Nuclear Theory·nucl-th

Thursday·April 13, 2017

15 papers—9 primary·6 cross-listed

10
[Submitted on 11 Apr 2017] (cross-list from hep-ph)
Effective field theories for van der Waals interactions
Nora Brambilla🇩🇪 · Vladyslav Shtabovenko🇩🇪 · Jaume Tarrús Castellà🇩🇪 · Antonio Vairo🇩🇪
Van der Waals interactions between two neutral but polarizable systems at a separation $R$ much larger than the typical size of the systems are at the core of a broad sweep of contemporary problems in settings ranging from atomic, molecular and condensed matter physics to strong interactions and gravity. We reexamine the dispersive van der Waals interactions between two hydrogen atoms. The novelty of the analysis resides in the usage of nonrelativistic EFTs of QED. In this framework, the van der Waals potential acquires the meaning of a matching coefficient in an EFT suited to describe the low energy dynamics of an atom pair. It may be computed systematically as a series in $R$ times some typical atomic scale and in the fine structure constant $α$ . The van der Waals potential gets short range contributions and radiative corrections, which we compute in dimensional regularization and renormalize here for the first time. Results are given in $d$ spacetime dimensions. One can distinguish among different regimes depending on the relative size between $1/ R$ and the typical atomic bound state energy $m α^{2}$ . Each regime is characterized by a specific hierarchy of scales and a corresponding tower of EFTs. The short distance regime is characterized by $1/ R ≫ m α^{2}$ and the LO van der Waals potential is the London potential. We compute also NNNLO corrections. In the long distance regime we have $1/ R ≪ m α^{2}$ . In this regime, the van der Waals potential contains contact terms, which are parametrically larger than the Casimir-Polder potential that describes the potential at large distances. In the EFT the Casimir-Polder potential counts as a NNNLO effect. In the intermediate distance regime, $1/ R \sim m α^{2}$ , a significantly more complex potential is obtained which we compare with the two previous limiting cases. We conclude commenting on the hadronic van der Waals case.
Comments:
Journal version. 27 pages, 11 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th); Atomic Physics (physics.atom-ph)
arXiv:
1704.03476 [pdf]
PRD(2017)·21 citations
11
[Submitted on 12 Apr 2017] (cross-list from nucl-ex)
Collective flow from AA, pA to pp collisions - Toward a unified paradigm
Wei Li🇺🇸
I give an overview of the latest development in understanding collective phenomena in high-multiplicity hadronic final state from relativistic nucleus-nucleus, proton-nucleus and proton-proton collisions. Upon reviewing the experimental data and confronting them with theoretical models, a unified paradigm in describing the observed collectivity across all hadronic collision systems is emerging. Potential future paths toward addressing key open questions, especially on collectivity in small systems (pp, pA), are discussed.
Comments:
9 pages, 6 figures, plenary contribution to Quark Matter 2017, February 5-11 (2017), Chicago (IL), USA
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1704.03576 [pdf]
NPA(2017)·22 citations
12
[Submitted on 12 Apr 2017] (cross-list from nucl-ex)
Single-neutron knockout from $^{20} C$ and the structure of $^{19} C$
J.W. Hwang🇰🇷 · S. Kim🇰🇷 · Y. Satou🇰🇷 · N.A. Orr🇫🇷 · Y. Kondo🇯🇵 · T. Nakamura🇯🇵 · J. Gibelin🇫🇷 · N.L. Achouri🇫🇷 · T. Aumann🇩🇪 · H. Baba🇯🇵 · F. Delaunay🇫🇷 · P. Doornenbal🇯🇵 and 33 other authors
The low-lying unbound level structure of the halo nucleus $^{19} C$ has been investigated using single-neutron knockout from $^{20} C$ on a carbon target at 280 MeV/nucleon. The invariant mass spectrum, derived from the momenta of the forward going beam velocity $^{18} C$ fragment and neutrons, was found to be dominated by a very narrow near threshold ( $E_{rel}$ = 0.036(1) MeV) peak. Two less strongly populated resonance-like features were also observed at $E_{rel}$ = 0.84(4) and 2.31(3) MeV, both of which exhibit characteristics consistent with neutron $p$ -shell hole states. Comparisons of the energies, measured cross sections and parallel momentum distributions to the results of shell-model and eikonal reaction calculations lead to spin-parity assignments of $5/ 2_{1}^{+}$ and $1/ 2_{1}^{-}$ for the levels at $E_{x}$ = 0.62(9) and 2.89(10) MeV with $S_{n}$ = 0.58(9) MeV. Spectroscopic factors were also deduced and found to be in reasonable accord with shell-model calculations. The valence neutron configuration of the $^{20} C$ ground state is thus seen to include, in addition to the known $1 s_{1/2}^{2}$ component, a significant $0 d_{5/2}^{2}$ contribution. The level scheme of $^{19} C$ , including significantly the $1/ 2_{1}^{-}$ cross-shell state, is well accounted for by the YSOX shell-model interaction developed from the monopole-based universal interaction.
Comments:
Physics Letters B, in press
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1704.03601 [pdf]
PLB(2017)·21 citations
13
[Submitted on 12 Apr 2017] (cross-list from cond-mat.quant-gas)
