电子-离子对撞机上开展核子及其激发态研究的建议

核子及其激发态性质研究一直是中高能核物理的一个重要研究领域。然而,到目前为止,对核子及其激发态内部结构的了解还处在初级阶段。首先介绍了核子及其激发态研究现状,指出了三夸克模型在描述核子特别是核子激发态内部结构方面存在很大的缺陷。为解决传统三夸克模型的不足,有一种新的观点认为虽然独立的五夸克态不存在,但是核子及其共振态中存在可观的五夸克激发。这种五夸克图像提供了一个描述核子内部结构的新见解,给出了与经典三夸克图像相当不同的核子激发态谱预言,还有待实验检验。目前国内外正在论证的电子–离子对撞机(EIC)将是研究核子结构下一代最重要的加速器装置,被视为"超级电子显微镜"。由于EIC有较高的能量和亮度,特别是低本底等优势,可以开展核子及其激发态性质的研究以及新强子态研究。     

Super scattering phenomenon in active spherical nanoparticles

Localized surface electromagnetic resonances in spherical nanoparticles with gain are investigated by using the Mie theory. Due to the coupling between the gain and resonances, super scattering phenomenon is raised and the total scattering efficiency is increased by over six orders of magnitude. The dual frequency resonance induced by the electric dipole term of the particle is observed. The distributions of electromagnetic field and the Poynting vector around nanoparticles are provided for better understanding different multipole resonances. Finally, the scattering properties of active spherical nanoparticles are investigated when the sizes of nanoparticles are beyond the quasi-static limit. It is noticed that more highorder multipole resonances can be excited with the increase of the radius. Besides, all resonances dominated by multipole magnetic terms can only appear in dielectric materials.     

Electric and magnetic excitations in anisotropic broadside-coupled triangular-split-ring resonators

The electric and magnetic resonances of anisotropic broadside-coupled triangular-split-ring resonators are studied for different incident wave excitations. It is shown that the higher order modes exist in both electric and magnetic resonances. It is observed that the incident electric field couples to the magnetic resonance of the designed structure under different excitations. Multiple resonance features due to the anisotropy of the structure are found in the case of different excitations and the nature of these resonances can be regulated as either an electric or a magnetic mode for different frequencies. In this way, a resonant effective permittivity or permeability can be obtained. Hence, controllable properties of the constitutive material parameters (i.e. electric or magnetic resonances, negative values, etc.) can be determined by changing the incident wave excitation.     

Conditions that must be satisfied by crossing-symmetric finite-energy sum-rules

It is shown that there can be no exact solution of a crossing-symmetric finite-energy sum-rule in terms of a finite number of towers of zero-width resonances. If the Regge behaviour in a channel is to come from the resonances in the same channel, and not from some background term, there must either be appreciable overlap of broad resonances, or an infinite number of Regge trajectories. If complete crossing-symmetry is to be achieved, Regge cuts, as well as poles, must be incorporated. The above statements are supported by mathematical models; and the conclusion is that finite-energy sum-role bootstrap calculations with a finite number of towers of resonances should be treated with extreme caution, for they can, at best, be only very approximate.     

Fast parameter fit of two randomly overlapping Lorentzians

Two randomly overlapping Lorentzians can be separated mathematically by calculating all their significant parameters in a least-squares procedure. This works nearly without iterations and leads to reliable parameters for resonances, half-widths, intensities, or amplitudes independent of the actual phase. Either real or imaginary parts of resonances may be the subject of calculation. Preliminary knowledge of parameters is not necessary. Under some conditions more than two Lorentzians can be separated.     

Measurement of Interproton, Nuclear Spin Dipolar Couplings in Liquid Crystalline Samples by Combining Variable Angle Sample Spinning, Isotope Dilution, and Deuterium Decoupling

The proton NMR spectra of liquid crystalline samples can be simplified by selective, partial deuteration followed by deuterium decoupling. This leaves strong peaks from the protons at the undeuterated sites, but also weak resonances from the coupling of these protons to those at low abundance (2% in the present case) at the deuterated sites. The weak resonances can be separated from the strong by recording spectra while spinning the sample at a series of angles to the magnetic field.     

Elastic resonances of a periodic array of fluid-filled cylindrical cavities embedded in an elastic matrix

The resonant scattering by a periodic infinite array of fluid-filled cylindrical cavities in an elastic matrix is studied. The exact reflection and transmission coefficients of the array are calculated by means of a multiple scattering formalism taking into account all the interactions between the cavities. Numerical results are next given for low frequencies for which only the longitudinal and transverse zero modes propagate. A first study based on the analysis of the transmission coefficients clearly shows that the resonances of the array can be classified into two sets: those close to the resonances of a single cavity and those due to a resonant coupling between a cavity and its nearer neighbors. The resonant coupling is due to the interaction between the whispering-gallery surface waves propagating around each cavity. In the case of cavities with very close spacing, it is observed that the dispersion curves of the waves propagating along the array can also be classified into two sets: those with a positive group velocity have cut-off frequencies that correspond to the resonances of a single cavity, those with a negative group velocity have cut-off frequencies that correspond to the resonances resulting from the strong coupling. A new method for the analysis of the resonances is presented. It is based on the properties of the scattering matrix and consists in studying the resonant eigenvalues of the scattering matrix of the array once the background is removed. For the detection of very fine resonances, as well as in the separation of several resonances very close to each other, this method proves to be more efficient than one based on the analysis of the reflection and transmission coefficients.     

