Nuclear Theory·nucl-th

Tuesday·April 3, 2018

12 papers—7 primary·5 cross-listed

01
Excitation of $^{229}$ Th nuclei in laser plasma: the energy and half-life of the low-lying isomeric state
P.V. Borisyuk · E.V. Chubunova · N.N. Kolachevsky · Yu.Yu. Lebedinskii · O.S. Vasiliev · E.V. Tkalya
The results of experimental studies of the low-energy isomeric state in the $^{229}$ Th nucleus are presented. The work is consisted of several stages. During the first stage $^{229}$ Th nuclei were excited with the inverse internal conversion to the low-lying isomeric level in plasma that was formed by laser pulse at the $^{229}$ Th-containing target surface. Then thorium ions having excited nuclei were extracted from the plasma by an external electrical field and implanted into thin SiO $_{2}$ film grown on a silicon substrate (that is a dielectric material with about 9 eV band-gap). Gamma decay of isomeric nuclei was registered during the second stage by the general methods of the electron spectroscopy after the photon-electron emission from the silicon substrate. Substitution of the photon registration with the electron one allowed us to increase the desired signal by several orders of magnitude and detect the $^{229}$ Th nuclei decay. During the third stage the electron spectra from standard Xe VUV source was obtained that allowed determining the energy of photons. In order to prove that the detected signal is caused by isomeric $^{229}$ Th nuclei decay a series of experiments was carried. The analysis of electron spectra gives the following results: the energy of the nuclear transition is $E_{is} = 7.1 (_{- 0.2}^{+ 0.1})$ ~eV, the half-life of the isomeric level in bare nucleus in vacuum is $T_{1/2} = 1880 \pm 170$ ~s, the reduced probability of the isomeric nuclear transition is $B_{W.u.} (M 1; 3/ 2^{+} \to 5/ 2^{+}) = (3.3 \pm 0.3) \times 1 0^{- 2}$ .
nucl-thnucl-exphysics.opticsphysics.plasm-ph12 citations
02
A pseudo-conformal equation of state in compact-star matter from topology change and hidden symmetries of QCD
Yong-Liang Ma🇨🇳 · Hyun Kyu Lee🇰🇷 · Won-Gi Paeng🇰🇷 · Mannque Rho🇫🇷
We construct a new effective field theory approach to the equation of state (EoS), dubbed pseudo-confomal model "PCM," for nuclear and compact star matter entirely in terms of effective hadron degrees of freedom. The possible transition at $n \sim (2 - 4) n_{0}$ (where $n_{0}$ is the normal nuclear matter density) from hadron degrees of freedom to strongly-coupled quark degrees of freedom, giving rise to a soft-to-hard changeover in the EoS that can accommodate the massive stars observed, is effectuated by the topology change at $n_{1/2} \gsim 2 n_{0}$ from skyrmions to half-skyrmions without involving local order-parameter fields. The mechanism exploits possible emergence of hidden scale and local symmetries of QCD at high density, leading to a precocious "pseudo-conformal" sound velocity $v_{s}^{2} = 1/3$ (in unit of $c = 1$ ) for $n \gsim 3 n_{0}$ . The resulting prediction signals a drastic departure from standard nuclear many-body theory in the density regime involved in the massive stars. We suggest that the tidal deformability implemented in gravitational waves coming from coalescing neutron stars in LIGO/Virgo-type observations could pin down the location of the topology change density $n_{1/2}$ .
nucl-thastro-ph.HEhep-phSCPMA(2019)·24 citations
03
The Non-Quenching of $g_{A}$ in Nuclei and Emergent Scale Symmetry in Dense Baryonic Matter
Yan-Ling Li🇨🇳 · Yong-Liang Ma🇨🇳 · Mannque Rho🇫🇷
How the axial coupling constant $g_{A}$ in nuclear Gamow-Teller transitions described in shell model gets "quenched" to a universal constant close to 1 can be explained by nuclear correlations in Fermi-liquid fixed point theory using a scale-symmetric chiral Lagrangian supplemented with hidden local symmetric vector mesons. Contrary to what one might naively suspect -- and has been discussed in some circles, there is no fundamental quenching at nuclear matter density due to QCD condensates. When the density of many-body systems treated with the same Lagrangian increases beyond the density $n = n_{1/2} \gsim 2 n_{0}$ (where $n_{0}$ is the normal nuclear matter density) at which skyrmions representing baryons fractionize to half-skyrmions, with the $ρ$ meson driven toward the vector manifestation fixed point and a scalar meson $σ$ driven to the dilaton-limit fixed point with the nucleons parity-doubled, the dense matter supports the "pseudo-conformal" sound velocity for $n \gsim n_{1/2}$ while the trace of the energy momentum tensor remains non-vanishing. A plausible interpretation is that this signals the emergence of scale symmetry not explicitly present or hidden in QCD in the vacuum. The fundamental constant $g_{A}$ , unaffected by QCD condensates for $n < n_{1/2}$ , does go to 1 as the dilaton-limit fixed point is approached before arriving at chiral restoration, but it is not directly related to the "quenched $g_{A}$ " in nuclei which can be explained as a Fermi-liquid fixed point quantity. The mechanism that produces a precocious pseudo-conformal sound velocity is expected to impact on the tidal deformability $Λ$ in gravity waves from coalescing neutron stars.
