Nuclear Theory·nucl-th

Thursday·March 3, 2016

12 papers—4 primary·8 cross-listed

01
[Submitted on 2 Mar 2016]
Investigating the alpha-clustering on the surface of $^{120}$ Sn via ( $p$ , $p α$ ) reaction and the validity of the factorization approximation
Kazuki Yoshida · Kosho Minomo · Kazuyuki Ogata
The $^{120}$ Sn( $p$ , $p α$ ) $^{116}$ Cd reaction at 392 MeV is investigated with the distorted wave impulse approximation (DWIA) framework. We show that this reaction is very peripheral mainly because of the strong absorption of $α$ by the reaction residue $^{116}$ Cd, and the $α$ -clustering on the nuclear surface can be probed clearly. We investigate also the validity of the so-called factorization approximation that has frequently been used so far. It is shown that the kinematics of $α$ in the nuclear interior region is significantly affected by the distortion of $^{116}$ Cd, but it has no effect on the reaction observables because of the strong absorption in that region.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1603.00638 [pdf]
PRC(2016)·43 citations
02
[Submitted on 2 Mar 2016]
Structure of the number projected BCS wave function
J. Dukelsky · S. Pittel · C. Esebbag
We study the structure of the number projected BCS (PBCS) wave function in the particle-hole basis, displaying its similarities with coupled clusters theory (CCT). The analysis of PBCS together with several modifications suggested by the CCT wave function is carried out for the exactly solvable Richardson model involving a pure pairing hamiltonian acting in a space of equally-spaced doubly-degenerate levels. We point out the limitations of PBCS to describe the non-superconducting regime and suggest possible avenues for improvement.
Comments:
6 pages, 4 figures. To be published in Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th); Superconductivity (cond-mat.supr-con)
arXiv:
1603.00642 [pdf]
PRC(2016)·12 citations
03
[Submitted on 2 Mar 2016]
Constraining the density dependence of the symmetry energy using the multiplicity and average $p_{T}$ ratios of charged pions
M.D. Cozma🇷🇴
The charged pion multiplicity ratio in intermediate energy heavy-ion collisions, a probe of the density dependence of symmetry energy above the saturation point, has been proven in a previous study to be extremely sensitive to the strength of the isovector $Δ$ (1232) potential in nuclear matter. As there is no knowledge, either from theory or experiment, about the magnitude of this quantity, the extraction of constraints on the slope of the symmetry energy at saturation by using exclusively the mentioned observable is hindered at present. It is shown that, by including the ratio of average $p_{T}$ of charged pions $⟨ p_{T}^{(π^{+})} ⟩ / ⟨ p_{T}^{(π^{-})} ⟩$ in the list of fitted observables, the noted problem can be circumvented. A realistic description of this observable requires accounting for the interaction of pions with the dense nuclear matter environment by the incorporation of the so called $S$ -wave and $P$ -wave pion optical potentials. This is performed within the framework of a quantum molecular dynamics transport model that enforces the conservation of the total energy of the system. It is shown that constraints on the slope of the symmetry energy at saturation density and the strength of the $Δ$ (1232) potential can be simultaneously extracted. A symmetry energy with a value of the slope parameter $L >$ 50 MeV is favored, at 1 $σ$ confidence level, from a comparison with published FOPI experimental data. A precise constraint will require experimental data more accurate than presently available, particularly for the charged pion multiplicity ratio, and better knowledge of the density and momentum dependence of the pion potential for the whole range of these two variables probed in intermediate energy heavy-ion collisions.
Comments:
22 pages, 17 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1603.00664 [pdf]
PRC(2017)·52 citations
04
[Submitted on 2 Mar 2016]
Tagged spectator deep-inelastic scattering off the deuteron as a tool to study neutron structure
W. Cosyn🇧🇪 · M. Sargsian🇺🇸
We give an overview of a model to describe deep-inelastic scattering (DIS) off the deuteron with a spectator proton, based on the virtual nucleon approximation (VNA). The model accounts for the final-state interactions (FSI) of the DIS debris with the spectator proton. Values of the rescattering cross section are obtained by fits to high-momentum spectator data. By using the so-called "pole extrapolation method", free neutron structure functions can be obtained by extrapolating low-momentum spectator proton data to the on-shell neutron pole. We apply this method to the BONuS data set and find a surprising Bjorken $x$ dependence, indicating a possible rise of the neutron to proton structure function ratio at high $x$ .
Comments:
6 pages, 4 figures, proceedings of POETIC6
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1603.00685 [pdf]
EPJ Web Conf.(2016)·1 citation
05
[Submitted on 1 Mar 2016] (cross-list from astro-ph.HE)
The unreasonable weakness of r-process cosmic rays in the neutron-star-merger nucleosynthesis scenario
Koutarou Kyutoku · Kunihito Ioka
We reach the robust conclusion that, by combining the observed cosmic rays of r-process elements with the fact that the velocity of the neutron-star-merger ejecta is much higher than that of the supernova ejecta, either (1) the reverse shock in the neutron-star-merger ejecta is a very inefficient accelerator that converts less than 0.003% of the ejecta kinetic energy to the cosmic-ray energy or (2) the neutron star merger is not the origin of the Galactic r-process elements. We also find that the acceleration efficiency should be less than 0.1% for the reverse shock of the supernova ejecta with the observed cosmic rays lighter than the iron.
Comments:
5 pages, 1 figure
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1603.00467 [pdf]
ApJ(2016)·15 citations
06
[Submitted on 1 Mar 2016] (cross-list from hep-lat)
The interplay of the sign problem and the infinite volume limit: gauge theories with a theta term
Yiming Cai🇺🇸 · Thomas Cohen🇺🇸 · Ari Goldbloom-Helzner🇺🇸 · Brian McPeak🇺🇸
QCD and related gauge theories have a sign problem when a $θ$ -term is included; this complicates the extraction of physical information from Euclidean space calculations as one would do in lattice studies. The sign problem arises in this system because the partition function for configurations with fixed topological charge $Q$ , $Z_{Q}$ , are summed weighted by $exp (i Qθ)$ to obtain the partition function for fixed $θ$ , $Z (θ)$ . The sign problem gets exponentially worse numerically as the space-time volume is increased. Here it is shown that apart from the practical numerical issues associated with large volumes, there are some interesting issues of principle. A key quantity is the energy density as a function of $θ$ , $ε (θ) = - lo g (Z (θ)) / V$ . This is expected to be well defined in the large 4-volume limit. Similarly, one expects the energy density for a fixed topological density $ε ~ (Q / V) = - lo g (Z_{Q}) / V$ to be well defined in the limit of large 4-volumes. Intuitively, one might expect that if one had the infinite volume expression for $ε ~ (Q / V)$ to arbitrary accuracy, that one could reconstruct $ε (θ)$ by directly summing over the topological sectors of the partition function. We show here that there are circumstances where this is not the case. In particular, this occurs in regions where the curvature of $ε (θ)$ is negative.
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1603.00478 [pdf]
PRD(2016)·3 citations
07
[Submitted on 2 Mar 2016] (cross-list from nucl-ex)
Open Heavy Flavor in QCD Matter and in Nuclear Collisions
Francesco Prino🇮🇹 · Ralf Rapp🇺🇸
We review the experimental and theoretical status of open heavy-flavor (HF) production in high-energy nuclear collisions at RHIC and LHC. We first overview the theoretical concepts and pertinent calculations of HF transport in QCD matter, including perturbative and non-perturbative approaches in the quark-gluon plasma, effective models in hadronic matter, as well as implementations of heavy-quark (HQ) hadronization. This is followed by a brief discussion of bulk evolution models for heavy-ion collisions and initial conditions for the HQ distributions which are needed to calculate HF spectra in comparison to observables. We then turn to a discussion of experimental data that have been collected to date at RHIC and LHC, specifically for the nuclear suppression factor and elliptic flow of semileptonic HF decays, D mesons, non-prompt $J / ψ$ from B-meson decays, and b-jets. Model comparisons to HF data are conducted with regards to extracting the magnitude, temperature and momentum-dependence of HF transport coefficients from experiment.
