Nuclear Theory·nucl-th

Wednesday·March 7, 2018

10 papers—4 primary·6 cross-listed

01
Hot fusion reactions with deformed nuclei for synthesis of superheavy nuclei: an extension of the fusion-by-diffusion model
K. Hagino
The fusion-by-diffusion model proposed by Swiatecki {\it et al.} [Phys. Rev. C71, 014602 (2005)] has provided a simple and convenient tool to estimate evaporation residue cross sections for superheavy nuclei. I extend this model by taking into account deformation of the target nucleus, and discuss the role of orientation of deformed target in hot fusion reactions at energies around the Coulomb barrier. To this end, I introduce an injection point for the diffusion process over an inner barrier which depends on the orientation angle. I apply this model to the $^{48}$ Ca+ $^{248}$ Cm reaction and show that the maximum of evaporation residue cross section appears at an energy slightly above the height of the capture barrier for the side collision, for which the effective inner barrier is considerably lower than that for the tip collision, thus enhancing the diffusion probability. I also discuss the energy dependence of the injection point, and show that a large part of the energy dependence found in the previous analyses can be attributed to the deformation effect of a target nucleus.
nucl-thnucl-exPRC(2018)·40 citations
02
$α$ decay properties of $^{296}$ Og within the two-potential approach
Jun-Gang Deng · Jie-Cheng Zhao · Jiu-Long Chen · Xi-Jun Wu · Xiao-Hua Li
The present work is a continuations of our previous paper [J.-G. Deng, et al., Chin. Phys. C, {\bf41}: 124109 (2017)]. In present work, the $α$ decay half-life of unknown nucleus $^{296}$ Og is predicted within the two-potential approach and the hindrance factors of all 20 even-even nuclei in the same region with $^{296}$ Og, i.e. proton number $82 < Z < 126$ and neutron number $152 < N < 184$ , from $^{250}$ Cm to $^{294}$ Og are extracted. The prediction is 1.09 ms within a factor of 5.12. In addition, based on the latest experimental data, a new set of parameters of $α$ decay hindrance factors for the even-even nuclei in this region considering the shell effect and proton-neutron interaction are obtained.
nucl-thnucl-exCPC(2018)·19 citations
03
Nuclear quantum shape-phase transitions in odd-mass systems
S. Quan · Z. P. Li · D. Vretenar · J. Meng
Microscopic signatures of nuclear ground-state shape phase transitions in odd-mass Eu isotopes are explored starting from excitation spectra and collective wave functions obtained by diagonalization of a core-quasiparticle coupling Hamiltonian based on energy density functionals. As functions of the physical control parameter -- the number of nucleons -- theoretical low-energy spectra, two-neutron separation energies, charge isotope shifts, spectroscopic quadrupole moments, and $E 2$ reduced transition matrix elements accurately reproduce available data, and exhibit more pronounced discontinuities at neutron number $N = 90$ , compared to the adjacent even-even Sm and Gd isotopes. The enhancement of the first-order quantum phase transition in odd-mass systems can be attributed to a shape polarization effect of the unpaired proton which, at the critical neutron number, starts predominantly coupling to Gd core nuclei that are characterized by larger quadrupole deformation and weaker proton pairing correlations compared to the corresponding Sm isotopes.
nucl-thnucl-exPRC(2018)·30 citations
04
Electric structure of shallow D-wave states in Halo EFT
J. Braun🇩🇪 · W. Elkamhawy🇩🇪 · R. Roth🇩🇪 · H.-W. Hammer🇩🇪
We compute the electric form factors of one-neutron halo nuclei with shallow D-wave states up to next-to-leading order and the E2 transition from the S-wave to the D-wave state up to leading order in Halo Effective Field Theory (Halo EFT). The relevant degrees of freedom are the core and the halo neutron. The EFT expansion is carried out in powers of $R_{cor e} / R_{ha l o}$ , where $R_{cor e}$ and $R_{ha l o}$ denote the length scales of the core and the halo, respectively. We propose a power counting scenario for weakly-bound states in one-neutron Halo EFT and discuss its implications for higher partial waves in terms of universality. The scenario is applied to the $\frac{5}{2}^{+}$ first excited state and the $\frac{1}{2}^{+}$ ground state of $^{15} C$ . We obtain several universal correlations between electric observables and use data for the E2 transition $\frac{5}{2}^{+} \to \frac{1}{2}^{+}$ together with ab initio results from the No-Core Shell Model to predict the quadrupole moment.
