Nuclear Theory·nucl-th

Wednesday·December 21, 2016

18 papers—10 primary·8 cross-listed

01
[Submitted on 20 Dec 2016]
Effects of volume corrections and resonance decays on cumulants of net-charge distributions in a Monte Carlo hadron resonance gas model
Hao-jie Xu🇨🇳
The effects of volume corrections and resonance decays (the resulting correlations between positive charges and negative charges) on cumulants of net-proton distributions and net-charge distributions are investigated by using a Monte Carlo hadron resonance gas ({\tt MCHRG}) model. The required volume distributions are generated by a Monte Carlo Glauber ({\tt MC-Glb}) model. Except the variances of net-charge distributions, the {\tt MCHRG} model with more realistic simulations of volume corrections, resonance decays and acceptance cuts can reasonably explain the data of cumulants of net-proton distributions and net-charge distributions reported by the STAR collaboration. The {\tt MCHRG} calculations indicate that both the volume corrections and resonance decays make the cumulant products of net-charge distributions deviate from the Skellam expectations: the deviations of $S σ$ and $κ σ^{2}$ are dominated by the former effect while the deviations of $ω$ are dominated by the latter one.
Comments:
A Monte Carlo hadron resonance gas (MCHRG) model is proposed to study the cumulants of multiplicity distributions. 6 pages, 2 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1612.06485 [pdf]
PLB(2017)·25 citations
02
[Submitted on 20 Dec 2016]
Pion Production in Rare Isotope Collisions
M.B. Tsang · J. Estee · H. Setiawan · W.G. Lynch · J. Barney · M.B. Chen · G. Cerizza · P. Danielewicz · J. Hong · P. Morfouace · R. Shane · S. Tangwancharoen and 6 other authors
Pion energy spectra are presented for central collisions of neutron-rich 132Sn+124Sn and neutron-deficient 108Sn+112Sn systems using simulations with Boltzmann-Uehling-Uhlenbeck transport model. These calculations, which incorporate isospin-dependent mean field potentials for relevant baryons and mesons, display a sensitivity to the pion spectra that could allow significant constraints on the density dependence of the symmetry energy and its mean field potential at supra-saturation densities. The predicted sensitivity increases with the isospin asymmetry of the total system and decreases with incident energy.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1612.06561 [pdf]
PRC(2017)·42 citations
03
[Submitted on 20 Dec 2016]
Collinear cluster tri-partition: Kinematics constraints and stability of collinearity
Patric Holmvall🇸🇪 · Ulli Köster🇫🇷 · Andreas Heinz🇸🇪 · Thomas Nilsson🇸🇪
A new mode of nuclear fission has been proposed by the FOBOS collaboration, called Collinear Cluster Tri-partition (CCT), suggesting that three heavy fission fragments can be emitted perfectly collinearly in low-energy fission. It is surprising that CCT escaped observation for so long given the relatively high reported yield, of roughly 0.5% relative to binary fission. These claims call for an independent verification with a different experimental technique. Verification experiments based on direct observation of CCT fragments with fission fragment spectrometers require guidance with respect to the allowed kinetic energy range, which we present in this paper. We discuss corresponding model calculations which, if CCT is found in such verification experiments, could indicate how the breakups proceed. We also study the intrinsic stability of collinearity. Three different decay models are used, which span together the timescales of three-body fission. These models are used to calculate the possible kinetic energy ranges of CCT fragments in 235U(n,f) and 252Cf(sf). We use semi-classical trajectory calculations with a Monte-Carlo method to study the intrinsic stability of collinearity. CCT has a high net Q-value, but in a sequential decay, the intermediate steps are energetically and geometrically unfavorable or even forbidden. Moreover, perfect collinearity is extremely unstable, and broken by the slightest perturbation. According to our results, the central fragment would be very difficult to detect due to its low kinetic energy, raising the question of why previous experiments could not detect a missing-mass signature corresponding to CCT. We find that a realization of CCT would require an unphysical fine-tuning of the initial conditions. Our results enable independent experimental verification and encourage further critical theoretical studies of CCT.
Comments:
20 pages, 19 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1612.06583 [pdf]
PRC(2017)·11 citations
04
[Submitted on 20 Dec 2016]
Recent progress on dense nuclear matter in skyrmion approaches
Yong-Liang Ma🇨🇳 · Mannque Rho🇫🇷
The Skyrme model provides a novel unified approach to nuclear physics. In this approach, single baryon, baryonic matter and medium-modified hadron properties are treated on the same footing. Intrinsic density dependence (IDD) reflecting the change of vacuum by compressed baryonic matter figures naturally in the approach. In this article, we review the recent progress on accessing dense nuclear matter by putting baryons treated as solitons, namely, skyrmions, on crystal lattice with accents on the implications in compact stars.
Comments:
Published version. Typos are corrected
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1612.06600 [pdf]
SCPMA(2017)·32 citations
05
[Submitted on 20 Dec 2016]
Monopole transition strength function of $^{12}$ C in three- $α$ model
Souichi Ishikawa
The energy level structure of $^{12}$ C nucleus at a few MeV above the three- $α$ threshold is still unsatisfactory known. For instance, most microscopic calculations predicted that there exist one $0^{+}$ -state in this energy region besides the well known Hoyle state, while some experimental and theoretical studies show the existing of two $0^{+}$ -states. In this paper, I will take a three- $α$ -boson (3 $α$ ) model for bound and continuum states in $^{12}$ C, and study a transition process from the $^{12}$ C( $0_{1}^{+}$ ) ground state to 3 $α$ $0^{+}$ continuum states by the electric monopole ( $E 0$ ) operator. The strength distribution of the process will be calculated as a function of $3 α$ energy using the Faddeev three-body theory. The Hamiltonian for the $3 α$ system consists of two- and three- $α$ potentials, and some three- $α$ potentials with different range parameters will be examined. Results of the strength function show a double-peaked bump at low energy region, which can be considered as two $0^{+}$ -states. The peak at higher energy may originate from a 3 $α$ resonant state. However, it is unlikely that the peak at the lower energy is related to a resonant state, which suggests that it may be due to so called "ghost anomaly". Distributions of decaying particles are also calculated.
Comments:
5 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1612.06653 [pdf]
PRC(2016)·4 citations
06
[Submitted on 20 Dec 2016]
On the Implications of Energy and Momentum Conservation for Particle Emission in A+A Collisions at SPS Energies
Antoni Szczurek🇵🇱 · Mirosław Kiełbowicz🇵🇱 · Andrzej Rybicki🇵🇱
We construct a simple model of heavy ion collisions, local in the impact parameter plane, and appropriate for the SPS energy range. This model can be regarded as a new realization of the "fire-streak" approach, originally applied to studies of lower energy nucleus-nucleus reactions. Starting from local energy and momentum conservation, we nicely describe the broadening of the pion rapidity distribution when going from central to peripheral Pb+Pb collisions at $s_{N N}$ =17.3 GeV. The results of our calculations are compared with SPS experimental data. We discuss the resulting implications on the role of energy and momentum conservation for the dynamics of particle production in heavy ion collisions. A specific space-time picture emerges, where the longitudinal evolution of the system strongly depends on the position in the impact parameter ( $b_{x}$ , $b_{y}$ ) plane. This picture is consistent with our earlier findings on the longitudinal evolution of the system as deduced from electromagnetic effects on charged pion directed flow, and can provide an explanation for specific low- $p_{T}$ phenomena seen in the fragmentation region of Pb+Pb collisions.
Comments:
Corrected version, accepted for publication in Phys. Rev. C (13 pages, 9 figures)
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1612.06694 [pdf]
PRC(2017)·16 citations
07
[Submitted on 20 Dec 2016]
Rapidity-dependent jet energy loss in small systems with finite-size effects and running coupling
Chanwook Park🇨🇦 · Chun Shen🇺🇸 · Sangyong Jeon🇨🇦 · Charles Gale🇨🇦
