{keV})=4.66\ifmmode\pm\else\textpm\fi{}0.14\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{b}$.Conclusions: Including a halo-EFT description of $^{15}\mathrm{C}$ within precise models of reactions is confirmed to be an excellent way to relate the reaction cross sections and the structure of the nucleus. Its systematic expansion enables us to establish how the reaction process is affected by that structure and deduce which nuclear-structure observables are actually probed in the collision. From this, we can infer valuable information on both the structure of $^{15}\mathrm{C}$ and its synthesis through the $^{14}\mathrm{C}(n,\ensuremath{\gamma})^{15}\mathrm{C}$ radiative capture at astrophysical energies.

The ratio method has been developed to improve the study of one-neutron halo nuclei through reactions. By taking the ratio of angular distributions for two processes, viz. breakup and elastic scattering, this new observable is nearly independent of the reaction mechanism and hence much more sensitive to the projectile structure than the cross sections for each single process. We study the extension of the ratio method to proton-rich nuclei and also explore the optimum experimental conditions for measuring this new observable. We compare accurate dynamical calculations of reactions for proton-rich projectiles to the prediction of the ratio method. We use the dynamical eikonal approximation that provides good results for this kind of reactions at intermediate energy. Our tests for 8B, an archteypical one-proton halo nucleus, on Pb, Ni, and C targets at 44 MeV/nucleon show that, the ratio works less well than for neutron halos due to the non-negligible Coulomb interaction between the valence proton and the target. Nevertheless, the ratio method still provides pertinent information about nuclear structure on the proton-rich side of the valley of stability. Interestingly the method is not affected if energy ranges-or bins-are considered in the projectile continuum. This makes the ratio easier to measure experimentally by increasing the breakup cross section. We also extend our analysis to 17F, 25Al, and 27P, whose study is of interest to both nuclear astrophysics and nuclear structure. We show that, albeit less precise than for one-neutron halo nuclei, nuclear-structure information can be inferred from the ratio method applied to exotic proton-rich nuclei. In particular, when the valence proton is loosely bound in an $s$ or $p$ orbital, viz. for proton halo nuclei, detailed structure information can be obtained through this new reaction observable.

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 Be11, the archetypical one-neutron halo nucleus, impinging on C12 at 68 MeV/nucleon, which are usual experimental conditions for such measurements. The low-energy constants of the description of Be11 are fit to experimental data as well as to predictions of an ab initio nuclear-structure model. Results: The one-neutron knockout reaction is confirmed to be purely peripheral, the parallel-momentum distribution of the remaining core is sensitive only to the asymptotics of the ground-state wave function 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: The one-neutron knockout cross section can be used to infer information about the tail of the ground-state wave function, 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., SCOPUS: ar.j, info:eu-repo/semantics/published

We analyze the breakup of the one-neutron halo nucleus 11Be measured at 520 MeV/nucleon at GSI on Pb and C targets within an eikonal description of the reaction including a proper treatment of special relativity. The Coulomb term of the projectile-target interaction is corrected at first order, while its nuclear part is described at the optical limit approximation. Good agreement with the data is obtained using a description of 11Be, which fits the breakup data of RIKEN. This solves the apparent discrepancy between the dB(E1)/dE estimations from GSI and RIKEN for this nucleus., SCOPUS: ar.j, info:eu-repo/semantics/published

In this contribution to the proceedings of the International Nuclear Physics Conference 2019, I review recent developments made in reaction models used to analyse data measured at radioactive-ion beam facilities to study exotic nuclear structures. I focus in particular on reactions like elastic scattering and breakup, which are used to study halo nuclei. Although these peculiar nuclei challenge usual nuclear-structure models, some can now be computed ab initio. This brief review illustrates the progresses made in nuclear-reaction theory in the last few years to improve the description of the projectile within reaction models. I dedicate this contribution to the memory of Mahir Hussein, who has significantly contributed to this field and who passed away in May this year., Comment: Contribution to the proceedings of the International Nuclear Physics Conference 2019. 8 pages, 8 figures

