Nuclear Theory·nucl-th

Friday·March 9, 2018

8 papers—4 primary·4 cross-listed

01
[Submitted on 7 Mar 2018]
Responses of the chiral-magnetic-effect-sensitive sine observable to resonance backgrounds in heavy-ion collisions
Yicheng Feng🇺🇸 · Jie Zhao🇺🇸 · Fuqiang Wang🇺🇸
A new sine observable, $R_{Ψ_{2}} (Δ S)$ , has been proposed to measure the chiral magnetic effect (CME) in heavy-ion collisions; $Δ S = ⟨ sin φ_{+} ⟩ - ⟨ sin φ_{-} ⟩$ , where $φ_{\pm}$ are azimuthal angles of positively and negatively charged particles relative to the reaction plane and averages are event-wise, and $R_{Ψ_{2}} (Δ S)$ is a normalized event probability distribution. Preliminary STAR data reveal concave $R_{Ψ_{2}} (Δ S)$ distributions in 200 GeV Au+Au collisions. Studies with a multiphase transport (AMPT) and anomalous-viscous Fluid Dynamics (AVFD) models show concave $R_{Ψ_{2}} (Δ S)$ distributions for CME signals and convex ones for typical resonance backgrounds. A recent hydrodynamic study, however, indicates concave shapes for backgrounds as well. To better understand these results, we report a systematic study of the elliptic flow ( $v_{2}$ ) and transverse momentum ( $p_{T}$ ) dependences of resonance backgrounds with toy-model simulations and central limit theorem (CLT) calculations. It is found that the concavity or convexity of $R_{Ψ_{2}} (Δ S)$ depends sensitively on the resonance $v_{2}$ (which yields different numbers of decay $π^{+} π^{-}$ pairs in the in-plane and out-of-plane directions) and $p_{T}$ (which affects the opening angle of the decay $π^{+} π^{-}$ pair). Qualitatively, low $p_{T}$ resonances decay into large opening-angle pairs and result in more `back-to-back' pairs out-of-plane, mimicking a CME signal, or a concave $R_{Ψ_{2}} (Δ S)$ . Supplemental studies of $R_{Ψ_{3}} (Δ S)$ in terms of the triangular flow ( $v_{3}$ ), where only backgrounds exist but any CME would average to zero, are also presented.
Comments:
11 pages, 8 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1803.02860 [pdf]
PRC(2018)·20 citations
02
[Submitted on 8 Mar 2018]
Three-body Faddeev equations in two-particle Alt-Grassberger-Sandhas form with Distorted-Wave-Born-approximation amplitudes as effective potentials
A. M. Mukhamedzhanov
In this paper, I prove that the sub-Coulomb $A (d, p) B$ reaction amplitude, which is a solution of the three-body Faddeev equations in the Alt-Grassberger-Sandhas (AGS) form, is peripheral if a peripheral is the corresponding DWBA amplitude. Hence the Faddeev's reaction amplitude for the sub-Coulomb $A (d, p) B$ reactions can also be parametrized in terms of the ANC of the $(n A)$ bound state. First, I consider the original AGS equations with separable potentials and prove that such equations are peripheral at sub-Coulomb energies. After that, the two-particle AGS equations are derived for the general potentials for sub-Coulomb transfer reactions. The effective AGS potentials are expressed in terms of the DWBA amplitudes for the sub-Coulomb reactions. Again, I demonstrate that the amplitude of the $A (d, p) B$ transfer reaction obtained from the AGS equation is peripheral and can be parametrized in terms of the ANC for the $(n A)$ bound state because the corresponding DWBA amplitude is peripheral. Finally, the AGS equations are generalized by including the optical nuclear potentials in the same manner as it is done in the DWBA. The obtained two-particle AGS equations contain the DWBA effective potentials with distorted waves generated by the sum of the nuclear optical and the channel Coulomb potentials. The AGS equation for the $A (d, p) B$ reactions is analyzed above the Coulomb barrier and it is shown again that the reaction amplitude satisfying generalized AGS equation with optical potentials depends on the ANC if a peripheral is the DWBA amplitude. The two-body AGS equations are generalized by including the intermediate three-body continuum and more than one bound state in each channel.
Comments:
23 pages, 12 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1803.02958 [pdf]
PRC(2018)·3 citations
03
[Submitted on 8 Mar 2018]
Neutron-proton scattering and singular potentials
Mahmut Elbistan · Pengming Zhang · Janos Balog
We consider a Bargmann-type rational parametrization of the nucleon scattering phase shifts. Applying Marchenko's method of quantum inverse scattering we show that the scattering data suggest a singular repulsive core of the potential of the form $2/ r^{2}$ and $6/ r^{2}$ in natural units, for the $^{3} S_{1}$ and $^{1} S_{0}$ channels respectively. The simplest solution in the $^{3} S_{1}$ channel contains three parameters only but reproduces all features of the potential and bound state wave function within one percent error. We also consider the $^{3} S_{1}$ - $^{3} D_{1}$ coupled channel problem with the coupled channel Marchenko inversion method.
Comments:
39 pages. Extended version. Title changed, presentation improved and a new appendix on the coupled channel problem added
Subjects:
Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
arXiv:
1803.03047 [pdf]
J.Phys.G(2018)·2 citations
04
[Submitted on 8 Mar 2018]
Modeling neutrino-induced charged pion production on water at T2K kinematics
Alexis Nikolakopoulos🇧🇪 · Raúl González-Jiménez🇧🇪 · Kajetan Niewczas🇧🇪 · Jan Sobczyk🇵🇱 · Natalie Jachowicz🇧🇪
Pion production is a significant component of the signal in accelerator-based neutrino experiments. Over the last years, the MiniBooNE, T2K and MINERvA collaborations have reported a substantial amount of data on (anti)neutrino-induced pion production on the nucleus. However, a comprehensive and consistent description of the whole data set is still missing. We aim at improving the current understanding of neutrino-induced pion production on the nucleus. To this end, the comparison of experimental data with theoretical predictions, preferably based on microscopic models, is essential to disentangle the different reaction mechanisms involved in the process. To describe single-pion production (SPP) we use a hybrid model that combines a low- and a high-energy approach. The low-energy model (LEM) contains resonances and background terms. At high invariant masses, a high-energy model based on a Regge approach is employed. The model is implemented in the nucleus using the relativistic plane wave impulse approximation (RPWIA). We present a comparison of the hybrid-RPWIA and LEM with the recent neutrino-induced charged current $1 π^{+}$ production cross section on water reported by T2K. In order to judge the impact of final-state interactions (FSI) we confront our results with those of the NuWro Monte Carlo generator. The hybrid-RPWIA model and NuWro compare favorably to the data, albeit that FSI are not included in the former. These results complement our previous work [Phys. Rev. D 97, 013004 (2018)] where we compared the models to the MINERvA and MiniBooNE $1 π^{+}$ data. The hybrid-RPWIA model tends to overpredict both the T2K and MINERvA data in kinematic regions where the largest suppression due to FSI is expected, and agrees remarkably well with the data in other kinematic regions. On the contrary, the MiniBooNE data is underpredicted over the whole kinematic range.
Comments:
7 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1803.03163 [pdf]
PRD(2018)·27 citations

Affiliations

first authorsco-authorsvia INSPIRE

Responses of the chiral-magnetic-effect-sensitive sine observable to resonance backgrounds in heavy-ion collisions

Three-body Faddeev equations in two-particle Alt-Grassberger-Sandhas form with Distorted-Wave-Born-approximation amplitudes as effective potentials

Neutron-proton scattering and singular potentials

Modeling neutrino-induced charged pion production on water at T2K kinematics

Affiliations