Nuclear Theory·nucl-th

Tuesday·November 26, 2019

15 papers—12 primary·3 cross-listed

01
Initial state fluctuations of QCD conserved charges in heavy-ion collisions
Mauricio Martinez🇺🇸 · Matthew D. Sievert🇺🇸 · Douglas E. Wertepny🇮🇱 · Jacquelyn Noronha-Hostler🇺🇸
We initialize the Quantum Chromodynamic conserved charges of baryon number, strangeness, and electric charge arising from gluon splitting into quark-antiquark pairs for the initial conditions of relativistic heavy-ion collisions. A new Monte Carlo procedure that can sample from a generic energy density profile is presented, called Initial Conserved Charges in Nuclear Geometry (ICCING), based on quark and gluon multiplicities derived within the color glass condensate (CGC) effective theory. We find that while baryon number and electric charge have nearly identical geometries to the energy density profile, the initial strangeness distribution is considerable more eccentric and is produced primarily at the hot spots corresponding to temperatures of $T ≳ 400$ MeV for PbPb collisions at $s_{N N} = 5.02$ TeV.
nucl-thhep-ph35 citations
02
Influence of strong magnetic field on the structure properties of strange quark stars
Fatemeh Kayanikhoo🇮🇷 · Kazem Naficy🇮🇷 · Gholam Hossein Bordbar🇮🇷
We investigate the thermodynamic properties of strange quark matter under the strong magnetic field in the framework of the MIT bag model in two cases of bag constants. We consider two cases of the magnetic field, the uniform magnetic field and the density-dependent magnetic field to calculate the equation of state of strange quark matter. For the case of density-dependent magnetic field, we use a Gaussian equation with two free parameters $β$ and $θ$ and use two different sets of the parameters for the magnetic field changes (a slow and a fast decrease of the magnetic field from the center to the surface). Our results show that the energy conditions based on the limitation of the energy-momentum tensor, are satisfied in the corresponding conditions. We also show that the equation of state of strange quark matter becomes stiffer by increasing the magnetic field. In this paper, we also calculate the structure parameters of a pure strange quark star using the equation of state. We investigate the compactification factor ( $2 M / R$ ) and the surface redshift of star in different conditions. The results show that the strange quark star is denser than the neutron star and it is more compact in the presence of the stronger magnetic field. As another result, the compactification factor increases when we use a slow increase of the magnetic field from the surface to the center. Eventually, we compare our results with the observational results for some strange star candidates, and we find that the structure of the strange star candidates is comparable to that of the star in our model.
nucl-thastro-ph.SRgr-qcEPJA(2020)·18 citations
03
Transitions between hyperfine structure states of antiprotonic $^{4} He$ at collisions with medium atoms: interaction \emph{ab initio}
A.V. Bibikov🇷🇺 · G.Ya. Korenman🇷🇺 · S.N. Yudin🇷🇺
Collisions of metastable antiprotonic helium atoms with atoms of the medium induce, among other processes, transitions between hyperfine structure (HFS) states, as well as shifts and broadening of microwave M1 spectral lines. In order to obtain matrix potential of interaction between $(p ˉ He^{+})$ and $He$ , we have calculated the potential energy surface (PES) in the framework of unrestricted Hartree-Fock method taking into account electron correlations in the second-order perturbation theory (MP2). With this potential, the system of close-coupling equations for HFS channels is solved numerically. Cross sections and transition rates, shifts and broadening of M1 spectral lines are calculated. They are used to obtain a numerical solution of the master equation that determines the time evolution of the HFS-states density matrix. The results are compared with the experimental data and with the results of model calculation.
nucl-thphysics.atom-phMoscow Univ.Phys.Bull.(2020)·2 citations
04
Basis Light-Front Quantization for a Chiral Nucleon-Pion Lagrangian
Weijie Du🇺🇸 · Yang Li🇺🇸 · Xingbo Zhao🇨🇳 · Gerald A. Miller🇺🇸 · James P. Vary🇺🇸
We present the first application of the Basis Light-Front Quantization method to a simple chiral model of the nucleon-pion system as a relativistic bound state for the physical proton. The light-front mass-squared matrix of the nucleon-pion system is obtained within a truncated basis. The mass and the corresponding light-front wave function (LFWF) of the proton are computed by numerical diagonalization of the resulting mass-squared matrix. With the boost invariant LFWF, we calculate the probability density distribution of the pion's longitudinal momentum fraction and the Dirac form factor of the proton.