These notes summarise the lectures I gave during the summer school "International Scientific Meeting on Nuclear Physics" at La R\'abida in Spain in June 2018. They offer an introduction to nuclear-reaction theory, starting with the basics in quantum scattering theory followed by the main models used to describe breakup reactions: the Continuum Discretised Coupled Channel method (CDCC),the Time-Dependent approach (TD) and the eikonal approximation. These models are illustrated on the study of the exotic structure of halo nuclei., Comment: 42 pages, 16 figures, contrib. Procs. of the International Scientific Meeting on Nuclear Physics [La R\'abida (Spain) 18th-22th June 2018], submitted to Springer Proceedings in Physics

This work focuses on the development of an adiabatic correction to the eikonal model. The preliminary results computed for the Coulomb-dominated breakup of the one-neutron halo nucleus \(^{11}\mathrm {Be}\) at 69A MeV are encouraging. Further analyses on the accuracy of the correction have still to be performed.

Through this study we propose to use sub-Coulomb transfer to investigate the one-neutron halo phenomenon within nuclear excited states since this method could naturally guarantee the peripherality of the transfer. Zero-range ADWA calculations are performed with the final nucleus bound under different conditions. It can be observed that there is a clear enhancement of the interaction cross sections when the nucleus is loosely bound within an s orbital.

We reanalyze the experiment of Schmitt et al. on the $^{10}\mathrm{Be}(d,p)^{11}\mathrm{Be}$ transfer reaction [Phys. Rev. Lett. 108, 192701 (2012)] by exploring the beam-energy and angular ranges at which the reaction is strictly peripheral. We consider the adiabatic distorted wave approximation (ADWA) to model the reaction and use a Halo-EFT description of $^{11}\mathrm{Be}$ to systematically explore the sensitivity of our calculations to the short-range physics of the $^{10}\mathrm{Be}\ensuremath{-}n$ wave function. We find that by selecting the data at low beam energy and forward scattering angle the calculated cross sections scale nearly perfectly with the asymptotic normalization coefficient (ANC) of the $^{11}\mathrm{Be}$ bound states. Following these results, a comparison of our calculations with the experimental data gives a value of ${C}_{1s1/2}=0.785\ifmmode\pm\else\textpm\fi{}0.03\phantom{\rule{0.16em}{0ex}}{\mathrm{fm}}^{\ensuremath{-}1/2}$ for the ${\frac{1}{2}}^{+}$ ground-state ANC and ${C}_{0p1/2}=0.135\ifmmode\pm\else\textpm\fi{}0.005\phantom{\rule{0.16em}{0ex}}{\mathrm{fm}}^{\ensuremath{-}1/2}$ for the ${\frac{1}{2}}^{\ensuremath{-}}$ excited state, which are in perfect agreement with the ab initio calculations of Calci et al., who obtain ${C}_{1/{2}^{+}}^{\mathit{ab}\phantom{\rule{0.28em}{0ex}}\mathit{initio}}=0.786\phantom{\rule{0.16em}{0ex}}{\mathrm{fm}}^{\ensuremath{-}1/2}$ and ${C}_{1/{2}^{\ensuremath{-}}}^{\mathit{ab}\phantom{\rule{0.28em}{0ex}}\mathit{initio}}=0.129\phantom{\rule{0.16em}{0ex}}{\mathrm{fm}}^{\ensuremath{-}1/2}$ [Phys. Rev. Lett. 117, 242501 (2016)].

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 et al. [Phys. Rev. C 90, 034617 (2014)10.1103/PhysRevC.90.034617] 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 Be11 impinging on C12 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., SCOPUS: ar.j, info:eu-repo/semantics/published

We present a description of the breakup of halo nuclei in peripheral nuclear reactions by coupling a model of the projectile motivated by halo effective field theory with a fully dynamical treatment of the reaction using the dynamical eikonal approximation. Our description of the halo system reproduces its long-range properties, i.e., binding energy and asymptotic normalization coefficients of bound states and phase shifts of continuum states. As an application we consider the breakup of $^{11}\mathrm{Be}$ in collisions on Pb and C targets. Taking the input for our halo-EFT-inspired description of $^{11}\mathrm{Be}$ from a recent ab initio calculation of that system yields a good description of the Coulomb-dominated breakup on Pb at energies up to about 2 MeV, with the result essentially independent of the short-distance part of the halo wave function. However, the nuclear dominated breakup on C is more sensitive to short-range physics. The role of spectroscopic factors and possible extensions of our approach to include additional short-range mechanisms are also discussed.

