Nuclear Theory·nucl-th

Tuesday·October 15, 2019

22 papers—13 primary·9 cross-listed

01
Relativistic energy-density functional approach to magnetic-dipole excitation and its sum rule
Tomohiro Oishi · Goran Kruzic · Nils Paar
Magnetic-dipole (M1) excitations of $^{18}$ O and $^{42}$ Ca nuclei are investigated within a relativistic nuclear energy density functional framework. In our last work \cite{2019OP}, these nuclei are found to have unique M1 excitation and its sum rule, because of their characteristic structure: the system consists of the shell-closure core plus two neutrons. For a more systematic investigation of the M1 mode, we have implemented a framework based on the relativistic nuclear energy density functional (RNEDF). For benchmark, we have performed the RNEDF calculations combined with the random-phase approximation (RPA). We evaluate the M1 excitation of $^{18}$ O and $^{42}$ Ca, whose sum-rule value (SRV) of the M1 transitions can be useful to test the computational implementation \cite{2019OP}. We also apply this RNEDF method to $^{208}$ Pb, whose M1 property has been precisely measured \cite{1979Holt,1987Koehler,1988Laszewski,2016Birkhan}. Up to the level of the M1 sum rule, our result is in agreement with the experiments, except the discrepancy related with the quenching factors for $g$ coefficients.
nucl-thastro-ph.HEnucl-ex0 citations
02
Fano effect on the neutron elastic scattering by open-shell nuclei
K. Mizuyama🇻🇳 · N. Nhu Le🇻🇳 · T. V. Nhan Hao🇻🇳
By focusing on the asymmetric shape of cross section, we analyze the pairing effect on the partial wave components of cross section for neutron elastic scattering off stable and unstable nuclei within the Hartree-Fock-Bogoliubov (HFB) framework. Explicit expressions for Fano parameters $q_{l j}$ and $ϵ_{l j}$ have been derived and the pairing effects have been analyzed in term of these parameters, and the Fano effect was found on the neutron elastic scattering off the stable nucleus in terms of the pairing correlation. Fano effect was appeared as the asymmetric line-shape of the cross section caused by the small absolute value of $q_{l j}$ due to the small pairing effect on the deep-lying hole state of the stable nucleus. In the case of the unstable nuclei, the large $q_{l j}$ value is expected because of the small absolute value of the Fermi energy. The quasiparticle resonance with the large $q_{l j}$ forms the Breit-Wigner type shape in the elastic scattering cross section.
nucl-thPRC(2020)·5 citations
03
The JETSCAPE framework: p+p results
A. Kumar🇺🇸 · Y. Tachibana🇺🇸 · D. Pablos🇺🇸 · C. Sirimanna🇺🇸 · R. J. Fries🇺🇸 · A. Angerami🇺🇸 · S. A. Bass🇺🇸 · S. Cao🇺🇸 · Y. Chen🇺🇸 · J. Coleman🇺🇸 · L. Cunqueiro🇺🇸 · T. Dai🇺🇸 and 34 other authors
The JETSCAPE framework is a modular and versatile Monte Carlo software package for the simulation of high energy nuclear collisions. In this work we present a new tune of JETSCAPE, called PP19, and validate it by comparison to jet-based measurements in $p + p$ collisions, including inclusive single jet cross sections, jet shape observables, fragmentation functions, charged hadron cross sections, and dijet mass cross sections. These observables in $p + p$ collisions provide the baseline for their counterparts in nuclear collisions. Quantifying the level of agreement of JETSCAPE results with $p + p$ data is thus necessary for meaningful applications of JETSCAPE to A+A collisions. The calculations use the JETSCAPE PP19 tune, defined in this paper, based on version 1.0 of the JETSCAPE framework. For the observables discussed in this work calculations using JETSCAPE PP19 agree with data over a wide range of collision energies at a level comparable to standard Monte Carlo codes. These results demonstrate the physics capabilities of the JETSCAPE framework and provide benchmarks for JETSCAPE users.
nucl-thhep-exnucl-exPRC(2020)·62 citations
04
Unveiling the nuclear matter EoS from neutron star properties: a supervised machine learning approach
Márcio Ferreira · Constança Providência
We explore supervised machine learning methods in extracting the non-linear maps between neutron stars (NS) observables and the equation of state (EoS) of nuclear matter. Using a Taylor expansion around saturation density, we have generated a set of model independent EoS describing stellar matter constrained by nuclear matter parameters that are thermodynamically consistent, causal, and consistent with astrophysical observations. From this set, the full non-linear dependencies of the NS tidal deformability and radius on the nuclear matter parameters were learned using two distinct machine learning methods. Due to the high accuracy of the learned non-linear maps, we were able to analyze the impact of each nuclear matter parameter on the NS observables, identify dependencies on the EoS properties beyond linear correlations and predict which stars allow us to draw strong constraints.
nucl-thJCAP(2021)·55 citations
05
Theoretical Study of Spin Observables in $p d$ Elastic Scattering at Energies $T_{p} = 800 - 1000$ MeV
M. N. Platonova🇷🇺 · V. I. Kukulin🇷🇺
Various spin observables (analyzing powers and spin-correlation parameters) in $p d$ elastic scattering at $T_{p} = 800 - 1000$ MeV are analyzed within the framework of the refined Glauber model. The theoretical model uses as input spin-dependent $N N$ amplitudes obtained from the most recent partial-wave analysis and also takes into account the deuteron $D$ wave and charge-exchange effects. Predictions of the refined Glauber model are compared with the existing experimental data. Reasonable agreement between the theoretical calculations and experimental data at low momentum transfers $∣ t ∣ ≲ 0.2$ (GeV/ $c)^{2}$ is found for all observables considered. Moderate discrepancies found in this region are shown to be likely due to uncertainties in the input $N N$ amplitudes. Qualitative agreement at higher momentum transfers is also found for most observables except the tensor ones with mixed $x$ and $z$ polarization components. Possible reasons for observed deviations of the model calculations from the data at $∣ t ∣ > 0.2$ (GeV/ $c)^{2}$ are discussed.
nucl-thEPJA(2020)·7 citations
06
Speed of sound constraints on maximally rotating neutron stars
Ch. Margaritis · P.S. Koliogiannis · Ch.C. Moustakidis
The observation of maximally rotating neutron stars (in comparison to nonrotating ones) may provide more information on the behavior of nuclear matter at high densities. We provide a theoretical treatment concerning the effects of the upper bound of the sound speed in dense matter on the bulk properties of maximally rotating (at mass-shedding limit) neutron stars. In particular, we consider two upper bounds for the speed of sound, $v_{s} = c$ and $v_{s} = c / 3$ , and the one provided by the relativistic kinetic theory. We investigate to what extent the possible predicted (from various theories and conjectures) upper bounds on the speed of sound constrain the ones of various key quantities, including the maximum mass and the corresponding radius, Keplerian frequency, Kerr parameter and moment of inertia. We mainly focus on the lower proposed limit, $v_{s} = c / 3$ , and we explore in which mass region a rotating neutron star collapses to a black hole. In any case, useful relations of the mentioned bulk properties with the transition density are derived and compared with the corresponding nonrotating cases. We concluded that the proposed limit $v_{s} = c / 3$ leads to dramatic decrease on the values of the maximum mass, Kerr parameter and moment of inertia preventing a neutron star to reach values which derived with the consideration of realistic equations of state or from other constraints. Possible measurements of the Kerr parameter and moment of inertia would shed light on these issues and help to reveal the speed of sound bound in dense matter.
