Opening angle and dineutron correlations in knockout reactions with Borromean two-neutron halo nuclei

Background: Knockout reactions with proton targets provide an invaluable tool to access the properties of twoneutron halo nuclei. Recently, experimental results for the average opening angle as a function of the intrinsic neutron momentum in 11Li have shown a localization of dineutron correlations on the nucleus surface. Purpose: Study the model dependence and the effect of distortion and absorption on the opening angle distributions to assess the reliability of this observable to extract properties of Borromean two-neutron halo nuclei. Method: A quasifree sudden model is used to describe the knockout process, where absorption effects are modeled by the eikonal S matrix between the proton target and the core of the Borromean nucleus. Final states in momentum space are built within a three-body model for the projectile, which enables the description of momenta and opening angle distributions. Results: A strong dependence on absorption effects is found for the opening angle at large intrinsic momenta, while the region of lower momenta is mostly insensitive to them. Reasonable agreement with the available data is obtained for 11Li at low momenta with weights for s and p waves different from those previously reported, showing a model dependence in their extraction. For 19B, test calculations show marked sensitivity to small p-wave components. Conclusions: The opening angle for (p, pn) knockout reactions on Borromean nuclei at small intrinsic momenta is a reliable observable mostly sensitive to the structure of the Borromean nucleus. For larger momenta, the reaction mechanism leads to a larger distortion of the distribution. In the case of nuclei with small components of opposite parity to the dominant ones, this observable can be used to explore them. The relation between dineutron in coordinate space and opening angle in momentum space is found to be model dependent.Ministerio de Ciencia de España, Innovación y Universidades. FIS2017-88410-PPrograma de Investigación e Innovación de la Unión Europea Marie Skłodowska Curie.101023609Fondo Social Europeo y la Junta de Andalucía (PAIDI 2020

Opening angle and dineutron correlations in knockout reactions with Borromean two-neutron halo nuclei

Background: Knockout reactions with proton targets provide an invaluable tool to access the properties of twoneutron halo nuclei. Recently, experimental results for the average opening angle as a function of the intrinsic neutron momentum in 11Li have shown a localization of dineutron correlations on the nucleus surface. Purpose: Study the model dependence and the effect of distortion and absorption on the opening angle distributions to assess the reliability of this observable to extract properties of Borromean two-neutron halo nuclei. Method: A quasifree sudden model is used to describe the knockout process, where absorption effects are modeled by the eikonal S matrix between the proton target and the core of the Borromean nucleus. Final states in momentum space are built within a three-body model for the projectile, which enables the description of momenta and opening angle distributions. Results: A strong dependence on absorption effects is found for the opening angle at large intrinsic momenta, while the region of lower momenta is mostly insensitive to them. Reasonable agreement with the available data is obtained for 11Li at low momenta with weights for s and p waves different from those previously reported, showing a model dependence in their extraction. For 19B, test calculations show marked sensitivity to small p-wave components. Conclusions: The opening angle for (p, pn) knockout reactions on Borromean nuclei at small intrinsic momenta is a reliable observable mostly sensitive to the structure of the Borromean nucleus. For larger momenta, the reaction mechanism leads to a larger distortion of the distribution. In the case of nuclei with small components of opposite parity to the dominant ones, this observable can be used to explore them. The relation between dineutron in coordinate space and opening angle in momentum space is found to be model dependent.Ministerio de Ciencia de España, Innovación y Universidades. FIS2017-88410-PPrograma de Investigación e Innovación de la Unión Europea Marie Skłodowska Curie.101023609Fondo Social Europeo y la Junta de Andalucía (PAIDI 2020

Transfer to the continuum calculations of quasifree (p,pn) and (p,2p) reactions

Nucleon removal (p, pn) and (p, 2p) reactions at intermediate energies have gained renewed attention in recent years as a tool to extract information from exotic nuclei. The information obtained from these experiments is expected to be sensitive to deeper portions of the wave function of the removed nucleon than knockout reactions with heavier targets. In this contribution, we present calculations for (p, 2p) and (p, pn) reactions performed within the so-called transfer to the continuum method (TR*). Results for stable and unstable nuclei are presented, and compared with experimental data, when availabl

