Nuclear Theory·nucl-th

Friday·March 20, 2015

10 papers—3 primary·7 cross-listed

01
[Submitted on 18 Mar 2015]
Interferometric signatures of the temperature dependence of the specific shear viscosity in heavy-ion collisions
Christopher Plumberg🇺🇸 · Ulrich Heinz🇺🇸
Recent work has shown that a temperature dependence of the shear viscosity to entropy ratio, $η / s$ , influences the collective flow pattern in heavy-ion collisions in characteristic ways that can be measured by studying hadron transverse momentum spectra and their anisotropies. Here we point out that it also affects the pair momentum dependence of the Hanbury-Brown $-$ Twiss (HBT) radii (the source size parameters extracted from two-particle intensity interferometry) and the variance of their event-by-event fluctuations. This observation establishes interferometric signatures as useful observables to complement the constraining power of single-particle spectra on the temperature dependence of $η / s$ .
Comments:
v2 - minor correction to Figure 6 and appropriate changes to relevant text v3 - improved calculations including p+p multiplicity fluctuations, implemented changes recommended by referee
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1503.05605 [pdf]
PRC(2015)·14 citations
02
[Submitted on 19 Mar 2015]
Event simulations in a transport model for intermediate energy heavy ion collisions: Applications to multiplicity distributions
S. Mallik · S. Das Gupta · G. Chaudhuri
We perform transport model calculations for central collisions of mass 120 on mass 120 at laboratory beam energy in the range 20 MeV/nucleon to 200 MeV/nucleon. A simplified yet accurate method allows calculation of fluctuations in systems much larger than what was considered feasible in a well-known and already existing model. The calculations produce clusters. The distribution of clusters is remarkably similar to that obtained in equilibrium statistical model.
Comments:
6 pages, 5 figures, Accepted in Physical Review C
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1503.05840 [pdf]
PRC(2015)·32 citations
03
[Submitted on 19 Mar 2015]
Uncertainty Quantification and Propagation in Nuclear Density Functional Theory
N. Schunck · J.D. McDonnell · D. Higdon · J. Sarich · S.M. Wild
Nuclear density functional theory (DFT) is one of the main theoretical tools used to study the properties of heavy and superheavy elements, or to describe the structure of nuclei far from stability. While on-going efforts seek to better root nuclear DFT in the theory of nuclear forces [see Duguet et al., this issue], energy functionals remain semi-phenomenological constructions that depend on a set of parameters adjusted to experimental data in finite nuclei. In this paper, we review recent efforts to quantify the related uncertainties, and propagate them to model predictions. In particular, we cover the topics of parameter estimation for inverse problems, statistical analysis of model uncertainties and Bayesian inference methods. Illustrative examples are taken from the literature.
Comments:
Proceedings of the "Second International Workshop on Perspectives on Nuclear Data for the Next Decade", 14-17 October 2014, Bruyères-le-Châtel, France
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1503.05894 [pdf]
EPJA(2015)·29 citations
04
[Submitted on 18 Mar 2015] (cross-list from astro-ph.HE)
Supporting the existence of the QCD critical point by compact star observations
David E. Alvarez-Castillo🇷🇺 · David Blaschke🇷🇺
In order to prove the existence of a critical end point (CEP) in the QCD phase diagram it is sufficient to demonstrate that at zero temperature $T = 0$ a first order phase transition exists as a function of the baryochemical potential $μ$ , since it is established knowledge from ab-initio lattice QCD simulations that at $μ = 0$ the transition on the temperature axis is a crossover. We present the argument that the observation of a gap in the mass-radius relationship for compact stars which proves the existence of a so-called third family (aka "mass twins") will imply that the $T = 0$ equation of state of compact star matter exhibits a strong first order transition with a latent heat that satisfies $Δ ϵ / ϵ_{c} > 0.6$ . Since such a strong first order transition under compact star conditions will remain first order when going to symmetric matter, the observation of a disconnected branch (third family) of compact stars in the mass-radius diagram proves the