arXiv subjects

A. Deltuva

Publications and source records attributed to A. Deltuva.

At least 55 records · Page 3Linked to original sources

arXiv2018

Weak sensitivity of three-body ($d,p$) reactions to $np$ force models

Adiabatic distorted-wave approximation (ADWA) study of three-body $(d,p)$ transfer reactions [G.W. Bailey, N.K. Timofeyuk, and J.A. Tostevin, Phys. Rev. Lett. 117, 162502 (2016)] reported strong sensitivity of cross sections to the neutron-proton $(np)$ interaction model when the nucleon-nucleus optical potential is nonlocal. The verification of this unusual finding using more reliable methods is aimed for in the present work. A rigorous Faddeev-type three-body scattering theory is applied to the study of $(d,p)$ transfer reactions. The equations for transition operators are solved in the momentum-space partial-wave framework. Differential cross sections for $^{26}$Al$(d,p)^{27}$Al reactions are calculated using nonlocal nuclear optical potentials and a number of realistic $np$ potentials. Only a weak dependence on the $np$ force model is observed, typically one order of magnitude lower than in the previous ADWA study. The shape of the angular distribution of the experimental data is well reproduced. Cross sections of $(d,p)$ transfer reactions calculated using a rigorous three-body method show little sensitivity to the $np$ interaction model. This indicates a failure of the ADWA in the context of nonlocal potentials. Some evident shortcomings of the ADWA are pointed out.

nucl-th↗

arXiv2018

Comment on "Sensitivity of ($d,p$) Reactions to High $n$-$p$ Momenta and the Consequences for Nuclear Spectroscopy Studies"

Using adiabatic distorted-wave approximation (ADWA) with nonlocal optical potentials (NLOP) for $(d,p)$ transfer reactions [G.W. Bailey, N.K. Timofeyuk, and J.A. Tostevin, Phys. Rev. Lett. 117, 162502 (2016)] reported strong sensitivity to the $n$-$p$ force model. This sensitivity disappears in rigorous three-body Faddeev-type results. Some shortcomings of ADWA with NLOP are pointed out.

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arXiv2018

Tetraneutron: Rigorous continuum calculation

The four-neutron system is studied using exact continuum equations for transition operators and solving them in the momentum-space framework. A resonant behavior is found for strongly enhanced interaction but not a the physical strength, indicating the absence of an observable tetraneutron resonance, in contrast to a number of earlier works. As the transition operators acquire large values at low energies, it is conjectured that this behavior may explain peaks in many-body reactions even without a resonance.

nucl-th↗

arXiv2018

Measurement of double-polarization asymmetries in the quasi-elastic $^3\vec{\mathrm{He}}(\vec{\mathrm{e}},\mathrm{e}'\mathrm{p})$ process

We report on a precise measurement of double-polarization asymmetries in electron-induced breakup of $^3\mathrm{He}$ proceeding to $\mathrm{pd}$ and $\mathrm{ppn}$ final states, performed in quasi-elastic kinematics at $Q^2 = 0.25\,(\mathrm{GeV}/c)^2$ for missing momenta up to $250\,\mathrm{MeV}/c$. These observables represent highly sensitive tools to investigate the electromagnetic and spin structure of $^3\mathrm{He}$ and the relative importance of two- and three-body effects involved in the breakup reaction dynamics. The measured asymmetries cannot be satisfactorily reproduced by state-of-the-art calculations of $^3\mathrm{He}$ unless their three-body segment is adjusted, indicating that the spin-dependent part of the nuclear interaction governing the three-body breakup process is much smaller than previously thought.

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arXiv2018

Three-neutron resonance study using transition operators

Existing bound-state type calculations of three-neutron resonances yield contradicting results. A direct study of the three-neutron continuum using rigorous scattering equations with realistic potentials and search for possible resonances is aimed. Faddeev-type integral equations for three-neutron transition operators are solved in the momentum-space partial-wave framework. The evolution of resonances is studied by enhancing the strength of the two-neutron interaction in partial waves with nonzero orbital momentum. Calculated three-neutron transition operators exhibit resonant behavior for sufficiently large enhancement factors; pole trajectories in the complex-energy energy plane are extracted from their energy dependence. However, the resonant behavior completely disappears for the physical interaction strength. There are no physically observable three-neutron resonant states consistent with presently accepted interaction models.