nucl-thastro-ph.HEgr-qcPRD(2020)·29 citations
07
Study of $Ξ^{-}$ hypernuclei in the Skyrme-Hartree-Fock approach
Yun Jin🇨🇳 · Xian-Rong Zhou🇨🇳 · Yi-Yuan Cheng🇨🇳 · H.-J. Schulze🇮🇹
The properties of $Ξ^{-}$ hypernuclei are studied systematically using a two-dimensional Skyrme-Hartree-Fock approach combined with three different $Ξ N$ Skyrme forces fitted to reproduce the existing data. We explore the impurity effect of a single $Ξ^{-}$ hyperon on the radii, deformations, and density distributions of the nuclear core and point out qualitative differences between the different forces. We find that the $Ξ^{-}$ removal energy of $_{Ξ p}^{13}$ B [ $^{12}$ C(g.s.)+ $Ξ^{-}$ (1p)] calculated by the SLX3 force is 0.7 MeV, which is in good agreement with a possible value of $0.82 \pm 0.17$ MeV from the KEK E176 experiment. The theoretical prediction for this weakly bound state depends strongly on the deformation of the nuclear core, which is analyzed in detail.
nucl-thEPJA(2020)·19 citations
08
Multipole expansion of densities in the deformed relativistic Hartree-Bogoliubov theory in continuum
Cong Pan · Kaiyuan Zhang · Shuangquan Zhang
The deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) has been proved one of the best models to probe the exotic structures in deformed nuclei. In DRHBc, the potentials and densities are expressed in terms of the multipole expansion with Legendre polynomials, the dependence on which has only been touched for light nuclei so far. In this paper, taking a light nucleus $^{20}$ Ne and a heavy nucleus $^{242}$ U as examples, we investigated the dependence on the multipole expansion of the potentials and densities in DRHBc. It is shown that the total energy converges well with the expansion truncation both in the absence of and presence of the pairing correlation, either in the ground state or at a constrained quadrupole deformation. It is found that to reach a same accuracy of the total energy, even to a same relative accuracy by percent, a larger truncation is required by a heavy nucleus than a light one. The dependence of the total energy on the truncation increases with deformation. By decompositions of the neutron density distribution, it is shown that a higher-order component has a smaller contribution. With the increase of deformation, the high-order components get larger, while at the same deformation, the high-order components of a heavy nucleus play a more important role than that of a light one.
nucl-thIJMPE(2019)·38 citations
09
Calculated fission-fragment mass yields and average total kinetic energies of heavy and superheavy nuclei
M. Albertsson · B.G. Carlsson · T. Døssing · P. Möller · J. Randrup · S. Åberg
Fission-fragment mass and total-kinetic-energy (TKE) distributions following fission of even-even nuclides in the region $74 \leq Z \leq 126$ and $92 \leq N \leq 230$ , comprising 896 nuclides have been calculated using the Brownian shape-motion method. The emphasis is the region of superheavy nuclei. To show compatibility with earlier results the calculations are extended to include earlier studied regions. An island of asymmetric fission is obtained in the superheavy region, $106 \leq Z \leq 114$ and $162 \leq N \leq 176$ , where the heavy fragment is found to be close to $^{208}$ Pb and the light fragment adjusts accordingly. Most experimentally observed $α$ -decay chains of superheavy nuclei with $Z > 113$ terminate by spontaneous fission in our predicted region of asymmetric fission. In these cases, the pronounced large asymmetry is accompanied by a low TKE value compatible with measurements.
nucl-thEPJA(2020)·22 citations
10
Analyses of multi-pion Bose-Einstein correlations for granular sources with coherent pion-emission droplets
Ghulam Bary🇨🇳 · Wei-Ning Zhang🇨🇳 · Peng Ru🇨🇳 · Jing Yang🇨🇳
The ALICE Collaboration measure the three- and four-pion Bose-Einstein correlations (BECs) in Pb-Pb collisions at the Large Hadron Collider (LHC). It is speculated that the significant suppressions of multi-pion BECs are due to a considerable degree of coherent pion emission in the collisions. In this paper, we study the multi-pion BEC functions in a granular source model with coherent pion-emission droplets. We find that the intercepts of multi-pion correlation functions at the relative momenta near zero are sensitive to droplet number in the granular source. They decrease with decreasing droplet number. The three-pion correlation functions for the evolving granular sources with momentum-dependent partially coherent pion-emission droplets are in basic agreement with the experimental data in Pb-Pb collisions at $s_{N N} = 2.76$ TeV at the LHC. However, the model results of four-pion correlation function are inconsistent with the experimental data. The investigations of the normalized multi-pion correlation functions of the granular sources indicate that there is an interesting enhancement of the normalized four-pion correlation function in moderate relative-momentum region.
nucl-thCPC(2021)·14 citations
11
Probing the neutron skin with ultrarelativistic isobaric collisions
Hanlin Li🇨🇳 · Hao-jie Xu🇨🇳 · Ying Zhou🇨🇳 · Xiaobao Wang🇨🇳 · Jie Zhao🇺🇸 · Lie-Wen Chen🇨🇳 · Fuqiang Wang🇨🇳
Particle production in ultrarelativistic heavy ion collisions depends on the details of the nucleon density distributions in the colliding nuclei. We demonstrate that the charged hadron multiplicity distributions in isobaric collisions at ultrarelativistic energies provide a novel approach to determine the poorly known neutron density distributions and thus the neutron skin thickness in finite nuclei, which can in turn put stringent constraints on the nuclear symmetry energy.
nucl-thnucl-exPRL(2020)·97 citations
12
Do electromagnetic effects survive in the production of lepton pairs in nucleus-nucleus collisions ?
Antoni Szczurek🇵🇱
We discuss production of $J / ψ$ and $e^{+} e^{-}$ pairs in semicentral and peripheral collisions of heavy ions at high energies. We focus on photoproduction mechanism. We present explanation of results of the ALICE collaboration for low transverse momentum production of $J / ψ$ as well as results obtained by the STAR collaboration for $e^{+} e^{-}$ production, also at low transverse momenta. We conclude that such effects are important also in this new corner (semi-central processes) of the phase space.
nucl-thhep-phPoS(2020)·0 citations
13
Shear viscosity in microscopic calculations of A+A collisions at energies of Nuclotron-based Ion Collider fAcility (NICA)
M. Teslyk🇳🇴 · L. Bravina🇳🇴 · O. Panova🇳🇴 · O. Vitiuk🇳🇴 · E. Zabrodin🇳🇴
Time evolution of shear viscosity $η$ , entropy density $s$ , and their ratio $η / s$ in the central area of central gold-gold collisions at NICA energy range is studied within the UrQMD transport model. The extracted values of energy density, net baryon density and net strangeness density are used as input to (i) statistical model of ideal hadron gas to define temperature, baryo-chemical potential and strangeness chemical potential, and to (ii) UrQMD box with periodic boundary conditions to study the relaxation process of highly excited matter. During the relaxation stage, the shear viscosity is determined in the framework of Green-Kubo approach. The procedure is performed for each of 20 time slices, corresponding to conditions in the central area of the fireball at times from 1~fm/ $c$ to 20~fm/ $c$ . For all tested energies the ratio $η / s$ reaches minimum, $(η / s)_{min} \approx 0.3$ at $t \approx 5$ ~fm/ $c$ . Then it increases up to the late stages of the system evolution. This rise is accompanied by the drop of both, temperature and strangeness chemical potential, and increase of baryo-chemical potential.
nucl-thhep-phnucl-exPRC(2020)·13 citations
14
Inhomogeneous chiral condensates in three-flavor quark matter
Stefano Carignano🇪🇸 · Michael Buballa🇩🇪
We investigate the effect of strange quark degrees of freedom on the formation of inhomogeneous chiral condensates in a three-flavor Nambu--Jona-Lasinio model in mean-field approximation. A Ginzburg-Landau study complemented by a stability analysis allow us to determine in a general way the location of the critical and Lifshitz points, together with the phase boundary where the (partially) chirally restored phase becomes unstable against developing inhomogeneities, without resorting to specific assumptions on the shape of the chiral condensate. We discuss the resulting phase structure and study the influence of the bare strange-quark mass $m_{s}$ and the axial anomaly on the size and location of the inhomogeneous phase compared to the first-order transition associated with homogeneous matter. We find that, as a consequence of the axial anomaly, critical and Lifshitz point split. For realistic strange-quark masses the effect is however very small and becomes sizeable only for small values of $m_{s}$ .
↳ hep-phnucl-thPRD(2020)·40 citations
15
Large Sound Speed in Dense Matter and the Deformability of Neutron Stars
Brendan Reed🇺🇸 · C. J. Horowitz🇺🇸
The historic first detection of the binary neutron star merger GW170817 by the LIGO-Virgo collaboration has set a limit on the gravitational deformability of neutron stars. In contrast, radio observations of PSR J0740+6620 find a very massive neutron star. Tension between the small deformability and the large maximum mass may suggest that the pressure rises rapidly with density and thus the speed of sound in dense matter is likely a large fraction of the speed of light. We use these observations and simple constant sound-speed model equations of state to set a lower bound on the maximum speed of sound in neutron stars. If the tidal deformability of a 1.4 $M_{⊙}$ neutron star is less than 600, as is suggested by subsequent analyses of GW170817, we find that the sound speed in the cores of neutron stars is likely larger than the conformal limit of $c / 3$ . Implications of this for our understanding of both hadronic and quark-gluon descriptions of dense matter are discussed.
↳ astro-ph.HEgr-qcnucl-thPRC(2020)·66 citations
16
New Insight about the Effective Restoration of U_A(1) Symmetry
Xiang Li🇨🇳 · Wei-jie Fu🇨🇳 · Yu-xin Liu🇨🇳
The effective restoration of the U_{A}(1) symmetry is revisited by implementing the functional renormalization group approach combining with the 2+1 flavor Polyakov-loop quark-meson model. A temperature-dependent 't Hooft term is taken to imitate the restoration of the U_{A}(1) symmetry. Order parameters, meson spectrum and mixing angles, especially the pressure and the entropy density of the system are calculated to explore the effects of different U_{A}(1) symmetry restoration patterns. We show then that the temperature for the restoration of the U_{A}(1) symmetry is much higher than that for the chiral symmetry SU_{A}(3).
↳ hep-phnucl-thPRD(2020)·10 citations
17
Precision Measurements of Fundamental Interactions with (Anti)Neutrinos
R. Petti🇺🇸
We discuss the main limitations of past neutrino scattering experiments and possible ways to address them in a next-generation program of precision measurements of fundamental interactions with (anti)neutrinos. A reduction of the longstanding precision gap with respect to electron scattering experiments could provide interesting synergies with the existing efforts in the fixed-target, collider, and nuclear physics communities.
↳ hep-exhep-phnucl-exnucl-th13 citations
18
Mass structure and pressure forces inside the nucleon
Cédric Lorcé (Ecole Polytechnique and CNRS)🇫🇷
We summarize recent works on the question of the nucleon mass decomposition and the 2D relativistic distribution of pressure forces on the light front. All these mechanical properties are encoded in the energy-momentum tensor of the system which can be constrained using various types of high-energy lepton-nucleon scatterings. Some further developments for targets with spin $> 1/2$ are also reported.
↳ hep-phnucl-th1 citation
19
Strong decays of the higher excited $Λ_{Q}$ and $Σ_{Q}$ baryons
Qi-Fang Lü🇨🇳 · Xian-Hui Zhong🇨🇳
In this work, we preform a systematic study of the strong decays for the higher singly heavy baryon resonances $Λ_{Q} (3 S)$ , $Λ_{Q} (2 P)$ , $Λ_{Q} (2 D)$ , $Λ_{Q} (1 F)$ , $Σ_{Q} (3 S)$ , $Σ_{Q} (2 P)$ , $Σ_{Q} (2 D)$ , and $Σ_{Q} (1 F)$ within the $^{3} P_{0}$ model. Our results show that most of the $λ -$ mode higher excited $Λ_{Q}$ and $Σ_{Q}$ states have a relatively narrow width, and mainly decay into two-body final states with one heavy meson plus one light baryon. Our calculations provide abundant theoretical information and demonstrate the general feature for these higher states, which may be valuable for future experimental searches and establishing the singly heavy baryon spectrum.