nucl-thhep-phPRC(2018)·11 citations
04
Fluctuations in the $^{235}$ U(n,f) cross section
G.F. Bertsch🇺🇸 · David Brown🇺🇸 · E.D. Davis🇺🇸
We examine the autocorrelation function of the $^{235}$ U(n,f) reaction with a view to quantify the presence of intermediate structure in the cross section. Fluctuations due to compound nucleus resonances on the eV energy scale are clearly visible up to $\sim 100$ keV neutron energies. Structure on the one-keV energy scale is not present as a systematic feature of the correlation function, although it is present in the data covering the region around 20 keV.
nucl-thPRC(2018)·10 citations
05
Microscopic optical potentials including breakup effects for elastic scattering
Shoya Ogawa · Ryo Horinouchi · Masakazu Toyokawa · Takuma Matsumoto
We construct a microscopic optical potential including breakup effects for elastic scattering of weakly-binding projectiles within the Glauber model, in which a nucleon-nucleus potential is derived by the $g$ -matrix folding model. The derived microscopic optical potential is referred to as the eikonal potential. For $d$ scattering, the calculation with the eikonal potential reasonably reproduces the result with an exact calculation estimated by the continuum-discretized coupled-channels method. As the properties of the eikonal potential, the inaccuracy of the eikonal approximation used in the Glauber model is partially excluded. We also analyse the $^{6}$ He scattering from $^{12}$ C with the eikonal potential and show its applicability to the scattering with many-body projectiles.
nucl-thPTEP(2019)·1 citation
06
Medium-induced gluon emission via transverse and longitudinal scattering in dense nuclear matter
Le Zhang🇨🇳 · De-Fu Hou🇨🇳 · Guang-You Qin🇨🇳
We study the medium-induced gluon emission from a hard quark jet traversing the dense nuclear matter within the framework of deep inelastic scattering off a large nucleus. We extend the previous work and compute the single gluon emission spectrum including both transverse and longitudinal momentum exchanges between the hard jet parton and the medium constituents. On the other hand, with only transverse scattering and using static scattering centers for the traversed medium, our induced gluon emission spectrum in the soft gluon limit reduces to the Gyulassy-Levai-Vitev one-rescattering-one-emission formula.
nucl-thhep-phnucl-exPRC(2018)·9 citations
07
Event patterns from negative pion spectra in proton-proton and nucleus-nucleus collisions at SPS
Ya-Hui Chen🇨🇳 · Fu-Hu Liu🇨🇳 · Edward K. Sarkisyan-Grinbaum🇨🇭
Rapidity-dependent transverse momentum spectra of negatively charged pions measured at different rapidities in proton-proton collisions at the Super Proton Synchrotron (SPS) at various energies within its Beam Energy Scan (BES) program are investigated by using one- and two-component standard distributions where the chemical potential and spin property of particles are implemented. The rapidity spectra are described by a double-Gaussian distribution. At the stage of kinetic freeze-out, the event patterns are structured by the scatter plots in the three-dimensional subspaces of velocity, momentum and rapidity. The results of the studies of the rapidity-independent transverse mass spectra measured at mid-rapidity in proton-proton collisions are compared with those based on the similar transverse mass spectra measured in the most central beryllium-beryllium, argon-scandium and lead-lead collisions from the SPS at its BES energies.
nucl-thhep-exhep-phnucl-exCPC(2018)·4 citations
08
Non-hydrodynamic quasinormal modes and equilibration of a baryon dense holographic QGP with a critical point
Romulo Rougemont (IIP, Brazil)🇧🇷 · Renato Critelli (Sao Paulo U.)🇧🇷 · Jorge Noronha (Sao Paulo U.)🇧🇷
We compute the homogeneous limit of non-hydrodynamic quasinormal modes (QNM's) of a phenomenologically realistic Einstein-Maxwell-Dilaton (EMD) holographic model for the Quark-Gluon Plasma (QGP) that is able to: i) {\it quantitatively} describe state-of-the-art lattice results for the QCD equation of state and higher order baryon susceptibilities with $2 + 1$ flavors and physical quark masses up to highest values of the baryon chemical potential currently reached in lattice simulations; ii) describe the nearly perfect fluidity of the strongly coupled QGP produced in ultrarelativistic heavy ion collisions; iii) give a very good description of the bulk viscosity extracted via some recent Bayesian analyzes of hydrodynamical descriptions of heavy ion experimental data. This EMD model has been recently used to predict the location of the QCD critical point in the QCD phase diagram, which was found to be within the reach of upcoming low energy heavy ion collisions. The lowest quasinormal modes of the $S O (3)$ rotationally invariant quintuplet, triplet, and singlet channels evaluated in the present work provide upper bounds for characteristic equilibration times describing how fast the dense medium returns to thermal equilibrium after being subjected to small disturbances. We find that the equilibration times in the different channels come closer to each other at high temperatures, although being well separated at the critical point. Moreover, in most cases, these equilibration times decrease with increasing baryon chemical potential while keeping temperature fixed.