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arXiv2017

Neutron-${}^{19}\mathrm{C}$ scattering: Towards including realistic interactions

Low-energy neutron-${}^{19}$C scattering is studied in the three-body $n + n + {}^{18}$C model using a realistic $nn$ potential and a number of shallow and deep $n$-${}^{18}$C potentials, the latter supporting deeply-bound Pauli-forbidden states that are projected out. Exact Faddeev-type three-body scattering equations for transition operators including two- and three-body forces are solved in the momentum-space partial-wave framework. Phase shift, inelasticity parameter, and cross sections are calculated. For the elastic $n$-${}^{19}$C scattering in the $J^Π=0^+$ partial wave the signatures of the Efimov physics, i.e., the pole in the effective-range expansion and the elastic cross section minimum, are confirmed for both shallow and deep models, but with clear quantitative differences between them, indicating the importance of a proper treatment of deeply-bound Pauli-forbidden states. In contrast, the inelasticity parameter is mostly correlated with the asymptotic normalization coefficient of the ${}^{19}$C bound state. Finally, in the regime of very weak ${}^{19}$C binding and near-threshold (bound or virtual) excited ${}^{20}$C state the standard Efimovian behaviour of the $n$-${}^{19}$C scattering length and cross section was confirmed, resolving the discrepancies between earlier studies by other authors [I. Mazumdar, A. R. P. Rau, V. S. Bhasin, Phys. Rev. Lett. 97 (2006) 062503; M. T. Yamashita, T. Frederico, L. Tomio, Phys. Rev. Lett. 99 (2007) 269201].

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arXiv2017

Universality in fermionic dimer-dimer scattering

Collisions of two fermionic dimers near the unitary limit are studied using exact four-particle equations for transition operators in momentum space. Universal properties of dimer-dimer phase shifts and effective range expansion (ERE) parameters are determined. The inclusion of the fourth-order momentum term in the ERE significantly extends its validity to higher collision energies. The dimer-dimer scattering length and effective range are determined in the unitary limit as well as their corrections arising due to the finite range of the two-fermion interaction. These results are of considerably higher accuracy as compared to previous works, but confirm most of the previous results except for the lattice effective field theory calculations.

cond-mat.quant-gas↗

arXiv2017

Core-excitation effects in ${}^{20}\mathrm{O}(d,p){}^{21}\mathrm{O}$ transfer reactions: Suppression or enhancement?

${}^{20}\mathrm{O}(d,p){}^{21}\mathrm{O}$ transfer reactions are described using momentum-space Faddeev-type equations for transition operators and including the vibrational excitation of the ${}^{20}\mathrm{O}$ core. The available experimental cross section data at 10.5 MeV/nucleon beam energy for the ${}^{21}\mathrm{O}$ ground state $\frac52^+$ and excited state $\frac12^+$ are quite well reproduced by our calculations including the core excitation. Its effect can be roughly simulated reducing the single-particle cross section by the corresponding spectroscopic factor. Consequently, the extraction of the spectroscopic factors taking the ratio of experimental data and single-particle cross section at this energy is a reasonable procedure. However, at higher energies core-excitation effects are much more complicated and have no simple relation to spectroscopic factors. We found that core-excitation effects are qualitatively very different for reactions with the orbital angular momentum transfer $\ell=0$ and $\ell=2$, suppressing the cross sections for the former and enhancing for the latter, and changes the shape of the angular distribution in both cases. Furthermore, the core-excitation effect is a result of a complicated interplay between its contributions of the two- and three-body nature.

