Nuclear Theory·nucl-th

Friday·August 31, 2018

11 papers—9 primary·2 cross-listed

01
In-Medium Charmonium Production in Proton-Nucleus Collisions
Xiaojian Du🇺🇸 · Ralf Rapp🇺🇸
We study charmonium production in proton-nucleus ( $p$ -A) collisions focusing on final-state effects caused by the formation of an expanding medium. Toward this end, we utilize a rate equation approach within a fireball model as previously employed for a wide range of heavy-ion collisions, adapted to the small systems in $p$ -A collisions. The initial geometry of the fireball is taken from a Monte-Carlo event generator where initial anisotropies are caused by fluctuations. We calculate the centrality and transverse-momentum dependent nuclear modification factor ( $R_{p A}$ ) as well as elliptic flow ( $v_{2}$ ) for both $J / ψ$ and $ψ (2 S)$ and compare them to experimental data from RHIC and the LHC. While the $R_{p A}$ s show an overall fair agreement with most of the data, the large $v_{2}$ values observed in $p$ -Pb collisions at the LHC cannot be accounted for in our approach. While the former finding generally supports the formation of a near thermalized QCD medium in small systems, the discrepancy in the $v_{2}$ suggests that its large observed values are unlikely to be due to the final-state collectivity of the fireball alone.
nucl-thhep-phnucl-exJHEP(2019)·80 citations
02
Nuclear magnetic moments in covariant density functional theory
Jian Li🇨🇳 · J. Meng🇨🇳
The nuclear magnetic moment is an important physical observable and serves as a useful tool for the stringent test of nuclear models. For the past decades, the covariant density functional theory and its extension have been proved to be successful in describing the nuclear ground-states and excited states properties. However, a long-standing problem is its failure to predict magnetic moments. This article reviews the recent progress in the description of the nuclear magnetic moments within the covariant density functional theory. In particular, the magnetic moments of spherical odd-A nuclei with doubly closed shell core plus or minus one nucleon and deformed odd-A nuclei.
nucl-thFront.Phys.(Beijing)(2018)·23 citations
03
Structure of eta' mesonic nuclei in a relativistic mean field theory
Daisuke Jido🇯🇵 · Hanayo Masutani🇯🇵 · Satoru Hirenzaki🇯🇵
The structure and the energy spectrum of the $η^{'}$ mesonic nuclei are investigated in a relativistic mean field theory. One expects a substantial attraction for the $η^{'}$ meson in finite nuclei due to the partial restoration of chiral symmetry in the nuclear medium. Such a hadronic scale interaction for the $η^{'}$ mesonic nuclei may provide modification of the nuclear structure. The relativistic mean field theory is a self-contained model for finite nuclei which provides the saturation property within the model, and is good to investigate the structure change of the nucleus induced by the $η^{'}$ meson. Using the local density approximation for the mean fields, we solve the equations of motion for the nucleons and the $η^{'}$ meson self-consistently, and obtain the nuclear density distribution and the $η^{'}$ energy spectrum for the $η^{'}$ mesonic nuclei. We take $^{12}$ C, $^{16}$ O and $^{40}$ Ca for the target nuclei. We find several bound states of the $η^{'}$ meson for these nuclei thanks to the attraction for $η^{'}$ in nuclei. We also find a sufficient change of the nuclear structure especially for the $1 s$ bound state of $η^{'}$ . This implies that the production of the $1 s$ bound state in nuclear reaction may be suppressed.
nucl-thPTEP(2019)·7 citations
04
Symmetries of the interacting boson model
P. Van Isacker🇫🇷
In this contribution the symmetry properties of the interacting boson model of Arima and Iachello are reviewed. While the concept of a dynamical symmetry is by now a familiar one, this is not necessarily so for the extended notions of partial dynamical symmetry and quasi dynamical symmetry, which can be beautifully illustrated in the context of the interacting boson model. The main conclusion of the analysis is that dynamical symmetries are scarce while their partial and quasi extensions are ubiquitous.
