Nuclear Theory·nucl-th

Monday·September 28, 2015

14 papers—6 primary·8 cross-listed

01
Additional strange resonances from Lattice QCD
Michał Marczenko🇵🇱
Recent Lattice QCD (LQCD) studies suggest that there are missing resonances in the strange sector of the Hadron Resonance Gas (HRG) model. By adopting the continuous Hagedorn mass spectrum, we present how different medium compositions influence the HRG predictions of conserved charge fluctuations. It is shown that missing strange resonances may be partially accounted for by applying the Hagedorn mass spectrum extracted from experimentally established hadrons. On the other hand, the strange-baryonic spectra, extracted from LQCD results for fluctuations, are found to be consistent with the unconfirmed states in the Particle Data Group (PDG) database, whilst the strange-mesonic spectrum points towards yet undiscovered states in the intermediate mass region.
nucl-thhep-latJ.Phys.Conf.Ser.(2016)·0 citations
02
Extension and parameterization of high-order density dependence in Skyrme forces
Xueyu Xiong🇨🇳 · Junchen Pei🇨🇳 · Wenjun Chen🇨🇳
The three-body force is indispensable in nuclear energy density functionals which leads to a density dependent two-body term in the Hartree-Fock approach. Usually a single factional power of density dependency has been adopted. We consider the possibility of an additional higher-order density dependence in extended Skyrme forces. As a result, new extended Skyrme parametertizations based on the SLy4 force are obtained and the improvements in descriptions of global nuclei have been demonstrated. The higher-order term can also substantially affect nuclear properties in the high density region in general ways.
nucl-thPRC(2016)·20 citations
03
Matching effective few-nucleon theories to QCD
Johannes Kirscher🇮🇱
The emergence of complex macroscopic phenomena from a small set of parameters and microscopic concepts demonstrates the power and beauty of physical theories. A theory which relates the wealth of data and peculiarities found in nuclei to the small number of parameters and symmetries of quantum chromodynamics is by that standard of exceptional beauty. Decade-long research on computational physics and on effective field theories facilitate the assessment of the presumption that quark masses and strong and electromagnetic coupling constants suffice to parameterize the nuclear chart. By presenting the current status of that enterprise, this article touches the methodology of predicting nuclei by simulating the constituting quarks and gluons and the development of effective field theories as appropriate representations of the fundamental theory. While the nuclear spectra and electromagnetic responses analyzed computationally so far with lattice QCD are in close resemblance to those which intrigued experimentalists a century ago, they also test the theoretical understanding which was unavailable to guide the nuclear pioneers but developed since then. This understanding is shown to be deficient in terms of correlations amongst nuclear observables and their sensitivity to fundamental parameters. By reviewing the transition from one effective field theory to another, from QCD to pionful chiral theories to pionless and eventually to cluster theories, we identify some of those deficiencies and conceptual problems awaiting a solution before QCD can be identified as the high-energy theory from which the nuclear landscape emerges.
nucl-thhep-latIJMPE(2016)·6 citations
04
Microscopic calculations of the characteristics of radiative nuclear reactions for double-magic nuclei
Oleg Achakovskiy · Sergei Kamerdzhiev · Victor Tselyaev · Mikhail Shitov
The neutron capture cross sections and average radiative widths of neutron resonances for two double-magic nuclei 132Sn and 208Pb have been calculated using the microscopic photon strength functions, which were obtained within the microscopic self-consistent version of the extended theory of finite Fermi systems in the time blocking approximation. For the first time, the microscopic PSFs have been obtained within the fully self-consistent approach with exact accounting for the single particle continuum (for 208Pb). The approach includes phonon coupling effects in addition to the standard RPA approach. The known Skyrme force has been used. The calculations of nuclear reaction characteristics have been performed with the EMPIRE 3.1 nuclear reaction code. Here, three nuclear level density (NLD) models have been used: the so-called phenomenological GSM, the EMPIRE specific (or Enhanced GSM) and the microscopical combinatorial HFB NLD models. For both considered characteristics we found a significant disagreement between the results obtained with the GSM and HFB NLD models. For 208Pb, a reasonable agreement has been found with systematics for the average radiative widths values with HFB NLD and with the experimental data for the HFB NLD average resonance spacing D0, while for these two quantities the differences between the values obtained with GSM and HFB NLD are of several orders of magnitude. The discrepancies between the results with the phenomenological EGLO PSF and microscopic RPA or TBA are much less for the same NLD model.
