Nuclear Theory·nucl-th

Wednesday·January 26, 2022

9 papers—4 primary·5 cross-listed

01
Universal Properties of Weakly Bound Two-Neutron Halo Nuclei
Masaru Hongo🇺🇸 · Dam Thanh Son🇺🇸
We construct an effective field theory of a two-neutron halo nucleus in the limit where the two-neutron separation energy $B$ and the neutron-neutron two-body virtual energy $ϵ_{n}$ are smaller than any other energy scale in the problem, but the scattering between the core and a single neutron is not fine-tuned, and the Efimov effect does not operate. The theory has one dimensionless coupling which formally runs to a Landau pole in the ultraviolet. We show that many properties of the system are universal in the double fine-tuning limit. The ratio of the mean-square matter radius and charge radius is found to be $⟨ r_{m}^{2} ⟩ / ⟨ r_{c}^{2} ⟩ = A f (ϵ_{n} / B)$ , where $A$ is the mass number of the core and $f$ is a function of the ratio $ϵ_{n} / B$ which we find explicitly. In particular, when $B ≫ ϵ_{n}$ , $⟨ r_{m}^{2} ⟩ / ⟨ r_{c}^{2} ⟩ = \frac{2}{3} A$ . The shape of the the $E 1$ dipole strength function also depends only on the ratio $ϵ_{n} / B$ and is derived in explicit analytic form. We estimate that for the $^{22}$ C nucleus higher-order corrections to our theory are of order 20% or less if the two-neutron separation energy is less than 100 keV and the $s$ -wave scattering length between a neutron and a $^{20}$ C nucleus is less than 2.8 fm.
nucl-thcond-mat.quant-gashep-thPRL(2022)·25 citations
02
Photoproduction of pion pairs at high energy and small angles
S. Gevorkyan🇷🇺 · I. Larin🇺🇸 · R. Miskimen🇺🇸 · E. Smith🇺🇸
We explore the photoproduction mechanisms for charged and neutral pion pairs off a heavy nucleus at threshold. We calculate the production of charged pairs in the Coulomb field of the nucleus in the Born approximation using explicit expressions for the differential cross sections and their connection with the total cross-section. The production of sigma mesons at threshold and their subsequent decay into pions is an important mechanism and is investigated quantitatively in a framework that can be used for both charged and neutral pions. Sigma mesons can be produced via electromagnetic (photon exchange) or strong (omega exchange) interactions. For neutral pions, another important production mechanism consists of the two-step process where charged pions are produced first and then charge exchange into two neutral pions. Differential and total cross sections are computed for each production mechanism.
nucl-thPRC(2022)·2 citations
03
Rare Isotope Formation in Complete Fusion and Multinucleon Transfer Reactions in Collisions of 48Ca +248Cm around Coulomb Barrier Energies
Peng-Hui Chen · Fei Niu · Xin-Xing Xu · Zu-Xing Yang · Xiang-Hua Zeng · Zhao-Qing Feng
Within the framework of the dinuclear system model, the reaction mechanisms for synthesizing target-like isotopes from Bk to compound nuclei Lv are thoroughly investigated in complete and incomplete fusion reaction of $^{48}$ Ca + $^{248}$ Cm around Coulomb barrier energies. Production cross-section of $^{292, 293}$ Lv as a function of excitation energy in fusion-evaporation reactions and target-like isotopic yields in multinucleon transfer reactions are evaluated, in which a statistical approach is used to describe the decay process of excited nuclei. The available experimental data can be reproduced well with the model reasonably. The products of all possible formed isotopes in the dynamical pre-equilibrium process for collision partners at incident energy $E_{lab}$ = 5.5 MeV/nucleon are exported, systematically. It is found that the quasi-fission fragments are dominant in the yields. The optimal pathway from the target to compound nuclei shows up along the valley of potential surface energy. The effective impact parameter of two colliding partners leading to compound nuclei is selected from head-on collision to semi-central collision with $L$ = 52 $ℏ$ . The timescale boundary between complete fusion and multinucleon transfer reactions is about 5.7 $\times 1 0^{- 21}$ s with effective impact parameters. Synthesis cross-section of unknown neutron-rich actinides from Bk to Rf have been predicted around several nanobarns.
nucl-thPRC(2022)·4 citations
04
Operator overlaps in harmonic oscillator bases with different oscillator lengths
L.M. Robledo🇪🇸
We apply a formalism recently developed to carry out Generator Coordinate Method calculations using a set of Hartree- Fock- Bogoliubov wave functions, where each of the members of the set can be expanded in an arbitrary basis. In this paper it is assumed that the HFB wave functions are expanded in Harmonic Oscillator (HO) bases with different oscillator lengths. General expressions to compute the required matrix elements of arbitrary operators are given. The application of the present formalism to the case of fission is illustrated with an example.
nucl-thcond-mat.str-elquant-phPRC(2022)·10 citations
05
Color-flavor dependence of the Nambu-Jona-Lasinio model and QCD phase diagram
Aftab Ahmad🇵🇰 · Ali Murad🇵🇰
We study the dynamical chiral symmetry breaking/restoration for the various numbers of light quarks flavors $N_{f}$ and colors $N_{c}$ , using the Nambu-Jona-Lasinio (NJL) model of quarks, dressed with a color-flavor dependence of effective coupling. Initially, we set $N_{f} = 2$ , and varying the number of colors $N_{c}$ , we find that the dynamical chiral symmetry is broken when $N_{c}$ exceeds to its critical value $N_{c}^{c} \approx 2.2$ . Secondly, we take $N_{c} = 3$ , and varying $N_{f}$ , we observed that the dynamical chiral symmetry is restored when $N_{f}$ reaches to its critical value $N_{f}^{c} \approx 8$ . The strong interplay observed between $N_{c}$ and $N_{f}$ , i.e., $N_{c}$ anti-screens the strong interactions by strengthening the dynamical mass and quark-antiquark condensate, while $N_{f}$ screens the strong interaction by suppressing both the parameters. We further sketch the quantum chromodynamics (QCD) phase diagram at finite temperature $T$ and quark chemical potential $μ$ for various $N_{c}$ and $N_{f}$ . At finite $T$ and $μ$ , we observed that the critical number of colors $N_{c}^{c}$ enhances while the critical number of flavors $N_{f}^{c}$ suppresses as $T$ and $μ$ increases. Of course, the parameters $T$ and $μ$ produce the screening effect. Consequently, the critical temperature $T_{c}$ , $μ_{c}$ and co-ordinates of the critical endpoint $(T_{c}^{E}, μ_{c}^{E})$ in the QCD phase diagram enhances as $N_{c}$ increases while suppresses when $N_{f}$ increases. Our findings agree with the Lattice QCD and Schwinger-Dyson equations predictions.
↳ hep-phnucl-thCPC(2022)·7 citations
06
Production characteristics of light (anti-)nuclei from (anti-)nucleon coalescence in heavy ion collisions at energies employed at the RHIC beam energy scan
Xiang-Yu Zhao🇨🇳 · Yan-Ting Feng🇨🇳 · Feng-Lan Shao🇨🇳 · Rui-Qin Wang🇨🇳 · Jun Song🇨🇳
With the kinetic freeze-out nucleons and antinucleons obtained from the quark combination model, we study the production of light nuclei and antinuclei in the (anti-)nucleon coalescence mechanism in relativistic heavy ion collisions. We derive analytic formulas of the momentum distributions of different light nuclei and apply them to compute transverse momentum ( $p_{T}$ ) spectra of (anti-)deuterons ( $d$ , $d ˉ$ ) and (anti-)tritons ( $t$ , $t ˉ$ ) in Au-Au collisions at $s_{N N} =$ 7.7, 11.5, 19.6, 27, 39, 54.4 GeV. We find that the experimental data available for these $p_{T}$ spectra can be well reproduced. We further study the yields and yield ratios of different light (anti-)nuclei and naturally explain their interesting behaviors as a function of the collision energy. We especially point out that the multi-particle yield ratio $tp / d^{2}$ should be carefully corrected from hyperon weak decays for protons to probe the production characteristics of light nuclei. All of our results show that the coalescence mechanism for (anti-)nucleons plays a dominant role for the production of light nuclei and antinuclei at the RHIC beam energy scan energies.