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arXiv2017

Universal behavior of few-boson systems using potential models

The universal behavior of a three-boson system close to the unitary limit is encoded in a simple dependence of many observables in terms of few parameters. For example the product of the three-body parameter $κ_*$ and the two-body scattering length $a$, $κ_* a$ depends on the angle $ξ$ defined by $E_3/E_2=\tan^2ξ$. A similar dependence is observed in the ratio $a_{AD}/a$ with $a_{AD}$ the boson-dimer scattering length. We use a two-parameter potential to determine this simple behavior and, as an application, to compute $a_{AD}$ for the case of three $^4$He atoms.

cond-mat.quant-gas↗

arXiv2017

Four-body calculation of ${}^2\mathrm{H}(d,p){}^3\mathrm{H}$ and ${}^2\mathrm{H}(d,n){}^3\mathrm{He}$ reactions above breakup threshold

Nucleon transfer reactions in deuteron-deuteron collisions at energies above the three- and four-body breakup threshold are described using exact four-body equations for transition operators that are solved in the momentum-space framework. Differential cross sections, analyzing powers, polarizations, and spin transfer coefficients are obtained using realistic two-nucleon potentials and including the Coulomb repulsion between protons. Overall good agreement between predictions and experimental data is found. Most remarkable discrepancies are seen around the minima of the differential cross section at higher energies and in the outgoing nucleon polarization at lower energies.

nucl-th↗

arXiv2016

Calculation of three-body nuclear reactions with angular-momentum and parity-dependent optical potentials

Angular-momentum or parity-dependent nonlocal optical potentials for nucleon-${}^{16}\mathrm{O}$ scattering able to fit differential cross section data over the whole angular regime are developed and applied to the description of deuteron-${}^{16}\mathrm{O}$ scattering in the framework of three-body Faddeev-type equations for transition operators. Differential cross sections and deuteron analyzing powers for elastic scattering and ${}^{16}\mathrm{O}(d,p){}^{17}\mathrm{O}$ transfer reactions are calculated using a number of local and nonlocal optical potentials and compared with experimental data. Angular-momentum or parity-dependence of the optical potential turns out to be quite irrelevant in the considered three-body reactions while nonlocality is essential for a successful description of the differential cross section data, especially in transfer reactions.

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arXiv2016

Benchmark calculation of p-3H and n-3He scattering

p-3H and n-3He scattering in the energy range above the n-3He but below the d-d thresholds is studied by solving the 4-nucleon problem with a realistic nucleon-nucleon interaction. Three different methods -- Alt, Grassberger and Sandhas, Hyperspherical Harmonics, and Faddeev-Yakubovsky -- have been employed and their results for both elastic and charge-exchange processes are compared. We observe a good agreement between the three different methods, thus the obtained results may serve as a benchmark. A comparison with the available experimental data is also reported and discussed.

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arXiv2016

Role of core excitation in (d,p) transfer reactions

[Background:] Recent work found that core excitation can be important in extracting structure information from (d,p) reactions. [Purpose:] Our objective is to systematically explore the role of core excitation in (d,p) reactions, and understand the origin of the dynamical effects. [Method:] Based on the particle-rotor model of $n+^{10}$Be, we generate a number of models with a range of separation energies ($S_n=0.1-5.0$ MeV), while maintaining a significant core excited component. We then apply the latest extension of the momentum-space based Faddeev method, including dynamical core excitation in the reaction mechanism to all orders, to the $^{10}$Be(d,p)$^{11}$Be like reactions, and study the excitation effects for beam energies from $E_d=15-90$ MeV. [Results:] We study the resulting angular distributions and the differences between the spectroscopic factor that would be extracted from the cross sections, when including dynamical core excitation in the reaction, to that of the original structure model. We also explore how different partial waves affect the final cross section. [Conclusions:] Our results show a strong beam energy dependence of the extracted spectroscopic factors that become smaller for intermediate beam energies. This dependence increases for loosely bound systems.

nucl-th↗

arXiv2016

Three-cluster breakup in deuteron-deuteron collisions: single-scattering approximation