existence of a CEP in QCD. For the equation of state of the twins the quark matter description is based on a QCD-motivated chiral approach with higher-order quark interactions in the Dirac scalar and vector coupling channels. For hadronic matter we select a relativistic mean-field equation of state with density-dependent couplings. Since the nucleons are treated in the quasi-particle framework, an excluded volume has been included for the nuclear equation of state at super-saturation density that takes into account the finite size of the nucleons. Furthermore we show results of a Bayesian analysis (BA) using disjunct M-R constraints for extracting probability measures for cold, dense matter equations of state. This study reveals that measuring the radii of neutron star twins has the potential to support the existence of a first order phase transition for compact star matter.
Comments:
6 pages, prepared for the Proceedings of the Conference "9th International Workshop on Critical Point and Onset of Deconfinement - CPOD2014", 17-21 November 2014, ZiF (Center of Interdisciplinary Research), University of Bielefeld, Germany
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1503.05576 [pdf]
PoS(2015)·6 citations
05
[Submitted on 19 Mar 2015] (cross-list from nucl-ex)
New measurement of the excited states in $^{11}$ B via the elastic resonance scattering of $^{10}$ Be + p
Y. D. Liu · H. W. Wang · Y. G. Ma · X. G. Cao · G. Q. Zhang · D. Q. Fang · M. Lyu · W. B. He · Z. T. Dai · C. Li · C. L. Zhou · S. Q. Ye and 12 other authors
The elastic resonance scattering protons decayed from $^{11}$ B to the ground state of $^{10}$ Be were measured using the thick-target technique in inverse kinematics at the Heavy Ion Research Facility in Lanzhou (HIRFL). The obtained excitation functions were well described by a multichannel R-matrix procedure under the kinematics process assumption of resonant elastic scattering. The excitation energy of the resonant states ranges from 13.0 to 17.0 MeV, and their resonant parameters such as the resonant energy E $_{x}$ , the spin-parity J $^{π}$ , and the proton-decay partial width $Γ_{p}$ were determined from R-matrix fits to the data. Two of these states around E $_{x}$ = 14.55 MeV [J $^{π}$ = (3/2 $^{+}$ , 5/2 $^{+}$ ), $Γ_{p}$ = 475 $\pm$ 80 keV] and E $_{x}$ = 14.74 MeV [J $^{π}$ = 3/2 $^{-}$ , $Γ_{p}$ = 830 $\pm$ 145 keV], and a probably populated state at E $_{x}$ = 16.18 MeV [J $^{π}$ =(1/2 $^{-}$ , 3/2 $^{-}$ ), $Γ_{p}$ $<$ 60 keV], are respectively assigned to the well-known states in $^{11}$ B at 14.34 MeV, 15.29 MeV, and 16.43 MeV. The isospin of these three states were previously determined to be T = 3/2, but discrepancies exist in widths and energies due to the current counting statistics and energy resolution. We have compared these states with previous measurements, and the observation of the possibly populated resonance is discussed.
Comments:
7 pages, 2 tables, 7 figures; Physical Review C (2015) accepted
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1503.05630 [pdf]
PRC(2015)·2 citations
06
[Submitted on 19 Mar 2015] (cross-list from nucl-ex)
Different mechanism of two-proton emission from proton-rich nuclei $^{23}$ Al and $^{22}$ Mg
Y.G. Ma🇨🇳 · D.Q. Fang🇨🇳 · X.Y. Sun🇨🇳 · P. Zhou🇨🇳 · Y. Togano🇯🇵 · N. Aoi🇯🇵 · H. Baba🇯🇵 · X.Z. Cai🇨🇳 · X.G. Cao🇨🇳 · J.G. Chen🇨🇳 · Y. Fu🇨🇳 · W. Guo🇨🇳 and 34 other authors
Two-proton relative momentum ( $q_{pp}$ ) and opening angle ( $θ_{pp}$ ) distributions from the three-body decay of two excited proton-rich nuclei, namely $^{23}$ Al $\to$ p + p + $^{21}$ Na and $^{22}$ Mg $\to$ p + p + $^{20}$ Ne, have been measured with the projectile fragment separator (RIPS) at the RIKEN RI Beam Factory. An evident peak at $q_{pp} \sim 20$ MeV/c as well as a peak in $θ_{pp}$ around 30 $^{\circ}$ are seen in the two-proton break-up channel from a highly-excited $^{22}$ Mg. In contrast, such peaks are absent for the $^{23}$ Al case. It is concluded that the two-proton emission mechanism of excited $^{22}$ Mg is quite different from the $^{23}$ Al case, with the former having a favorable diproton emission component at a highly excited state and the latter dominated by the sequential decay process.
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1503.05631 [pdf]
PLB(2015)·41 citations
07
[Submitted on 19 Mar 2015] (cross-list from astro-ph.HE)
Quantum Field Theoretic Treatment of Pion Production via Proton Synchrotron Radiation in Strong Magnetic Fields: Effects of Landau Levels