↳ hep-phhep-exnucl-thPRC(2022)·11 citations
07
Investigating the predicted breathing-mode excitation of the Hoyle state
K. C. W. Li · F. D. Smit · P. Adsley · R. Neveling · P. Papka · E. Nikolskii · J. W. Brümmer · L. M. Donaldson · M. Freer · M. N. Harakeh · F. Nemulodi · L. Pellegri and 16 other authors
Knowledge of the low-lying monopole strength in $^{12} C$ $-$ the Hoyle state in particular $-$ is crucial for our understanding of both the astrophysically important $3 α$ reaction and of $α$ -particle clustering. Multiple theoretical models have predicted a breathing mode of the Hoyle State at $E_{x} \approx 9$ MeV, corresponding to a radial in-phase oscillation of the underlying $α$ clusters. The $^{12} C (α, α^{'})^{12} C$ and $^{14} C (p, t)^{12} C$ reactions were employed to populate states in $^{12}$ C in order to search for this predicted breathing mode. A self-consistent, simultaneous analysis of the inclusive spectra with R-matrix lineshapes, together with angular distributions of charged-particle decay, yielded clear evidence for excess monopole strength at $E_{x} \approx 9$ MeV which is highly collective. Reproduction of the experimentally observed inclusive yields using a fit, with consistent population ratios for the various broad states, required an additional source of monopole strength. The interpretation of this additional monopole resonance as the breathing-mode excitation of the Hoyle state would provide evidence supporting a $D_{3 h}$ symmetry for the Hoyle state itself. The excess monopole strength may complicate analysis of the properties of the Hoyle state, modifying the temperature dependence of the $3 α$ rate at $T_{9} ≳ 2$ and ultimately, the predicted nucleosynthesis in explosive stars.
↳ nucl-exnucl-thPLB(2022)·12 citations
08
Strong decays of multi-strangeness baryon resonances in the quark model
Ahmad Jafar Arifi🇰🇷 · Daiki Suenaga🇯🇵 · Atsushi Hosaka🇯🇵 · Yongseok Oh🇰🇷
Decay properties of multi-strangeness $Ξ$ and $Ω$ baryon resonances are investigated within the constituent quark model by including relativistic corrections. The strong decay widths of various $Ξ$ and $Ω$ resonances are computed and tested for internal quark configurations to pin down their spin-parity ( $J^{P}$ ) quantum numbers and internal structures. We found that the Roper-like resonances in the multi-strangeness sector have large decay widths bearing resemblances to their siblings in light and heavy baryon sectors. In addition, we obtained the decay ratio for the $Ω (2012)$ as $Γ (Ω \to Ξ K ˉ π) /Γ (Ω \to Ξ K ˉ) = 4.5%$ , which is consistent with the experimental data when $J^{P} = 3/ 2^{-}$ is assigned. This observation holds the possibility that the $Ω (2012)$ could naturally be explained as a three-quark state in the quark model. The decays of other low-lying $Ξ$ and $Ω$ resonances are systematically analyzed, which would be useful to unveil the structure of these resonances in future experiments.
↳ hep-phhep-exnucl-thPRD(2022)·38 citations
09
Kinetics of hydrodynamic pions in chiral perturbation theory
Juan M. Torres-Rincon🇪🇸 · Derek Teaney🇺🇸
We determine the kinetic coefficients of ultrasoft pions using chiral perturbation theory at finite temperature close to the chiral limit. This is used to compute the axial charge diffusion and damping coefficients in the hydrodynamic effective theory for these pion waves. We show that to provide a leading order answer for these coefficients one needs to explore the dynamics of hard, soft, and ultrasoft pion modes, which are represented microscopically by the appropriate kinetic and hydrodynamic descriptions..
↳ hep-phnucl-thPRD(2022)·5 citations

Affiliations

first authorsco-authorsvia INSPIRE