Nuclear Theory·nucl-th

Wednesday·May 29, 2019

11 papers—5 primary·6 cross-listed

01
Quadrupole dominance in light Cd and Sn isotopes
A.P. Zuker🇫🇷
Shell model calculations with the neutron effective charge as single free parameter describe well the \bet and \bef rates for $N \leq 64$ in the Cd and Sn isotopes. The former exhibit weak permanent deformation corroborating the prediction of a pseudo SU3 symmetry, which remains of heuristic value in the latter, though the pairing force erodes the quadrupole dominance. Calculations in $1 0^{7}$ and $1 0^{10}$ -dimensional spaces exhibit almost identical patterns: A vindication of the shell model. For $N \geq 64$ quadrupole dominance is accentuated in the Cd isotopes and gives way to seniority dominance for the Sn isotopes.
nucl-thnucl-ex2 citations
02
Rotational excitations in near neutron-drip line nuclei: the birth and death of particle-bound rotational bands and the extension of nuclear landscape beyond spin zero neutron drip line
A. V. Afanasjev · N. Itagaki · D. Ray
Two new mechanisms active in rotating nuclei located in the vicinity of neutron drip line have been discovered. Strong Coriolis interaction acting on high- $j$ orbitals transforms particle-unbound (resonance) nucleonic configurations into particle-bound ones with increasing angular momentum. The point of the transition manifests the birth of particle-bound rotational bands. Alternative possibility of the transition from particle-bound to resonance rotational band (the death of particle-bound rotational bands) with increasing spin also exists but it is less frequent in the calculations. The birth of particle-bound rotational bands provides a mechanism for the extension of nuclear landscape to neutron numbers which are larger than those of the neutron drip line in non-rotating nuclei.
nucl-thPLB(2019)·8 citations
03
Superheavy nuclei in microscopic collective Hamiltonian approach: the impact of beyond mean field correlations on the ground state and fission properties
Z. Shi · A. V. Afanasjev · Z. P. Li · J. Meng
The impact of beyond mean field effects on the ground state and fission properties of superheavy nuclei has been investigated in a five-dimensional collective Hamiltonian based on covariant density functional theory. The inclusion of dynamical correlations reduces the impact of the $Z = 120$ shell closure and induces substantial collectivity for the majority of the $Z = 120$ nuclei which otherwise are spherical at the mean field level (as seen in the calculations with the PC-PK1 functional). Thus, they lead to a substantial convergence of the predictions of the functionals DD-PC1 and PC-PK1 which are different at the mean field level. On the contrary, the predictions of these two functionals remain distinctly different for the $N = 184$ nuclei even when dynamical correlations are included. These nuclei are mostly spherical (oblate) in the calculations with PC-PK1 (DD-PC1). Our calculations for the first time reveal significant impact of dynamical correlations on the heights of inner fission barriers of superheavy nuclei with soft potential energy surfaces, the minimum of which at the mean field level is located at spherical shape. These correlations affect the fission barriers of the nuclei, which are deformed in the ground state at the mean field level, to a lesser degree.
nucl-thPRC(2019)·33 citations
04
Bayesian updating for data adjustments and multi-level uncertainty propagation within Total Monte Carlo
E. Alhassan · D. Rochman · H. Sjöstrand · A. Vasiliev · A.J. Koning · H. Ferroukhi
In this work, a method is proposed for combining differential and integral benchmark experimental data within a Bayesian framework for nuclear data adjustments and multi-level uncertainty propagation using the Total Monte Carlo method. First, input parameters to basic nuclear physics models implemented within the state of the art nuclear reactions code, TALYS, were sampled from uniform distributions and randomly varied to produce a large set of random nuclear data files. Next, a probabilistic data assimilation was carried out by computing the likelihood function for each random nuclear data file based first on only differential experimental data (1st update) and then on integral benchmark data (2nd update). The individual likelihood functions from the two updates were then combined into a global likelihood function which was used for the selection of the final 'best' file. The proposed method has been applied for the adjustment of $^{208}$ Pb in the fast neutron energy region below 20 MeV. The 'best' file from the adjustments was compared with available experimental data from the EXFOR database as well as evaluations from the major nuclear data libraries and found to compare favourably.
nucl-th1 citation
05
Consistency of two different approaches to determine the strength of a pairing residual interaction in the rare-earth region
Nurhafiza M. Nor🇲🇾 · Nor-Anita Rezle🇲🇾 · Kai-Wen Kelvin-Lee🇲🇾 · Meng-Hock Koh🇲🇾 · L. Bonneau🇫🇷 · P. Quentin🇻🇳
Two fits of the pairing residual interaction in the rare-earth region are independently performed. One is made on the odd-even staggering of masses by comparing measured and explicitly calculated three-point binding-energy differences centered on odd-even nuclei. Another deals with the moments of inertia of the first 2+ states of well deformed even-even nuclei upon comparing experimental data with the results of Inglis-Belyaev moments (supplemented by a crude estimate of the so-called Thouless-Valatin corrections). The sample includes 24 even-even and 31 odd-mass nuclei selected according to two criteria: they should have good rotor properties and should not correspond to low pairing-correlation regimes in their ground states. Calculations are performed in the self-consistent Hartree-Fock plus BCS framework (implementing a self-consistent blocking in the case of odd-mass nuclei). The Skyrme SIII parametrization is used in the particle-hole channel and the fitted quantities are the strengths of |Tz|=1 proton and neutron seniority residual interactions. As a result, the two fits yield sets of strengths in excellent agreement: about 0.1% for the neutron parameters and 0.2% for protons. In contrast when one performs such a fit on odd-even staggering from quantities deduced from BCS gaps or minimal quasiparticle energies in even-even nuclei, as is traditional, one obtains results significantly different from those obtained in the same nuclei by a fit of moments of inertia. As a conclusion, beyond providing a phenomenological tool for microscopic calculations in this region, we have illustrated the proposition made in the seminal paper of Bohr, Mottelson and Pines that moments of inertia and odd-even staggering in selected nuclei were excellent measuring sticks of nuclear pairing correlations.
nucl-thPRC(2019)·17 citations
06
Nuclear-matter distribution in the proton-rich nuclei $^{7}$ Be and $^{8}$ B from intermediate energy proton elastic scattering in inverse kinematics
A.V. Dobrovolsky · G.A. Korolev · A.G. Inglessi · G.D. Alkhazov · G. Colò · I. Dillmann · P. Egelhof · A. Estradé · F. Farinon · H. Geissel · S.Ilieva · Y. Ke and 16 other authors
Absolute differential cross sections for elastic $p^{7}$ Be and $p^{8}$ B small-angle scattering were measured in inverse kinematics at an energy of 0.7 GeV/u at GSI Darmstadt. The hydrogen-filled ionization chamber IKAR was used as an active target to detect the recoil protons. The projectile tracking and isotope identification were performed with multi-wire proportional chambers and scintillation detectors. The measured cross sections were analysed using the Glauber multiple-scattering theory. The root-mean-square (rms) nuclear matter radii $R_{m} = 2.42 (4)$ fm for $^{7}$ Be and $R_{m} = 2.58 (6)$ fm for $^{8}$ B were obtained. The radial density distribution deduced for $^{8}$ B exhibits a proton halo structure with the rms halo radius $R_{h} = 4.24 (25)$ fm. A comparison of the deduced experimental radii is displayed with existing experimental and theoretical data.
↳ nucl-exnucl-thNPA(2019)·22 citations
07
On pseudorapidity distribution in p-Pb and Xe-Xe collisions at high energy based on the three-source Landau hydrodynamic model
Li-Na Gao🇨🇳 · Zhen-Hu Li🇨🇳 · Er-Qin Wang🇨🇳
The pseudorapidity distributions of charged particles produced in p-Pb collisions and Xe-Xe collisions at LHC energies are described by the revised Landau hydrodynamic model. The research results are in agreement with the experimental data measured by ALICE collaboration at LHC. The related parameters are obtained and analyzed. And, we extracted the values of the squared speed of sound for central source are between 0.4 and 0.5.
↳ hep-phnucl-thIndian J.Phys.(2021)·0 citations
08
Questioning quark-gluon plasma formation in small collision systems
Thomas A. Trainor🇺🇸
A recent letter published in the journal Nature reports observation at the relativistic heavy ion collider (RHIC) of quark-gluon plasma (QGP) formation in small asymmetric collision systems denoted as $p$ -Au, $d$ -Au and $^{3}$ He-Au. The claimed phenomenon, described as `short-lived QGP droplets,' is inferred from a combination of Glauber Monte Carlo simulations, measurement of two azimuth Fourier amplitudes $v_{2}$ and $v_{3}$ and hydro theory calculations. While that claim follows a trend in recent years to report `signals' conventionally attributed to QGP as appearing also in smaller collision systems, the new result remains surprising in the context of expectations before first RHIC operation that small systems, e.g. $d$ -Au collisions, would provide control experiments in which a QGP was unlikely to appear. An alternative interpretation of the recent RHIC result is that small-system control experiments do convey an important message: The `signals' conventionally attributed to QGP formation in larger A-A collisions do not actually represent that phenomenon in any system. The present study reviews a broad array of experimental evidence for or against QGP formation in several collision systems. It examines in particular hydro theory descriptions of spectra and correlations usually interpreted to support QGP formation. Available evidence suggests that data features conventionally attributed to QGP formation represent either minimum-bias jet production or a nonjet azimuth quadrupole with properties inconsistent with a hydro hypothesis.
↳ hep-phnucl-th6 citations
09
Chiral phase transition in (2 + 1)-flavor QCD
Heng-Tong Ding🇨🇳 · Prasad Hegde🇮🇳 · Olaf Kaczmarek🇨🇳 · Frithjof Karsch🇩🇪 · Anirban Lahiri🇩🇪 · Sheng-Tai Li🇨🇳 · Swagato Mukherjee🇺🇸 · Peter Petreczky🇺🇸
The chiral phase transition temperature $T_{c}^{0}$ is a fundamental quantity of QCD. To determine this quantity we have performed simulations of (2 + 1)-flavor QCD using the Highly Improved Staggered Quarks (HISQ/tree) action on $N_{τ} = 6, 8$ and 12 lattices with aspect ratios $N_{σ} / N_{τ}$ ranging from 4 to 8. In our simulations the strange quark mass is fixed to its physical value $m_{s}^{phy}$ , and the values of two degenerate light quark masses $m_{l}$ are varied from $m_{s}^{phy} /20$ to $m_{s}^{phy} /160$ which correspond to a Goldstone pion mass $m_{π}$ ranging from 160 MeV to 55 MeV in the continuum limit. By investigating the light quark mass dependence and the volume dependence of various chiral observables, e.g. chiral susceptibilities and Binder cumulants, no evidence for a first order phase transition in our current quark mass window is found. Two estimators $T_{60}$ and $T_{δ}$ are proposed to extract the chiral phase transition temperature $T_{c}^{0}$ in the chiral and continuum limit and our current estimate for $T_{c}^{0}$ is $13 2_{- 6}^{+ 3}$ MeV.
↳ hep-lathep-phhep-thnucl-thPoS(2019)·14 citations
10
Strong isospin symmetry breaking in light scalar meson production
N.N. Achasov🇷🇺 · G.N. Shestakov🇷🇺
Isospin symmetry breaking is discussed as a tool for studying the nature and production mechanisms of light scalar mesons. We are concerned with isospin breaking effects with an amplitude $\sim m_{d} - m_{u}$ (instead of the usual $\sim m_{d} - m_{u}$ ), where $m_{u}$ and $m_{d}$ are the $u$ and $d$ quark masses, whose magnitude and phase vary with energy in a resonance-like way characteristic of the $K K ˉ$ threshold region. We consider a variety of reactions that can experimentally reveal (or have revealed) the mixing of $a_{0}^{0} (980)$ and $f_{0} (980)$ resonances that breaks the isotopic invariance due to the mass difference between $K^{+}$ and $K^{0}$ mesons. Experimental results on the search for $a_{0}^{0} (980) - f_{0} (980)$ mixing in $f_{1} (1285) \to f_{0} (980) π^{0} \to π^{+} π^{-} π^{0}$ and $η (1405) \to f_{0} (980) π^{0} \to π^{+} π^{-} π^{0}$ decays suggest a broader perspective on the isotopic symmetry breaking effects due to the $K^{+}$ and $K^{0}$ mass difference. It has become clear that not only the $a_{0}^{0} (980) - f_{0} (980)$ mixing but also any mechanism producing $K K ˉ$ pairs with a definite isospin in an S wave gives rise to such effects, thus suggesting a new tool for studying the nature and production mechanisms of light scalars. Of particular interest is the case of a large isotopic symmetry breaking in the $η (1405) \to f_{0} (980) π^{0} \to π^{+} π^{-} π^{0}$ decay due to the occurrence of anomalous Landau thresholds (logarithmic triangle singularities), i.e., due to the $η (1405) \to (K^{*} K ˉ + K ˉ^{*} K) \to (K^{+} K^{-} + K^{0} K ˉ^{0}) π^{0} \to f_{0} (980) π^{0} \to π^{+} π^{-} π^{0}$ transition (where it is of fundamental importance that the $K^{*}$ meson has a finite width).
↳ hep-phhep-exnucl-thPhys.Usp.(2019)·14 citations
11
Time-dependent relaxation of observables in complex quantum systems
Alexander Volya · Vladimir Zelevinsky
We consider time-dependent relaxation of observables in quantum systems of chaotic and regular type. We show that the spread of the wave function in the Hilbert space is determined by the survival probability which is known to have pre-exponential, exponential, and long-term power-law limiting behaviors. This result relies on complexity of the wave functions and thus is generic to many systems. In the chaotic limit modeled by the Gaussian Orthogonal Ensemble we show that the survival probability obtained analytically also fully defines the relaxation timescale of observables. This is not the case in general, using realistic nuclear shell model and the quadrupole moment as an observable we demonstrate that the relaxation time is significantly longer than defined by the survival probability of the initial state. An example of the non-chaotic limit of coherent and squeezed states provides an additional illustration.
↳ quant-phnucl-th0 citations

Affiliations

first authorsco-authorsvia INSPIRE