nucl-thFront.Phys.(Beijing)(2018)·1 citation
05
$α$ Decays in Superstrong Static Electric Fields
Dong Bai · Zhongzhou Ren
Superstrong static electric fields could deform Coulomb barriers between $α$ clusters and daughter nuclei, and bring up the possibility of speeding up $α$ decays. We adopt a simplified model for the spherical $α$ emitter $^{212}$ Po and study its responses to superstrong static electric fields. We find that, superstrong electric fields with field strengths $∣ E ∣ \sim 0.1$ MV/fm could turn the angular distribution of $α$ emissions from isotropic to strongly anisotropic, and speed up $α$ decays by more than one order of magnitude. We also study the influences of superstrong electric fields along the Po isotope chains, and discuss the implications of our studies on $α$ decays in superstrong monochromatic laser fields. The study here might be helpful for future theoretical studies of $α$ decay in realistic superstrong laser fields.
nucl-thCommun.Theor.Phys.(2018)·11 citations
06
Woods-Saxon-Gaussian Potential and Alpha-Cluster Structures of Alpha+Closed Shell Nuclei
Dong Bai🇨🇳 · Zhongzhou Ren🇨🇳
The Woods-Saxon-Gaussian (WSG) potential is proposed as a new phenomenological potential to describe systematically the level scheme, electromagnetic transitions, and alpha-decay half-lives of the alpha-cluster structures in various alpha+closed shell nuclei. It modifies the original Woods-Saxon (WS) potential with a shifted Gaussian factor centered at the nuclear surface. We determine the free parameters in the WSG potential by reproducing the correct level scheme of $^{212} Po =^{208} Pb + α$ . It is found that the resulting WSG potential matches with the M3Y double-folding potential at the surface region and makes corrections to the inner part of the cluster-core potential. We also find that the WSG potential with the almost same parameters determined for $^{212}$ Po (except for a rescaled radius) could also be used to describe alpha-cluster structures in $^{20} Ne =^{16} O + α$ and $^{44} Ti =^{40} Ca + α$ . In all three cases, the calculated values of the level schemes, electromagnetic transitions, and alpha-decay half-lives agree with the experimental data, which shows that the WSG potential could indeed grasp many important features of the alpha-cluster structures in alpha+closed shell nuclei. The study here is a useful complement to the existing cluster-core potentials in literature. The Gaussian form factor centered at the nuclear surface might also help deepen our understanding on the alpha-cluster formation taking place around the same place.
nucl-thCPC(2018)·16 citations
07
Pions in magnetic field at finite temperature
Shijun Mao🇨🇳
Pions in external magnetic field are investigated in the frame of a Pauli-Villars regularized Nambu--Jona-Lasinio model. The meson propagators in terms of quark bubbles in Ritus and Schwinger schemes are analytically derived, and pion masses are numerically calculated in the Ritus scheme. For neutral and charged pions at finite temperature, there exist respectively one and three mass jumps at the corresponding Mott transition points, due to the discrete energy levels of the two constituent quarks in magnetic field.
nucl-thhep-phPRD(2019)·65 citations
08
Collective flows of $α$ -clustering $^{12} C$ + $^{197} Au$ by using different flow analysis methods
S. Zhang🇨🇳 · Y. G. Ma🇨🇳 · J. H. Chen🇨🇳 · W. B. He🇨🇳 · C. Zhong🇨🇳