nucl-thPRC(2020)·14 citations
05
Neutron pairing with medium polarization beyond the Landau approximation
M. Urban🇫🇷 · S. Ramanan🇮🇳
We revisit the long-standing problem of the superfluid transition temperature $T_{c}$ in dilute neutron matter. It is well known that $T_{c}$ is strongly affected by medium polarization effects (screening) which modify the pairing interaction in the medium. We study these effects within the random-phase approximation (RPA). It turns out that the widely used Landau approximation is sufficient only at densities below about 0.002 fm $^{- 3}$ . At higher densities, the full RPA leads to stronger screening than the Landau approximation.
nucl-thPRC(2020)·18 citations
06
Low-density in-medium effects on light clusters from heavy-ion data
Helena Pais🇵🇹 · Rémi Bougault🇫🇷 · Francesca Gulminelli🇫🇷 · Constança Providência🇵🇹 · Eric Bonnet🇫🇷 · Bernard Borderie🇫🇷 · Abdelouahad Chbihi🇫🇷 · John D. Frankland🇫🇷 · Emmanuelle Galichet🇫🇷 · Diégo Gruyer🇫🇷 · Maxime Henri🇫🇷 · Nicolas Le Neindre🇫🇷 and 4 other authors
The modification of the ground state properties of light atomic nuclei in the nuclear and stellar medium is addressed, using chemical equilibrium constants evaluated from a new analysis of the intermediate energy heavy-ion (Xe $+$ Sn) collision data measured by the INDRA collaboration. Three different reactions are considered, mainly differing by the isotopic content of the emission source. The thermodynamic conditions of the data samples are extracted from the measured multiplicities allowing for a parametrization of the in-medium modification, determined with the single hypothesis that the different nuclear species in a given sample correspond to a unique common value for the density of the expanding source. We show that this correction, which was not considered in previous analyses of chemical constants from heavy ion collisions, is necessary, since the observables of the analyzed systems show strong deviations from the expected results for an ideal gas of free clusters. This data set is further compared to a relativistic mean-field model, and seen to be reasonably compatible with a universal correction of the attractive $σ$ -meson coupling.
nucl-thastro-ph.HEPRL(2020)·40 citations
07
The formation region of emitted $α$ and heavier particles inside radioactive nuclei
W. M. Seif · A. M. H. Abdelhady
We investigate the formation distance ( $R_{0}$ ) from the center of the radioactive parent nucleus at which the emitted cluster is most probably formed. The calculations are microscopically performed starting from solving the time-independent Schrödinger wave equation for the $α$ -core system, using nuclear potential based on the Skyrme-SLy4 nucleon-nucleon interaction and folding Coulomb potential, to determine the incident and transmitted wave functions of the system. Our results advocate that the emitted cluster is mostly formed in the pre-surface region of the nucleus, under the effect of Pauli blocking from the saturated core density. The deeper $α$ -formation distance inside the nucleus gives rise to less preformation probability, and indicates more stable nucleus of longer half-life. Also, the $α$ -particle tends to be formed at a bit deeper region inside the nuclei having larger isospin asymmetry and in the closed shell nuclei. Regarding the emitted nuclei heavier than $α$ -particle, we find that the formation distance of the emitted clusters heavier than $α$ -particle increases with increasing the isospin asymmetry of the formed cluster, rather than with increasing its mass number. The partial half-life of a certain cluster-decay mode increases upon increasing either the mass number or the isospin asymmetry of the emitted cluster.
