Nuclear Theory·nucl-th

Thursday·April 30, 2020

13 papers—9 primary·4 cross-listed

01
Description of the low-lying collective states of $^{96}$ Zr based on the quadrupole-collective Bohr Hamiltonian
E.V. Mardyban · E.A. Kolganova · T.M. Shneidman · R.V. Jolos · N. Pietralla
Experimental data on $^{96}$ Zr indicate coexisting spherical and deformed structures with small mixing amplitudes. Several collective low-lying states and E2 and M1 transitions are observed for this nucleus. The quadrupole-collective Bohr Hamiltonian depending on both $β$ and $γ$ shape variables with a potential having spherical and deformed minima, is applied consideration of these data. The relative depth of two minima, height and width of the barrier, rigidity of the potential near both minima are determined so as to achieve a satisfactory description of the observed properties of the low-lying collective quadrupole states of $^{96}$ Zr. Good agreement with the experimental data on the excitation energies, $B (E 2)$ and $B (M 1; 2_{2}^{+} \to 2_{1}^{+})$ reduced transition probabilities is obtained. It is shown that the low-energy structure of $^{96}$ Zr can be described in a satisfactory way within the Geometrical Collective Model with a potential function supporting shape coexistence without other restrictions of its shape. However, the excitation energy of the $2_{2}^{+}$ state can be reproduced only if the rotation inertia coefficient is taken by four times smaller than the vibrational one in the region of the deformed well. It is shown also that shell effects are important for the description of the $B (M 1; 2_{2}^{+} \to 2_{1}^{+})$ and $B (M 1; 3_{1}^{+} \to 2_{1}^{+})$ transition probabilities. An indication for the influence of the pairing vibrational mode on the $0_{2}^{+} \to 0_{1}^{+}$ transition is confirmed in agreement with the previous result.
nucl-thPRC(2020)·12 citations
02
Heavy-ion physics: freedom to do hot, dense, exciting QCD
Maria Elena Tejeda-Yeomans🇲🇽
In these two lectures I review the basics of heavy-ion collisions at relativistic energies and the physics we can do with them. I aim to cover the basics on the kinematics and observables in heavy-ion collider experiments, the basics on the phenomenology of the nuclear matter phase diagram, some of the model building and simulations currently used in the heavy-ion physics community and a selected list of amazing phenomenological discoveries and predictions.
nucl-thhep-phnucl-exCERN Yellow Rep.School Proc.(2021)·11 citations
03
Pomeron-LQCD model of $J /Ψ$ photo-production on the nucleon
T.-S. H. Lee🇺🇸
Based on the vector meson dominance assumption, a Hamiltonian model has been developed to investigate $J /Ψ$ photo-production reaction on the nucleon by using the $J /Ψ$ -nucleon potential extracted from a lattice QCD calculation of Phys. Rev. D{\bf 82}, 091501 (2010). It is found that the predicted total cross sections are comparable to the recent data of $J /Ψ$ photo-production reaction from Jefferson Laboratory. The model is then extended to include the two-gluon exchange amplitude modeled by Donnachie and Lanshoff within Regge Phenomenology. The resulting Pomeron-LQCD model can then explain the data up to invariant mass $W =$ 300 GeV. Future improvements needed to reduce the uncertainties of the predictions are discussed. The need of an accurate extraction of $J /Ψ$ -N potential at short distances from LQCD is illustrated.
nucl-thhep-lathep-phnucl-ex5 citations
04
Excitation of $^{229 m}$ Th at Inelastic Scattering of Low Energy Electrons
E. V. Tkalya
Excitation of the anomalously low lying nuclear isomer $^{229 m}$ Th $(3/ 2^{+}, 8.28 \pm 0.17$ eV) in the process of inelastic electron scattering is studied theoretically in the framework of the perturbation theory for the quantum electrodynamics. The calculated cross sections of $^{229 m}$ Th by the extremely low energy electrons in the range 9 eV--12 eV for the Th atom and Th $^{1 +, 4 +}$ ions lie in the range $1 0^{- 25}$ -- $1 0^{- 26}$ cm $^{2}$ . Being so large, the cross section opens up new possibilities for the effective non-resonant excitation of $^{229 m}$ Th in experiments with an electron beam or electron (electric) current. This can be crucial, since the energy of the isomeric state is currently known with an accuracy insufficient for the resonant excitation by photons. In addition, the cross section of the time reversed process is also large, and as a consequence, the probability of the non-radiative $^{229 m}$ Th decay via the conduction electrons in metal is $\approx 1 0^{6}$ s $^{- 1}$ , that is, close to the internal conversion probability in the Th atom.
nucl-thPRL(2020)·36 citations
05
Internal conversion of the low energy $^{229 m}$ Th isomer in the Thorium anion
E. V. Tkalya · R. Si
A process of the decay of the anomalously low lying nuclear isomer $^{229 m}$ Th $(3/ 2^{+}, 8.28 \pm 0.17$ eV) in the Thorium anion (Th $^{-}$ ) via the internal conversion (IC) channel is studied. We show that the half life of the nuclear isomer in the $6 d_{3/2}^{3} 7 s_{1/2}^{2}$ ground state and in the $6 d_{3/2}^{2} 7 s_{1/2}^{2} 7 p_{1/2}^{1}$ excited state of Th $^{-}$ is $\approx 1.5$ and $\approx 1.1$ times bigger than in the $6 d_{3/2}^{2} 7 s_{1/2}^{2}$ ground state of the Th atom. The IC probabilities in the anion decreases despite the decay via the additional $6 d_{3/2}$ or $7 p_{1/2}$ electrons. This counterintuitive result is a consequence: a) of a decrease in the amplitudes of the $6 d_{3/2}$ and $7 s_{1/2}$ wave functions near the nucleus due to an increase in their diffuseness of upon the addition of extra electron, b) of mutual compensation in the IC probability due to a kinematic factor, which depends on the energy of the conversion electron in the continuum as $E_{c}^{- 1/2}$ , and the $E_{c}^{1/4}$ growth of the amplitudes of the electron wave functions.
nucl-thPRC(2020)·8 citations
06
Decay of the low-energy nuclear $^{229 m}$ Th isomer via atomic Rydberg states
E. V. Tkalya
In the paper, a unique process of the decay of the $^{229 m}$ Th( $3/ 2^{+}, 8.28 \pm 0.17$ eV) low energy nuclear isomer via the internal conversion (IC) channel on Rydberg states is considered for the first time. The Rydberg atom $^{229 m}$ Th $^{+} + e_{R y}^{-}$ is a unique object where IC is possible exclusively on the Rydberg electron $e_{R y}^{-}$ . It is shown that in the $^{229 m}$ Th $^{4 +} + e_{R y}^{-}$ system a) IC on the electron states with relatively small values of the principal quantum number $n$ and the orbital moment $l$ is practically completely suppressed, b) IC probability, $W_{I C}$ , on the $ψ_{n s_{1/2}} (r)$ states is proportional to $∣ ψ_{n s_{1/2}} (0) ∣^{2}$ and can be related with the energy of the hyperfine interaction of the Rydberg electron with the nucleus, c) $W_{I C}$ decreases rapidly with the increase of $n$ in the range from 10 to 50, and in the range $n ≳ 150$ $W_{I C}$ changes as $Const / n^{3}$ typical for hydrogen-like ions, d) at $n \approx 10$ --30, $W_{I C}$ as a function of $l$ has a characteristic "knee" between $l = 3$ and $l = 4$ , i.e. a three order of magnitude decrease of $W_{I C}$ due to the qualitative change in the ratio between the centrifugal and shielding potentials.
nucl-thPRC(2019)·9 citations
07
Nuclear Symmetry Energy and Neutron Skin Thickness of $^{208} P b$ using a finite range effective interaction
D. Behera · S. K. Tripathy · T. R. Routray · B. Behera
We use a finite range simple effective interaction to construct nuclear equations of state for the study of the density dependence of the nuclear symmetry energy. The EoSs provide good descriptions of the nuclear symmetry energy at a subsaturation density $ρ_{c} = 0.11$ fm $^{- 3}$ and at a density around two times the saturation density $ρ_{0}$ . We obtain a correlation between the neutron skin thickness in $^{208}$ Pb and the density slope parameter at the subsaturation density. A linear relation is obtained between the neutron skin thickness and the parameter $β^{'} = \frac{L ( ρ _{c} )}{3 E _{s} ( ρ _{0} )}$ , where $E_{s} (ρ_{0})$ and $L (ρ_{c})$ are respectively the nuclear symmetry energy at saturation density and the density slope parameter at the subsaturation density.
nucl-thPhys.Scripta(2020)·13 citations
08
Thouless-Valatin moment of inertia and removal of the spurious mode in the linear response theory
Markus Kortelainen
Symmetry breaking at the mean-field level leads to an appearance of a symmetry restoring Nambu-Goldstone (NG) mode in the linear response theory. These modes represent a special kind of collective motion of the system. However, they can interfere with the calculated intrinsic physical excitations and, hence, they are often called as spurious modes. I discuss translational and rotational NG mode and the inertia parameter associated with these modes, by using the finite amplitude method formalism. I will also discuss how to remove spurious mode from the calculated transition strength function.
nucl-thJ.Phys.Conf.Ser.(2020)·1 citation
09
Mixed phase transition from hypernuclear matter to deconfined quark matter fulfilling mass-radius constraints of neutron stars
M. Shahrbaf🇮🇷 · D. Blaschke🇵🇱 · S. Khanmohamadi🇮🇷
A recent solution of the hyperon puzzle by a first order phase transition to color superconducting quark matter is revisited in order to replace the Maxwell construction by an interpolation method which describes a mixed phase. To do this, we apply for the first time the finite-range polynomial interpolation method for constructing a transition between hadronic and quark matter phases to the situation that is characterized in the literature as the reconfinement problem. For the description of the hadronic phase the lowest order constrained variational method is used while for the quark phase the nonlocal Nambu-Jona-Lasinio model with constant (model nlNJLA) and with density-dependent (model nlNJLB) parameters is employed. Applying the replacement interpolation method to both quark matter models results in a hybrid equation of state that allows a coexistence of nuclear matter, hypernuclear matter and quark matter in a mixed phase between the pure hadronic and quark phases which can also be realized in the structure of the corresponding hybrid star sequences. The predicted hybrid stars fulfill the constraints on the mass-radius relation for neutron stars obtained from recent observations.
nucl-thastro-ph.HEhep-phJ.Phys.G(2020)·22 citations
10
The Neutron Star Outer Crust Equation of State: A Machine Learning approach
Murarka Utsav Anil · Kinjal Banerjee · Tuhin Malik · Constança Providência
Constructing the outer crust of the neutron stars requires the knowledge of the Binding Energy (BE) of the atomic nuclei. Although the BE of a lot of the nuclei is experimentally determined and can be obtained from the AME data table, for the others we need to depend on theoretical models. There exist a lot of physical theories to predict the BE, each with its own strengths and weaknesses. In this paper, we apply Machine Learning (ML) algorithms on AME2016 data set to predict the Binding Energy {of atomic nuclei}. The novel feature of our work is that it is model independent. We do not assume or use any nuclear physics model but use only ML algorithms directly on the AME2016 data set. Our results are further refined by using another ML algorithm to train the errors of the first algorithm, and repeating this process iteratively. Our best algorithm gives $σ_{rms} \approx 0.58$ MeV for Binding Energy on randomized testing sets. This is comparable to all physics models or ML improved physics models studied in literature till date. Using the predictions of our Machine Learning algorithm, we construct the outer crust equation of state (EoS) of a neutron star and show that our model is comparable to existing models. This work also demonstrates the use of various ML algorithms and a detailed analysis on how we arrived at our best algorithm. It will help the physics community in understanding how to choose an ML algorithm which would be suited for their data set. Our algorithms and best fit model is also made publicly available for the use of the community.
↳ physics.comp-phnucl-thJCAP(2022)·26 citations
11
The three-dimensional distribution of quarks in momentum space
Alessandro Bacchetta🇮🇹 · Filippo Delcarro🇺🇸 · Cristian Pisano🇮🇹 · Marco Radici🇮🇹
We present the distribution of unpolarized quarks in a transversely polarized proton in three-dimensional momentum space. Our results are based on consistent extractions of the unpolarized and Sivers transverse momentum dependent parton distributions (TMDs).
↳ hep-phnucl-thPLB(2022)·85 citations
12
Complete NLO QCD study of single- and double-quarkonium hadroproduction in the colour-evaporation model at the Tevatron and the LHC
Jean-Philippe Lansberg🇫🇷 · Hua-Sheng Shao🇫🇷 · Nodoka Yamanaka🇫🇷 · Yu-Jie Zhang🇨🇳 · Camille Noûs🇫🇷
We study the Single-Parton-Scattering (SPS) production of double quarkonia (J/psi+J/psi, J/psi+Upsilon, and Upsilon+Upsilon) in pp and pp(bar) collisions at the LHC and the Tevatron as measured by the CMS, ATLAS, LHCb, and D0 experiments in the Colour-Evaporation Model (CEM), based on the quark-hadron-duality, including Next-to-Leading Order (NLO) QCD corrections up to alpha_s^5. To do so, we also perform the first true NLO --up to alpha_s^4-- study of the p_T-differential cross section for single-quarkonium production. This allows us to fix the non-perturbative CEM parameters at NLO accuracy in the region where quarkonium-pair data are measured. Our results show that the CEM at NLO in general significantly undershoots these experimental data and, in view of the other existing SPS studies, confirm the need for Double Parton Scattering (DPS) to account for the data. Our NLO study of single-quarkonium production at mid and large p_T also confirms the difficulty of the approach to account for the measured p_T spectra; this is reminiscent of the impossibility to fit single-quarkonium data with the sole 3S18 NRQCD contribution from gluon fragmentation. We stress that the discrepancy occurs in a kinematical region where the new features of the improved CEM are not relevant.
↳ hep-phhep-exnucl-exnucl-thPLB(2020)·44 citations
13
Critical point fluctuations: Finite size and global charge conservation effects
Roman V. Poberezhnyuk🇺🇦 · Oleh Savchuk🇺🇦 · Mark I. Gorenstein🇺🇦 · Volodymyr Vovchenko🇺🇸 · Kirill Taradiy🇩🇪 · Viktor V. Begun🇵🇱 · Leonid Satarov🇩🇪 · Jan Steinheimer🇩🇪 · Horst Stoecker🇩🇪
We investigate simultaneous effects of finite system size and global charge conservation on thermal fluctuations in the vicinity of a critical point. For that we consider a finite interacting system which exchanges particles with a finite reservoir (thermostat), comprising a statistical ensemble that is distinct from the common canonical and grand canonical ensembles. As a particular example the van der Waals model is used. The global charge conservation effects strongly influence the cumulants of particle number distribution when the system size is comparable to that of the reservoir. If the system size is large enough to capture all the physics associated with the interactions, the global charge conservation effects can be accurately described and corrected for analytically, within a recently developed subensemble acceptance method. The finite size effects start to play a significant role when the correlation length grows large due to proximity of the critical point or when the system is small enough to be comparable to an eigenvolume of an individual particle. We discuss our results in the context of fluctuation measurements in heavy-ion collisions.
↳ hep-phnucl-exnucl-thPRC(2020)·31 citations

Affiliations

first authorsco-authorsvia INSPIRE