nucl-thEPJ Web Conf.(2016)·2 citations
05
A three-body model for the analysis of quasi-free scattering reactions in inverse kinematics
Antonio M. Moro
A new method to calculate cross sections for $(p, p n)$ and $(p, 2 p)$ reactions measured under inverse kinematics conditions is proposed. The method uses the prior form of the scattering transition amplitude, and replaces the exact three-body wave function appearing in this expression by an expansion in terms of $p$ - $n$ or $p$ - $p$ states, covering the physically relevant excitation energies and partial waves. A procedure of discretization, similar to that used in continuum-discretized coupled-channels calculations, is applied in order to make this expansion finite and numerically tractable. The proposed formalism is non-relativistic but several relativistic kinematical corrections are applied to extend its applicability to energies of current interest. The underlying optical potentials for the entrance and exit channels are generated microscopically, by folding an effective density-dependent G-matrix with the density of the composite nucleus. Numerical calculations for $^{12}$ C( $p$ , $2 p$ ), $^{12}$ C( $p$ , $p n$ ) and $^{23}$ O( $p$ , $p n$ ) at $\sim$ 400~MeV/nucleon are presented to illustrate the method. The role of final-state interactions and Pauli principle between the outgoing nucleons is also discussed.
nucl-thPRC(2015)·38 citations
06
Nuclear rotation in the continuum
K. Fossez🇺🇸 · W. Nazarewicz🇺🇸 · Y. Jaganathen🇺🇸 · N. Michel🇫🇷 · M. Płoszajczak🇫🇷
$Background:$ Atomic nuclei often exhibit collective rotational-like behavior in highly excited states, well above the particle emission threshold. What determines the existence of collective motion in the continuum region, is not fully understood. $Purpose:$ In this work, by studying the collective rotation of the positive-parity deformed configurations of the one-neutron halo nucleus $^{11}$ Be, we assess different mechanisms that stabilize collective behavior beyond the limits of particle stability. $Method:$ To solve a particle-plus-core problem, we employ a non-adiabatic coupled-channel formalism and the Berggren single-particle ensemble, which explicitly contains bound states, narrow resonances, and the scattering continuum. We study the valence-neutron density in the intrinsic rotor frame to assess the validity of the adiabatic approach as the excitation energy increases. $Results:$ We demonstrate that collective rotation of the ground band of $^{11}$ Be is stabilized by (i) the fact that the $ℓ = 0$ one-neutron decay channel is closed, and (ii) the angular momentum alignment, which increases the parentage of high- $ℓ$ components at high spins; both effects act in concert to decrease decay widths of ground-state band members. This is not the case for higher-lying states of $^{11}$ Be, where the $ℓ = 0$ neutron-decay channel is open and often dominates. $Conclusion:$ We demonstrate that long-lived collective states can exist at high excitation energy in weakly bound neutron drip-line nuclei such as $^{11}$ Be.
nucl-thPRC(2016)·29 citations
07
Heavy Quarkonium in a Holographic Basis
Yang Li🇺🇸 · Pieter Maris🇺🇸 · Xingbo Zhao🇺🇸 · James P. Vary🇺🇸
We study the heavy quarkonium within the basis light-front quantization approach. We implement the one-gluon exchange interaction and a confining potential inspired by light-front holography. We adopt the holographic light-front wavefunction (LFWF) as our basis function and solve the non-perturbative dynamics by diagonalizing the Hamiltonian matrix. We obtain the mass spectrum for charmonium and bottomonium. With the obtained LFWFs, we also compute the decay constants and the charge form factors for selected eigenstates. The results are compared with the experimental measurements and with other established methods.
↳ hep-phnucl-thPLB(2016)·173 citations
08
Dynamical transition between two mesons and a tetraquark
I. A. Toledano Juarez🇲🇽 · G. Toledo Sanchez🇲🇽
We consider a system composed of two identical light quarks ( $q q$ ) and two identical antiquarks ( $Q ˉ Q ˉ$ ) that can be linked either as two mesons or as a tetraquark, incorporating quantum correlations between identical particles and an effective many-body potential between particles. We perform a 3-D Monte Carlo simulation of the system, considering the configurations allowed to form: i) Only two mesons, ii) Only tetraquark and iii) two mesons and tetraquark . We characterize each case and determine whether it is energetically more favorable to form a tetraquark or two mesons, as a function of the interparticle separation distance which, for a fixed number of particles, can be identified as a particle density. We determine how the two mesons, which dominate the low density regime, mixes with a tetraquark state as the density increases. Properties like the mean square radius and the two-particle correlation function are found to reflect such transition, and we provide a parameterization of the diquark correlation function in the isolated case. We track the dynamical flipping among configurations to determine the recombination probability, exhibiting the importance of the tetraquark state. We analize the four-body potential evolution and show that its linear behavior is preserved, although the slope can reflect the presence of a mixed state. Results are shown for several light-quarks to heavy-antiquarks mass ratios whenever they are found to be relevant.
↳ hep-phnucl-thPRC(2015)·1 citation
09
Nucleosynthesis in the Ejecta of Neutron Star Mergers
Dirk Martin · Albino Perego · Almudena Arcones · Oleg Korobkin · Friedrich-Karl Thielemann
Heavy elements like gold, platinum or uranium are produced in the r-process, which needs neutron-rich and explosive environments. Neutron star mergers are a promising candidate for an r-process site. They exhibit three different channels for matter ejection fulfilling these conditions: dynamic ejecta due to tidal torques, neutrino-driven winds and evaporating matter from the accretion disk. We present a first study of the integrated nucleosynthesis for a neutrino-driven wind from a neutron star merger with a hyper-massive neutron star. Trajectories from a recent hydrodynamical simulation are divided into four different angle regions and post-processed with a reaction network. We find that the electron fraction varies around $Y_{e} \approx 0.1 - 0.4$ , but its distribution differs for every angle of ejection. Hence, the wind ejecta do not undergo a robust r-process, but rather possess distinct nucleosynthesis yields depending on the angle range. Compared to the dynamic ejecta, a smaller amount of neutron-rich matter gets unbound, but the production of lighter heavy elements with $A ≲ 130$ in the neutrino-driven wind can complement the strong r-process of the dynamic ejecta.
↳ astro-ph.SRastro-ph.HEnucl-thPoS(2015)·5 citations
10
Undersaturation of quarks at early stages of relativistic nuclear collisions: the hot glue initial scenario and its observable signatures
H. Stoecker🇩🇪 · M. Beitel🇩🇪 · T.S. Biró🇭🇺 · L.P. Csernai🇳🇴 · K. Gallmeister🇩🇪 · M.I. Gorenstein🇩🇪 · C. Greiner🇩🇪 · I.N. Mishustin🇩🇪 · M. Panero🇮🇹 · S. Raha🇮🇳 · L.M. Satarov🇩🇪 · S. Schramm🇩🇪 and 8 other authors
The early stage of high multiplicity nuclear collisions is represented by a nearly quarkless, hot, deconfined pure gluon plasma. This new scenario should be characterized by a suppression of high $p_{T}$ photons and dileptons as well as by reduced baryon to meson ratios. We present the numerical results for central Pb+Pb collisions at the LHC energies by using the ideal Bjorken hydrodynamics with time-dependent quark fugacity. It is shown that about 25\% of final total entropy is generated during the hydrodynamic evolution of chemically undersaturated quark-gluon plasma.
