不同气氛下多孔硅中电子偶素湮没行为研究

使用正电子湮没谱学方法,在不同气氛下对电化学腐蚀法制备的多孔硅中电子偶素的湮没行为进行了系统的研究.正电子湮没寿命谱测试结果表明,样品中存在长达40 ns的电子偶素湮没成分,并且进入多孔硅膜层的正电子约有80%形成电子偶素,具有非常高的电子偶素产额;在氧气气氛下,由于气体导致o-Ps发生自旋转化猝灭是使多孔硅样品中电子偶素寿命缩短的主要原因.结合正电子寿命-动量关联谱测量结果,分析了不同气氛下多孔硅样品中电子偶素湮没寿命及动量变化关系,讨论了多孔硅中电子偶素的湮没机理以及气氛对孔径计算理论模型的影响. 关键词： 电子偶素 正电子湮没谱学方法 多孔硅     

Unified treatment of positron annihilation and positronium formation

The effects of the positron (e(+)) annihilation in e(+) scattering by the H atom are included directly in the Hamiltonian as an absorption potential, and hence the finite lifetimes Gamma(ns) of positronium (Ps) in states ns are automatically taken account of. The Schr?dinger equation is solved using the hyperspherical close-coupling method. The annihilation and Ps formation are shown to be inseparable near the Ps(1s) threshold E(th); Ps formation constitutes just an indirect pathway to annihilation. The annihilation cross section, which would diverge near E(th) if Gamma(1s) were infinite, connects smoothly across E(th) to the cross section for Ps formation, which is meaningful only at energies well above E(th).     

Thep - \bar p decays ofP-wave quarkonium and the helicity characteristics of massless QCD

We consider the exclusive \(p - \bar p\) decays of the quarkoniumP-states. Due to the helicity conservation of massless QCD the \(p - \bar p\) mode is forbidden in this limit for the¹ P ₁ and the³ P ₀ states. The angular distributions for the decays of the remaining states in the cascade \(^3 S\prime _1 \to \gamma ^3 P_J \to \gamma p\bar p\) are specific to QCD and can serve as a test of the theory. The same is true of the formation process \(p\bar p \to ^3 P_J \to ^3 S_1 \gamma \) . In lowest order QCD we obtain overall branching ratios for charmonium of the order of 10^?4.     

Inclusive photoproduction of polarized 3P1 quarkonium

We analyse inclusive photoproduction of polarized ³P₁ quarkonium in the framework of QCD. To separate non-perturbative and perturbative parts in the density matrix of the produced quarkonium we use a method, which is equivalent to the diagrammatic expansion widely used in analyzing deeply inelastic scattering. A systematic expansion in a small velocity v, with which a heavy quark moves inside the quarkonium in its rest frame, is performed for the non-perturbative parts, and they are expressed as matrix elements in non-relativistic QCD. At the leading order of v there are four matrix elements representing non-perturbative physics. The perturbative parts are calculated at the leading order of coupling constants. Some numerical results, especially numerical results for HERA, are given.     

Lifetimes and decays of energy levels in Si and P

The mean lifetimes of 15 levels in ³⁰Si and of 7 levels in ³⁰P have been measured by the Doppler-shift attenuation method. Limits on the lifetimes of a further 8 levels in ³⁰Si and of the 3018 keV level in ³⁰P have been obtained. Branching ratios and excitation energies have been measured in both nuclei. The levels were populated by the reactions ²⁷Al(α, p)³⁰Si and ²⁷Al(α, n)³⁰P at α-particle bombarding energies of 5.0, 6.3 and 8.0 MeV. Theγ-rays were detected with a Ge(Li)-NaI(Tl) escape suppressed and pair escape spectrometer.     

SU(3) analysis of annihilation contributions and CP violating relations in B\to P P decays

Several methods proposed to measure the angle in the KM unitarity triangle assumed that the tree contribution to is purely due to annihilation contributions and is negligibly small. This assumption has to be tested in order to have a correct interpretation of the experimental data. In this paper we show that using SU(3) symmetry, the smallness of the tree contribution can be tested in a dynamic model-independent way. We also derive several relations between CP violating rate differences for decays without assuming the smallness of the annihilation contributions. These relations provide important tests for the standard model of CP violation. Received: 5 January 1999 / Revised version: 4 March 1999 / Published online: 18 June 1999     

Two- and three-point energy correlations in Hadronice + e − annihilation

Correlations between the energies incident on two or three detectors arounde ⁺ e ^? annihilation events are considered as a probe of the QCD structure of the events. Practical methods for deducing two-detector energy correlations (which give the mean product of energies incident on two detectors as a function of their angular separation) from measured events are devised. Analytical formulae for energy correlations from QCD perturbation theory are given, but it is found that large corrections from hadron formation obscure these symptotic predictions at available energies. Correlations between the final state and the incominge ^± beam direction are discussed, and observables are presented which measure the angular distributions of planes of final particles with respect to the beam axis (but do not require explicit determination of the planes). Finally, three-detector energy correlatons and their moments are treated, and methods for investigating planar structures ine ⁺ e ^? annihilation events are devised.     

Electromagnetic annihilation of e+e− into quarkonium states with even charge conjugation

We calculate the production of narrow resonances with even charge conjugation ${}^3\text{P}{}_{\mathrm{J}}\text{=1,2}$ in e⁺e^? annihilation in the quarkonium and vectordominance models. We give unitarity bounds for $\text{Γ(}{}^3\text{P}{}_{\mathrm{J}}\text{→ e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{)}$ in terms of $\text{Γ(}{}^3\text{P}{}_{\mathrm{J}}\text{→ γγ)}$ and $\text{Γ(}{}^3\text{P}{}_{\mathrm{J}}\text{→ e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{)}$. The electromagnetic production dominates through the neutral current at low energies independent of details of the model. For masses above 10 GeV the situation is reversed.     

The magnitude of annihilation and penguin contributions to charm-meson decays

A consistent treatment of color singlet and octet contributions in the spectator constituent gluon model for pseudoscalar meson decays is attempted. The result comes out one order of magnitude too small to explain the observed life-time difference of D⁰ and D⁺. Furthermore, it is found that ‘penguin’ interactions in the annihilation channel may give contributions to the asymmetry of the (D⁰ → K⁺K^?)/(D⁰ → π⁺π^?) ratio of the order of the phase-space difference or larger. Finally, it is argued that annihilation cannot explain the $\text{ΔI =}\text{1}\text{2}$ rule for kaon decays; dynamical effects including the penguin interactions seem still to be needed.     

Time and temperature dependent three-quantum annihilation and lifetime of positronium in alumina powder

The relative three-quantum yieldP ₃ and the lifetime of ortho-positronium generated by alumina fine powders were studied as a function of temperature and of time. A strong variation in theP ₃ value and a constant value of the long lifetime component are interpreted as the existence of two positronium states, one in the interparticle free volume, the second as positronium absorbed to the surface. The latter state is quenched by surface impurities.     

Observation of 1(-)0(-) final states from psi(2S) decays and e(+)e(-) annihilation

Using CLEO data collected from CESR e(+)e(-) collisions at the psi(2S) resonance and nearby continuum at sqrt[s]=3.67 GeV, we report the first significantly nonzero measurements of light vector-pseudoscalar hadron pair production (including rhopi, omegapi, rhoeta, and K(*0)K0 ) and the pi(+)pi(-)pi(0) final state, both from psi(2S) decays and direct e(+)e(-) annihilation.     

Further study of D+ s decays into π-π+π+

A Dalitz plot analysis of the OZI rule violating decay D⁺ _s into π^-π⁺π⁺ is presented using different partial wave approaches. Scalar and vector waves are described by K-matrices; their production is parameterized in a P-vector approach. Alternatively, Breit–Wigner amplitudes and Flatté parametrization are used. Special emphasis is devoted to scalar mesons. The f₀(980) resonance provides the most significant contribution. Adding f₀(1500) to the scalar wave leads to an acceptable fit while introduction of f₀(1370) and/or f₀(1710) does not lead to significant improvements. A scan of the scalar wave optimizes for M=1452 ± 22 MeV/c ². When f₀(1710) is added, the mass uncertainty increases, and the fit yields M=1470 ± 60 MeV/c ² which is fully compatible with the nominal f₀(1500) mass. The scalar wave seems to exhibit a phase motion of 270° units in the mass range from 1200 to 1650 MeV/c ². PACS 11.80.Et; 13.20.Fc; 14.40.Cs