nucl-thhep-phJ.Phys.G(2019)·11 citations
05
First Measurement of the Ti $(e, e^{'}) X$ Cross Section at Jefferson Lab
H. Dai🇺🇸 · M. Murphy🇺🇸 · V. Pandey🇺🇸 · D. Abrams🇺🇸 · D. Nguyen🇺🇸 · B. Aljawrneh🇺🇸 · S. Alsalmi🇺🇸 · A. M. Ankowski🇺🇸 · J. Bane🇺🇸 · S. Barcus🇺🇸 · O. Benhar🇮🇹 · V. Bellini and 45 other authors
To probe CP violation in the leptonic sector using GeV energy neutrino beams in current and future experiments using argon detectors, precise models of the complex underlying neutrino and antineutrino interactions are needed. The E12-14-012 experiment at Jefferson Lab Hall A was designed to perform a combined analysis of inclusive and exclusive electron scatterings on both argon ( $N = 22$ ) and titanium ( $Z = 22$ ) nuclei using GeV energy electron beams. The measurement on titanium nucleus provides essential information to understand the neutrino scattering on argon, large contribution to which comes from scattering off neutrons. Here we report the first experimental study of electron-titanium scattering as double differential cross section at beam energy $E = 2.222$ GeV and electron scattering angle $θ = 15.541$ deg, measured over a broad range of energy transfer, spanning the kinematical regions in which quasielastic scattering and delta production are the dominant reaction mechanisms. The data provide valuable new information needed to develop accurate theoretical models of the electromagnetic and weak cross sections of these complex nuclei in the kinematic regime of interest to neutrino experiments.
↳ nucl-exhep-exnucl-thPRC(2018)·44 citations
06
Halo structure of $^{8}$ B determined from intermediate energy proton elastic scattering in inverse kinematics
G.A. Korolev🇷🇺 · A.V. Dobrovolsky🇷🇺 · A.G. Inglessi🇷🇺 · G.D. Alkhazov🇷🇺 · P. Egelhof🇩🇪 · A. Estrade🇩🇪 · I. Dillmann🇩🇪 · F. Farinon🇩🇪 · H. Geissel🇩🇪 · S. Ilieva🇩🇪 · Y. Ke🇩🇪 · A.V. Khanzadeev🇷🇺 and 15 other authors
The absolute differential cross section for small-angle proton elastic scattering on the proton-rich $^{8}$ B nucleus has been measured in inverse kinematics for the first time. The experiment was performed using a secondary radioactive beam with an energy of 0.7 GeV/u at GSI, Darmstadt. The active target, namely hydrogen-filled time projection ionization chamber IKAR, was used to measure the energy, angle and vertex point of the recoil protons. The scattering angle of the projectiles was simultaneously determined by the tracking detectors. The measured differential cross section is analyzed on the basis of the Glauber multiple scattering theory using phenomenological nuclear-density distributions with two free parameters. The radial density distribution deduced for $^{8}$ B exhibits a halo structure with the root-mean-square (rms) matter radius $R_{m} = 2.58 (6)$ fm and the rms halo radius $R_{h} = 4.24 (25)$ fm. The results on $^{8}$ B are compared to those on the mirror nucleus $^{8}$ Li investigated earlier by the same method. A comparison is also made with previous experimental results and theoretical predictions for both nuclei.
↳ nucl-exnucl-thPLB(2018)·43 citations
07
Beam energy dependence of squeeze-out effect on the directed and elliptic flow in Au+Au collisions at high baryon density region
Chao Zhang🇨🇳 · Jiamin Chen🇨🇳 · Xiaofeng Luo🇨🇳 · Feng Liu🇨🇳 · Yasushi Nara🇯🇵
We present a detailed analysis of the beam energy dependence of the mechanisms for the generation of directed and elliptic flows in Au+Au collisions focusing on the role of hadronic rescattering and spectator shadowing within a microscopic transport model JAM with different equation of state. A systematic study of the beam energy dependence is performed for Au+Au collisions at $s_{N N} = 2.3 - 62.4$ GeV. The transition of the dynamical origin of the directed flow is observed. We find that the initial Glauber type nucleon-nucleon collisions generate negative $v_{1}$ for nucleons at midrapidity due to the presence of spectator matter, and this negative nucleon $v_{1}$ is turned to be positive by the meson-baryon interactions at the beam energy region of $s_{N N} < 30$ GeV. In