Influence of target deformation and deuteron breakup in ( d , p ) transfer reactions

Background: The effect of core excitations in transfer reactions of the form A ( d , p ) B has been reexamined by some recent works by using the Faddeev–Alt–Grassberger–Sandhas reaction formalism. The effect was found to affect significantly the calculated cross sections and to depend strongly and nonlinearly on the incident deuteron energy. Purpose: Our goal is to investigate these effects within a coupled-channel formulation of the scattering problem which, in addition to being computationally less demanding than the Faddeev counterpart, may help shed some light onto the physical interpretation of the cited effects. Method: We use an extended version of the continuum-discretized coupled-channel (CDCC) method with explicit inclusion of target excitations within a coupled-channel Born approximation (CDCC-BA) formulation of the transfer transition amplitude. We compare the calculated transfer cross sections with those obtained with an analogous calculation omitting the effect of target excitation. We consider also an adiabatic coupled-channel (ACC) method. Our working example is the 10 Be ( d , p ) 11 Be reaction. Results: We find that the two considered methods (CDCC-BA and ACC) reproduce fairly well the reported energy dependence of the core excitation effect. The main deviation from the pure three-body model calculation (i.e., omitting core excitations) is found to mostly originate from the destructive interference of the direct one-step transfer and the two-step transfer following target excitation. Conclusions: The proposed method; namely, the combination of the CDCC method and the CCBA formalism, provides a useful and accurate tool to analyze transfer reactions including explicitly, when needed, the effect of target excitations and projectile breakup. The method could be useful for other transfer reactions induced by weakly bound projectiles, including halo nuclei.Ministerio de Economía y Competitividad de España y Fondos FEDER. FIS2014-53448-C2-1-PPrograma Horizonte 2020 de la Unión Europea. 65400

Interplay of projectile breakup and target excitation in reactions induced by weakly bound nuclei

Reactions involving weakly bound nuclei require formalisms able to deal with continuum states. The majority of these formalisms struggle to treat collective excitations of the systems involved. For continuumdiscretized coupled channels (CDCC), extensions to include target excitation have been developed but have only been applied to a small number of cases.Junta de Andalucía FQM160 P07-FQM-02894Ministerio de Economía y Competitividad FIS2014-53448-C2-1-

Influence of target deformation and deuteron breakup in ( d , p ) transfer reactions

Background: The effect of core excitations in transfer reactions of the form A ( d , p ) B has been reexamined by some recent works by using the Faddeev–Alt–Grassberger–Sandhas reaction formalism. The effect was found to affect significantly the calculated cross sections and to depend strongly and nonlinearly on the incident deuteron energy. Purpose: Our goal is to investigate these effects within a coupled-channel formulation of the scattering problem which, in addition to being computationally less demanding than the Faddeev counterpart, may help shed some light onto the physical interpretation of the cited effects. Method: We use an extended version of the continuum-discretized coupled-channel (CDCC) method with explicit inclusion of target excitations within a coupled-channel Born approximation (CDCC-BA) formulation of the transfer transition amplitude. We compare the calculated transfer cross sections with those obtained with an analogous calculation omitting the effect of target excitation. We consider also an adiabatic coupled-channel (ACC) method. Our working example is the 10 Be ( d , p ) 11 Be reaction. Results: We find that the two considered methods (CDCC-BA and ACC) reproduce fairly well the reported energy dependence of the core excitation effect. The main deviation from the pure three-body model calculation (i.e., omitting core excitations) is found to mostly originate from the destructive interference of the direct one-step transfer and the two-step transfer following target excitation. Conclusions: The proposed method; namely, the combination of the CDCC method and the CCBA formalism, provides a useful and accurate tool to analyze transfer reactions including explicitly, when needed, the effect of target excitations and projectile breakup. The method could be useful for other transfer reactions induced by weakly bound projectiles, including halo nuclei.Ministerio de Economía y Competitividad de España y Fondos FEDER. FIS2014-53448-C2-1-PPrograma Horizonte 2020 de la Unión Europea. 65400

A transfer to the continuum formalism for the study of (p, pn) and (p, 2p) reactions on unstable nuclei.

In this work, we present a new reaction form alism to describe these reactions and obtain nuclear inform ation from them, which we have called Transfer to the Continuum. With this formalism, we undertake the analysis of several (p,pn) and (p,2p) reactions on both stable and exotic nuclei at interm ediate energies, and provide an answer for the open problem of the reduction or “quenching” of spectroscopic factors as a function of the proton-neutron asym metry. We also extend the formalism to study the exotic Borrom ean nuclei, building a reliable method to relate experimental energy distributions to nuclear structure calculations

Equation of state for nucleonic and hyperonic neutron stars with mass and radius constraints

We obtain a new equation of state for the nucleonic and hyperonic inner core of neutron stars that fulfils the 2 M⊙ observations as well as the recent determinations of stellar radii below 13 km. The nucleonic equation of state is obtained from a new parameterization of the FSU2 relativistic mean-field functional that satisfies these latest astrophysical constraints and, at the same time, reproduces the properties of nuclear matter and finite nuclei while fulfilling the restrictions on high-density matter deduced from heavy-ion collisions. On the one hand, the equation of state of neutron star matter is softened around saturation density, which increases the compactness of canonical neutron stars leading to stellar radii below 13 km. On the other hand, the equation of state is stiff enough at higher densities to fulfil the 2 M⊙ limit. By a slight modification of the parameterization, we also find that the constraints of 2 M⊙ neutron stars with radii around 13 km are satisfied when hyperons are considered. The inclusion of the high magnetic fields present in magnetars further stiffens the equation of state. Hyperonic magnetars with magnetic fields in the surface of ~1015 G and with values of ~1018 G in the interior can reach maximum masses of 2 M⊙ with radii in the 12-13 km range

Benchmarking Faddeev and transfer-to-the-continuum calculations for ( p , p N ) reactions

Background: Nucleon-knockout reactions on proton targets (p, pN) have experienced a renewed interest due to the availability of inverse-kinematics experiments with exotic nuclei. Various theoretical descriptions have been used to describe these reactions, such as the distorted-wave impulse approximation, the Faddeev-type formalism, and the transfer-to-the-continuum method. Purpose: Our goal is to benchmark the observables computed with the Faddeev and transfer-to-the-continuum formalisms in the intermediate energy regime relevant for the experimental (p, pn) and (p, 2p) studies. Method: We analyze the 11Be(p, pn) 10Be reaction for different beam energies, binding energies, and orbital quantum numbers with both formalisms to assess their agreement for different observables. Results: We obtain a good agreement in all cases considered, within ≈10%, when the input potentials are taken consistently and realistically. Conclusions: The results of this work prove the consistency and accuracy of both methods, setting an indication on the degree of systematic uncertainties applicable when using them to extract spectroscopic information from (p, pN) reactions.Ministerio de Ciencia, Innovación y Universidades de España y fondos FEDER. FIS2017-88410-PPrograma de investigación e innovación Horizonte 2020 de la Unión Europea. No. 654002.Alexander von Humboldt Foundation. Alemania. LTU-1185721-HFST-

The equation of state for the nucleonic and hyperonic core of neutron stars

We re-examine the equation of state for the nucleonic and hyperonic inner core of neutron stars that satisfies the 2M⊙ observations as well as the recent determinations of stellar radii below 13 km, while fulfilling the saturation properties of nuclear matter and finite nuclei together with the constraints on the high-density nuclear pressure coming from heavy-ion collisions. The recent nucleonic FSU2R and hyperonic FSU2H models are updated in order to improve the behaviour of pure neutron matter at subsaturation densities. The corresponding nuclear matter properties at saturation, the symmetry energy, and its slope turn out to be compatible with recent experimental and theoretical determinations. We obtain the mass, radius, and composition of neutron stars for the two updated models and study the impact on these properties of the uncertainties in the hyperon-nucleon couplings estimated from hypernuclear data. We find that the onset of appearance of each hyperon strongly depends on the hyperon-nuclear uncertainties, whereas the maximum masses for neutron stars differ by at most 0.1M⊙, although a larger deviation should be expected tied to the lack of knowledge of the hyperon potentials at the high densities present in the centre of 2M⊙ stars. For easier use, we provide tables with the results from the FSU2R and FSU2H models for the equation of state and the neutron star mass-radius relation