Determination of the density and temperature dependence of the shear viscosity of a unitary Fermi gas based on hydrodynamic flow
Marcus Bluhm🇺🇸 · Jiaxun Hou🇺🇸 · Thomas Schaefer🇺🇸
We determine the shear viscosity of the ultracold Fermi gas at unitarity in the normal phase using hydrodynamic expansion data. The analysis is based on a generalized fluid dynamic framework which ensures a smooth transition between the fluid dynamic core of the cloud and the ballistic corona. We use expansion data taken by Joseph et al. and measurements of the equation of state by Ku et al. We find that the shear viscosity to particle density ratio just above the critical temperature is $η / n ∣_{T_{c}} = 0.41 \pm 0.11$ . We also obtain evidence that the shear viscosity to entropy density ratio has a minimum slightly above $T_{c}$ with $η / s ∣_{min} = 0.50 \pm 0.10$ .
Comments:
Version to appear in PRL
Subjects:
Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th)
arXiv:
1704.03720 [pdf]
PRL(2017)·30 citations
14
[Submitted on 12 Apr 2017] (cross-list from hep-ph)
Quasi-distribution amplitudes for pion and kaon via the nonlocal chiral-quark model
Seung-il Nam🇰🇷
We investigate the pseudoscalar (PS) meson ( $π$ and $K$ ) quasi-distribution amplitude (QDA), which is supposed to be an asymptotic analog to the meson distribution amplitude (DA) $ϕ_{π, K} (x)$ in the limit of the large longitudinal PS-meson momentum, i.e. $p_{3} \to \infty$ , in the nonperturbative region. For this purpose, we employ the nonlocal chiral-quark model (NLChQM) in the light-front formalism with a minimal Fock-state for the mesons $\sim q q ˉ$ at the low-energy scale parameter of the model $Λ \sim 1$ GeV. As a trial, we extract the transverse-momentum distribution amplitude (TMDA) from the light-front wave function within the model, and convert it to QDA with help of the virtuality-distribution amplitude. By doing that, we derive an analytical expression for the nonperturbative QDA with the current-quark mass correction up to $O (Δ m_{q})$ . Numerically, we confirm that the obtained TMDA reproduces the experimental data for the photon-pion transition form factor $F_{γ γ^{*} π^{0}} (Q^{2})$ at the low- $Q^{2}$ qualitatively well. We also observe that the obtained QDA approaches to DA as $p_{3}$ increases, showing the symmetric and asymmetric curves with respect to $x$ for the pion and kaon, respectively, due to the current-quark mass difference $m_{u, d} ≪ m_{s}$ . Assigning $ξ \equiv 2 x - 1$ , the moments $⟨ ξ^{n} ⟩_{π, K}$ are computed, using the pion and kaon QDAs, and there appear only a few percent deviations in the moments for $p_{3} ≳ 30Λ$ in comparison to the values calculated directly from DAs. It turns out that the higher moments are more sensitive to the change of $p_{3}$ , whereas the lower ones depend less on it.
Comments:
12 pages, 8 figures, accepted for publication via Mod. Phys. Lett. A
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1704.03824 [pdf]
Mod.Phys.Lett.A(2017)·28 citations
15
[Submitted on 12 Apr 2017] (cross-list from nucl-ex)
Disentangling flow and signals of Chiral Magnetic Effect in U+U, Au+Au and p+Au collisions
Prithwish Tribedy (for the STAR Collaboration)🇺🇸
We present STAR measurements of the charge-dependent three-particle correlator $γ^{a, b} = ⟨ cos (ϕ_{1}^{a} + ϕ_{2}^{b} - 2 ϕ_{3})⟩ / v_{2} {2}$ and elliptic flow $v_{2} {2}$ in U+U, Au+Au and p+Au collisions at RHIC. The difference $Δ γ = γ (opposite - sign) - γ (same - sign)$ measures charge separation across the reaction plane, a predicted signal of the Chiral Magnetic Effect (CME). Although charge separation has been observed, it has been argued that the measured separation can also be explained by elliptic flow related backgrounds. In order to separate the two effects, we perform measurements of the $γ$ -correlator where background expectations differ from magnetic field driven effects. A differential measurement of $γ$ with the relative pseudorapidity ( $Δ η$ ) between the first and second particles indicate that $Δ γ$ in peripheral A+A and p+A collisions are dominated by short-range correlations in $Δ η$ . However, a relatively wider component of the correlation in $Δ η$ tends to vanish the same way as projected magnetic field as predicted by MC-Glauber simulations.
Comments:
4 pages, 2 figures, proceedings for Quark Matter 2017
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1704.03845 [pdf]
NPA(2017)·24 citations

Affiliations

first authorsco-authorsvia INSPIRE

Effective field theories for van der Waals interactions

Collective flow from AA, pA to pp collisions - Toward a unified paradigm

Single-neutron knockout from 20C and the structure of 19C

Determination of the density and temperature dependence of the shear viscosity of a unitary Fermi gas based on hydrodynamic flow

Quasi-distribution amplitudes for pion and kaon via the nonlocal chiral-quark model

Disentangling flow and signals of Chiral Magnetic Effect in U+U, Au+Au and p+Au collisions

Affiliations

Single-neutron knockout from $^{20} C$ and the structure of $^{19} C$