↳ hep-phhep-exnucl-thPRD(2020)·36 citations
20
Two-Photon-Exchange effects in $e p \to e n π^{+}$ and their corrections to separated cross sections $σ_{L,T,LT,TT}$ at small $- t$
Hui-Yun Cao🇨🇳 · Hai-Qing Zhou🇨🇳
In this work, the two-photon-exchange (TPE) effects in $e p \to e n π^{+}$ at small $- t$ are discussed within a hadronic model. Under the pion dominance approximation the TPE contribution to the amplitude can be described by a scalar function in the limit $m_{e} \to 0$ . The TPE contributions to the amplitude and the unpolarized differential cross section are both estimated when only the elastic intermediate state is considered. We find that the TPE corrections to the unpolarized differential cross section are about from $- 4%$ to $- 20%$ at $Q^{2} = 1$ -- $1.6$ GeV $^{2}$ . After considering the TPE corrections to the experimental data sets of unpolarized differential cross section, we analyze the TPE corrections to the separated cross sections $σ_{L,T,LT,TT}$ . We find that the TPE corrections (at $Q^{2} = 1$ -- $1.6$ GeV $^{2}$ ) to $σ_{L}$ are about from $- 10%$ to $- 30%$ , to $σ_{T}$ are about $20%$ , and to $σ_{LT,TT}$ are much larger. By these analysis, we conclude that the TPE contributions in $e p \to e n π^{+}$ at small $- t$ are important to extract the separated cross sections $σ_{L,T,LT,TT}$ and the electromagnetic magnetic form factor of $π^{+}$ in the experimental analysis.
↳ hep-phnucl-exnucl-thPRC(2020)·5 citations
21
Different space-time freeze-out picture -- an explanation of different $Λ$ and $Λ ˉ$ polarization?
O. Vitiuk🇳🇴 · L. Bravina🇳🇴 · E. Zabrodin🇳🇴
Thermal vorticity in non-central Au+Au collisions at energies $7.7 \leq s \leq 62.4$ GeV is calculated within the UrQMD transport model. Tracing the $Λ$ and $Λ ˉ$ hyperons back to their last interaction point we were able to obtain the temperature and the chemical potentials at the time of emission by fitting the extracted bulk characteristics of hot and dense medium to statistical model of ideal hadron gas. Then the polarization of both hyperons was calculated. The polarization of $Λ$ and $Λ ˉ$ increases with decreasing energy of nuclear collisions. The stronger polarization of $Λ ˉ$ is explained by the different space-time distributions of $Λ$ and $Λ ˉ$ and by different freeze-out conditions of both hyperons.
↳ hep-phnucl-exnucl-thPLB(2020)·81 citations
22
Quantum Tomography Measures Entanglement in Collider Reactions
John C. Martens🇺🇸 · John P. Ralston🇺🇸 · Daniel Tapia Takaki🇺🇸
Entanglement in high energy and and nuclear reactions is receiving great attention. A proper description of these reactions uses density matrices, and the express of entanglement in terms of {\it separability}. Quantum tomography bypasses field-theoretic formalism to determine density matrices in terms of experimental observables. We review recent work applying quantum tomography to practical experimental data analysis. We discuss the relation between separability, as defined in quantum information science, and factorization, as defined in high energy physics. When factorization applies, it comes from using separable probes, which tomographically determine separable projections of entangled density matrices.
↳ hep-phnucl-thquant-ph1 citation

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