Nuclear Theory·nucl-th

Wednesday·April 22, 2020

13 papers—10 primary·3 cross-listed

01
Investigation of neutron density distribution of $^{208}$ Pb nucleus when the proton density is constrained to its experimental distribution
A. R. Abdulghany
In this study, two novel improvements for the theoretical calculation of the neutron distributions are presented. First, the available experimental proton distributions are used as a constraint rather than inferred from the calculation. Second, the recently proposed distribution formula, d3pF, is used for the neutron density, which is more detailed than the usual shapes, for the first time in nuclear structure calculation. A semi-microscopic approach for binding energy calculation is considered in this study, however, the proposed improvements can be introduced to any other approach. The ground state binding energy and neutron density distribution of $^{208}$ Pb nucleus are calculated by optimizing the binding energy considering three different distribution formulae. The implementation of the proposed improvements leads to a qualitative and quantitative improvement in the calculation of the binding energy and neutron density distribution. The calculated binding energy agrees with the experimental value, and the calculated neutron density shows fluctuations within the nuclear interior, which agrees with the predictions of self-consistent approaches.
nucl-thCPC(2020)·5 citations
02
Anomaly in decay of 8Be and 4He -- can an observed light boson mediate low energy nucleon-nucleon interactions ?
M. Veselsky🇨🇿 · V. Petousis🇨🇿 · J. Leja🇸🇰
We present a hypothesis that the anomaly in the folding angle distribution of electron-positron pairs, emitted in the decay of the excited levels of nucleus $^{8}$ Be and $^{4}$ He can be related to the cluster structure of the decaying state. Furthermore, we present a hypothesis that the potentially observed boson with re st mass $m_{X}$ =17 MeV can mediate the nucleon-nucleon interaction at the low-energy regime of QCD, in particular in the weakly bound cluster state p+ $^{7}$ Li, $^{3}$ H. We present a possible equations of state of symmetric nuclear matter corresponding to the vector meson mass $m_{v}$ =17 MeV, obtained using relativistic mean field theory of nuclear force, QHD-I in particular, with physically relevant incompessibility K $_{0}$ =240-260 MeV and the values of couplings $g_{v}$ , $g_{s}$ lower than unity. Based on concepts of chiral symmetry breaking, we show that reduction of the rest mass of pseudoscalar particle from physical value $m_{π}$ =135 MeV to $m_{X}$ =17 MeV is equivalent to reduction of the quark mass from dynamical value around 310 MeV down to current quark mass around 5 MeV ( $\frac{m _{X}^{2}}{m _{q, c u r r}} ≃ \frac{m _{π}^{2}}{m _{q, d y n}}$ ). Corresponding version of Goldberger-Treiman relation leads to the value of coupling close to the results from relativistic mean field theory of nuclear force. Both model approaches thus point towards apparent restoration of chiral symmetry in nucleon-nucleon interaction at large distances, possibly via bounce into false instanton vacuum. Observation of boson with rest mass $m_{X}$ =17 MeV in the decay of high lying excited states of $^{8}$ Be and $^{4}$ He can possibly resolve one of the longest lasting open questions in nuclear physics.
nucl-thhep-phnucl-exJ.Phys.G(2021)·10 citations
03
Light $p$ -shell nuclei with cluster structures ( $4 \leq A \leq 16$ ) in nuclear matter
Gerd Röpke
The composition of hot and dense nuclear matter is calculated including the $1 p$ -shell nuclei $4 \leq A \leq 16$ . In-medium shifts, in particular Pauli blocking, are determined by the intrinsic wave function of the nuclei. Results are given within a shell-model approach for the nucleon wave function. Light nuclei are not always well described by the shell model. The 'clustered' nucleus $^{8}$ Be exhibits strong correlation effects because of $α$ -like clustering. Intrinsic cluster structures are also significant for the nuclei $^{6}$ Li, $^{7}$ Li, $^{7}$ Be, and $^{9}$ Be. The contribution of the relatively rare elements Li, Be, and B, to the equation of state (EoS) of matter near the saturation density is overestimated in simple approaches such as the nuclear statistical equilibrium (NSE) model. Both, the treatment of continuum correlations and the account of in-medium modifications are considered for the contribution of $^{5}$ He and $^{4}$ H clusters. Compared to the extended NSE including unstable nuclei, the contributions of the corresponding P $_{3/2}$ channel with $A = 5, Z = 2$ and P $_{2}$ channel with $A = 4, Z = 1$ , respectively, to the EoS are strongly suppressed at high densities owing to Pauli blocking effects. For the shifts of the binding energies of the light $p$ -shell nuclei, simple fit formula are given to calculate the composition of hot and dense matter in a wide parameter range.
