Nuclear Theory·nucl-th

Tuesday·January 30, 2018

11 papers—7 primary·4 cross-listed

01
Precision mass measurements on neutron-rich rare-earth isotopes at JYFLTRAP - reduced neutron pairing and implications for the $r$ -process calculations
M. Vilen · J.M. Kelly · A. Kankainen · M. Brodeur · A. Aprahamian · L. Canete · T. Eronen · A. Jokinen · T. Kuta · I.D. Moore · M.R. Mumpower · D.A. Nesterenko and 7 other authors
The rare-earth peak in the $r$ -process abundance pattern depends sensitively on both the astrophysical conditions and subtle changes in nuclear structure in the region. This work takes an important step elucidating the nuclear structure and reducing the uncertainties in $r$ -process calculations via precise atomic mass measurements at the JYFLTRAP double Penning trap. $^{158}$ Nd, $^{160}$ Pm, $^{162}$ Sm, and $^{164 - 166}$ Gd have been measured for the first time and the precisions for $^{156}$ Nd, $^{158}$ Pm, $^{162, 163}$ Eu, $^{163}$ Gd, and $^{164}$ Tb have been improved considerably. Nuclear structure has been probed via two-neutron separation energies $S_{2 n}$ and neutron pairing energy metrics $D_{n}$ . The data do not support the existence of a subshell closure at $N = 100$ . Neutron pairing has been found to be weaker than predicted by theoretical mass models. The impact on the calculated $r$ -process abundances has been studied. Substantial changes resulting in a smoother abundance distribution and a better agreement with the solar $r$ -process abundances are observed.
nucl-exastro-ph.HEastro-ph.SRnucl-thPRL(2018)·57 citations
02
Effective-range function methods for charged particle collisions
David Gaspard · Jean-Marc Sparenberg
Different versions of the effective-range function method for charged particle collisions are studied and compared. In addition, a novel derivation of the standard effective-range function is presented from the analysis of Coulomb wave functions in the complex plane of the energy. The recently proposed effective-range function denoted as $Δ_{ℓ}$ [Phys. Rev. C 96, 034601 (2017)] and an earlier variant [Hamilton et al., Nucl. Phys. B 60, 443 (1973)] are related to the standard function. The potential interest of $Δ_{ℓ}$ for the study of low-energy cross sections and weakly bound states is discussed in the framework of the proton-proton $^{1} S_{0}$ collision. The resonant state of the proton-proton collision is successfully computed from the extrapolation of $Δ_{ℓ}$ instead of the standard function. It is shown that interpolating $Δ_{ℓ}$ can lead to useful extrapolation to negative energies, provided scattering data are known below one nuclear Rydberg energy (12.5 keV for the proton-proton system). This property is due to the connection between $Δ_{ℓ}$ and the effective-range function by Hamilton et al. that is discussed in detail. Nevertheless, such extrapolations to negative energies should be used with caution because $Δ_{ℓ}$ is not analytic at zero energy. The expected analytic properties of the main functions are verified in the complex energy plane by graphical color-based representations.
nucl-thPRC(2018)·15 citations
03
Tilted-axis wobbling in odd-mass nuclei
R. Budaca
A triaxial rotor Hamiltonian with a rigidly aligned high- $j$ quasiparticle is treated by a time-dependent variational principle, using angular momentum coherent states. The resulting classical energy function have three unique critical points in a space of generalized conjugate coordinates, which can minimize the energy for specific ordering of the inertial parameters and a fixed angular momentum state. Due to the symmetry of the problem, there are only two unique solutions, corresponding to wobbling motion around a principal axis and respectively a tilted-axis. The wobbling frequencies are obtained after a quantization procedure and then used to calculate $E 2$ and $M 1$ transition probabilities. The analytical results are employed in the study of the wobbling excitations of $^{135}$ Pr nucleus, which is found to undergo a transition from low angular momentum transverse wobbling around a principal axis toward a tilted-axis wobbling at higher angular momentum.