contrast, above 30 GeV there is no spectator shadowing at midrapidity, and initial nucleon-nucleon collisions do not generate directed flow, but subsequent rescatterings among produced particles generate negative $v_{1}$ for nucleons. It is demonstrated that negative pion-directed flows are mostly generated by the interaction with the spectator matter. It is also shown that the squeeze-out effect is largely suppressed in the case of softening, which leads to the enhancement of elliptic flow around $s_{N N} = 5 - 7$ GeV. The elliptic flow at midrapidity above 10 GeV is not influenced by the squeeze-out due to spectator matter, while its effect is seen at the forward rapidity range of $y / y_{c.m.} > 0.5$ , which decreases as beam energy increases.
↳ nucl-exhep-exhep-phnucl-thPRC(2018)·31 citations
08
Nearly isentropic flow at sizeable $η / s$
Aleksi Kurkela🇨🇭 · Urs Achim Wiedemann🇨🇭 · Bin Wu🇨🇭
Non-linearities in the harmonic spectra of hadron-nucleus and nucleus-nucleus collisions provide evidence for the dynamical response to azimuthal spatial eccentricities. Here, we demonstrate within the framework of transport theory that even the mildest interaction correction to a picture of free-streaming particle distributions, namely the inclusion of one perturbatively weak interaction ("one-hit dynamics"), will generically give rise to all observed linear and non-linear structures. We further argue that transport theory naturally accounts within the range of its validity for realistic signal sizes of the linear and non-linear response coefficients observed in azimuthal momentum anisotropies with a large mean free path of the order of the system size in peripheral ( $\sim 50%$ centrality) PbPb or central pPb collisions. The shear viscosity to entropy density ratio $η / s$ of such a transport theory is approximately an order of magnitude larger than that of an almost perfect fluid. The phenomenological success of transport simulations thus challenges the perfect fluid paradigm of ultra-relativistic nucleus-nucleus and hadron-nucleus collisions.
↳ hep-phhep-exnucl-exnucl-thPLB(2018)·67 citations
09
High Precision Statistical Landau Gauge Lattice Gluon Propagator Computation vs. the Gribov-Zwanziger approach
David Dudal🇧🇪 · Orlando Oliveira🇵🇹 · Paulo J. Silva🇵🇹
The compatibility of the results from the Gribov-Zwanziger tree level prediction and lattice simulations, using large statistical ensembles, for the Landau gauge gluon propagator are investigated, thereby complementing earlier work using small-scale statistics. Our results show that the data is well described by the tree level estimate only up to momenta $p ≲ 1$ GeV while clearly favoring the so-called Refined Gribov-Zwanziger scenario, implying particular relations between certain possible $d = 2$ condensates. We also provide a global fit of the lattice data which interpolates between the above scenario at low momenta and the usual continuum one-loop renormalization improved perturbation theory after introducing an infrared log-regularizing term.
↳ hep-lathep-phhep-thnucl-thAnnals Phys.(2018)·78 citations
10
Methods for separation of deuterons produced in the medium and in jets in high energy collisions
Natasha Sharma🇮🇳 · Tony Perez🇺🇸 · Andy Castro🇺🇸 · Lokesh Kumar🇮🇳 · Christine Nattrass🇺🇸
Coalescence has long been used to describe the production of light (anti-)nuclei in heavy ion collisions. The same underlying mechanism may also exist in jets when a proton and a neutron are close enough in phase space to form a deuteron. We model deuteron production in jets by applying an afterburner to protons and neutrons produced in PYTHIA for $p$ + $p$ collisions at a center of mass energy $s =$ 7 TeV. PYTHIA provides a reasonable description of the proton spectra and the shape of the deuteron spectrum predicted by the afterburner is in agreement with the data. We show that the rise in the coalescence parameter $B_{2}$ with momentum observed in data is consistent with coalescence in jets. We show that di-hadron correlations can be used to separate the contributions from the jet and the underlying event. This model predicts that the conditional coalescence parameter in the jet-like correlation should be independent of the trigger momentum.
↳ hep-phnucl-thPRC(2018)·13 citations

Affiliations

first authorsco-authorsvia INSPIRE