Recently the ratio of triangular flow to the elliptic flow ( $v_{3} / v_{2}$ ) of hadrons was proposed as a probe to detect the pattern of $α$ -clustering $^{12} C$ in $^{12} C$ + $^{197} Au$ collisions at relativistic energy by a participant plane method (Phys. Rev. C 95, 064904 (2017)). In experimental event plane method, Q-cumulant method and two-particle correlation method with rapidity gap always were used for measurement of collective flow only by means of momentum space. By comparing collective flow through the different methods, the ratio of $v_{3} / v_{2}$ could be taken as an experimental probe to distinguish different $α$ -clustering structure of $^{12} C$ .
nucl-thhep-phnucl-exEPJA(2018)·23 citations
09
Pseudo-rapidity distribution from a perturbative solution of viscous hydrodynamics for heavy ion collisions at RHIC and LHC
Ze Fang Jiang🇨🇳 · C. B. Yang🇨🇳 · Chi Ding🇨🇳 · Xiang-Yu Wu🇨🇳
The charged-particle's final state spectrum is derived from an analytic perturbative solution for the relativistic viscous hydrodynamics. By taking into account the longitudinal acceleration effect in relativistic viscous hydrodynamics, the pseudorapidity spectrum describes well the nucleus-nucleus colliding systems at RHIC and LHC. Based on both the extracted longitudinal acceleration parameters $λ^{*}$ and a phenomenological description of the $λ^{*}$ , the charged-particle's pseudorapidity distributions for $s_{N N}$ = 5.44 TeV Xe+Xe collisions are computed from the final state expression in a limited space-time rapidity $η_{s}$ region.
nucl-thhep-phhep-thCPC(2018)·11 citations
10
Reinterpreting the weak mixing angle from atomic parity violation in view of the Cs neutron rms radius measurement from COHERENT
Matteo Cadeddu🇮🇹 · Francesca Dordei🇮🇹
Using the model independent average neutron rms radius of $^{133} Cs$ and $^{127} I$ obtained from the analysis of the coherent elastic neutrino-nucleus scattering data of the COHERENT experiment, we remove the long-standing $1.5 σ$ tension between the Standard Model prediction and the weak mixing angle measurement from the atomic parity violation (APV) in caesium. The updated APV result becomes $sin^{2} ϑ_{W} = 0.239_{- 0.007}^{+ 0.006}$ , to be compared with the Standard Model prediction at low momentum transfer, $sin^{2} ϑ_{W}^{SM} = 0.23857 (5)$ . Moreover, exploiting the fact that the APV result is highly sensitive to the caesium neutron rms radius, $R_{n}$ , and assuming that the Standard Model is correct, we combine the APV and the COHERENT measurements in order to get a better determination of $R_{n}$ . The value of $R_{n} = 5.42 \pm 0.31 fm$ is obtained, improving significantly the current uncertainty. This result allows to infer a meaningful value of the caesium neutron skin, the difference between the neutron and proton distribution radii, equal to $Δ R_{n p} = 0.62 \pm 0.31 fm$ , showing for the first time a $2 σ$ deviation from zero.
↳ hep-phnucl-thPRD(2019)·78 citations
11
Valence Quark Transversity at Small $x$
Yuri V. Kovchegov🇺🇸 · Matthew D. Sievert🇺🇸
In our previous work we established a formalism which allows one to determine the small- $x$ asymptotics of any transverse momentum-dependent parton distribution function (TMD PDF) of the proton at small values of strong coupling. In this paper we apply this formalism to the valence quark transversity TMD. We relate the valence quark transversity to the transversely polarized dipole scattering amplitude, written in terms of the fundamental transversely-polarized "Wilson line" operator, an expression for which we derive explicitly as well. We then write down the evolution equation for the transversely polarized dipole amplitude. Solving that equation we arrive at the following small- $x$ asymptotics of the valence quark transversity in the large- $N_{c}$ limit: \begin{align} h_{1T}^v (x, k_T^2) \sim h_{1T}^{\perp \, v} (x, k_T^2) \sim \left( \frac{1}{x} \right)^{-1 + 2 \, \sqrt{\frac{\alpha_s \, N_c}{2 \, \pi}} } . \notag \end{align} This result is in agreement with one of the two possible small- $x$ asymptotics for the transverse structure function found previously by Kirschner, Mankiewicz, Schäfer, and Szymanowski.
↳ hep-phnucl-thPRD(2019)·52 citations

Affiliations

first authorsco-authorsvia INSPIRE