Weak decays of heavy baryons in the light-front approach

In this work, we analyse semi-leptonic and non-leptonic weak decays of the heavy baryons: Λ_b,Ξ_b,?_b and Λ_c,Ξ_c,?_c. For non-leptonic decay modes, we study only the factorizable channels induced by the external Wemission. The two spectator quarks in the baryonic transitions are treated as a diquark and form factors are calculated in the light-front approach. Using the results for form factors, we also calculate some corresponding semi-leptonic and non-leptonic decay widths. We find that our results are comparable with the available experimental data and other theoretical predictions. Decay branching fractions for many channels are found to reach the level 10~(-3)~10~(-2),which is promising for discovery in future measurements at BESIII, LHCb and Belle II. The SU(3) symmetry in semi-leptonic decays is examined and sources of symmetry breaking are discussed.     

层子模型中重子的半轻子衰变和高能中微子反应

本文从层子模型的结构观点出发,应用文献[1]中的层子与轻子的弱相互作用等效哈密顿量和文献[2]中给出的(1/2)⁺重子波函数及文献[3]中定出的参数,对(1/2)⁺重子的半轻子衰变和高能中微子的弹性和准弹性反应进行了讨论。文中得到的(1/2)⁺重子的半轻子衰变的理论结果与实验符合较好;得到的ΔS=0过程的轴矢形状因子和ν_μ+n→p+μ^-过程的截面在误差范围内均与实验相符合;得到的ΔS=1过程的轴矢形状因子和ν_μ+p→Λ+μ⁺过程的截面与目前实验给出的粗略结果也是符合的。特别需要指出的是,本文在讨论反应问题时,理论中所包含的参数全部从电磁过程定出,在给出的轴矢形状因子和截面公式中没有引进新的参数。     

The transition form factors for semi-leptonic weak decays of J/ψ in QCD sum rules

Within the standard model, we investigate the semi-leptonic weak decays of J/ψ. The various form factors of J/ψ making the transition to a single charmed meson (D^(*) _(d,s)) are studied in the framework of QCD sum rules. These form factors fully determine the rates of the weak semi-leptonic decays of J/ψ and provide valuable information on non-perturbative QCD effects. Our results indicate that the decay rate of the semi-leptonic weak decay mode J/ψ→D^(*)- _s+e⁺+ν_e is at the order of 10^-10. PACS 13.20.Gd; 13.25.Gv; 11.55.Hx     

Semi-leptonic weak and electromagnetic interactions in nuclei:: Parity violations in electron scattering and weak neutral currents

A general result for the difference in differential cross sections for electron scattering between any two nuclear levels with incident longitudinally polarized right- and left-handed electrons is derived. This difference must involve the parity-violating weak interaction at least linearly and can be used to study weak neutral currents as pointed out by Feinberg. A V — A structure for the weak neutral currents is assumed with a semi-leptonic current-current interaction, and the electromagnetic interaction is treated in the one-photon-exchange approximation. The result is expressed in terms of the same set of reduced matrix elements of the multipoles of the nuclear currents which govern all electromagnetic and weak transitions between these levels. A previously developed unified analysis of semi-leptonic weak and electromagnetic interactions in nuclei which determines one-body transition densities, including their spin and spatial dependences, through electron scattering provides nuclear transitions to serve as known analyzers in testing the structure of this part of the weak interaction. Examples are given using Weinberg's model of the weak neutral currents. Feinberg's result for elastic scattering from spin-0 nuclei is rederived and two new examples using previously determined one-body densities are discussed : the 1⁺0 → 0⁺1 (3.56 MeV) transition in ⁶Li and the 0⁺0 → 1⁺ 1(15.1 MeV) transition in ¹²C.     

Modulated magnetic phase of structurally heterogeneous easy-plane weak ferromagnets

The modulated magnetic phase of a structurally heterogeneous easy-plane weak ferromagnet is considered in terms of the thermodynamic Landau theory of phase transitions. The temperature and field dependences of the main magnetic order modulation parameters are determined. The results obtained are compared with the experimental data obtained for the orientational phase transition into a modulated magnetic state that occurs in hematite and iron borate crystals doped with diamagnetic ions to create structural heterogeneity. The proposed theoretical model is shown to describe the entire set of experimental results consistently with some exceptions.     

Search for new physics at a super-<Emphasis Type="Italic">B</Emphasis> factory

The importance of a super-B factory in the search for new physics, in particular, due to CP-odd phase(s) from physics beyond the standard model is surveyed. The first point to emphasize is that we now know how to directly measure all three angles of the unitarity triangle very cleanly, i.e. without theoretical assumptions with irreducible theory error ≲1%. However, this requires much more luminosity than is currently available atB-factories. Direct searches via penguin-dominated hadronic modes as well as radiative, pair-leptonic and semi-leptonic decays are also discussed. Null tests of the SM are stressed as these will play a crucial role especially if the effects of BSM phase(s) onB-physics are small.     

A detailed analysis ofD-,D s - andB-meson transition form factors and the determination of |V cb |

We study various transition form factors in semi-leptonic decays ofD-,D _s -,B- andB _s -mesons using the pole dominance assumption. The vector current form factor is found to have only a negligible contribution to the decay rates involving pseudoscalar to vector transitions. In view of this fact we evaluate the form factors from present experimental data on the exclusive semi-leptonic decay rateΓ and the ratioΓ _l /Γ _T of the longitudinal and transverse partial decay rates. Some non-leptonic two-body decay rates are also investigated using the factorization ansatz. Consistency with the semi-leptonic decays is found. The transition form factors of theD- andD _s -mesons are found to contradict the predictions of quark model. In contrast, the experimental data on the transition form factors ofB-mesons are found to be consistent with the quark model predictions. The KM matrix element |V _cb | is determined to be |V _cb |=0.040±0.010, a value somewhat smaller than is usually chosen.     

Formation of local space-charge densities in gas breakdown in magnetic fields

Experimental and theoretical data on the dependence of the delay time of breakdown on the longitudinal and transverse magnetic field strength are given. The theoretical data correlate with the analogous experimental dependence with weak irradiation of the discharge interval. Equivalent-pressure theory gives satisfactory agreement with experiment in the breakdown of atmospheric-pressure gases in a transverse magnetic field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 36–40, May, 1988.     

On the weak decays of high-mass hadrons

Several arguments for the dominance of certain types of non-leptonic weak decays of strange particles are examined for their applicability to high-mass hadrons. Arguments based on asymptotic freedom, duality, current algebra and PCAC, and coloured fermion quarks are all found to be weaker than for strange decays. Specific calculations in the Glashow-Iliopoulos-Maiani charm scheme yield total semi-leptonic decay rates of 20% or more. Estimates of branching ratios for two-body decays of charmed mesons are given, and remarks are made about charmed baryon decays.     

Macroscopic quantum tunnelling in the r.f. SQUID with S-c-S point contacts

Summary The experimental results on quantum decay of metastable flux states in the r.f. SQUID containing different S-c-S point contacts as the weak link are compared with various theoretical models. The formulae following from the RSJ model with weak and strong damping and the microscopic treatment of quantum effects in S-c-S junctions are analysed. It is concluded that only the latter theory provides a quantitative agreement with the experimental values.     

Determination of the parameters of rotational and translational diffusion of a resonant medium by nonlinear polarization spectroscopy

A complete theoretical interpretation of the experimental data on the transformation of the polarization state of a weak wave in a layer of resonant medium (methane) depending on the intensity of high-power counterpropagating wave is presented in terms of the vector theory of radiation-matter interaction. A method for the experimental determination of the coefficients of rotational and translational gas diffusion is developed based on the theoretical calculation of two types of dichroism and birefringence and the use of experimental data on the change in the probe wave polarization at saturation of the resonant transition by the intensity of a counterpropagating wave with two different (linear and circular) field polarizations. This method also takes into account low backscattering of the strong wave field from optical path inhomogeneities.     

Growth of Bose-Einstein condensates from thermal vapor

We report on a quantitative study of the growth process of (87)Rb Bose-Einstein condensates. By continuous evaporative cooling we directly control the thermal cloud from which the condensate grows. We compare the experimental data with the results of a theoretical model based on quantum kinetic theory. We find quantitative agreement with theory for the situation of strong cooling, whereas in the weak cooling regime a distinctly different behavior is found in the experiment.     

Strong-symmetry-breaking limit of SU(3) Skyrme model and bound-kaon approach to strangeness

The semi-leptonic weak decays of hyperons are investigated in the Skyrme model. The vector currents for strangeness-changing processes are shown to have a very similar structure in the strong-symmetry-breaking limit in the SU(3) collective-coordinate method, proposed by Yabu and Ando, with those in the bound-kaon approach to strangeness by Callan and Klebanov. It is also shown that the quite differentN _c dependence between them becomes also to coincide with each other in the limit.Dedicated to Prof. Erich Schmid on the occasion of his 60th birthday     

Restoring universality

In models of weak and electromagnetic interactions with six or more quarks, universality and, in some cases, the V-A structure of leptonic and semi-leptonic interactions have to be put in by hand. We show how both properties remerge naturally if replacing the usual SU(2) weak isospin group by a large SU(4) group, which also lends itself quite naturally to grand unifications (including strong interactions). The model needs eight quarks and two charged heavy leptons, and features, nesides universality and V-A, non-equality of neutral current scattering of ν's on leptons and on hadrons, and very reasonable relations for (bare) fermion masses.     

Radiative corrections in weak semi-leptonic processes at low energy: a two-step matching determination*

We focus on the chiral Lagrangian couplings describing radiative corrections to weak semi-leptonic decays and relate them to the decay amplitude of a lepton, computed by Braaten and Li at one loop in the standard model. For this purpose, we follow a two-step procedure. A first matching, from the standard model to Fermi theory, yields a relevant set of counterterms. The latter are related to chiral couplings thanks to a second matching, from Fermi theory to the chiral Lagrangian, which is performed using the spurion method. We show that the chiral couplings of physical relevance obey integral representations in a closed form, expressed in terms of QCD chiral correlators and vertex functions. We deduce exact relations among the couplings, as well as numerical estimates which go beyond the usual approximation.Received: 16 May 2005, Published online: 19 July 2005     

Experimental Sensitivities on Searching for Rare and Forbidden Decays of Charm Mesons at BES-III

We discuss the Monte Carlo studies of searching for the rare and forbidden pure-leptonic and semi-leptonic decays of D^+,0 and D⁺_s mesons, based on a full Monte Carlo simulation for the BES-III detector, with the BES-III Offline Software System. The experimental sensitivities of searching for 36 rare and forbidden charm meson decays are estimated.     

LHC能量下D介子的核修正因子

高能质子-质子(p-p)和质子-原子核(p-A)碰撞过程中产生的D介子是分析碰撞后生成的饱和胶子性质的重要途经。考虑领头阶下的强耦合效应,在色玻璃凝聚理论(CGC)框架下研究了LHC(Large Hadron Collider, LHC)能量下p-p(p-A)碰撞过程中的D介子产生。采用由KLR-AdS/CFT色偶极模型通过傅里叶变换得到的偶极关联因子,同时利用Glauber模型考虑冷核物质效应,计算了质心能量为5.02 TeV时质子-铅核(p-Pb)碰撞中不同碰撞中心度下D介子的产生截面,并在此基础上研究了p-Pb碰撞中D介子产生及其半轻子衰变过程中的核修正因子。通过与大型强子对撞机(LHC)实验结果比较发现:考虑强耦合效应后的理论结果与ALICE和LHCb合作组的最新实验数据符合得更好。最后,本文对LHC碰撞质心能量为8.16 TeV时p-Pb碰撞中D介子产生的核修正因子给出了理论预言, 结果显示此能量下核修正因子理论值比5.02 TeV时略大。     

Nonstationary wave turbulence in an elastic plate

We report experimental results on the decay of wave turbulence in an elastic plate obtained by stopping the forcing from a stationary turbulent state. In the stationary case, the forcing is seen to induce some anisotropy and a spectrum in disagreement with the weak turbulence theory. After stopping the forcing, almost perfect isotropy is restored. The decay of energy is self-similar and the observed decaying spectrum is in better agreement with the prediction of the weak turbulence theory. The dissipative part of the spectrum is partially consistent with the theoretical prediction based on previous work by Kolmakov. This suggests that the nonagreement with the weak turbulence theory is mostly due to a spurious effect of the forcing related to the finite size of the system.