Longitudinal dynamics of particle production and rapidity-dependent jet energy loss are investigated in small and asymmetric colliding systems. We utilize an improved version of \textsc{martini} in which two improvements are implemented to calculate the effect of the strongly coupled QGP droplet on jet energy loss. We show that those realistic prescriptions improve the results of nuclear modification factor calculations. We also observe visible energy loss of jets in a thermal background of high-multiplicity p-Pb collisions, and a clear correlation between the energy loss and elliptic flow coefficients for energetic particles. We conclude that systematic measurements of jet quenching in central collisions of small systems can support the formation of the QGP droplet.
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1612.06754 [pdf]
Nucl.Part.Phys.Proc.(2017)·23 citations
08
[Submitted on 20 Dec 2016]
Extracting $q^$ from single inclusive data at RHIC and at the LHC for different centralities: a new puzzle?
Carlota Andres🇪🇸 · Nestor Amesto🇪🇸 · Matthew Luzum🇪🇸 · Carlos A. Salgado🇪🇸 · Pia Zurita🇪🇸
We present here an extraction of the jet transport coefficient, $q^$ , using RHIC and LHC single-inclusive high- $p_{T}$ data for different centralities. We fit a $K$ -factor that determines the deviation of this coefficient from an ideal estimate, $K \equiv q^/ (2 ϵ^{3/4})$ , where $ϵ$ is given by hydrodynamic simulations. As obtained already in previous studies, this $K$ -factor is found to be larger at RHIC than at the LHC. However it is, unexpectedly, basically no-dependent on the centrality of the collision. Taken at face value this result, the $K$ -factor would not depend on local properties of the QGP as temperature, but on global collision variables such as the center of mass energy.
Comments:
4 pages, 4 figures, proceedings for the 8th International Conference on Hard and Electromagnetic Probes of High-energy Nuclear Collisions (Hard Probes 2016)
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1612.06781 [pdf]
Nucl.Part.Phys.Proc.(2017)·5 citations
09
[Submitted on 20 Dec 2016]
Search for $α$ -cluster states in even-even Cr isotopes
M. A. Souza🇧🇷 · H. Miyake🇧🇷
The $α + core$ structure is investigated in even-even Cr isotopes from the viewpoint of the local potential model. The comparison of $Q_{α} / A$ values for even-even Cr isotopes and even-even $A = 46, 54, 56, 58$ isobars indicates that $^{46}$ Cr and $^{54}$ Cr are the most favorable even-even Cr isotopes for $α$ -clustering. The ground state bands of the two Cr isotopes are calculated through a local $α + core$ potential with two variable parameters. The calculated spectra give a very good description of most experimental $^{46}$ Cr and $^{54}$ Cr levels. The reduced $α$ -widths, rms intercluster separations and $B (E 2)$ transition rates are determined for the ground state bands. The calculations reproduce the order of magnitude of the available experimental $B (E 2)$ values without using effective charges and indicate that the first members of the ground state bands present a stronger $α$ -cluster character. The volume integral per nucleon pair and rms radius obtained for the $α +^{50}$ Ti potential are consistent with those reported previously in the analysis of $α$ elastic scattering on $^{50}$ Ti.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1612.06805 [pdf]
EPJA(2017)·13 citations
10
[Submitted on 20 Dec 2016]
Neutron Moderation Theory Taking into Accout the Thermal Motion of Moderating Medium Nuclei
V.D. Rusov · V.A. Tarasov · S.A. Chernezhenko · A.A. Kakaev · V.P. Smolyar
In this paper we present the analytical expression for the neutron scattering law for an isotropic source of neutrons, obtained within the framework of the gas model with the temperature of the moderating medium as a parameter. The obtained scattering law is based on the solution of the kinematic problem of elastic scattering of neutrons on nuclei in the L-system in the general case. I.e. both the neutron and the nucleus possess the arbitrary velocity vectors in the L-system. For the new scattering law the flux densities and neutron moderation spectra depending on the temperature are obtained for the reactor fissile medium. The expressions for the moderating neutrons spectra allow reinterpreting the physical nature of the underlying processes in the thermal region.
Comments:
26 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1612.06838 [pdf]
EPJA(2017)·5 citations

Affiliations

first authorsco-authorsvia INSPIRE