nucl-thPRC(2020)·36 citations
04
Skewness of mean transverse momentum fluctuations in heavy-ion collisions
Giuliano Giacalone🇫🇷 · Fernando G. Gardim🇧🇷 · Jacquelyn Noronha-Hostler🇺🇸 · Jean-Yves Ollitrault🇫🇷
We propose the skewness of mean transverse momentum, $⟨ p_{t} ⟩$ , fluctuations as a fine probe of hydrodynamic behavior in relativistic nuclear collisions. We describe how the skewness of the $⟨ p_{t} ⟩$ distribution can be analyzed experimentally, and we use hydrodynamic simulations to predict its value. We predict in particular that $⟨ p_{t} ⟩$ fluctuations have positive skew, which is significantly larger than if particles were emitted independently. We elucidate the origin of this result by deriving generic formulas relating the fluctuations of $⟨ p_{t} ⟩$ to the fluctuations of the early-time thermodynamic quantities. We postulate that the large positive skewness of $⟨ p_{t} ⟩$ fluctuations is a generic prediction of hydrodynamic models.
nucl-thhep-exhep-phnucl-exPRC(2021)·51 citations
05
Fusion hindrance of $^{48}$ Ti + $^{138}$ Ba reaction
K.K. Rajesh · M.M. Musthafa
We have already measured the ER excitation function of $^{48}$ Ti + $^{138}$ Ba reaction around the Coulomb barrier. While a detailed report of measurement of ER excitation function of $^{48}$ Ti + $^{138}$ Ba is available in literature, the present paper compares it with other channels forming the same compound nucleus. The experiment was performed at IUAC, New Delhi for lab energies from 189.3 to 234.4 MeV, where the ER cross sections show an abrupt fall beyond 160.03 MeV. The decrease in ER cross section is attributed to non compound nuclear reaction such as quasi-fission (QF). A comparison with statistical model code PACE 4 also shows significant deviation of the experimental data from theoretical predictions. When this reaction is compared with $^{86}$ Kr + $^{100}$ Mo and $^{64}$ Ni + $^{122}$ Sn forming the same compound nucleus $^{186} P t^{*}$ , the symmetric systems show more ERs than the asymmetric one and it is against the general trend. Preliminary study predict the influence of deformation and isospin asymmetry in the abrupt fall of ER cross section than that of the symmetric systems. A detailed theoretical analysis of the systems are in progress and will be published shortly.
nucl-th0 citations
06
Probing the electromagnetic fields in ultrarelativistic collisions with leptons from $Z^{0}$ decay and charmed mesons
Yifeng Sun🇮🇹 · Salvatore Plumari🇮🇹 · Vincenzo Greco🇮🇹
Ultrarelativistic heavy ion collisions are expected to generate a huge electromagnetic field, $e B \approx 1 0^{18} G a u ss$ , that induces a splitting of the directed flow, $v_{1} = ⟨ p_{x} / p_{T} ⟩$ , of charged particles and anti-particles. Such a splitting for charmed meson manifests even for neutral particle/anti-particles pairs ( $D^{0}, D^{0}$ ), hence being also a unique probe of the formation of the quark-gluon plasma phase. For the first time here we show that electromagnetic field may generate a $v_{1} (D^{0}) - v_{1} (D^{0})$ as huge as the one recently observed at LHC against early expectations. Within this new research topic we point out a novel measurement: $v_{1}$ of leptons from $Z^{0}$ decay and its correlation to that of $D$ and $B$ mesons. The correlation for $Δ v_{1}$ of $l^{+} - l^{-}$ , $D^{0} - D^{0}$ and $B^{0} - B^{0}$ would provide a strong probe of the electromagnetic origin of the splitting and hence of the formation of a quark-gluon plasma phase with heavy quarks as degrees of freedom. The case of the $v_{1} (l^{\pm})$ presents features due to the peculiar form of the $p_{T}$ spectrum never appreciated before in the study of heavy ion collisions. We specifically predict a sudden change of the $Δ v_{1} (p_{T})$ of leptons at $p_{T} = 45$ GeV $/ c$ , that can be traced back to a universal relation of $Δ v_{1}$ with the slope of the $p_{T}$ particle distribution and the integrated effect of the Lorentz force.
nucl-thPLB(2021)·33 citations
07
