Nuclear Theory·nucl-th

Thursday·February 23, 2017

9 papers—6 primary·3 cross-listed

01
[Submitted on 22 Feb 2017]
Structure and decay at rapid proton capture waiting points
D. Hove · E. Garrido · A. S. Jensen · H. O. U. Fynbo · D. V. Fedorov · N. T. Zinner
We investigate the region of the nuclear chart around $A ≃ 70$ from a three-body perspective, where we compute reaction rates for the radiative capture of two protons. One key quantity is here the photon dissociation cross section for the inverse process where two protons are liberated from the borromean nucleus by photon bombardment. We find a number of peaks at low photon energy in this cross section where each peak is located at the energy corresponding to population of a three-body resonance. Thus, for these energies the decay or capture processes proceed through these resonances. However, the next step in the dissociation process still has the option of following several paths, that is either sequential decay by emission of one proton at a time with an intermediate two-body resonance as stepping stone, or direct decay into the continuum of both protons simultaneously. The astrophysical reaction rate is obtained by folding of the cross section as function of energy with the occupation probability for a Maxwell-Boltzmann temperature distribution. The reaction rate is then a function of temperature, and of course depending on the underlying three-body bound state and resonance structures. We show that a very simple formula at low temperature reproduces the elaborate numerically computed reaction rate.
Comments:
4 pages, 3 figures, conference proceedings, published
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1702.06719 [pdf]
Few Body Syst.(2017)·2 citations
02
[Submitted on 22 Feb 2017]
Combining few-body cluster structures with many-body mean-field methods
D. Hove · E. Garrido · A. S. Jensen · P. Sarriguren · H. O. U. Fynbo · D. V. Fedorov · N. T. Zinner
Nuclear cluster physics implicitly assumes a distinction between groups of degrees-of-freedom, that is the (frozen) intrinsic and (explicitly treated) relative cluster motion. We formulate a realistic and practical method to describe the coupled motion of these two sets of degrees-of-freedom. We derive a coupled set of differential equations for the system using the phenomenologically adjusted effective in-medium Skyrme type of nucleon-nucleon interaction. We select a two-nucleon plus core system where the mean-field approximation corresponding to the Skyrme interaction is used for the core. A hyperspherical adiabatic expansion of the Faddeev equations is used for the relative cluster motion. We shall specifically compare both the structure and the decay mechanism found from the traditional three-body calculations with the result using the new boundary condition provided by the full microscopic structure at small distance. The extended Hilbert space guaranties an improved wave function compared to both mean-field and three-body solutions. We shall investigate the structures and decay mechanism of $^{22}$ C ( $^{20}$ C+n+n). In conclusion, we have developed a method combining nuclear few- and many-body techniques without losing the descriptive power of each approximation at medium-to-large distances and small distances respectively. The coupled set of equations are solved self-consistently, and both structure and dynamic evolution are studied.
Comments:
4 pages, 3 figures, conference proceedings, published
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1702.06720 [pdf]
Few Body Syst.(2017)·3 citations
03
[Submitted on 22 Feb 2017]
Analytic matrix elements with shifted correlated Gaussians
D.V. Fedorov
Matrix elements between shifted correlated Gaussians of various potentials with several form-factors are calculated analytically. Analytic matrix elements are of importance for the correlated Gaussian method in quantum few-body physics.
Subjects:
Nuclear Theory (nucl-th); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
arXiv:
1702.06784 [pdf]
Few Body Syst.(2017)·11 citations
04
[Submitted on 22 Feb 2017]
Analysis of recent CLAS data on $f_{1} (1285)$ photoproduction
Xiao-Yun Wang🇨🇳 · Jun He🇨🇳
Based on the experimental data released recently by the CLAS Collaboration, the $f_{1} (1285)$ photoproduction off a proton target is investigated in an effective Lagrangian approach. In our model, $s$ -channel, $u$ -channel, and $t$ -channel Born terms are included to calculate the differential cross sections, which are compared with the recent CLAS experiment. An interpolating Reggeized treatment is applied to the $t$ channel, and it is found that the $t$ -channel contribution is dominant in the $f_{1} (1285)$ photoproduction and the $u$ -channel contribution is responsible for the enhancement at backward angles. The present calculation does not take into account any explicit $s$ -channel nucleon-resonance contribution; nevertheless, our model provides a good description of the main features of the data. It suggests small couplings of the $f_{1} (1285)$ and the nucleon resonances in this energy region.
Comments:
5 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1702.06848 [pdf]
PRD(2017)·21 citations
05
[Submitted on 22 Feb 2017]
Photoproduction of $γ p \to K^{+} Λ^{*} (1520)$ and decay of $Λ^{*} (1520) \to K^{-} p$ in the Reggeized framework
Byung-Geel Yu🇰🇷 · Kook-Jin Kong🇰🇷
Photoproduction of the $Λ^{*} (1520)$ resonance of spin-parity $\frac{3}{2}^{-}$ off the proton target is investigated within the Regge framework where the $t$ -channel reggeization is applied for the $K (494) + K^{*} (892) + K_{2}^{*} (1430)$ exchanges in the Born amplitude. The present model is based on the two basic ingredients; the one is the minimal gauge prescription for the convergence of the reaction and the other is the role of the $K_{2}^{*}$ crucial to be consistent with high energy data. The cross sections for the total, differential and photon polarization asymmetry are reproduced without fit parameters and compared with existing data. The LAMP2 and LEPS measurements of the angular distribution of the $K^{-}$ in the $Λ^{*} (1520) \to K^{-} p$ decay are investigated and found to be dominated by the decay of $Λ^{*}$ with helicity $\pm 3/2$ based on the analysis of the density matrix elements related. Detailed discussion on the density matrix elements is given to clarify the analysis of the observable. The reaction mechanism is featured by the dominance of the contact term with the $K$ and $K_{2}^{*}$ exchanges following in the low energy region. The $K^{*}$ exchange appears in minor role. At high energies beyond $E_{γ} \approx 5$ GeV the role of $K_{2}^{*}$ exchange leads over other exchanges in the reaction process.
Comments:
10 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1702.06929 [pdf]
PRC(2017)·13 citations
06
[Submitted on 22 Feb 2017]
Particle distribution in intense fields in a light-front Hamiltonian approach
Guangyao Chen🇺🇸 · Xingbo Zhao🇨🇳 · Yang Li🇺🇸 · Kirill Tuchin🇺🇸 · James P. Vary🇺🇸
We study the real-time evolution of an electron influenced by intense electromagnetic fields using the time-dependent basis light-front quantization (tBLFQ) framework. We focus on demonstrating the non-perturbative feature of the tBLFQ approach through a realistic application of the strong coupling QED problem, in which the electromagnetic fields are generated by an ultra-relativistic nucleus. We calculate transitions of an electron influenced by such electromagnetic fields and we show agreement with light-front perturbation theory when the atomic number of the nucleus is small. We compare tBLFQ simulations with perturbative calculations for nuclei with different atomic numbers, and obtain the significant higher-order contributions for heavy nuclei. The simulated real-time evolution of the momentum distribution of an electron evolving inside the strong electromagnetic fields exhibits significant non-perturbative corrections comparing to light-front perturbation theory calculations. The formalism used in this investigation can be extended to QCD problems in heavy ion collisions and electron ion collisions.
Comments:
13 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th)
arXiv:
1702.06932 [pdf]
PRD(2017)·18 citations
07
[Submitted on 21 Feb 2017] (cross-list from hep-ph)
Twist-2 matching of transverse momentum dependent distributions
Daniel Gutierrez-Reyes🇪🇸 · Ignazio Scimemi🇪🇸 · Alexey A. Vladimirov🇩🇪
We systematically study the large- $q_{T}$ (or small- $b$ ) matching of transverse momentum dependent (TMD) distributions to the twist-2 integrated parton distributions. Performing operator product expansion for a generic TMD operator at the next-to-leading order (NLO) we found the complete set of TMD distributions that match twist-2. These are unpolarized, helicity, transversity, pretzelosity and linearly polarized gluon distributions. The NLO matching coefficients for these distributions are presented. The pretzelosity matching coefficient is zero at the presented order, however, it is evident that it is non-zero in the following orders. This result offers a natural explanation of the small value of pretzelosity found in phenomenological fits. We also demonstrate that the cancellation of rapidity divergences by the leading order soft factor imposes the necessary requirement on the Lorentz structure of TMD operators, which is supported only by the TMD distributions of leading dynamical twist. Additionally, this requirement puts restrictions on the $γ_{5}$ -definition in the dimensional regularization.
Comments:
7 pages; In v2 we correct a sign typo. Conclusions are unchanged
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1702.06558 [pdf]
PLB(2017)·51 citations
08
[Submitted on 22 Feb 2017] (cross-list from hep-ph)
Multiplicity Dependence of Non-extensive Parameters for Strange and Multi-Strange Particles in Proton-Proton Collisions at $s = 7$ TeV at the LHC
Arvind Khuntia🇮🇳 · Sushanta Tripathy🇮🇳 · Raghunath Sahoo🇮🇳 · Jean Cleymans🇿🇦
The transverse momentum ( $p_{T}$ ) spectra in proton-proton collisions at $s$ = 7 TeV, measured by the ALICE experiment at the LHC are analyzed with a thermodynamically consistent Tsallis distribution. The information about the freeze-out surface in terms of freeze-out volume, temperature and the non-extenisivity parameter, $q$ , for $K_{S}^{0}$ , $Λ + Λ ˉ$ , $Ξ^{-} + Ξ ˉ^{+}$ and $Ω^{-} + Ω ˉ^{+}$ are extracted by fitting the $p_{T}$ spectra with Tsallis distribution function. The freeze-out parameters of these particles are studied as a function of charged particle multiplicity density ( $d N_{c h} / d η$ ). In addition, we also study these parameters as a function of particle mass to see any possible mass ordering. The strange and multi-strange particles show mass ordering in volume, temperature, non-extensive parameter and also a strong dependence on multiplicity classes. It is observed that with increase in particle multiplicity, the non-extensivity parameter, $q$ decreases, which indicates the tendency of the produced system towards thermodynamic equilibration. The increase in strange particle multiplicity is observed to be due to the increase of temperature and not to the size of the freeze-out volume.
Comments:
Version similar to the published version in EPJA
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1702.06885 [pdf]
EPJA(2017)·52 citations
09
[Submitted on 22 Feb 2017] (cross-list from astro-ph.SR)
The Core-Collapse Supernova Explosion Mechanism
B. Müller (Queen's University Belfast, Monash University)🇬🇧
The explosion mechanism of core-collapse supernovae is a long-standing problem in stellar astrophysics. We briefly outline the main contenders for a solution and review recent efforts to model core-collapse supernova explosions by means of multi-dimensional simulations. We discuss several suggestions for solving the problem of missing or delayed neutrino-driven explosions in three-dimensional supernova models, including -- among others -- variations in the microphysics and large seed perturbations in convective burning shells. Focusing on the neutrino-driven mechanism, we summarise currents efforts to predict supernova explosion and remnant properties based on first-principle models and on more phenomenological approaches.
Comments:
Invited review to appear in the International Astronomical Union Proceedings Serie (IAU Symposium 329, "The Lives and Death Throes of Massive Stars"). 8 pages, 2 figures
Subjects:
Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1702.06940 [pdf]
IAU Symp.(2016)·14 citations

Affiliations

first authorsco-authorsvia INSPIRE