The radiative decay of the Λ(1405)

A recent result for the branching ratio for the decay of the kaonic hydrogen atom to Λγ is used to derive a value for the transition moment for the decay Λ(1405) → Λγ. Two solutions are found, −0.29 < κ < −0.07 and 0.60 < κ < 0.81 proton magnetons, giving decay widths of Γ(Λ(1405) → Λγ) = 6 ± 6 and 74 ± 22 keV, respectively.     

Λc重子谱疑难(英文)

Λ_c+重子家族存在一个疑难,也就是重夸克有效理论预言的轨道角动量为L=2的多重态中JP=3/2+的态在实验上是缺失的,而且已发现的Λ_c（2765）+和Λ_c（2940）+的JP量子数仍然未知。在本工作中,我们使用双夸克图像计算了重子的质量,研究了Λ_c（2765）+和Λ_c（2940）+的可能归类以及仍缺失的具有L=2和JP=3/2+量子数的Λ_c+态,进而指出Λ_c（2880）+的峰结构中实际上已经包含了L=2、JP=3/2+这一缺失态,并建议Λ_c（2765）+和Λ_c（2940）+的量子数应分别为2S（1/2+）和2P（1/2-）。There is a puzzle in the Λ_c+ family, i.e., one member with JP=3/2+ is missing in a L=2 multiplet which the heavy quark effective theory predicts, and JP's of Λ_c(2765)+ and Λ_c(2940)+ are unknown. Using a light diquark picture to calculate baryon masses, we study possible assignments of two Λ_c's with unknown JP and the missing Λ_c+ with 3/2+ for L=2, and we find the most probable possibility that the peak corresponding to Λ_c(2880)+ actually includes a missing member with spin 3/2+ for L=2 and that quantum numbers of Λ_c(2765)+ and Λ_c(2940)+ are 2S(1/2+) and 2P (1/2-), respectively.     

The ratio of decay constants ƒB/ƒD

The result ƒ_B≈ƒ_D which had been obtained from sum rules and lattice calculations, and which contradicts the naïve prediction ƒ_p1/√M_p, is rederived using a simple argument based on semilocal parton-hadron duality. Is is argued that both here and in sum rules the key point is the use of semilocal duality instead of the bound-state wave functions.     

Measurement of the mass of the Λb baryon

In a data sample of four million hadronic Z decays collected with the ALEPH detector at LEP, four Λ_b baryon candidates are exclusively reconstructed in the Λ_b → Λ_c⁺π⁻ channel, with the Λ_c⁺ decaying into pK⁻π⁺, , or Λπ⁺π⁺π⁻. The probability of the observed signal to be due to a background fluctuation is estimated to be 4.2 × 10⁻⁴. The mass of the Λ_b is measured to be 5614±21 (stat.) ± 4 (syst.) MeV/c².     

Mesonic and non-mesonic decay widths of ΛC

Results are reported on the precise measurement of the lifetime and the weak-decay branching ratios with charged particle(π⁻ and proton) emission from _Λ¹²C formed via ¹²C(π⁺,K⁺) reaction. The π⁻ mesonic decay width is consistent with the calculations including the pion wave function distortion effect. We observed large contribution of the neutron-stimulated decay widths, Γ(Λ + n → n + n), in the non-mesonic weak decay, which cannot be explained by the current theoretical calculations.     

ΣΛ Conversion in ΛH and in other S-shell hypernuclei

The binding energy of the Λ-particle in the $\text{J =}\text{1}\text{2}\text{and}\text{3}\text{2}$ states of _Λ³H and the doublet and quartet Λ-d scattering lengths are calculated with a separable ΛN-ΣN potential matrix, fitted to experimental data in ΛN and ΣN channels. The dependence of the results on ΛΣ coupling is explained in terms of a perturbative treatment of ΛΣ coupling. This perturbative treatment is also applied in a qualitative discussion of the effects of ΛΣ conversion in the J = 0 and 1 states of _Λ⁴H-_Λ⁴He and in the $\text{J =}\text{1}\text{2}$ state of _Λ⁵He. The importance of three-body ΛNN forces caused by ΣΛ coupling is stressed.     

Measurement of the proton spectra from non-mesonic weak decay of ΛHe, ΛLi and ΛC

The results of a measurement of the proton spectra following the non-mesonic weak decay of ⁵_ΛHe, ⁷_ΛLi and ¹²_ΛC are presented and discussed. The experiment was performed at the (e⁺ e⁻) collider DAΦNE at Laboratori Nazionale di Frascati of INFN. It is the first measurement for ⁷_ΛLi, and for all the spectra the lower limit on the energy of the protons is 15 MeV, never reached before. All the spectra show a similar shape, namely a peak at around 80 MeV as expected for the free Λp→np weak reaction, with a low energy rise that should be due to final state interactions and/or two-nucleon induced weak processes. The decay spectrum of ⁵_ΛHe is somehow similar to the ones reported by previous measurements and theoretical calculations, but the same does not happen for the ¹²_ΛC one.     