Laser-induced continuum structure in multiphoton ionisation

Dressed-state resonances can be induced in photoionisation continua by radiative coupling from energetically accessible bound states. Such resonances lead to enhanced photoionisation rates and interference minima. We present results on the effects of saturation and Rabi oscillations on ion yields and asymmetries in AC Stark-split photoelectron spectra.     

Regge poles in the collective model of the nuclear giant multipole resonances

Giant nuclear resonance states, of higher multipolarity than dipole, have recently been observed in hadron and electron scattering. They may possibly be described by the collective Goldhaber-Teller model as extended to the higher multipolarity case, and as generalized to include spin-isospin vibrations and spin waves. Based on such a model, we show that the multipole resonances, together with the conventional dipole resonances, can be generated by the motion of a few basic Regge poles through the complex angular momentum plane. This viewpoint unifies all the resonances with a given spin-isospin character but arbitrary value of the multipolarity, and suggests the existence of the higher-multipole resonances as a consequence of the existence of the dipole resonance. We also analyze these Regge poles in terms of collective surface waves (“creeping waves”) circumnavigating the nucleus, and we determine their phase velocities and attenuations. Finally, the giant resonances them selves are explained as a resonant reinforcement of phase-matched surface waves.     

Structure of resonances and formation of stationary points in symmetrical chains of bilinear oscillators

Dynamics of strongly nonlinear systems can in many cases be modelled by bilinear oscillators, which are the oscillators whose springs have different stiffnesses in compression and tension. This underpins the analysis of a wide range of phenomena, from oscillations of fragmented structures, connections and mooring lines to deformation of geological media. Single bilinear oscillators were studied previously and the presence of multiple resonances both super- and sub-harmonic was found. Less attention was paid to systems of multiple bilinear oscillators that describe many natural and engineering processes such as for example the behaviour of fragmented solids. Here we fill this gap concentrating on the simplest case – 1D symmetrical chains of bilinear oscillators. We show that the presence and structure of resonances in a symmetric chain of bilinear oscillators with fixed ends depends upon the number of oscillating masses. Two elementary chains act as the basic ones: a single mass bilinear chain (a mass connected to the fixed points by two bilinear springs) that behaves as a linear oscillator with a single resonance and a two mass chain that is a coupled bilinear oscillator (two masses connected by three bilinear springs). The latter has multiple resonances. We demonstrate that longer chains either do not have resonances or get decomposed, in the resonance, into either the single mass or two mass elementary chains with stationary masses in between. The resonance frequencies are inherited from the basic chains of decomposition. We show that if the number of masses is odd the chain can be decomposed into the single mass bilinear chains separated by stationary masses. It then inherits the resonances of the single mass bilinear chain. The chains with the number of masses minus 2 divisible by 3 can be decomposed into the two mass bilinear chains separated by stationary masses and inherit the resonances of the two mass chains. The chains whose lengths satisfy both criteria (such as chains with 5, 11, 17 … masses) allow both types of resonances.     

Tunneling mechanism of light transmission through metallic films

A mechanism of light transmission through metallic films is proposed, assisted by tunneling between resonating buried dielectric inclusions. This is illustrated by arrays of Si spheres embedded in Ag. Strong transmission peaks are observed near the Mie resonances of the spheres. The interaction among various planes of spheres and interference effects between these resonances and the surface plasmons of Ag lead to mixing and splitting of the resonances. Transmission is proved to be limited only by absorption. For small spheres, the effective dielectric constant of the resulting material can be tuned to values close to unity, and a method is proposed to turn the resulting materials invisible.     

Near-field spectroscopy of surface plasmons in flat gold nanoparticles

We use near-field interference spectroscopy with a broadband femtosecond, white-light probe to study local surface plasmon resonances in flat gold nanoparticles (FGNPs). Depending on nanoparticle dimensions, local near-field extinction spectra exhibit none, one, or two resonances in the range of visible wavelengths (1.6-2.6 eV). The measured spectra can be accurately described in terms of interference between the field emitted by the probe aperture and the field reradiated by driven FGNP surface plasmon oscillations. The measured resonances are in good agreement with those predicted by calculations using discrete dipole approximation. We observe that the amplitudes of these resonances are dependent upon the spatial position of the near-field probe, which indicates the possibility of spatially selective excitation of specific plasmon modes.     

Axial resonances in the open and hidden charm sectors

A SU(4) flavor symmetrical Lagrangian is constructed for the interaction of the pseudo-scalar mesons with the vector mesons. SU(4) symmetry is broken to SU(3) by suppression of terms in the Lagrangian where the interaction should be driven by charmed mesons. Chiral symmetry can be restored by setting this new SU(4) symmetry-breaking parameters to zero. Unitarization in coupled channels leads to the dynamical generation of resonances. Many known axial resonances can be identified including the new controversial X(3872) and the structure found recently by Belle around 3875MeV in the hidden charm sector. Also new resonances are predicted, some of them with exotic quantum numbers.     

Bhabha to Møller cross section ratios in the energy range 2.15–2.45 MeV

The cross sections for Bhabha and Møller scattering have been investigated in the energy range 2.1–2.4 MeV using monoenergetic positrons and electrons to search for hypothetical resonances superimposed to the continuum predicted by quantum electro dynamics. Bhabba-to-Mott, Møller-to-Mott and Møller-to-Bhabha cross section ratios were measured. The Bhabha-to-Mott ratios could be determined with statistical errors of typically 1% and remaining systematic errors not exceeding the statistical ones. No resonances in Bhabha scattering were observed. Limits for the intrinsic widths of hypothetical resonances are given. For the first time upper limits are deduced from our data for hypothetical resonances in the Møller scattering cross section in the MeV range. Additionally, Møller-to-Bhabha cross section ratios could be determined with good precision. A good agreement between the experimental and theoretical Møller-to-Bhabha ratios can be stated calling in question the recently predicted existence of series of narrow, unresolvable resonances in the Bhabha scattering cross section.     

Giant Kerr nonlinearity induced by interacting dark resonances

A scheme for giant enhancement of the Kerr nonlinearity in a four-level system with double dark resonances is proposed. Compared with that generated in a single-dark-resonance system, the Kerr nonlinearity can be enhanced by several orders of magnitude with vanishing linear absorption. We attribute this dramatic enhancement to the interaction of dark resonances.     

Enhanced transmission through periodic arrays of subwavelength holes: the role of localized waveguide resonances

By using the rigid full-vectorial three-dimensional finite-difference time-domain method, we show that the enhanced transmission through a metallic film with a periodic array of subwavelength holes results from two different resonances: (i) localized waveguide resonances where each air hole can be considered as a section of metallic waveguide with both ends open to free space, forming a low-quality-factor resonator, and (ii) well-recognized surface plasmon resonances due to the periodicity. These two different resonances can be characterized from electromagnetic band structures in the structured metal film. In addition, we show that the shape effect in the enhanced transmission through the Au film with subwavelength holes is attributed to the localized waveguide resonance.     

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研究了在三开口劈裂金属纳米环中,当入射场偏振方向不同时出现的多极局域表面等离激元共振现象及折射率传感特性。研究表明,当入射场偏振方向分别沿x 轴和y 轴时,在可见光-近红外区域分别激发起两个和三个明显的共振峰。通过改变缺口的张角,能够实现对共振峰位和强度的可控调整。共振峰位处劈裂纳米环的近场分布表明,LHA(左半弧)和DRHA(双右半弧)之间等离激元的杂化耦合是形成上述共振的原因。劈裂纳米环的多极共振非常适合折射率传感应用。当改变周围环境折射率,入射场沿x 轴偏振时,折射率敏感度的最大值可达到1365nm/RIU;入射场沿y 轴偏振时,折射率敏感度最大值可达2229nm/RIU。     

Tuning of nanotube mechanical resonances by electric field pulling

We show here that field emission (FE) can be used to directly observe the vibration resonances nu(R) of carbon nanotubes (CNTs) and that the tension created by the applied field allows the tuning of these resonances by up to a factor of 10. The resonances are observable by the changes they create in the FE pattern or the emitted FE current. The tuning is shown to be linear in voltage and to follow from the basic physics of stretched strings. The method allows one to study the mechanical properties of individual multiwall carbon nanotubes within an ensemble and follow their evolution as the CNTs are modified. The tuning and detection should be useful for nanometric resonant devices.     

Hybrid waveguide-plasmon resonances in gold pillar arrays on top of a dielectric waveguide

We propose a hybrid waveguide-plasmon system consisting of gold pillar arrays on top of a dielectric waveguide. The formation of extraordinary transmissions induced by the hybrid waveguide-plasmon resonances is investigated by rigorous coupled-wave analysis. The characteristics of the hybrid resonances can be predicted by introducing the photonic crystal slab theory. Extremely narrow absorption peaks and the electromagnetically induced transparency-like optical property are demonstrated in our hybrid system.     

Detecting resonances in conservative maps using evolutionary algorithms

A numerical method is proposed for detecting resonances of conservative maps which reduces this task to an optimization problem. We then solve this problem using evolutionary algorithms, which are methods for global optimization inspired by biological evolution. The proposed methodology is simple and can be easily applied to maps of arbitrary dimensions. In this Letter we apply it to several examples of 2- and 4-dimensional conservative maps, with quite promising results concerning integrability, the location of resonances and the presence of chaotic regions surrounding the island chains that correspond to these resonances.