The determination of nucleus–nucleus potentials is important not only to describe the properties of the colliding system, but also to extract nuclear-structure information and for modelling nuclear reactions for astrophysics. We present the first determination of double-folding potentials based on chiral effective field theory at leading, next-to-leading, and next-to-next-to-leading order. To this end, we construct new soft local chiral effective field theory interactions. We benchmark this approach in the 16O–16O system, and present results for cross sections computed for elastic scattering up to 700 MeV in energy, as well as for the astrophysical S-factor of the fusion reaction., SCOPUS: ar.j, info:eu-repo/semantics/published

This is a brief report on the progress made towards an exact theory for (d,p) on heavy nuclei, which is important to determine neutron capture rates for r-process nuclei. We first discuss the role of core excitation in the framework of Faddeev equations. Following that, we provide the status of the Faddeev theory being developed in the Coulomb basis with separable interactions. We then present some recent developments on nonlocal nucleon optical potentials. Finally, the progress on the theory transfer to the continuum is summarized., SCOPUS: cp.p, info:eu-repo/semantics/published

Recently a variety of studies have shown the importance of including non-locality in the description of reactions. The goal of this work is to revisit the phenomenological approach to determining non-local optical potentials from elastic scattering. We perform a $\chi^2$ analysis of neutron elastic scattering data off $^{40}$Ca, $^{90}$Zr and $^{208}$Pb at energies $E \approx 5-40$ MeV, assuming a Perey and Buck or Tian, Pang, and Ma non-local form for the optical potential. We introduce energy and asymmetry dependencies in the imaginary part of the potential and refit the data to obtain a global parameterization. Independently of the starting point in the minimization procedure, an energy dependence in the imaginary depth is required for a good description of the data across the included energy range. We present two parameterizations, both of which represent an improvement over the original potentials for the fitted nuclei as well as for other nuclei not included in our fit. Our results show that, even when including the standard Gaussian non-locality in optical potentials, a significant energy dependence is required to describe elastic-scattering data.

Various corrections to the eikonal approximations are studied for two- and three-body nuclear collisionswith the goal to extend the range of validity of this approximation to beam energies of 10 MeV/nucleon.Wallace’s correction does not improve much the elastic-scattering cross sections obtained at the usual eikonalapproximation. On the contrary, a semiclassical approximation that substitutes the impact parameter by a complexdistance of closest approach computed with the projectile-target optical potential efficiently corrects the eikonalapproximation. This opens the possibility to analyze data measured down to 10 MeV/nucleon within eikonal-likereaction models., SCOPUS: ar.j, info:eu-repo/semantics/published

We present an account of the current status of the theoretical treatment of inclusive $(d,p)$ reactions in the breakup-fusion formalism, pointing to some applications and making the connection with current experimental capabilities. Three independent implementations of the reaction formalism have been recently developed, making use of different numerical strategies. The codes also originally relied on two different but equivalent representations, namely the prior (Udagawa-Tamura, UT) and the post (Ichimura-Austern-Vincent, IAV) representations. The different implementations have been benchmarked, and then applied to the Ca isotopic chain. The neutron-Ca propagator is described in the Dispersive Optical Model (DOM) framework, and the interplay between elastic breakup (EB) and non-elastic breakup (NEB) is studied for three Ca isotopes at two different bombarding energies. The accuracy of the description of different reaction observables is assessed by comparing with experimental data of $(d,p)$ on $^{40,48}$Ca. We discuss the predictions of the model for the extreme case of an isotope ($^{60}$Ca) currently unavailable experimentally, though possibly available in future facilities (nominally within production reach at FRIB). We explore the use of $(d,p)$ reactions as surrogates for $(n,\gamma)$ processes, by using the formalism to describe the compound nucleus formation in a $(d,p\gamma)$ reaction as a function of excitation energy, spin, and parity. The subsequent decay is then computed within a Hauser-Feshbach formalism. Comparisons between the $(d,p\gamma)$ and $(n,\gamma)$ induced gamma decay spectra are discussed to inform efforts to infer neutron captures from $(d,p\gamma)$ reactions. Finally, we identify areas of opportunity for future developments, and discuss a possible path toward a predictive reaction theory.