nucl-thCPC(2020)·6 citations
08
Equilibration and baryon densities attainable in relativistic heavy-ion collisions
Yu. B. Ivanov🇷🇺 · A. A. Soldatov🇷🇺
Kinetic equilibration of the matter and baryon densities attained in central region of colliding Au+Au nuclei in the energy range of $s_{N N} =$ 3.3--39 GeV are examined within the model of the three-fluid dynamics. It is found that the kinetic equilibration is faster at higher collision energies: the equilibration time (in the c.m. frame of colliding nuclei) rises from $\sim$ 5 fm/c at $s_{N N} =$ 3.3 GeV to $\sim$ 1 fm/c at 39 GeV. The chemical equilibration, and thus thermalization, takes longer. We argue that the presented time evolution of the net-baryon and energy densities in the central region is a necessary prerequisite of proper reproduction of bulk observables in midrapidity. We suggest that for informative comparison of predictions of different models it is useful to calculate an invariant 4-volume ( $V_{4}$ ), where the proper density the equilibrated matter exceeds certain value. The advantage of this 4-volume is that it does not depend on specific choice of the 3-volume in different studies and takes into account the lifetime of the high-density region, which also matters. The 4-volume $V_{4} =$ 100 fm $^{4}$ /c is chosen to compare the baryon densities attainable at different different energies. It is found that the highest proper baryon density increases with the collision energy rise, from $n_{B} / n_{0} \approx$ 4 at 3.3 GeV to $n_{B} / n_{0} \approx$ 30 at 39 GeV. These highest densities are achieved in the central region of colliding system.
nucl-thhep-phPRC(2020)·8 citations
09
Quasibound states of an antiproton and a hydrogen atom
Daniel Baye🇧🇪 · Jérémy Dohet-Eraly🇧🇪
Accurate three-body quantal calculations of the system composed of a proton, an antiproton, and an electron are performed in perimetric coordinates with the Lagrange-mesh method, an approximate variational calculation with the simplicity of a calculation on a grid. Quasibound states with respect to the $p ˉ$ + H( $n = 2$ ) threshold are obtained for $L = 60$ to 71 for various vibrational excitations. Their energies have accuracies up to about $1 0^{- 14}$ atomic units while less precise energies are determined for $L = 56 - 59$ broader resonances. Their structure is analyzed with the help of mean distances between the particles. These mean distances indicate that the proton-electron subsystem is in excited states, mostly $n = 2$ , as predicted by Sakimoto (Phys. Rev. A 98, 042503, 2018) with the Born-Oppenheimer approximation. A comparison performed with this approximation provides the accuracies of its energies and of its proton-antiproton mean distances.
nucl-thPRA(2020)·3 citations
10
Universal behavior of compact star based upon gravitational binding energy
Rongrong Jiang · Dehua Wen · Houyuan Chen
Similar to the compactness parameter ( $β = M / R$ ), the gravitational binding energy (GBE) is also a characteristic parameter which can reflect the internal structure of a neutron star and thus can be used to expressing the universal relations. Scaling by the stellar mass, this investigation demonstrates a perfect universal relation between the GBE and the moment of inertia, where both of the normal neutron stars and the quark stars satisfy the same universal relation. Moreover, a fine empirical relation between the GBE and the tidal deformability is proposed, where the difference of the relations can be used to distinguish wether a pulsar is a normal neutron star or a quark star if the stellar mass and the tidal deformability can be observed or estimated rather accurately. These universal relations provide a potential way to estimate the GBE if the stellar mass and the moment of inertia/the tidal deformability are precisely measured.
nucl-thastro-ph.HEPRD(2019)·22 citations
11
Response relation in Pb-Pb and p-Pb collisions at 5.02 TeV
De-Xian Wei🇨🇳 · Li-Juan Zhou🇨🇳 · Xin-Fei Li🇨🇳
We carry out simulations using a multi-phase transport (AMPT) model to describe the response relation between $v_{2}$ and $ε_{2}$ in Pb-Pb and p-Pb collisions at $s_{N N} = 5.02$ TeV, respectively. To simulate such relation, two methods have been introduced in the calculation: one is the directed response (DR) method, which correlates the outgoing particles with the initial anisotropy directly, and the other one is the cumulants response (CR) method, which is constructed from a cumulants correlation between outgoing particles. Based on calculations of the DR and CR methods, the response relations as a function of the transverse momentum are both shown in Pb-Pb and p-Pb collisions. By comparing the DR and CR methods, we found that the linear response relations are almost identical in all the present collisions. Similar results of linear+cubic response relations are also shown in the higher multiplicity systems, and it has become a significant difference in the lower multiplicity systems, i.e., the peripheral Pb-Pb collisions and p-Pb collisions. Throughout the whole $p_{T}$ -dependent simulations, the $κ_{2}$ in the linear response and in the linear+cubic response are almost identical, except for in the lower multiplicity systems by the DR method. If one implements a pseudorapidity gap by the CR calculation, the $p_{T}$ -dependent and $η$ -independent response relations are similarly shown in peripheral Pb-Pb systems and p-Pb systems, which may imply that a collective response exists in the most central p-Pb collisions. These collective behaviors are dominantly produced on the stage of the medium expansions.
nucl-thhep-phPRC(2020)·5 citations
12
Recent advances in the description of reactions involving exotic nuclei
Pierre Capel
In this contribution to the proceedings of the International Nuclear Physics Conference 2019, I review recent developments made in reaction models used to analyse data measured at radioactive-ion beam facilities to study exotic nuclear structures. I focus in particular on reactions like elastic scattering and breakup, which are used to study halo nuclei. Although these peculiar nuclei challenge usual nuclear-structure models, some can now be computed ab initio. This brief review illustrates the progresses made in nuclear-reaction theory in the last few years to improve the description of the projectile within reaction models. I dedicate this contribution to the memory of Mahir Hussein, who has significantly contributed to this field and who passed away in May this year.
nucl-thnucl-exJ.Phys.Conf.Ser.(2020)·0 citations
13
Conundrum for the free energy of a holonomous gluonic plasma at cubic order
Christiaan P. Korthals Altes🇫🇷 · Hiromichi Nishimura🇯🇵 · Robert D. Pisarski🇺🇸 · Vladimir V. Skokov🇺🇸
We compute the term $\sim g^{3}$ in the free energy for a $S U (N)$ gauge theory with nonzero holonomy at nonzero temperature. If the holonomy is generated kinematically by the introduction of gauge invariant sources coupled to Polyakov loops, the contribution of charged (off-diagonal) gluons to the free energy at order $g^{3}$ , $F^{(3 : c.g.)}$ , is singular: $F^{(3 : c.g.)} \neq = 0$ without holonomy, but $F^{(3 : c.g.)} = 0$ when the holonomy is nonzero, even infinitesimally. We show that the absence of the charged gluon contribution is required by gauge invariance alone and is therefore a universal feature.
↳ hep-thhep-lathep-phnucl-thPLB(2020)·9 citations
14
True muonium production in ultraperipheral $P b P b$ collisions
C. Azevedo🇧🇷 · V.P. Goncalves🇧🇷 · B.D. Moreira🇧🇷
In this paper we investigate the production of a true muonium state, which is an atom consisting of a $μ^{+} μ^{-}$ bound state, by $γ γ$ interactions in ultraperipheral $P b P b$ collisions considering an accurate treatment of the absorptive corrections and for the nuclear form factor. The rapidity distributions and cross sections are estimated considering the RHIC, LHC and FCC energies. Our results indicate that the experimental analysis can be useful to observe, for the first time, the true muonium state.
↳ hep-phhep-exnucl-thPRC(2020)·24 citations
15
Proton structure from a light-front Hamiltonian
Chandan Mondal. Siqi Xu · Jiangshan Lan · Xingbo Zhao · Yang Li · Dipankar Chakrabarti · James P. Vary
We obtain the electromagnetic form factors, the axial form factor, and the parton distribution functions of the proton from the eigenstates of a light-front effective Hamiltonian in the leading Fock representation suitable for low-momentum scale applications. The electromagnetic and the axial form factors are found to be in agreement with the available experimental data. The unpolarized, the helicity, and the transversity valence quark distributions, after QCD evolution, are consistent with the global QCD analyses. The tensor charge also agree the experimental data, while the axial charge is somewhat outside the experimental error bar.
↳ hep-phnucl-thPRD(2020)·97 citations

Affiliations

first authorsco-authorsvia INSPIRE