The ψ′-η′c hyperfine splitting

The hyperfine splitting of the radially excited states ψ′ and η′_c is studied within the framework of potential models. Some rigorous results are derived and some phenomenological approaches are commented on. The recent experimental result M(ψ′)?M(η′_c) = 93 MeV favours very short-range spin-spin forces and seems, on the other hand, difficult to accommodate if there is a sizeable effect of virtual D meson pairs on the charmonium mass spectrum.     

In search of the ηc

We argue that the X(2.88) detected in π^?p → γγ + n at 40 GeV/c cannot be the η_c. We discuss the possibility that a qq?cc? state is produced there, probably the same state discovered in radiative decay of the J/ψ. Only at much higher energies is the η_c expected to dominate over qq?cc? in the π^?p interaction. We also discuss coherent photoproduction and find that four quark state production would dominate over η_c.     

The quark-meson coupling model for Λ, Σ and Ξ hypernuclei

The quark-meson coupling (QMC) model, which has been successfully used to describe the properties of both infinite nuclear matter and finite nuclei, is applied to a systematic study of Λ, Σ and Ξ hypernuclei. Assumptions made in the present study are, (i) the (self-consistent) exchanged scalar, and vector, mesons couple only to the u and d quarks, and (ii) an SU(6) valence quark model for the bound nucleons and hyperon. The model automatically leads to a very weak spin-orbit interaction for the Λ in a hypernucleus. Effects of the Pauli blocking at the quark level, particularly in the open, coupled, ΣN-ΛN chanel (strong conversion), is also taken into account in a phenomenological way.     

Mechanisms of induced Λ-hyperon decay revisited: Contribution of correlated two-pion exchange

The contribution of correlated ππ-exchange to the induced Λ-hyperon cay is investigated. This mechanism is shown to give a noticeable contribution to the conversion rate from the spin-singlet state.     

Structure of a Λ-hypernucleus ΛY measured with the SKS spectrometer

We have measured an excitation energy spectrum of a Λ-hypernucleus _Λ⁸⁹Y via the (π⁺, K⁺) reaction by using the SKS spectrometer at KEK. The best quality data with the energy resolution of 1.63 MeV(FWHM) was obtained in the highest statistics so far. In the spectrum, we can find a splitting of the f-orbital of a Λ particle with the separation of 1.6±0.15 MeV(statistical error only), which may be attributed to the spin-orbit splitting.     

Coherence induced by incoherent pumping field and decay process in three-level Λ type atomic system

Following the method proposed by Kozlov et al. [Victor V. Kozlov, Yuri Rostovtsev, Marlan O. Scully, Phys. Rev. A 74 (2006) 063829], we have investigated the atomic coherence induced by incoherent pump and vacuum spontaneous decay process in a Λ type three-level atomic system. The system can be in a coherent population trapping state and multi-steady states in different conditions. Interestingly, two kinds of new states are derived from the system with different pumping rate and decaying rate. They are the “robust” steady state and the “weak” steady state. Under the action of pump field and vacuum reservoir, these two kinds of states exhibit stable or unstable characteristics, respectively. Moreover, by investigating the difference between these states, we reveal the mechanism of coherence excitation and level-population transition. The special feature of the Λ atomic system will promise fruitful applications in quantum optics.     

Temperature dependence of κc for type-II superconductors

The temperature dependence of the critical value κ_c of the Ginzburg-Landau parameter which separates type-II/1 from type-II/2 superconductors is theoretically computed by means of a microscopic calculation of the boson characteristic function at nonzero temperature, assuming that the temperature is not too close to T_c. Agreement with experimental data is satisfactory in the region $\text{0?T}\text{T}{}_{\mathrm{c}}\text{?0.6}$.     

Upper limit on the decay Σ(1385)→Σγ and cross section for γΣ→Λπ

Coherent Λπ⁻ production on Pb of 600 GeV Σ⁻ hyperons has been studied with the SELEX facility at Fermilab. Using the Primakoff formalism, we set a 90% CL upper limit on the radiative decay width Γ[Σ(1385)⁻→Σ⁻γ]<9.5 keV, and estimate the cross section for γΣ⁻→Λπ⁻ at  GeV to be 56±16 μb.     

Virtual corrections to the decay b → s + γ

We calculate the O(_s) virtual corrections to the matrix element for b → sγ, taking into account the contributions of the four-Fermi operator O₂ and the electromagnetic and color dipole-type operators. The results are combined with existing O(_s) Bremsstrahlung corrections in order to obtain the relevant inclusive rate. The new result drastically reduces the large scale dependence of the leading logarithmic approximation. It implies that a very accurate prediction for the branching ratio for B → X_sγ will become possible once also the corrections to the Wilson coefficients are available.