For the last decades, multiple international facilities have developed Radioactive-Ion Beams (RIB) to measure reaction processes including exotic nuclei. These measurements coupled with an accurate theoretical model of the reaction enable us to infer information about the structure of these nuclei. The partial-wave expansion provides a precise description of two-body collisions but has a large computational cost. To cope with this issue, the eikonal approximation is a powerful tool as it reduces the computational time and still describes the quantum effects observed in reaction observables. However, its range of validity is restricted to high energy and to forward scattering angles. In this work, we analyse the extension of the eikonal approximation to lower energies and larger angles through the implementation of two corrections. These aim to improve the treatment of the nuclear and Coulomb interactions within the eikonal model. The first correction is based on an expansion of the $T$-matrix while the second relies on a semi-classical approach. They permit to better account for the deflection of the projectile by the target, which is neglected in the standard eikonal model. The gain in accuracy of each correction is evaluated through the analyses of angular cross sections computed with the standard eikonal model, its corrections and the partial-wave expansion. These analyses have been performed for tightly bound projectiles ($^{10}\mathrm{Be}$) from intermediate energies (67 MeV/nucleon) down to energies of interest of future RIB facilities such as HIE-ISOLDE and ReA12 at MSU (10 MeV/nucleon)., 7 pages, 2 figures, contribution to 55th International Winter Meeting on Nuclear Physics (January 2017, Bormio, Italy)

The Coulomb-breakup method to extract the cross section for neutron radiative capture at astrophysical energies is analyzed in detail. In particular, its sensitivity to the description of the neutron-core continuum is ascertained. We consider the case of 14C(n, $\gamma$)15C for which both the radiative capture at low energy and the Coulomb breakup of 15C into 14C+n on Pb at 68 MeV/nucleon have been measured with accuracy. We confirm the direct proportionality of the cross section for both reactions to the square of the asymptotic normalization constant of 15C observed by Summers and Nunes [Phys. Rev. C 78, 011601 (2008)], but we also show that the 14C-n continuum plays a significant role in the calculations. Fortunately, the method proposed by Summers and Nunes can be improved to absorb that continuum dependence. We show that a more precise radiative-capture cross section can be extracted selecting the breakup data at forward angles and low 14C-n relative energies., Comment: Erratum added in the Appendix A

Background: The ratio method has been proposed as a means to remove the reaction model dependence in the study of halo nuclei. Purpose: Originally, it was developed for higher energies but given the potential interest in applying the method at lower energy, in this work we explore its validity at 20 MeV/nucleon. Method: The ratio method takes the ratio of the breakup angular distribution and the summed angular distribution (which includes elastic, inelastic and breakup) and uses this observable to constrain the features of the original halo wave function. In this work we use the Continuum Discretized Coupled Channel method and the Coulomb-corrected Dynamical Eikonal Approximation for the study. Results: We study the reactions of 11Be on 12C, 40Ca and 208Pb at 20 MeV/nucleon. We compare the various theoretical descriptions and explore the dependence of our result on the core-target interaction. Conclusions: Our study demonstrates that the ratio method is valid at these lower beam energies., Accepted for publication in Phys. Rev. C; 10 pages, 7 figures

Direct nuclear reactions are used to extract spectroscopic information about exotic nuclei. A spectroscopic factor (SF) is often extracted from measurements assuming a single-particle structure for the projectile. Being peripheral, these reactions are mostly sensitive to the asymptotic normalization coefficient (ANC) of the wave function. We study the accuracy of analysing peripheral reactions with a single-particle approximation of the nucleus. We consider a collective core+n model, in which the core can be excited. Fair agreement is obtained between the SF inferred from the single-particle approximation and the one obtained within the collective model when large SFs are concerned.

An exclusive study of 17 F breakup reactions has been performed at the FRIBs facility of the Laboratori Nazionali del Sud in Catania (Italy). The experiment has been performed with the aim of testing the accuracy of the Coulomb-breakup indirect technique used to infer radiative-capture cross sections at low energies. This technique has been used in the 7 Be ( p , γ)8 B case, but has never been tested. By measuring the breakup of 17F into 16 O + p , and comparing the inferred cross section for 16 O ( p ,γ)17 F to direct precise measurements, the influence of E2 transitions and higher-order effects, that are predicted to be significant in Coulomb-breakup reactions, can be evaluated. The first results and preliminary model comparison are reported.

A candidate of a neutron-halo nucleus, 31 Ne , contains a single neutron in the pf shell. Within Glauber and eikonal models, we analyze reactions used to study 31 Ne . We show in a 30 Ne + n model that the magnitudes of the total reaction and above all of the one-neutron removal cross sections of 31 Ne on 12 C and 208 Pb targets strongly depend on the orbital angular momentum of the valence neutron, thereby providing efficient ways to determine the structure of 31 Ne ground state. We also show that elastic-breakup observables exhibit a strong dependence upon the orbital of the valence neutron.

We study how EFT can improve the description of reactions used to study the structure of exotic nuclei. Using Halo EFT helps constraining the potential that simulates the interaction between the projectile constituents. It enables us to include ab initio results within the reaction model and to clearly identify the nuclear properties probed by the reaction. New local chiral EFT nucleon-nucleon interactions can also be used to derive nucleus-nucleus optical potentials from first principles, which can provide reliable inputs in reaction modelling., SCOPUS: cp.p, info:eu-repo/semantics/published

A halo nucleus is built from a core and at least one weakly bound neutron or proton. To understand this unique cluster structure, lots of efforts have been undertaken. During the past decades, the (d, p) reaction has been widely used in experiments and has become an important tool for extracting single-particle properties of nuclei. In this work, our goal is to obtain the Asymptotic Normalization Coefficient (ANC) of the halo nuclei 11Be using the ADWA method. We perform the analysis for the 10Be(d, p)11Be stripping reaction at Ed =21.4, 18, 15, and 12MeV for the ground state and first excited state of the composite nucleus 11Be. The experimental measurement was carried out at Oak Ridge National Laboratory by Schmitt et al. [1] The sensitivity of the calculations to the optical potential choice is also checked. Overall, the transfer process becomes more peripheral at lower energies and forward angles. Investigation in this area is the best way to extract a reliable ANC from the experimental data. For the ground state of 11Be, the ANC obtained using our method shows perfect agreement with the one obtained by Ab initio calculations (C Ab=0.786 fm-1/2) [2]., SCOPUS: cp.p, info:eu-repo/semantics/published

The Dynamical Eikonal Approximation (DEA) is briefly presented. Resuts obtained within this model for the breakup of 11 Be on both light and heavy targets are shown and compared to experiment. The Coulomb Corrected Eikonal (CCE) model is detailed and analysed through comparison with the DEA.

Coulomb breakup is used to infer radiative-capture cross sections at astrophysical energies. We test theoretically the accuracy of this indirect technique in the particular case of 15C, for which both the Coulomb breakup to ^{14}C+n and the radiative capture 14C(n,{\gamma})15C have been measured. We analyse the dependance of Coulomb-breakup calculations on the projectile description in both its initial bound state and its continuum. Our calculations depend not only on the Asymptotic Normalisation Coefficient (ANC) of the 15C ground state, but also on the 14C-n continuum. This questions the method proposed by Summers and Nunes [Phys. Rev. C 78, 011601 (2008), ibid. 78, 069908 (2008)], which assumes that an ANC can be directly extracted from the comparison of calculations to breakup data. Fortunately, the sensitivity to the continuum description can be absorbed in a normalisation constant obtained by a simple {\chi}2 fit of our calculations to the measurements. By restricting this fit to low 14C-n energy in the continuum, we can achieve a better agreement between the radiative-capture cross sections inferred from the Coulomb-breakup method and the exact ones. This result revives the Coulomb-breakup technique to infer neutron radiative-capture capture to loosely-bound states, which would be very useful for r- and s-process modelling in explosive stellar environments., Comment: 8 pages, 7 figures, contribution to the proceedings of the 54th International Winter Meeting on Nuclear Physics (25-29 January 2016, Bormio, Italy)

The study of exotic nuclear structures, such as halo nuclei, is usually performed through nuclear reactions. An accurate reaction model coupled to a realistic description of the projectile is needed to correctly interpret experimental data. In this contribution, I briefly summarise the assumptions made within the modelling of reactions involving halo nuclei. I describe briefly the Continuum-Discretised Coupled Channel method (CDCC) and the Dynamical Eikonal Approximation (DEA) in particular and present a comparison between them for the breakup of 15C on Pb at 68AMeV. I show the problem faced by the eikonal approximation at low energy and detail a correction that enables its extension down to lower beam energies. A new reaction observable is also presented. It consists of the ratio between angular distributions for two different processes, such as elastic scattering and breakup. This ratio is completely independent of the reaction mechanism and hence is more sensitive to the projectile structure than usual reaction observables, which makes it a very powerful tool to study exotic structures far from stability., SCOPUS: cp.j, info:eu-repo/semantics/published

A unitary factorization of the evolution operator at order four is derived from the Magnus expansion with a time-dependent potential. Its efficiency is tested on various mesh treatments of a forced harmonic oscillator. With respect to second order, accuracies are improved by more than an order of magnitude.

The Coulomb breakup of a weakly-bound nucleus is investigated by solving the time-dependent Schrodinger equation where the projectile follows a classical trajectory. The equation is solved iteratively with respect to time on angular and radial meshes. The time evolution of the breakup of the 11Be halo nucleus is visualized. The role of forbidden states is discussed with phase-equivalent potentials. The determination of the astrophysical S factor is tested on the 17F Coulomb breakup.

Supersymmetric transformations allow eliminating forbidden bound states from a potential without affecting its scattering properties. The Coulomb breakup of the 11 Be halo nucleus is studied by solving the time-dependent Schrodinger equation with phase-equivalent 10 Be–neutron interactions. The differences between breakup calculations with and without forbidden states are weak but the inelastic scattering to the 1/2 − state is more affected.

E-CDCC and DEA, two eikonal-based reaction models are compared to CDCC at low energy (e.g. 20AMeV) to study their behaviour in the regime at which the eikonal approximation is supposed to fail. We confirm that these models lack the Coulomb deflection of the projectile by the target. We show that a hybrid model, built on the CDCC framework at low angular momenta and the eikonal approximation at larger angular momenta gives a perfect agreement with CDCC. An empirical shift in impact parameter can also be used reliably to simulate this missing Coulomb deflection., Contribution to the proceedings of the Conference on "Advances in Radioactive Isotope Science" (ARIS2014). 6 pages, 4 figures

Extensions of the eikonal approximation to low energy (20 MeV/nucleon typically) are studied. The relation between the dynamical eikonal approximation (DEA) and the continuum-discretized coupled-channels method with the eikonal approximation (E-CDCC) is discussed. When Coulomb interaction is artificially turned off, DEA and E-CDCC are shown to give the same breakup cross section, within 3% error, of C15 on Pb208 at 20 MeV/nucleon. When the Coulomb interaction is included, the difference is appreciable and none of these models agrees with full CDCC calculations. An empirical correction significantly reduces this difference. In addition, E-CDCC has a convergence problem. By including a quantum-mechanical correction to E-CDCC for lower partial waves between C15 and Pb208, this problem is resolved and the result perfectly reproduces full CDCC calculations at a lower computational cost., SCOPUS: ar.j, info:eu-repo/semantics/published