We present results for the three-cluster breakup in deuteron-deuteron collisions at 130 and 270 MeV deuteron beam energy. The breakup amplitude is calculated using the first term in the Neumann series expansion of the corresponding exact four-nucleon equations. In analogy with nucleon-deuteron breakup where an equivalent approximation is compared with exact calculations, we expect this single-scattering approximation to provide a rough estimation of three-body breakup observables in quasifree configurations. We predict the nucleon-deuteron and deuteron-deuteron three-cluster breakup cross sections to be of a comparable size and thereby question the reliability of the recent experimental data [A. Ramazani-Moghaddam-Arani, Ph.D. thesis, University of Groningen, 2009; A. Ramazani-Moghaddam-Arani et al., EPJ Web of Conferences 3, 04012 (2010)] that is smaller by about three orders of magnitude. We also show that an equivalent single-scattering approximation provides a reasonable description of deuteron-deuteron elastic scattering at forward scattering angles.

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arXiv2015

Faddeev-type calculation of (d,n) transfer reactions in three-body nuclear systems

Exact Faddeev-type three-body equations are applied to the study of the proton transfer reactions $(d,n)$ in the system consisting of a nuclear core and two nucleons. The integral equations for the three-body transition operators are solved in the momentum-space framework including the Coulomb interaction via the screening and renormalization method. For a weakly bound final nucleus the calculation of the $(d,n)$ reaction is more demanding in terms of the screening radius as compared to the $(d,p)$ reaction. Well converged differential cross section results are obtained for $^{7}{Be}(d,n)^{8}{B}$, $^{12}{C}(d,n)^{13}{N}$, and $^{16}{O}(d,n)^{17}{F}$ reactions. A comparison with the corresponding $(d,p)$ reactions is made. The calculations fail to reproduce the shape of the angular distribution for reactions on $^{12}{C}$ but provide quite successful description for reactions on $^{16}{O}$, especially for the transfer to the $^{17}{F}$ excited state $1/2^+$ when using a nonlocal optical potential.

nucl-th↗

arXiv2015

Four-body calculation of elastic deuteron-deuteron scattering

Fully converged calculations of deuteron-deuteron elastic scattering observables are performed at energies above three- and four-body breakup threshold. Differential cross sections and analyzing powers are obtained using realistic nucleon-nucleon force models together with the Coulomb repulsion between protons. For all observables we find a very reasonable agreement with the available experimental data limited to deuteron beam energies up to 25.3 MeV.

nucl-th↗

arXiv2015

Measurement of the Doubly-Polarized $\vec{{^3}He}(\vecγ,n)pp$ Reaction at 16.5 MeV and Its Implications for the GDH Sum Rule

We report new measurements of the doubly-polarized photodisintegration of $^3$He at an incident photon energy of 16.5 MeV, carried out at the High Intensity $γ$-ray Source (HI$γ$S) facility located at Triangle Universities Nuclear Laboratory (TUNL). The spin-dependent double-differential cross sections and the contribution from the three--body channel to the Gerasimov-Drell-Hearn (GDH) integrand were extracted and compared with the state-of-the-art three--body calculations. The calculations, which include the Coulomb interaction and are in good agreement with the results of previous measurements at 12.8 and 14.7 MeV, can no longer describe the cross section results at 16.5 MeV. The GDH integrand was found to be about one standard deviation larger than the maximum value predicted by the theories.

nucl-ex↗

arXiv2015

Momentum-space calculation of ${}^4$He triatomic system with realistic potential

The system of three ${}^4\mathrm{He}$ atoms with realistic interactions is studied in the momentum-space framework. It is demonstrated that short and long-range difficulties encountered in the coordinate-space calculations can be reliably resolved in the momentum-space calculations. Well-converged and accurate results are obtained for the ground and excited trimer energies, atom-dimer scattering length, phase shifts, inelasticity parameters, and elastic and breakup cross sections. A significant correction to previously published results is found for the elastic cross section at very low energy.

physics.atom-ph↗