Tomoyuki Maruyama🇯🇵 · Myung-Ki Cheoun🇰🇷 · Toshitaka Kajino🇯🇵 · Yongshin Kwon🇰🇷 · Grant J. Mathews🇺🇸 · Chung-Yeol Ryu🇰🇷
We study pion production from proton synchrotron radiation in the presence of strong magnetic fields. We derive the exact proton propagator from the Dirac equation in a strong magnetic field by explicitly including the anomalous magnetic moment. In this exact quantum-field approach the magnitude of pion synchrotron emission turns out to be much smaller than that obtained in the semi-classical approach. However, we also find that the anomalous magnetic moment of the proton greatly enhances the production rate about by two order magnitude.
Comments:
18 pages, 8 figures
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1503.05635 [pdf]
PRD(2015)·17 citations
08
[Submitted on 19 Mar 2015] (cross-list from hep-ph)
Light Quarkonium - Glueball Mixing from a Holographic QCD
Takashi Yamaguchi🇯🇵 · Shinya Matsuzaki🇯🇵
We study the mixing structure of isospin-singlet scalars, the light quarkonium $(q ˉ q)$ and glueball $(g g)$ in two-flavor QCD, based on a holographic model of bottom-up hard-wall type. In the model the pure quarkonium and glueball states are unambiguously defined in terms of the different $U (1)_{A}$ charges in the restoration limit of the chiral $U (2)_{L} \times U (2)_{R}$ symmetry, in which the quarkonium gets massless as the chiral partner of the pion. Hence the $q ˉ q$ - $g g$ mixing arises in the presence of the nonzero chiral condensate or pion decay constant. At the realistic point where the pion decay constant and other hadron masses reach the observed amount, we predict the tiny mixing between the lightest quarkonia and glueball: The smallness of the mixing is understood by the slightly small ratio of the chiral and gluon condensate scales. The low-lying two scalar masses are calculated to be $≃ 1.25$ GeV and $≃ 1.77$ GeV, which are compared with masses of $f_{0} (1370)$ and $f_{0} (1710)$ . Our result implies that $f_{0} (1710)$ predominantly consists of glueball.
Comments:
8 pages, 2 eps figures, latex; typos fixed and references added, to appear in PRD
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1503.05727 [pdf]
PRD(2015)·1 citation
09
[Submitted on 19 Mar 2015] (cross-list from nucl-ex)
Evidence for $Δ (2200) 7/ 2^{-}$ from photoproduction and consequence for chiral-symmetry restoration at high mass
A.V. Anisovich🇩🇪 · V. Burkert🇺🇸 · J. Hartmann🇩🇪 · E. Klempt🇩🇪 · V.A. Nikonov🇩🇪 · E. Pasyuk🇺🇸 · A.V. Sarantsev🇩🇪 · S. Strauch🇺🇸 · U. Thoma🇩🇪
We report a partial-wave analysis of new data on the double-polarization variable $E$ for the reactions $γ p \to π^{+} n$ and $γ p \to π^{0} p$ and of further data published earlier. The analysis within the Bonn-Gatchina (BnGa) formalism reveals evidence for a poorly known baryon resonance, the one-star $Δ (2200) 7/ 2^{-}$ . This is the lowest-mass $Δ^{*}$ resonance with spin-parity $J^{P} = 7/ 2^{-}$ . Its mass is significantly higher than the mass of its parity partner $Δ (1950) 7/ 2^{+}$ which is the lowest-mass $Δ^{*}$ resonance with spin-parity $J^{P} = 7/ 2^{+}$ . It has been suggested that chiral symmetry might be restored in the high-mass region of hadron excitations, and that these two resonances should be degenerate in mass. Our findings are in conflict with this prediction.
Comments:
5 pages, 3 figures; Physics Letters B in press
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1503.05774 [pdf]
PLB(2017)·32 citations
10
[Submitted on 19 Mar 2015] (cross-list from nucl-ex)
Broad resonances and beta-decay
K. Riisager · H.O.U. Fynbo · S. Hyldegaard · A.S. Jensen
Beta-decay into broad resonances gives a distorted lineshape in the observed energy spectrum. Part of the distortion arises from the phase space factor, but we show that the beta-decay matrix element may also contribute. Based on a schematic model for p-wave continuum neutron states it is argued that beta-decay directly to the continuum should be considered as a possible contributing mechanism in many decays close to the driplines. The signatures in R-matrix fits for such decays directly to continuum states are discussed and illustrated through an analysis of the beta-decay of $^{8}$ B into $2^{+}$ states in $^{8}$ Be.
Comments:
27 pages, 5 figures
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1503.05792 [pdf]
NPA(2015)·7 citations

Affiliations

first authorsco-authorsvia INSPIRE