The open issues in the development of models for the breakup of exotic nuclei and the link with the extraction of structure information from experimental data are reviewed. The question of the improvement of the description of exotic nuclei within reaction models is approached in the perspective of previous analyses of the sensitivity of these models to that description. Future developments of reaction models are suggested, such as the inclusion of various channels within one model. The search for new reaction observables that can emphasize more details of exotic nuclear structure is also proposed., SCOPUS: ar.j, info:eu-repo/semantics/published

Rare isotopes are most often studied through nuclear reactions. Nuclear reactions can be used to obtain detailed structure information but also in connection to astrophysics to determine specific capture rates. In order to extract the desired information it is crucial to have a reliable framework that describes the reaction process accurately. A few recent developments for transfer and breakup reactions will be presented. These include recent studies on the reliability of existing theories as well as effort to reduce the ambiguities in the predicted observables., Comment: 12 pages, 6 figures, conference proceedings for CGS14, Guelph, September 2011

Recently a new observable to study halo nuclei was introduced, based on the ratio between breakup and elastic angular cross sections. This new observable is shown by the analysis of specific reactions to be independent of the reaction mechanism and to provide nuclear structure information of the projectile. Here we explore the details of this ratio method, including the sensitivity to binding energy and angular momentum of the projectile. We also study the reliability of the method with breakup energy. Finally, we provide guidelines and specific examples for experimentalists who wish to apply this method. © 2013 American Physical Society., SCOPUS: ar.j, info:eu-repo/semantics/published

Halo nuclei are exotic nuclei which exhibit a strongly clusterised structure: they can be seen as one or two valence nucleons loosely bound to a core. Being observed at the ridge of the valley of stability, halo nuclei are studied mostly through reactions. In this contribution the reaction models most commonly used to analyse experimental data are reviewed and compared to one another. A reaction observable built on the ratio of two angular distributions is then presented. This ratio enables removing most of the sensitivity to the reaction mechanism, which emphasises the effects of nuclear structure on the reaction., Invited talk given by Pierre Capel at the "10th International Conference on Clustering Aspects of Nuclear Structure and Dynamics" (Cluster12), Debrecen, Hungary, 24-28 September 2012. To appear in the Cluster12 Proceedings in the Open Access Journal of Physics: Conference Series (JPCS). (5 pages, 3 figures)

The angular distributions for elastic scattering and breakup of halo nuclei are analysed using a near-side/far-side decomposition within the framework of the dynamical eikonal approximation. This analysis is performed for 11Be impinging on Pb at 69AMeV. These distributions exhibit very similar features. In particular they are both near-side dominated, as expected from Coulomb-dominated reactions. The general shape of these distributions is sensitive mostly to the projectile-target interactions, but is also affected by the extension of the halo. This suggests that the link between elastic scattering and a possible loss of flux towards the breakup channel is not obvious., Talk given by Mahir Hussein at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS). (9 pages, 5 figures)

Breakup reactions are one of the main tools for the study of exotic nuclei, and in particular of their continuum. In order to get valuable information from measurements, a precise reaction model coupled to a fair description of the projectile is needed. We assume that the projectile initially possesses a cluster structure, which is revealed by the dissociation process. This structure is described by a few-body Hamiltonian involving effective forces between the clusters. Within this assumption, we review various reaction models. In semiclassical models, the projectile-target relative motion is described by a classical trajectory and the reaction properties are deduced by solving a time-dependent Schroedinger equation. We then describe the principle and variants of the eikonal approximation: the dynamical eikonal approximation, the standard eikonal approximation, and a corrected version avoiding Coulomb divergence. Finally, we present the continuum-discretized coupled-channel method (CDCC), in which the Schroedinger equation is solved with the projectile continuum approximated by square-integrable states. These models are first illustrated by applications to two-cluster projectiles for studies of nuclei far from stability and of reactions useful in astrophysics. Recent extensions to three-cluster projectiles, like two-neutron halo nuclei, are then presented and discussed. We end this review with some views of the future in breakup-reaction theory.