Strong Decays of Charm Mesons D_1~*(2680), D_3~*(2760), D_2~*(3000)

In this article, we assign the higher charm mesons D1_*(2680), D3_*(2760) and D2_*(3000) to be the 2S 1~-, 1D3~- and 1F 2~+ states, respectively, and study the two-body strong decays to the ground state charm mesons and light pseudoscalar mesons with the heavy meson effective theory. We obtain the ratios among the strong decays, which can be confronted to the experimental data in the future and shed light on the nature of those higher charm mesons.     

Enhanced cooling of hydrogen atoms by lithium atoms

We present calculated scattering lengths for collisions between various isotopic forms of lithium and hydrogen atoms interacting via singlet and triplet molecular states of LiH. We demonstrate that one bound triplet level is supported for each isotopomer 7LiH, 6LiH, 7LiD, and 6LiD. We obtain large calculated triplet scattering lengths that are stable against uncertainties in the potential. We present elastic and momentum transfer cross sections, and the corresponding rate coefficients, for hydrogen atoms colliding with 7Li atoms. We suggest that enhanced cooling of trapped atomic hydrogen by 7Li atoms is feasible.     

n-changing collisions of Rydberg atoms with ground-state atoms

The inelastic transitions between hydrogenic energy levels of a Rydberg atom induced in collisions with ground-state atoms are considered. The corresponding transition probability and cross section are calculated using the Fermi pseudopotential to describe the atom-Rydberg-atom interaction and a quasiclassical expression for the density distribution of the Rydberg electron.     

Semileptonic Decays of B_s~(**) Mesons into D_(s1) and D_(s2)~* in HQET

In the framework of the heavy quark effective theory,the leading order Isgur-Wise functions relevant to semileptonic decays of the orbitally P-wave excited B s meson states B**s,including the newly found narrow B s1(5830) and B**s2(5840) states,into the(D s1(2536),D*s2(2573)) doublet are calculated from QCD sum rules.With these universal form factors,the decay rates and branching ratios are also estimated.     

Exotic atoms

Some recent developments in the field of exotic atoms are presented. The improved quality of the accelerator facilities and the experimental techniques lead to a more precise determination of the observables. This opens new fields in nuclear and particle physics to which exotic atoms may contribute valuable knowledge.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

能攀登的原子

利用分子束外延方法在晶体表面沉积原子时 ,当基底的温度很低时 ,在覆盖原子的表面上常会出现许多凹凸不平的小丘 ,而不是光滑的平面 .但对于较高温度的基底 ,在小丘顶部的原子就会通过扩散向下移动到晶体的表面 .按照传统的理论 ,向上扩散的原子是可以忽略不计的 .近来 ,意大利Genova大学、中国科学院、美国橡树岭国家实验室共同合作的研究组的科学家们 (F .BuatierdeMon geot和ZhangZhenyu等 )发现 ,沉积在晶体表面的原子可以自发地向上扩散 ,从而在晶面上形成一些高于晶面的小山丘 .在过去的实验中 ,也观察到过这类纳米量级小丘的出现…     

Munucleon atoms

The paper presents the consideration of problems concerning formation and observation of munucleon atoms produced by the capture of negative muon by atoms of noble gases by means of theSR-method.     

Two-muonic atoms

X-ray transition energies for two-muonic atoms are calculated. The basis are relativistic self-consistent-field calculations including the corrections normally known in muonic atoms plus the vacuum polarization, magnetic interaction and retardation in the μ-μ-interaction, the specific mass correction and the configuration interaction.     

Reactions of excited atoms and molecules with atoms and molecules

Penning electron distributions arising from the ionization of Na and K by He (1s 2s ^1,3 S)-metastables in thermal collisions, as well as the absolute cross section for Penning ionization of Na by He (2³ S) and relative cross sections for ionization of Na and K by He(2¹ S) and He(2³ S) are measured. It is shown that under fairly general conditions the well depth ε* of the interaction potential between the metastable and the target particle can be obtained directly from the measured electron distributions. ε*-values are reported for the moleules He(1s 2s ^1,3 S)-Na(² S), K(² S) (^2,2Ω), and for He(1s 2s ^1,3 S)-Hg(¹ S)(^1,3Ω). These latter values are obtained from previously published measurements and are to be considered preliminary. Further, additional evidence is given, that Penning ionization with metastables is an electron exchange process.     

Reactions of excited atoms and molecules with atoms and molecules

From a He-beam excited by electron impact we eliminated the He(2¹ S) component to better than 0.5% by irradiating light from a He discharge. The quenching process ishv(2¹ P→2¹ S)+He(2¹ S)→He(2¹ P)→He(1¹ S +hv) (2¹ P 1)¹ S. By measuring the ions produced in collisions of the He-metastables with various target gases in a mass spectrometer, singlet to triplet Penning-cross section ratios were obtained. These ratios are without exception close to one, which is taken as evidence for the previously proposed electron exchange mechanism of the Penning ionization. In the case that more ions are produced in the collision of He (2¹ S) and He(2³ S) with a target gas, separate relative production cross sections are obtained for the two metastables. For the rare gases the measurements are performed at two temperatures of the He-beam, 320 and 90 °K. It is found that the cross section ratio of associative — to Penning ionization increases considerably as the temperature is decreased for both, He(2¹ S) and He(2³ S), the effect being much more pronounced for He(2¹ S). The results of this work are found to confirm conclusions drawn from measured energy distributions of the electrons ejected in the Penning process.     

Reactions of excited atoms and molecules with atoms and molecules

Ionizing collisions of long lived excited particles with atoms and molecules are studied by a cross beam technique. For the first time reactions of atoms in high Rydberg states are included in the investigation. In this paper we report relative cross sections for the production of the ions RH⁺, RH ₂ ⁺ , and H ₂ ⁺ by collisions of excited rare gas atoms R^* with H₂. With HD as the target molecule the isotope effect for the production of RD⁺ and RH⁺ has been determined. In the case of argon and krypton, ions are produced only by the high Rydberg states, whereas in the case of helium and neon only the metastable states contribute to a measurable extent. The data indicate, that the reaction mechanism is different in principle for metastable and highly excited atoms. Simple models are proposed to explain the experimental results.     

Hadronic atoms

Precision spectroscopy of hadronic atoms is a powerful tool to study the particle properties (mass and magnetic moment) as well as the hadron-nucleon (nucleus) strong-interaction parameters. Recent developments in hadronic-atom studies, pionic-atom and kaonic-atom spectroscopy in particular, are discussed.     

Projective representation of D_6 group in twisted bilayer graphene

Within the framework of continuum model, we study the projective representation of emergent D_6 point group in twisted bilayer graphene. We then construct tight-binding models of the lowest bands without and with external electromagnetic fields, based on the projective representation.     

High-resolution Reflection Spectroscopy ofCs D_2 Line Studied by High-order-harmonic Detection

In this paper, by numerical analysis the relationship of the modulation broaden index with modulation index using high-order-harmonic detection is investigated. Using the voltage modulation the 2f,4f and 6f harmonic signals about the reflection spectroscopy of 6S1/2(F = 4) →6P3/2 transition of the cesium D2 line are also be measured. The experimental results are in good agreement with the theoretical predictions. It is found that narrower line-width can be achieved by higher-harmonic detection than the line-width detected by direct absorption when the modulation index is smaller than 1.81, 2.98 and 4.14 for 2f, 4f, and 6f signals, respectively.     

《近代物理学中重大发现的再探索》连载④——原子的指纹

以现代的观点与工具重建了原子光谱一般规律的发现过程,通过案例具体介绍了归纳、整理科学事实的常用方法.     

Fermi gas of atoms

A rapidly developing field, experimental physics of ultracold gases of Fermi atoms, is briefly reviewed. The contribution of this field to fundamental physics is shown along with connection to other fields which explore systems of Fermi particles. The basic parameters of atomic Fermi gas are described together with its unique properties and advantages and disadvantages in comparison to other Fermi systems. The prospects of this field and its short history are considered. Research groups working in this field are listed.     

Polarizability of alkali atoms

The scalar and tensor components of static polarizability of alkali atoms Na, K, and Rb were calculated. The results were compared with available theoretical and experimental data.     

Photoionization of onion-type atoms

The photoionization of a two-shell (“onion“) endohedral A@C_N1@C_N2 is considered. The effect of the fullerenes shells upon photoelectron from atom A is taken into account substituting the action of the fullerene by two zero-thickness “bubble potentials.“ The fullerenes shells polarization is included assuming that the radius of the outer shell R ₂ is much bigger than the inner R ₁ and both much exceed the atomic radius r. The interaction between shells C_N1 and C_N2 is taken into account in the Random Phase Approximation (RPA). The effect of photoelectron scattering by both “bubble potentials“ is included in the RPA frame. As concrete examples, two endohedrals Ar@C₆₀@C₂₄₀ and Xe@C₆₀@C₂₄₀ are considered. We investigate 3p4 Ar and 5p Xe subshells.     

Magnetic supersusceptibility of atoms

Analytical expressions are obtained for supersusceptibility of atoms with filled shells in a uniform magnetic field harmonically depending on time. Dynamic and static supersusceptibilities are calculated for He, Be, and Ar in the Hartree-Fock approximation and in the random phase and exchange method (RPAE).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 46–54, October, 1976.