New approach to search for parity-even and parity-odd time-reversal violation beyond the Standard Model in a storage ring
N.N. Nikolaev🇷🇺 · F. Rathmann🇩🇪 · A.J. Silenko🇷🇺 · Yu. Uzikov🇷🇺
Time-reversal breaking and parity-conserving millistrong interactions, suggested in 1965, still remain a viable mechanism of CP-violation beyond the Standard Model. One of its possible manifestations is the T-odd asymmetry in the transmission of tensor-polarized deuterons through a vector-polarized hydrogen gas target. Upon the rotation of the deuteron polarization from the vertical direction into the ring plane, the T-odd asymmetries, odd against the reversal of the proton polarization in the target, will continuously oscillate with first or second harmonics of the spin precession frequency. The Fourier analysis of the oscillating T-odd asymmetries allows for an easy separation from background persistent in conventional experiments employing static vector and tensor polarizations.
nucl-thhep-exhep-phnucl-ex+1PLB(2020)·19 citations
08
Nucleons pair shell model in M-scheme
BingCheng He🇨🇳 · Yu Zhang🇨🇳 · Lei Li · YanAn Luo🇨🇳 · Feng Pan🇨🇳 · J. P. Draayer🇺🇸
The nucleon pair shell model (NPSM) is casted into the so-called M-scheme for the cases with isospin symmetry and without isospin symmetry. The odd system and even system are treated on the same foot. The uncoupled commutators for nucleon-pairs, which are suitable for M-scheme, are given. Explicit formula of matrix elements in M-scheme for overlap, one-body operators, two-body operators are obtained. It is found that the $c p u$ time used in calculating the matrix elements in M-scheme is much shorter than that in the J-scheme of NPSM.
nucl-thPRC(2020)·23 citations
09
Time-dependent generator coordinate method study of fission: mass parameters
Jie Zhao · Tamara Nikšić · Dario Vretenar · Shan-Gui Zhou
Collective mass tensors derived in the cranking approximation to the adiabatic time-dependent Hartree-Fock-Bogoliubov (ATDHFB) method are employed in a study of induced fission dynamics. Together with a collective potential determined in deformation-constrained self-consistent mean-field calculations based on nuclear energy density functionals, the mass tensors specify the collective Hamiltonian that governs the time evolution of the nuclear wave function from an initial state at equilibrium deformation, up to scission and the formation of fission fragments. In an illustrative calculation of low-energy induced fission of $^{228}$ Th, $^{230}$ Th, $^{234}$ U, and $^{240}$ Pu, we compare the non-perturbative and perturbative cranking ATDHFB mass tensors in the plane of axially-symmetric quadrupole and octupole deformations, as well as the resulting charge yields.
nucl-thnucl-exPRC(2020)·20 citations
10
The time-dependent generator coordinate method in nuclear physics
Marc Verriere🇺🇸 · David Regnier🇫🇷
The emergence of collective behaviors and the existence of large amplitude motions are both central features in the fields of nuclear structure and reactions. From a theoretical point of view, describing such phenomena requires increasing the complexity of the many-body wavefunction of the system to account for long-range correlations. One of the challenges, when going in this direction, is to keep the approach tractable within our current computational resources while gaining a maximum of predictive power for the phenomenon under study. In the Generator Coordinate Method (GCM), the many-body wave function is a linear superposition of (generally non-orthogonal) many-body states (the generator states) labeled by a few collective coordinates. Such a method has been widely used in structure studies to restore the symmetries broken by single-reference approaches. In the domain of reactions, its time-dependent version (TDGCM) has been developed and applied to predict the dynamics of heavy-ion collisions or fission where the collective fluctuations play an essential role. In this review, we present the recent developments and applications of the TDGCM in nuclear reactions. We recall the formal derivations of the TDGCM and its most common approximate treatment, the Gaussian Overlap Approximation. We also emphasize the Schrödinger Collective-Intrinsic Model (SCIM) variant focused on the inclusion of quasiparticle excitations into the description. Finally, we highlight several exploratory studies related to a TDGCM built on time-dependent generator states.
nucl-thFront.in Phys.(2020)·50 citations

Affiliations

first authorsco-authorsvia INSPIRE