↳ hep-phhep-thnucl-thPRD(2018)·26 citations
09
Cooling of Small and Massive Hyperonic Stars
Rodrigo Negreiros🇧🇷 · Laura Tolos🇩🇪 · Mario Centelles🇪🇸 · Angels Ramos🇪🇸 · Veronica Dexheimer🇺🇸
We perform cooling simulations for isolated neutron stars using recently developed equations of state for their core. The equations of state are obtained from new parametrizations of the FSU2 relativistic mean-field functional that reproduce the properties of nuclear matter and finite nuclei, while fulfilling the restrictions on high-density matter deduced from heavy-ion collisions, measurements of massive 2 $M_{⊙}$ neutron stars, and neutron star radii below 13 km. We find that two of the models studied, FSU2R (with nucleons) and in particular FSU2H (with nucleons and hyperons), show very good agreement with cooling observations, even without including extensive nucleon pairing. This suggests that the cooling observations are more compatible with an equation of state that produces a soft nuclear symmetry energy and, hence, generates small neutron star radii. However, both models favor large stellar masses, above $1.8 M_{⊙}$ , to explain the colder isolated neutron stars that have been observed, even if nucleon pairing is present.
↳ astro-ph.HEnucl-thApJ(2018)·65 citations
10
Pulsars as Weber gravitational wave detectors
Arpan Das🇮🇳 · Shreyansh S. Dave🇮🇳 · Oindrila Ganguly🇮🇳 · Ajit M. Srivastava🇮🇳
A gravitational wave passing through a pulsar will lead to a variation in the moment of inertia of the pulsar affecting its rotation. This will affect the extremely accurately measured spin rate of the pulsar as well as its pulse profile (due to induced wobbling depending on the source direction). The effect will be most pronounced at resonance and should be detectable by accurate observations of the pulsar signal. The pulsar, in this sense, acts as a remotely stationed Weber detector of gravitational waves whose signal can be monitored on earth. With possible gravitational wave sources spread around in the universe, pulsars in their neighborhoods can provide us a family of \textit{remote} detectors all of which can be monitored on earth. Even if GW are detected directly by earth based conventional detectors, such pulsar detectors can provide additional information for accurate determination of the source location. This can be of crucial importance for sources which do not emit any other form of radiation such as black hole mergers. For the gravitational wave events already detected by LIGO (and Virgo), our proposal suggests that one should look for specific pulsars which would have been disturbed by these events, and will transmit this disturbance via their pulse signals in any foreseeable future. If these future pulsar events can be predicted with accuracy then a focused effort can be made to detect any possible changes in the signals of those specific pulsars.
↳ astro-ph.HEgr-qcnucl-thPLB(2019)·8 citations
11
$^{9}$ Be+ $^{120}$ Sn scattering at near-barrier energies within a four body model
A. Arazi · J. Casal · M. Rodríguez-Gallardo · J. M. Arias · R. Lichtenthäler Filho · D. Abriola · O. A. Capurro · M. A. Cardona · P. F. F. Carnelli · E. de Barbará · J. Fernández Niello · J. M. Figueira and 5 other authors
Cross sections for elastic and inelastic scattering of the weakly-bound $^{9}$ Be nucleus on a $^{120}$ Sn target have been measured at seven bombarding energies around and above the Coulomb barrier. The elastic angular distributions are analyzed with a four-body continuum-discretized coupled-channels (CDCC) calculation, which considers $^{9}$ Be as a three-body projectile ( $α$ + $α$ + n). An optical model analysis using the São Paulo potential is also shown for comparison. The CDCC analysis shows that the coupling to the continuum part of the spectrum is important for the agreement with experimental data even at energies around the Coulomb barrier, suggesting that breakup is an important process at low energies. At the highest incident energies, two inelastic peaks are observed at 1.19(5) and 2.41(5) MeV. Coupled-channels (CC) calculations using a rotational model confirm that the first inelastic peak corresponds to the excitation of the 2 $_{1}^{+}$ state in $^{120}$ Sn, while the second one likely corresponds to the excitation of the 3 $_{1}^{-}$ state.
↳ nucl-exnucl-thPRC(2018)·30 citations
12
Probing confinement by direct photons and dileptons
V.V. Goloviznin🇺🇦 · A.V. Nikolskii🇷🇺 · A.M. Snigirev🇷🇺 · G.M. Zinovjev🇺🇦
The intensive synchrotron radiation resulting from quarks interacting with the collective confining color field in relativistic heavy ion collisions is discussed. The spectrum of photons with large transverse momentum is calculated and compared with the experimental data to demonstrate the feasibility of this type of radiation. A study of the earlier predicted azimuthal anisotropy in the angular distribution of dileptons with respect to the three-momentum of the pair is performed as well. This boundary-induced mechanism of lepton pair production is shown to possess the features that are distinctly different from the standard mechanisms and can potentially provide an efficient probe of quark-gluon plasma formation.
↳ hep-phnucl-exnucl-thEPJA(2019)·6 citations

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