↳ hep-phhep-exhep-latnucl-ex+1Astron.Nachr.(2015)·17 citations
11
Physical observables in the decay $Λ_{b} \to Λ_{c} (\to Λ + π) + τ^{-} + ν ˉ_{τ}$
Nurgul Habyl🇰🇿 · Thomas Gutsche🇩🇪 · Mikhail A. Ivanov🇷🇺 · Jürgen G. Körner🇩🇪 · Valery E. Lyubovitskij🇷🇺 · Pietro Santorelli🇮🇹
We analyze the tauonic semileptonic baryon decays $Λ_{b}^{0} \to Λ_{c}^{+} + τ^{-} + ν ˉ_{τ}$ with particular emphasis on the lepton helicity flip contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization components of the $Λ_{c}^{+}$ and the $τ^{-}$ , and the lepton-side forward-backward asymmetries. We use the covariant confined quark model to provide numerical results on these observables.
↳ hep-phnucl-thInt.J.Mod.Phys.Conf.Ser.(2015)·7 citations
12
Jet-Medium Interactions at NLO in a Weakly-Coupled Quark-Gluon Plasma
Jacopo Ghiglieri🇨🇭 · Guy D. Moore🇩🇪 · Derek Teaney🇺🇸
We present an extension to next-to-leading order in the strong coupling constant $g$ of the AMY effective kinetic approach to the energy loss of high momentum particles in the quark-gluon plasma. At leading order, the transport of jet-like particles is determined by elastic scattering with the thermal constituents, and by inelastic collinear splittings induced by the medium. We reorganize this description into collinear splittings, high-momentum-transfer scatterings, drag and diffusion, and particle conversions (momentum-preserving identity-changing processes). We show that this reorganized description remains valid to NLO in $g$ , and compute the appropriate modifications of the drag, diffusion, particle conversion, and inelastic splitting coefficients. In addition, a new kinematic regime opens at NLO for wider-angle collinear bremsstrahlung. These semi-collinear emissions smoothly interpolate between the leading order high-momentum-transfer scatterings and collinear splittings. To organize the calculation, we introduce a set of Wilson line operators on the light-cone which determine the diffusion and identity changing coefficients, and we show how to evaluate these operators at NLO.
↳ hep-phnucl-thJHEP(2016)·107 citations
13
Self-similar inverse cascade of magnetic helicity driven by the chiral anomaly
Yuji Hirono🇺🇸 · Dmitri Kharzeev🇺🇸 · Yi Yin🇺🇸
For systems with charged chiral fermions, the imbalance of chirality in the presence of magnetic field generates an electric current - this is the Chiral Magnetic Effect (CME). We study the dynamical real-time evolution of electromagnetic fields coupled by the anomaly to the chiral charge density and the CME current by solving the Maxwell-Chern-Simons equations. We find that the CME induces the inverse cascade of magnetic helicity towards the large distances, and that at late times this cascade becomes self-similar, with universal exponents. We also find that in terms of gauge field topology the inverse cascade represents the transition from linked electric and magnetic fields (Hopfions) to the knotted configuration of magnetic field (Chandrasekhar-Kendall states). The magnetic reconnections are accompanied by the pulses of the CME current directed along the magnetic field lines. We devise an experimental signature of these phenomena in heavy ion collisions, and speculate about implications for condensed matter systems.
↳ hep-thcond-mat.softhep-phnucl-thPRD(2015)·117 citations
14
Fractional Authorship in Nuclear Physics
B. Pritychenko
Large, multi-institutional groups or collaborations of scientists are engaged in nuclear physics research projects, and the number of research facilities is dwindling. These collaborations have their own authorship rules, and they produce a large number of highly-cited papers. Multiple authorship of nuclear physics publications creates a problem with the assessment of an individual author's productivity relative to his/her colleagues and renders ineffective a performance metrics solely based on annual publication and citation counts. Many institutions are increasingly relying on the total number of first-author papers; however, this approach becomes counterproductive for large research collaborations with an alphabetical order of authors. A concept of fractional authorship (the claiming of credit for authorship by more than one individual) helps to clarify this issue by providing a more complete picture of research activities. In the present work, nuclear physics fractional and total authorships have been investigated using nuclear data mining techniques. Historic total and fractional authorship averages have been extracted from the Nuclear Science References (NSR) database, and the current range of fractional contributions has been deduced. The results of this study and their implications are discussed and conclusions presented.
↳ cs.DLnucl-thphysics.soc-ph0 citations

Affiliations

first authorsco-authorsvia INSPIRE