nucl-thPRC(2018)·34 citations
04
J/psi with large pT probing the early stage of relativistic heavy ion collisions
Li Guansong (Tianjin U) · Li Yuhuan (Tianjin U) · Shi Wei (Tianjin U)
We study the charmonium suppression in different evolutions of quark gluon plasma (QGP) based on the transport model. In the colliding energies of Large Hadron Collider, charmonium final yields are dominated by the recombination of charm and anti-charm quarks in the deconfined phase. Heavy quark diffusions depend less on the shear viscosity of the bulk medium, which makes the J/psi nuclear modification factor in the entire pT bin shows weak dependence on the shear viscosity of QGP. However, charmonium with high transverse momentum pT, can only be produced in the early stage of nuclear collisions, and is sensitive to the initial energy density (or temperature) of QGP, and can be a probe of the initial dynamical evolutions of quark gluon plasma.
nucl-thhep-ph0 citations
05
Gamow-Teller transitions from high-spin isomers in $N = Z$ nuclei
H. Z. Liang · H. Sagawa · M. Sasano · T. Suzuki · M. Honma
Gamow-Teller (GT) transitions from high-spin isomers are studied using the sum-rule approach and the shell model. The GT transition strengths from the high-spin isomeric states show a stronger collectivity than those from the ground states in two $N = Z$ nuclei, $^{52}$ Fe and $^{94}$ Ag. It is argued that the spin-up and spin-down Fermi spheres involved in the GT transitions from the high-spin isomeric states play important roles. These Fermi spheres are analogous to the isospin-up and isospin-down Fermi spheres for the GT transitions from the ground states in $N > Z$ nuclei and create a strong collectivity.
nucl-thnucl-exPRC(2018)·7 citations
06
Light nuclei production as a probe of the QCD phase diagram
Kai-Jia Sun🇨🇳 · Lie-Wen Chen🇨🇳 · Che Ming Ko🇺🇸 · Jie Pu🇨🇳 · Zhangbu Xu🇺🇸
It is generally believed that the quark-hadron transition at small values of baryon chemical potentials $μ_{B}$ is a crossover but changes to a first-order phase transition with an associated critical endpoint (CEP) as $μ_{B}$ increases. Such a $μ_{B}$ -dependent quark-hadron transition is expected to result in a double-peak structure in the collision energy dependence of the baryon density fluctuation in heavy-ion collisions with one at lower energy due to the spinodal instability during the first-order phase transition and another at higher energy due to the critical fluctuations in the vicinity of the CEP. By analyzing the data on the $p$ , d and $^{3}$ H yields in central heavy-ion collisions within the coalescence model for light nuclei production, we find that the relative neutron density fluctuation $Δ ρ_{n} = ⟨(δ ρ_{n})^{2} ⟩ / ⟨ ρ_{n} ⟩^{2}$ at kinetic freeze-out indeed displays a clear peak at $s_{N N} = 8.8$ GeV and a possible strong re-enhancement at $s_{N N} = 4.86$ GeV. Our findings thus provide a strong support for the existence of a first-order phase transition at large $μ_{B}$ and its critical endpoint at a smaller $μ_{B}$ in the temperature versus baryon chemical potential plane of the QCD phase diagram.
nucl-thhep-phnucl-exPLB(2018)·129 citations
07
Origin of a maximum of astrophysical $S$ factor in heavy-ion fusion reactions at deep subbarrier energies
K. Hagino · A.B. Balantekin · N.W. Lwin · Ei Shwe Zin Thein
The hindrance phenomenon of heavy-ion fusion cross sections at deep subbarrier energies often accompanies a maximum of an astrophysical $S$ factor at a threshold energy for fusion hindrance. We argue that this phenomenon can naturally be explained when the fusion excitation function is fitted with two potentials, with a larger (smaller) logarithmic slope at energies lower (higher) than the threshold energy. This analysis clearly suggests that the astrophysical $S$ factor provides a convenient tool to analyze the deep subbarrier hindrance phenomenon, even though the $S$ factor may have a strong energy dependence for heavy-ion systems unlike that for astrophysical reactions.
nucl-thnucl-exPRC(2018)·6 citations
08
Toward Initial Conditions of Conserved Charges Part I: Spatial Correlations of Quarks and Antiquarks
M. Martinez🇺🇸 · Matthew D. Sievert🇺🇸 · Douglas E. Wertepny🇪🇸
In this paper, we study the spatial correlations among quarks and antiquarks produced at mid-rapidity by gluon pair production in the color glass condensate framework. This paper is the first part of a series in which we calculate a complete set of quark/quark, quark/antiquark, and antiquark/antiquark spatial correlation functions in heavy-light ion collisions, with the goal of incorporating their conserved charges into the initial conditions of hydrodynamics. The physical mechanisms captured in this calculation include geometric, entanglement, and interaction-mediated correlations. In this first paper, we construct the building blocks for the correlations arising from single- and double-pair production, studying in detail the single-pair case and the general features of the double-pair case. We find a rich correlation structure in transverse coordinate space, with different mechanisms dominating over different length scales, and we present explicit results for the quark-antiquark correlations in the single-pair production regime. We reserve a detailed discussion of the double-pair production regime for the next paper in this sequence.
↳ hep-phnucl-thJHEP(2018)·20 citations
09
Universality of Generalized Parton Distributions in Light-Front Holographic QCD
Guy F. de Teramond🇨🇷 · Tianbo Liu🇺🇸 · Raza Sabbir Sufian🇺🇸 · Hans Gunter Dosch🇩🇪 · Stanley J. Brodsky🇺🇸 · Alexandre Deur (HLFHS Collaboration)🇺🇸
The structure of generalized parton distributions is determined from light-front holographic QCD up to a universal reparametrization function $w (x)$ which incorporates Regge behavior at small $x$ and inclusive counting rules at $x \to 1$ . A simple ansatz for $w (x)$ which fulfills these physics constraints with a single-parameter results in precise descriptions of both the nucleon and the pion quark distribution functions in comparison with global fits. The analytic structure of the amplitudes leads to a connection with the Veneziano model and hence to a nontrivial connection with Regge theory and the hadron spectrum.
↳ hep-phhep-exhep-lathep-th+1PRL(2018)·174 citations
10
Proposal to look for the anomalous isotopic symmetry breaking in central diffractive production of the $f_{1} (1285)$ and $a_{0}^{0} (980)$ resonances at the LHC
N.N. Achasov🇷🇺 · G.N. Shestakov🇷🇺
At very high energies, and in the central region ( $x_{F} ≃ 0$ ), the double-Pomeron exchange mechanism gives the dominant contribution to the production of hadrons with the positive $C$ parity and isospin $I = 0$ . Therefore, the observation of resonances in the states with $I = 1$ will be indicative of their production or decay with the isotopic symmetry breaking. Here, we bear in mind the cases of the anomalous breaking of the isotopic symmetry, i.e., when the cross section of the process breaking the isospin is not of the order of $1 0^{- 4}$ of the cross section of the allowed process but of the order of $1%$ . The paper draws attention to the reactions $pp \to p (f_{1} (1285) / f_{1} (1420)) p \to p (π^{+} π^{-} π^{0}) p$ and $pp \to p (K K ˉ) p \to p (a_{0}^{0} (980)) p \to p (η π^{0}) p$ in which a similar situation can be realized, owing to the $K K ˉ$ loop mechanisms of the breaking of isotopic symmetry. We note that there is no visible background in the $π^{+} π^{-} π^{0}$ and $η π^{0}$ channels. Observation of the process $pp \to p (f_{1} (1285)) p \to p (π^{+} π^{-} π^{0}) p$ would be a confirmation of the first results from the VES and BESIII detectors, indicating the very large isospin breaking in the decay $f_{1} (1285)) \to π^{+} π^{-} π^{0}$ .
↳ hep-phhep-exnucl-thPRD(2018)·5 citations
11
Neutrinos, supernovae, and the origin of the heavy elements
Yong-Zhong Qian🇺🇸
Stars of ~8-100 solar masses end their lives as core-collapse supernovae (SNe). In the process they emit a powerful burst of neutrinos, produce a variety of elements, and leave behind either a neutron star or a black hole. The wide mass range for SN progenitors results in diverse neutrino signals, explosion energies, and nucleosynthesis products. A major mechanism to produce nuclei heavier than iron is rapid neutron capture, or the r process. This process may be connected to SNe in several ways. A brief review is presented on current understanding of neutrino emission, explosion, and nucleosynthesis of SNe.
↳ astro-ph.HEastro-ph.SRhep-phnucl-thSCPMA(2018)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE