Perturbative QCD and the exclusive decay of heavy quarkonium into a photon and two mesons

We consider the radiative decays of the ³S₁ ground state Q$\text{Q}$ into a real photon and two light pseudoscalar or vector mesons. For sufficiently large mass of the heavy quark Q, the decay, e.g. ? → γππ, can be calculated in perturbative QCD, provided that the photon does not carry away a predominant fraction of the available energy. We present differential and integrated Dalitz plot distributions and, for quarkonium states produced with transverse polarization in e⁺e^? annihilation, angular distributions of the orientation of the decay triangle relative to the beam direction.     

Measurement of the 85Rb(γ, n)84mRb cross-section in the energy range 10-19 MeV with bremsstrahlung photons

We study the charmonium 2S states ??? and ??? _c , and the bottomonium 2S states ???? and ??? _b , using the light-front quark model and the 2S state wave function of harmonic oscillator as the approximation of the 2S quarkonium wave function. The decay constants, transition form factors and masses of these mesons are calculated and compared with experimental data. Predictions of quantities such as Br(???????? _c ) are made. The 2S wave function may help us learn more about the structure of these heavy quarkonia.     

Survival of B c mesons in a hot plasma within a potential model

We extend a previous work on the study of heavy charmonia and bottomonia in a deconfined quark-gluon plasma by considering the B _c family of mesons. With the introduction of this bound state of a charm and a beauty quark, we investigate at finite temperature the behavior of the quarkonium, in an energy region between the ψ and the Y states.     

A string-breaking model of heavy meson decays

Within QCD, heavy quarkonia are viewed as a quark antiquark pair bound by a narrow chromoelectric flux tube. This flux can create light quark antiquark pairs accounting for the decay into mesons with heavy quantum numbers. This model is shown to be as consistent with current data on charmonium decays intoD-meson pairs and upsilon decay to \(B\bar B\) , as is the physically less appealing³ P ₀ model.     

QCD sum rules and radial excitations of light pseudoscalar and scalar mesons

The calculations of masses and decay constants of the radial excitations of light pseudoscalar and scalar mesons within the QCD sum rules method are briefly reviewed. The predictions are based on the 1/N _c -supported model spectra, which consist of an infinite number of infinitely narrow resonances, and on the assumption that the ground states of light scalar mesons may be considered as \(\bar qq\)-bound states. The results of the studies are compared with the existing experimental data and with the predictions of other theoretical approaches.     

Gluonic corrections to the decay rate of heavy quarkonium states into lepton pairs

We calculate one-gluon corrections to the decay rate of heavy quarkonium states into lepton pairs. We find that the correction due to one-gluon exchange is not very significant for charmonium, and for practical purposes only the relativistic kinematical effects need to be taken into account. For theY family the gluonic corrections are, relatively, of greater importance.     

The problem of radial excitations of light mesons and interpretation of the iota-meson

Radial (L=0) excitations of light (including strange) mesons are considered in the framework of the quark phenomenological model. The predicted spectrum of excitations is compared with experimentally observed resonances. The dependence of energy levels on quark masses is pointed out which explains the nearness of ρ (1600) and ? (1680) resonances. The possibility of interpreting the τ (1440)-resonance as a radial excitation of η (549) and η′ (958) mesons is analysed. The position of now unobserved states is calculated and proposed for the experimental check of the spectrum of radial excitations of light mesons.     

D→PS decays and the effective chiral Lagrangian for heavy and light mesons

Experimentally measuredD→PS decay rates are investigated using an effective chiral Lagrangian containingD mesons, light pseudoscalars and light scalars resonances. The strong and weak couplings of the scalar mesons toD mesons are introduced and predictions for unmeasuredD→PS branching ratios are made.     

Study of the heavy molecular states in the quark model with meson exchange interaction

Some charmonium-like resonances such as X(3872) can be interpreted as possible D^(*)D^(*) molecular states. Within the quark model, we study the structure of such molecular states and the similar B^(*)D^(*) molecular states by taking into account the light meson exchange (π, η, ρ, ω and σ) between two light quarks from different mesons.     

Meson wave functions and SU(3) symmetry breaking

The wave functions of the pseudoscalar and vector mesons (K, ?, K¹, ?) are found using the QCD sum rules and are used for the calculation of the heavy quarkonium two-particle decay widths.     

Radiative decays of quarkonia into Goldstone fermions

We consider the decay of³ S ₁ quarkonia into a photon and two Goldstone fermions in a model realizing supersymmetry in a nonlinear way. We derive a lower bound of 3.5 GeV for the scale of spontaneous supersymmetry breaking from Υ-decays. We show that the decay of a³ S ₁ quarkonium into two Goldstone fermions is forbidden in the order we consider.     

Associated neutrino mixing and neutrino oscillations in left-right electro weak gauge theory

The rare electromagnetic decay of a neutral pseudoscalar meson into a lepton pair is calculated in a bound state quark model. For heavy mesons, the leading QCD diagram is argued to be dominant allowing higher order QCD corrections to be neglected for the branching ratio of this decay to the two-photon decay. The experimentally interesting case of pion decay is treated separately, and the rates for competing processes (weak neutral currents, axions, technicolour ...) are estimated. We conclude that existing data may well allow for such contributions.     

Masses and electroweak properties of light mesons in the relativistic quark model

The masses, pseudoscalar and vector weak decay constants and electromagnetic form factors of light S-wave mesons are studied in the framework of the relativistic quark model based on the quasipotential approach. We use the same model assumptions and parameters as in our previous investigations of heavy meson and baryon properties. The masses and wave functions of the ground state and radially excited π, ρ, K, K^* and φ mesons, obtained by solving numerically the relativistic Schrödinger-like equation with the complete relativistic qq? potential including both spin-independent and spin-dependent terms, are presented. Novel relativistic expressions for the weak decay constants of the pseudoscalar and vector mesons are derived. It is shown that the intermediate negative-energy quark states give significant contributions which essentially decrease the decay constants bringing them in agreement with experimental data. The electromagnetic form factors of the pion, charged and neutral kaon are calculated in a broad range of the space-like momentum transfer. The corresponding charge radii are determined. All results agree well with the available experimental data.     

Meson decays in the non-relativistic quark model

Treating light as well as heavy pseudoscalar and vector mesons as non-relativistic quarkonia, we calculate various decay modes, including lowest QCD corrections. All decay modes studied are in good agreement with experiment, indicating that the quarkonium treatment is applicable to light mesons η, η′, π, also. Consistency of the quarkonium and current algebra treatments for the process π⁰ → 2λ leads to $\text{f}{}_{\mathrm{\pi }}\text{= (}\text{3}\text{2π}\text{)m}{}_{\mathrm{<mtext>u</mtext>}}\text{{1 ? (0.62/4π)α}{}_{\mathrm{<mtext>s</mtext>}}\text{(μ)},}\text{where}\text{m}{}_{\mathrm{<mtext>u</mtext>}}$ is the constituent u-quark mass, and $\text{f}{}_{\mathrm{\pi }}\text{? 93}\text{MeV}$.     

The puzzle of the D and D<Subscript>s</Subscript> mesons

We present a theoretical framework that accounts for the new D_J and D_sJ mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional P-wave quark-antiquark states and four-quark components. The narrowest states are basically P-wave quark-antiquark mesons, while the dominantly four-quark states are shifted above the corresponding two-meson threshold. We study the electromagnetic decay widths as basic tools to scrutiny their nature.     

坐标空间中构造的Breit夸克势与介子和夸克偶素的质量劈裂

构造夸克间的有效的相互作用势函数是强子物理中的重要研究课题,也是学科前沿问题之一.本文对坐标空间中的Breit夸克势函数的完整形式实施消除奇异因子的替代方法,构造出一个有效的夸克势.除了第一项库仑势和第七项常数项势,对其他的项都需进行重新构造,即对第二项和第四项做δ(r)→μ~3e~(-μr)/8π替代,对第三项做1/r→(1-e-μr)/r替代,对第五项和第六项做1/r~3→1-(1+μr)e~(-μr)/r~3替代,由此重新构造出新的势函数,然后用来计算质量劈裂,检验构造势的有效性.为此计算了一组含重介子和夸克偶素的质量劈裂.计算中屏蔽质量μ不是简单的常数,而是取与夸克质量m_i,m_j有关的变量.研究计算发现,只有当屏蔽质量μ取为关于夸克平均质量μ_a=(m_i+m_j)/2的洛朗级数形式μ=c_(-3)(μ_a+0.512)-3+c_(-2)(μ_a+0.512)~(-2)+c_(-1)(μ_a+0.512)~(-1)+c_0+c_1(μ_a+0.512)时重介子η_c-J/ψ,η_b-Υ(1s),还有χ_(c0)-χ_(c1)-χ_(c2)等的夸克偶素之间质量劈裂精确达到实验值,同时其他介子尤其是6个D介子质量精度都比以往得到较大幅度的改善.因此,本文构造出一个有效的夸克势模型.     

Fine-hyperfine structures ofc\bar c andb\bar b systems in a non-relativistic Hulthen plus linear potentialsystems in a non-relativistic Hulthen plus linear potential

The heavy mesons of the charmonium and upsilon family are described in an alternative static potential model chosen in a combination of Hulthen and linear potential. We find that the quark-confining potential in the form of an equal admixture of vector and scalar parts successfully explains the fine-hyperfine structures of \(c\bar c\) and \(b\bar b\) systems in a flavour-independent manner. The leptonic decay widths of the vector mesons ofψ and γ families are calculated taking into account the Poggio-Schnitzer correction. We obtain some of the bound states of the yet-to-be observed \(t\bar t\) system for thet-quark mass ranging from 50 to 200 GeV.     

Semileptonic Decays of Heavy Mesons to Light Pseudoscalar Mesons in the BS Formalism

The decay processes from heavy to light pseudoscalar mesons such as π, K, η,η' are studied in a relativistic constituent quark model based on the BS formalism. It is emphasized that the negative energy projector operators's contributions in the BS wavefunctions for light pseudoscalar mesons have to be considered. By taking into account these contributions, the previously encountered difficulties in calculating the decay constants and form factors are found to be removed. A11 the form factors for transitions such as D→π, D→K, D_s→K, D_s→η, D_s→η', B→π, B_s→K are estimated and the branching ratios for these semileptonic decays are calculated. The results of our calculations are consistent with experimental values.