Di-jet production in γ γ collisions at LEP2

The production of two high-p _T jets in the interactions of quasi-real photons in e ⁺ e ⁻ collisions at from 189 GeV to 209 GeV is studied with data corresponding to an integrated e ⁺ e ⁻ luminosity of 550 pb⁻¹. The jets reconstructed by the k _⊥ -cluster algorithm are defined within the pseudo-rapidity range −1<η<1 and with jet transverse momentum, p _T , above 3 GeV/c. The differential di-jet cross-section is measured as a function of the mean transverse momentum of the jets and is compared to perturbative QCD calculations. Deceased     

Strong decays Σ*→Σπ,Λπ and related strong coupling constant

We calculate the strong coupling constant g among the decuplet baryons, the octet baryons and the pseudoscalar mesons in the heavy baryon chiral perturbation theory with the light-cone QCD sum rules, and we study the strong decays Σ ^*→Λ π,Σ π. The numerical value of the strong coupling constant g is consistent with our previous calculation; the central values lead to small SU(3) breaking effects, less than 6%; and no definitive conclusion can be drawn due to the large uncertainties.     

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.     

High-intensity and high-brightness source of moderated positrons using a brilliant γ beam

Presently, large efforts are conducted toward the development of highly brilliant γ beams via Compton back scattering of photons from a high-brilliance electron beam, either on the basis of a normal-conducting electron linac or a (super-conducting) Energy Recovery Linac (ERL). Particularly, ERLs provide an extremely brilliant electron beam, thus enabling the generation of highest-quality γ beams. A 2.5 MeV γ beam with an envisaged intensity of 10¹⁵ photons s⁻¹, as ultimately envisaged for an ERL-based γ-beam facility, narrow band width (10⁻³), and extremely low emittance (10⁻⁴ mm² mrad²) offers the possibility to produce a high-intensity bright polarized positron beam. Pair production in a face-on irradiated W converter foil (200 μm thick, 10 mm long) would lead to the emission of 2×10¹³ (fast) positrons per second, which is four orders of magnitude higher compared to strong radioactive ²²Na sources conventionally used in the laboratory. Using a stack of converter foils and subsequent positron moderation, a high-intensity low-energy beam of moderated positrons can be produced. Two different source setups are presented: a high-brightness positron beam with a diameter as low as 0.2 mm, and a high-intensity beam of 3×10¹¹ moderated positrons per second. Hence, profiting from an improved moderation efficiency, the envisaged positron intensity would exceed that of present high-intensity positron sources by a factor of 100.     

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.     

Constraints of ξ-moments computed using QCD sum rules on piondistribution amplitude models

To date, the behavior of the pionic leading-twist distribution amplitude (DA) \begin{document}$ \phi_{2;\pi}(x,\mu) $\end{document} \begin{document}$ - $\end{document}which is a universal physical quantity and is introduced into high-energy processes involving pions based on the factorization theorem\begin{document}$ - $\end{document} is not completely consistent. The form of \begin{document}$ \phi_{2;\pi}(x,\mu) $\end{document} is usually described by phenomenological models and constrained by the experimental data on exclusive processes containing pions or the moments computed using QCD sum rules and the lattice QCD theory. Evidently, an appropriate model is extremely important to determine the exact behavior of \begin{document}$ \phi_{2;\pi}(x,\mu) $\end{document}. In this paper, by adopting the least squares method to fit the ξ-moments calculated using QCD sum rules based on the background field theory, we perform an analysis on several commonly used models of the pionic leading-twist DA in the literature; these include the truncation form of the Gegenbauer polynomial series, the light-cone harmonic oscillator model, the form extracted from the Dyson-Schwinger equations, the model from the light-front holographic AdS/QCD, and a simple power-law parametrization form.     

Learning about flavour structure from τ→eβγ and μ→eγ?

Current and upcoming experiments should improve the sensitivity to e _α →e _β γ decays by an order of magnitude. This paper assumes that one of the τ→e _β γ decays is observed, and explores the structure and consequences of the required new flavoured couplings. In simple models (a low-scale seesaw, leptoquarks) it is shown that the dipole vertex function is proportional to a product of flavoured matrices from the Lagrangian (a “Jarlskog-like” invariant), provided that the loop particles are weakly coupled to the Higgs. Secondly, if the dipole vertex function has a hierarchical structure, this might imply that only some of the τ→e _β γ modes can be observed, due to the “approximate zero” implied by the bound on μ→eγ. The assumptions underlying this potential test of a hierarchical structure are discussed.     

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.     

Rare decays of Λ b → Λ γ and Λ b → Λ l + l ? in universal extra-dimension model

The exclusive weak decay of Λ _b →Λ γ and Λ _b →Λ l ⁺ l ⁻ are investigated in the Appelquist–Cheng–Dobrescu model, which is an extension of the standard model in the presence of universal extra dimensions. Employing the transition form factors obtained in the light-cone sum rules, we analyze how the invariant-mass distribution, the forward–backward asymmetry and the polarization asymmetry of the Λ baryon of these decay modes can be used to constrain the only additional free parameter with respect to the standard model, namely, the radius, R, of the extra dimension. Our results indicate that the Kaluza–Klein modes can lead to approximately 25% suppression of the branching ratio of Λ _b →Λ γ; however, their contributions can bring about 10% enhancement to the decay rate of Λ _b →Λ l ⁺ l ⁻. It is shown that in the present scenario the zero position of the forward–backward asymmetry of Λ _b →Λ μ ⁺ μ ⁻ is sensitive to the compactification parameter R, while the measurement of polarizations of Λ baryon in the Λ _b decays are not a useful tool to provide any valuable information for the universal extra-dimension model.     

Theoretical predictions on α-decay properties of some unknown neutron-deficient actinide nuclei using machine learning

Neutron-deficient actinide nuclei provide a valuable window to probe heavy nuclear systems with large proton-neutron ratios. In recent years, several new neutron-deficient Uranium and Neptunium isotopes have been observed using α-decay spectroscopy [Z. Y. Zhang et al., Phys. Rev. Lett. 122, 192503 (2019); L. Ma et al., Phys. Rev. Lett. 125, 032502 (2020); Z. Y. Zhang et al., Phys. Rev. Lett. 126, 152502 (2021)]. In spite of these achievements, some neutron-deficient key nuclei in this mass region are still unknown in experiments. Machine learning algorithms have been applied successfully in different branches of modern physics. It is interesting to explore their applicability in α-decay studies. In this work, we propose a new model to predict the α-decay energies and half-lives within the framework based on a machine learning algorithm called the Gaussian process. We first calculate the α-decay properties of the new actinide nucleus \begin{document}$ {}^{214}{\rm{U}}$\end{document}. The theoretical results show good agreement with the latest experimental data, which demonstrates the reliability of our model. We further use the model to predict the α-decay properties of some unknown neutron-deficient actinide isotopes and compare the results with traditional models. The results may be useful for future synthesis and identification of these unknown isotopes.     

ω(→ π+π?π0) meson photoproduction on proton

The cross-section for the π ⁺ π ⁻ π ⁰ invariant mass distribution in the γp reaction in the GeV region is calculated. This reaction is assumed to proceed through the formation of the ω-meson in the intermediate state, because the production cross-section for this meson in the γp reaction in the GeV region is significant and it has a large branching ratio (88.8%) in the π ⁺ π ⁻ π ⁰ channel. The cross-sections for this reaction are calculated using the energy-dependent reaction amplitude, f _γp→ωp(0), extracted from the latest ω-meson photoproduction data. We use established procedure to calculate other factors, like width and propagator of the ω-meson, so that our calculation can provide reliable cross-section. The calculated results reproduce the measured π ⁺ π ⁻ π ⁰ invariant mass distribution spectra in the γp reaction.     

Simulation study of χc→J/Ψ+γ detection with J/Ψ→e+e? in pp collisions in the ALICE experiment at LHC

We present Monte Carlo preliminary results about the feasibility to detect the χ _c family in p-p collisions at 14 TeV in the ALICE Central Barrel at CERN LHC. The χ _c1 and χ _c2 were forced to decay in the radiative channel J/Ψ+γ→e ⁺ e ⁻+γ and were merged with a proton-proton non-biased collision. After Monte Carlo transport and simulation of the detector response, the e ⁺, e ⁻ and converted γ were reconstructed and identified in the ALICE ITS, TPC and TRD detectors. Separate signals corresponding to γ from χ _c1 and from χ _c2 were observed. The position and relative weight of the fit to gaussians agreed with the input values within the statistical limits. An erratum to this article can be found at     

基于压缩感知理论的非线性γ谱分析方法

γ谱分析是一种重要的放射性核素定量分析方法. 弱峰的检测和重叠峰的分解是γ 谱分析中的难点. 为了解决这两个问题, 基于压缩感知理论, 提出了一种新的γ 谱分析方法. 这一方法从谱仪对γ 谱调制的物理机理出发, 通过数学建模, 将γ 谱分析转化为一个以真实γ 谱为解的求逆问题, 并在压缩感知理论框架下, 运用γ 谱特征峰的稀疏性, 进行逆问题的求解, 直接获得γ 谱的估计结果. 数值模拟结果和蒙特卡洛模拟结果表明: 该方法能在降低统计涨落的同时, 有效减小谱仪调制带来的能谱展宽, 从而提高γ 谱分析精度. 关键词： γ谱分析')" href="#">γ谱分析 压缩感知 非线性 逆问题     

S wave of pion-pion scattering from data on the reaction π?p → π0π0n

The results of recent experiments performed at KEK, Brookhaven National Laboratory, the Institute for High-Energy Physics (Protvino), and CERN to study the reaction π ⁻ p → π ⁰ π ⁰ n are analyzed in detail. For S-wave pion-pion scattering in the channel of isospin I=0, new data are obtained for the phase shift δ ₀ ⁰ and the inelasticity parameter η ₀ ⁰ . Difficulties that arise in using, for the amplitudes of the S and D waves of the final π ⁰ π ⁰ system, physical solutions selected on the basis of partial-wave analyses are discussed. It is noteworthy that other solutions are preferable in principle in the region of the invariant mass m of the π ⁰ π ⁰ system above 1 GeV. With the aim of clarifying the situation and further studying the properties of the f ₀(980) resonance, it is proposed to perform, in the reaction π ⁻ p → π ⁰ π ⁰ n, an especially careful examination of the m region in the vicinity of the threshold. __________ Translated from Yadernaya Fizika, Vol. 67, No. 7, 2004, pp. 1380–1391. Original Russian Text Copyright ? 2004 by Achasov, Shestakov.     

B meson distribution amplitude from B→γ?ν

We reconsider the utility of the radiative decay B→γℓν with an energetic photon in the final state for determining parameters of the B-meson light-cone distribution amplitude. Including 1/m _b power corrections and radiative corrections at next-to-leading logarithmic order, we perform an improved analysis of the existing BABAR data. We find a provisional lower limit on the inverse moment of the B meson distribution amplitude, λ _B , which, due to the inclusion of radiative and power corrections, is significantly lower than the previous result. More data with large photon energy are, however, required to obtain reliable results, as should become available in the future from SuperB factories.     

Simulation of near-infrared photodiode detectors based on β-FeSi2/4H-SiC heterojunction

In this paper, we propose the near-infrared p-type β-FeSi₂/n-type 4H-SiC heterojunction photodetector with semiconducting silicide (β-FeSi₂) as the active region for the first time. Optoelectronic characteristics of the photodetector are simulated using a commercial simulator at room temperature. The results show that the photodetector has a good rectifying character and a good response to the near-infrared light. Interface states should be minimized to obtain a lower reverse leakage current. The response spectrum of the β-FeSi₂/4H-SiC detector, which consists of a p-type β-FeSi₂ absorption layer with a doping concentration of 1×10¹⁵ cm^-3 and a thickness of 2.5 μm, has a peak of 755 mA/W at 1.42 μm. The illumination of the SiC side obtains a higher responsivity than that of the β-FeSi₂ side. The results illustrate that the β-FeSi₂/4H-SiC heterojunction can be used as a near-infrared photodetector compatible with near-infrared optically-activated SiC-based power switching devices.     

Determination of sin2 θ weff using jet charge measurements in hadronic Z decays

The electroweak mixing angle is determined with high precision from measurements of the mean difference between forward and backward hemisphere charges in hadronic decays of the Z. A data sample of 2.5 million hadronic Z decays recorded over the period 1990 to 1994 in the ALEPH detector at LEP is used. The mean charge separation between event hemispheres containing the original quark and antiquark is measured for and events in subsamples selected by their long lifetimes or using fastD*’s. The corresponding average charge separation for light quarks is measured in an inclusive sample from the anticorrelation between charges of opposite hemispheres and agrees with predictions of hadronisation models with a precision of 2%. It is shown that differences between light quark charge separations and the measured average can be determined using hadronisation models, with systematic uncertainties constrained by measurements of inclusive production of kaons, protons andΛ’s. The separations are used to measure the electroweak mixing angle precisely as sin² ϑ _w ^eff =0.2322±0.0008(exp.stat.) ±0.0007(exp.syst.)±0.0008(sep.). The first two errors are due to purely experimental sources whereas the third stems from uncertainties in the quark charge separations. Supported by Dirección General de Investigación Científica y Técnica, Spain     

γ-射线辐照法制备氧化亚锰/石墨烯复合材料及其储锂性能研究

We report a γ-ray irradiation reduction method to prepare MnO/reduced graphene oxide (rGO) nanocomposite for the anode of lithium ion batteries. γ-Ray irradiation provides a clean way to generate homogeneously dispersed MnO nanoparticles with finely tuned size on rGO surface without the use of surfactant. The MnO/rGO composite enables a fully charge/discharge in 2 min to gain a reversible specific capacity of 546 (mA·h)/g which is 45% higher than the theoretical value of commercial graphite anode.     

Kl3γ+ decays revisited: Branching ratios and T-ODD momenta correlations

We calculate the branching ratios of the K ⁺ → π ⁰ l ⁺ ν _lγ (l = e, μ) decays, and the T-odd triple momenta correlations ξ = q · [p _l × p _π ]/M _K ³, due to the electromagnetic final-state interaction, in these processes. The contributions on the order of ω ⁻¹ and ω ⁰ to the corresponding amplitudes are treated exactly. For the branching ratios, the corrections on the order of ω are estimated and demonstrated to be small. We compare the results with those of other authors. In some cases our results differ considerably from the previous ones.