Comments:
89 pages, 30 figures, review article
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1603.00529 [pdf]
J.Phys.G(2016)·221 citations
08
[Submitted on 2 Mar 2016] (cross-list from hep-ph)
Chern-Simons diffusion rate across different phase transitions
Romulo Rougemont🇧🇷 · Stefano Ivo Finazzo🇧🇷
We investigate how the dimensionless ratio given by the Chern-Simons diffusion rate $Γ_{CS}$ divided by the product of the entropy density $s$ and temperature $T$ behaves across different kinds of phase transitions in the class of bottom-up non-conformal Einstein-dilaton holographic models originally proposed by Gubser and Nellore. By tuning the dilaton potential, one is able to holographically mimic a first order, a second order, or a crossover transition. In a first order phase transition, $Γ_{CS} / s T$ jumps at the critical temperature (as previously found in the holographic literature), while in a second order phase transition it develops an infinite slope. On the other hand, in a crossover, $Γ_{CS} / s T$ behaves smoothly, although displaying a fast variation around the pseudo-critical temperature. In all the cases, $Γ_{CS} / s T$ increases with decreasing $T$ . The behavior of the Chern-Simons diffusion rate across different phase transitions is expected to play a relevant role for the chiral magnetic effect around the QCD critical end point, which is a second order phase transition point connecting a crossover band to a line of first order phase transition. Our findings in the present work add to the literature the first predictions for the Chern-Simons diffusion rate across second order and crossover transitions in strongly coupled non-conformal, non-Abelian gauge theories.
Comments:
11 pages, 6 figures, version accepted for publication in Physical Review D
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1603.00553 [pdf]
PRD(2016)·4 citations
09
[Submitted on 2 Mar 2016] (cross-list from hep-ph)
Strong decay mode $J / ψ p$ of hidden charm pentaquark states $P_{c}^{+} (4380)$ and $P_{c}^{+} (4450)$ in $Σ_{c} D ˉ^{*}$ molecular scenario
Qi-Fang Lü🇨🇳 · Yu-Bing Dong🇨🇳
We study the strong decay channels $P_{c}^{+} (4380) \to J / ψ p$ and $P_{c}^{+} (4450) \to J / ψ p$ under $Σ_{c} D ˉ^{*}$ molecular state ansatz. With various spin-parity assignments, the partial decay widths of $J / ψ p$ final state are calculated. Our results show that all the $P$ wave $Σ_{c} D ˉ^{*}$ assignments are excluded, while $S$ wave $Σ_{c} D ˉ^{*}$ pictures for $P_{c} (4380)$ and $P_{c} (4450)$ are both allowed by present experimental data. The $J^{P} = 3/ 2^{-}$ $Σ_{c}^{*} D ˉ$ and $Σ_{c}^{*} D ˉ^{*}$ molecules are also discussed in the heavy quark limit, and find that the $Σ_{c}^{*} D ˉ$ system for $P_{c} (4380)$ is possible. More experimental information on spin-parities and partial decay widths and theoretical investigations on other decay modes are needed to clarify the nature of the two $P_{c}$ states.
Comments:
7 pages, 6 figures, 2 tables. More discussions are added. Version accepted by Phys. Rev. D
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1603.00559 [pdf]
PRD(2016)·82 citations
10
[Submitted on 2 Mar 2016] (cross-list from hep-ph)
Cool quark matter
Aleksi Kurkela🇨🇭 · Aleksi Vuorinen🇫🇮
We generalize the state-of-the-art perturbative Equation of State of cold quark matter to nonzero temperatures, needed in the description of neutron star mergers and core collapse processes. The new result is accurate to order g^5 in the gauge coupling, and is based on a novel framework for dealing with the infrared sensitive soft field modes of the theory. The zero Matsubara mode sector is treated using a dimensionally reduced effective theory, while the soft non-zero modes are resummed using the Hard Thermal Loop approximation. This combination of known effective descriptions offers unprecedented access to small but nonzero temperatures, both in and out of beta equilibrium.
Comments:
8 pages, 3 figures; v2: minor improvements, version published in PRL (without appendices)
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1603.00750 [pdf]
PRL(2016)·126 citations
11
[Submitted on 2 Mar 2016] (cross-list from hep-ph)
Thermo-magnetic properties of the strong coupling in the local Nambu--Jona-Lasinio model
Alejandro Ayala🇲🇽 · C. A. Dominguez🇿🇦 · L. A. Hernandez🇿🇦 · M. Loewe🇿🇦 · Alfredo Raya🇲🇽 · J. C. Rojas🇨🇱 · C. Villavicencio🇨🇱
We study the thermo-magnetic properties of the strong coupling constant G and quark mass M entering the Nambu-Jona-Lasinio model. For this purpose, we compute the quark condensate and compare it to lattice QCD (LQCD) results to extract the behavior of G and M as functions of the magnetic field strength and temperature. We find that at zero temperature, where the LQCD condensate is found to monotonically increase with the field strength, M also increases whereas G remains approximately constant. However, for temperatures above the chiral/deconfinement phase transitions, where the LQCD condensate is found to monotonically decrease with increasing field, M and G also decrease monotonically. For finite temperatures, below the transition temperature, we find that both G and M initially grow and then decrease with increasing field strength. To study possible consequences of the extracted temperature and magnetic field dependence of G and M, we compute the pressure and compare to LQCD results, finding an excellent qualitative agreement. In particular, we show that the transverse pressure, as a function of the field strength, is always negative for temperatures below the transition temperature whereas it starts off being positive and then becomes negative for temperatures above the transition temperature, also in agreement with LQCD results. We also show that for the longitudinal pressure to agree with LQCD calculations, the system should be described as a diamagnet. We argue that the turnover of M and G as functions of temperature and field strength is a key element that drives the behavior of the quark condensate going across the transition temperature and provides clues for a better understanding of the inverse magnetic catalysis phenomenon.
Comments:
9 pages, 11 figures. Improved analysis separating the vacuum, magnetic and thermo-magnetic contributions and re-scaling of the model's critical temperature. Added analysis on the behavior of the longitudinal and transverse pressures and its relation to the diamagnetic properties both below and above the critical temperature. Version to appear in Phys. Rev. D
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1603.00833 [pdf]
PRD(2016)·53 citations
12
[Submitted on 2 Mar 2016] (cross-list from hep-ph)
Amplitude analysis of $K ˉ N$ scattering
Cesar Fernandez-Ramirez🇲🇽
We present the results of a coupled-channel model for $K ˉ N$ scattering in the resonance region. The model fulfills unitarity, has the correct analytical properties for the amplitudes and the partial waves have the right threshold behavior. The parameters of the model have been established by fitting single-energy partial waves up to $J = 7/2$ and up to 2.15 GeV of center-of-mass energy. The $Λ^{*}$ and $Σ^{*}$ spectra has been obtained, providing a comprehensive picture of the $S = - 1$ hyperon spectrum. We use the structure of the hyperon spectrum and Regge phenomenology to gain insight on the nature of the $Λ (1405)$ resonances.
Comments:
Proceedings of the 39th Symposium on Nuclear Physics 2016 Cocoyoc, Mexico
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1603.00868 [pdf]
J.Phys.Conf.Ser.(2016)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE