Radiative scalar-meson decays f0(980) → ρ(ω)γ and a0(980) → ρ(ω)γ within the local Nambu-Jona-Lasinio model

The widths with respect to the radiative decays f ₀(980) → ργ and a ₀(980) → ωγ were calculated within the local Nambu-Jona-Lasinio model. The contributions of both quark and meson loops were taken into account. The latter and the former play a dominant role for the radiative decays of, respectively, the f ₀(980) and the a ₀(980) meson.     

Solvent effects on the S0→S2 absorption spectra of β-carotene

Absorption spectra of β -carotene in 31 solvents are measured in ambient conditions. Solvent effects on the 0--0 band energy, the bandwidth, and the transition moment of the S₀ → S₂ transition are analysed. The discrepancies between published results of the solvent effects on the 0--0 band energy are explained by taking into account microscopic solute-solvent interactions. The contributions of polarity and polarizability of solvents to 0--0 band energy and bandwidth are quantitatively distinguished. The 0--0 transition energy of the S₂ state at the gas phase is predicted to locate between 23000 and 23600~cm^-1.     

Near-threshold production of a0(980) mesons in πN and NN collisions and a0-f0 mixing

We consider near-threshold a ₀(980)-meson production in πN and NN collisions. An effective Lagrangian approach with one-pion exchange is applied to analyze different contributions to the cross section for different isospin channels. The Reggeon exchange mechanism is also evaluated for comparison. The results from πN reactions are used to calculate the contribution of the a ₀ meson to the cross sections and invariant mass distributions of the reactions and pp → ppK ⁺ K ⁻. It is found that the experimental observation of a ₀ ⁺ mesons in the reaction is much more promising than the observation of a ₀ ⁰ mesons in the reaction pp → ppK ⁺ K ⁻. Effects of isospin violation in the reactions pN → da ₀, pd → ³He(³H)a ₀, and dd → ⁴Hea ₀, which are induced by a ₀(980)-f ₀(980) mixing, are also analyzed. From Yadernaya Fizika, Vol. 66, No. 1, 2003, pp. 155–174. Original English Text Copyright ? 2003 by Kondratyuk, Bratkovskaya, Grishina, Büscher, Cassing, Str?her. This article was submitted by the authors in English.     

显微光谱研究半绝缘GaAs带边以上E0+Δ0光学性质

通过显微光致发光技术和显微拉曼(Raman)技术研究了半绝缘GaAs (SI-GaAs)晶体的带边附近的发光. 在光荧光谱中，观察到在高于GaAs带边0.348eV处有一个新的荧光峰. 结合Raman谱指认此发光峰来源于GaAs的E₀＋Δ₀能级的非平衡荧光发射. 同时, 通过研究E₀＋Δ₀能级的偏振、激发光强度依赖关系，以及温度依赖关系说明E₀＋Δ₀能级与带边E₀共享了共同的导带位置Γ₆，同时这也说明在GaAs中主要是导带的性质决定了材料的光学行为.同时，通过与n-GaAs和δ掺杂GaAs相比较，半绝缘GaAs晶体的E₀＋Δ₀能级的发光峰更能反映GaAs电子能级高临界点E₀＋Δ₀的能量位置和物理性质. 研究结果说明显微光致发光技术是研究半导体材料带边以上能级光学性质的一种非常有力的研究工具. 关键词： 半绝缘GaAs 显微光致发光 自旋轨道分裂     

2γ decays of scalar mesons (σ(600), f0(980), and a0(980)) in the Nambu-Jona-Lasinio model

The two-photon decay widths of scalar mesons σ(600), f ₀(980), and a ₀(980) are calculated in the framework of the local Nambu-Jona-Lasinio model. The contributions of the quark loops (Hartree-Fock approximation) and the meson loops (next 1/N _c approximation, where N _c is the number of colors) are taken into account. These contributions, as we show, are the values of the same order of magnitude. For the f ₀ decay the K-loop contribution turns out to play the dominant role. The results are in satisfactory agreement with modern experimental data.     

Quark-gluonium content of the scalar-isoscalar states f0(980), f0(1300), f0(1500), f0(1750), and f0(1420 ?70+150 ) from hadronic decays

On the basis of the decay couplings f ₀ → ππ, K , ηη, ηη′ found earlier in the study of analytical (IJ ^PC =00⁺⁺) amplitude in the mass range 450–1900 MeV, we analyze the quark-gluonium content of the resonances f ₀(980), f ₀(1300), f ₀(1500), and f ₀(1750) and the broad state f ₀(1420 ₋₇₀ ⁺¹⁵⁰ ). The K-matrix technique used in the analysis makes it possible to evaluate the quark-gluonium content both for the states with switched-off decay channels (bare states, f ₀ ^bare ) and for the real resonances. We observe a significant change in the quark-gluonium composition in the evolution from bare states to real resonances, which is due to the mixing of states in the transitions f ₀(m ₁) → real mesons → f ₀ (m ₂) responsible for the decay processes as well. For f ₀(980), the analysis confirmed the dominance of q component, thus proving the n /s composition found in the study of the radiative decays. For the mesons f ₀(1300), f ₀(1500), and f ₀(1750), the hadronic decays do not allow one to determine uniquely the n , s , and gluonium components, providing relative percentage only. The analysis shows that the broad state f ₀(1420 ₋₇₀ ⁺¹⁵⁰ ) can mix with the flavor singlet q component only, which is consistent with gluonium origin of the broad resonance. From Yadernaya Fizika, Vol. 66, No. 4, 2003, pp. 772–785. Original English Text Copyright ? 2003 by Anisovich, Nikonov, Sarantsev. This article was submitted by the authors in English.     

Upper limit for the Ξ0→Σ0γ radiative decay

We report here a new measurement of the upper limit for the branching ratio of the radiative weak decay Ξ⁰→Σ⁰γ of < 8.0×10⁻³ at the 90% confidence level. This is more than an order of magnitude less than previous limits and consistent with rates from similar decays.     

Determination of the 1S0 neutron-neutron scattering length in the nd breakup reaction at energies in the range En = 40?60 MeV

The first results are obtained in a kinematically complete experiment devoted to measuring the n + d → p + n + n reaction yield at energies in the range E _n = 40−60 MeV and various angles of divergence of two neutrons (Δθ = 4°, 6°, and 8°) in the geometry of neutron-neutron final-state interaction. The ¹ S ₀ neutron-neutron scattering length a _nn is determined by comparing the experimental energy dependence of the reaction yield with the results of a simulation in the Watson-Migdal approximation, which depend on a _nn . For E _n = 40 MeV and Δθ = 6° (the best statistics in the experiment), the value a _nn = −17.9 ± 1.0 fm was obtained. A further improvement of the experimental accuracy will make it possible to remove the existing disagreement of the results from different experiments.     

Scalar mesons in the decays η′ → 3π0 and η′ → π0π+π?

The decays η → 3π ⁰ and η → π ⁰ π ⁺ π ⁻ are considered within the isobar model. It is shown that, in order to explain the branching ratio and the shape of the Dalitz plot for the decay η′ → 3π ⁰, it is sufficient to take into account the contributions of the σ and a ₀ mesons. The inclusion of the σ meson is necessary for reproducing the shape of the distribution over the Dalitz plot. The branching ratio for the decay η′ → π ⁰ π ⁺ π ⁻ is obtained. The predictions for the distributions over the Dalitz plot for this decay are presented. These predictions depend strongly on model parameters.     

ρ(ω) → π0π0γ, ρ(ω) → ηπ0γ decays in the local quark Nambu-Jona-Lasinio model

The branching ratios and photon spectra of the rare processes ρ(ω) → π ⁰ π ⁰ γ, ρ(ω) → ηπ ⁰ γ are calculated in the framework of the standard local quark Nambu-Jona-Lasinio model. Three types of diagrams are considered: the quark box and the pole diagrams with scalar (σ, α ₀(980)) and vector (ρ, ω) mesons. The obtained estimates for the widths of the processes ρ(ω) → π ⁰ π ⁰ γ are in satisfactory agreement with existing experimental data. Predictions are made for the widths of the processes ρ(ω) → ηπ ⁰ γ. The text was submitted by the authors in English.     

单壁手性碳纳米管Γ点E1和E2振动模式

在卷曲法计算得到的单壁碳纳米管12个非简并的本征频率与手性和管径关系的基础上，继续讨论了简并的本征频率中E₁和E₂的振动模式，以及其频率与手性和管径的关系. 关键词： 单壁碳纳米管 手性管 振动模式.     

Cavity enhanced absorption spectroscopy measurements of?pressure-induced broadening and shift coefficients in?the?υ1+υ3 combination band of ammonia

Cavity enhanced absorption spectroscopy is performed using an external cavity diode laser operating around 1516 nm. We demonstrate a sensitivity of 6×10⁻⁸ cm⁻¹ Hz^−1/2 and utilise a simple method to measure pressure-induced broadening and shift coefficients. The broadening and shift coefficients for six gases (helium, neon, argon, xenon, oxygen and nitrogen) have been determined at room temperature for four transitions in the υ ₁+υ ₃ combination band of ammonia. Comparisons of the broadening coefficients with previous work in this region, where it exists, show good agreement. The broadening and shift coefficients of nitrogen and oxygen are also in good agreement with calculated values using the Robert and Bonamy theory. Both the broadening and shift coefficients show a clear trend through the rare gases, which can be explained in terms of the varying magnitude of the long range attractive forces operating between the colliding partners. We also demonstrate the application of the Parmenter–Seaver formalism to estimate the potential well depth of the ammonia dimer from the obtained broadening coefficients. The obtained well depth agrees well with theoretical calculations.     

On the possibility to measure the π0→γγ decay width and the γ?γ→π0 transition form factor with the KLOE-2 experiment

A possibility of KLOE-2 experiment to measure the width \varGamma_{p⁰ ?gg}\varGamma_{\pi^{0} \to\gamma\gamma} and the π ⁰ γγ ^∗ form factor F(Q ²) at low invariant masses of the virtual photon in the space-like region is considered. This measurement is an important test of the strong interaction dynamics at low energies. The feasibility is estimated on the basis of a Monte-Carlo simulation. The expected accuracy for \varGamma_{p⁰ ?gg}\varGamma_{\pi^{0} \to\gamma\gamma} is at a per cent level, which is better than the current experimental world average and theory. The form factor will be measured for the first time at Q ²≤0.1 GeV² in the space-like region. The impact of these measurements on the accuracy of the pion-exchange contribution to the hadronic light-by-light scattering part of the anomalous magnetic moment of the muon is also discussed.     

The first high-resolution infrared study of diazirinone, N2CO: Analysis of the Fermi-coupled ν1 and 2ν5 bands

The first validated detection of the elusive diazirinone molecule (N₂CO) in the gas phase was performed using high-resolution infrared spectra recorded in the 1810–2100 cm⁻¹ region. The ν₁ and 2ν₅ bands were identified at 2043.8 and 1863.3 cm⁻¹ close to the ab initio prediction [X.Q. Zeng, H. Beckers, H. Willner, J.F. Stanton, Angew. Chem. Int. Ed. 50 (2011) 1720–1723]. For these two bands, the individual lines exhibit a (2:1) intensity alternation, confirming a three membered ring structure (C_2V symmetry) for N₂CO. The major output of the ν₁ and 2ν₅ bands analysis is the first experimental determination of the ground-state rotational constants of cyclic N₂CO. The observed intensity pattern of the ν₁ and 2ν₅ bands is in agreement with the existence of a strong Fermi resonance coupling the 1¹ and 5² energy levels.     

Rovibrational constants for the ground state and ν8 = 1 state of ethylene-d3 (C2HD3) by high-resolution FTIR spectroscopy

The Fourier transform infrared (FTIR) spectrum of the ν₈ fundamental band of ethylene-d₃ (C₂HD₃) was recorded with a unapodized resolution of 0.0063 cm⁻¹ in the wavenumber region of 840–980 cm⁻¹. By assigning and fitting a total of 738 infrared transitions using a Watson’s A-reduced Hamiltonian in the I^r representation, rovibrational constants for the upper state (ν₈ = 1) up to all five quartic centrifugal distortion terms were derived for the first time. The root-mean-square (rms) deviation of the fit was 0.00076 cm⁻¹. The ground state rovibrational constants of C₂HD₃ were also determined for the first time by a fit of 450 combination-differences from the present infrared measurements, with rms deviation of 0.00075 cm⁻¹. Local frequency perturbations were not detected in the C-type ν₈ band of C₂HD₃ which is centred at 918.73199 ± 0.00007 cm⁻¹.     

Infrared diode laser spectroscopy of the ν3 fundamental band of the PO2 free radical

The asymmetric stretching fundamental of the PO₂ free radical in its ground electronic state has been measured between 1280 and 1360 cm⁻¹ using diode laser absorption spectroscopy. This new data set has been combined in a fit with an earlier, smaller infrared data set and with pure rotational transitions measured by microwave and laser magnetic resonance spectroscopies to provide a new set of parameters for the ground and ν₃ = 1 states of A₁ PO₂. These parameters can be used to calculate line positions in this band for transitions up to N = 50.     

Novel insights into the γγ?→π0 transition form factor

BaBar’s observation of significant deviations of the pion transition form factor (TFF) from the asymptotic expectation with Q ²>9 GeV² has brought about a serious crisis to the fundamental picture established for such a simple q[`(q)]q\bar{q} system by perturbative QCD, i.e. the dominance of collinear factorization at high momentum transfers for the pion TFF. We show that non-factorizable contributions due to open flavors in γγ ^∗→π ⁰ could be an important source that contaminates the pQCD asymptotic limit and causes such deviations with Q ²>9 GeV². Within an effective Lagrangian approach, the non-factorizable amplitudes can be related to intermediate hadron loops, i.e. K ^(∗) and D ^(∗) etc., and their corrections to the π ⁰ and η TFFs can be estimated.     

Chiral symmetry amplitudes in the S-wave isoscalar and isovector channels and the σ, f0(980), a0(980) scalar mesons

We use a non-perturbative approach which combines coupled channel Lippmann-Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the σ, f₀ and a₀ resonances. The ππ → ππ, phase shifts and inelasticities in the T = 0 scalar channel are well reproduced as well as the π⁰η and mass distributions in the T = 1 channel. Furthermore, the total and partial strong decay widths of the f₀ and a₀ resonances are properly reproduced. The results seem to indicate that chiral symmetry constraints at low energy and unitarity in coupled channels is the basic information contained in the meson-meson interaction below GeV.     

Magnetooptics of the 1D2 → 3F4 radiative transition in thulium:yttrium-aluminum garnet Tm3+:YAG

The spectra of luminescence and magnetic circular polarization of luminescence in the ¹ D ₂ → ³ F ₄ emission band in thulium:yttrium-aluminum garnet Tm³⁺:YAG (Tm³⁺:Y₃Al₅O₁₂) have been investigated at temperatures T = 78 and 293 K, respectively. Based on the analysis of the magnetooptical and optical spectra, the optical transitions between the Stark sublevels of the ³ F ₄ and ¹ D ₂ multiplets in Tm³⁺:YAG were identified. It is shown that the symmetry and energies of the Stark sublevels of the ³ F ₄, ¹ D ₂, and ³ H ₆ multiplets, found experimentally from magnetic and magnetooptical studies, confirm the results of theoretical calculations of the energy spectrum of the rare earth Tm³⁺ ion in YAG. Original Russian Text ? U.V. Valiev, J.B. Gruber, I.R. Gapdulkhakov, N.I. Juraeva, A.K. Mukhammadiev, Sh.A. Rakhimov, I.S. édel’man, 2009, published in Optika i Spektroskopiya, 2009, Vol. 106, No. 6, pp. 937–944.