Strong Decay Modes Research Articles

The anomalous suppression of π2(1670) → b1(1235) π

We show that current experimental data indicate that the strong decay mode π 2 → b 1 π is anomalously small (more than 3 times smaller than all other decay modes of the π 2. This acts as a powerful discriminator for and against various decay models. Non-relativistic quark models with spin-1 pair creation, e.g. 3 P 0 (flux-tube breaking) and 3 S 1 and 3 D 1 (chromo-electric string-breaking) models, as well as lowest order one-boson (in this case π) emission models, can accommodate the experimental data because of a quark-spin selection rule. Models that violate the selection rule, e.g. higher order one-boson emisson decay mechanisms, as well as mixing with other Fock states and relativistic effects, may be constrained by the small π 2 → b 1 π decay.

Dibaryon systems in chiral [formula omitted] quark model

The possible candidates of S-wave dibaryons with various strange numbers are studied under the chiral SU(3) quark model. It is shown that there are three types of baryon–baryon bound states. The states of the first type are called deuteron-like states. If chiral fields can provide enough attraction between interacting baryons, these systems, such as [ΞΩ−Ξ∗Ω](1,1/2), [ΞΞ](0,1), [NΩ](2,1/2) would be weakly bound. The states of the second type such as [Σ∗Δ](0,5/2), [Σ∗Δ](3,1/2), [ΔΔ](0,3) and [ΔΔ](3,0) are named as ΔΔ-like states. Due to the highly symmetric character in orbital space, these systems could be relatively deeply bound, but the strong decay modes of composed baryons cause the widths of the states much broader. The states of the third type are entitled as ΩΩ-like states. Due to the same symmetry character shown in the systems of the second type and the only weak decay mode of composed baryons, for instance in [ΩΩ](0,0), or at most one strong decay mode of composed baryons, for example in [Ξ∗Ω](0,1/2), these states are deeply bound states with narrow widths. The states of latter two types are most interesting new dibaryon states and should be carefully investigated both theoretically and experimentally.

Radiative decays of excited Lambda Q baryons in the bound state picture.

It is shown that, in the bound state picture, the ${\ensuremath{\Lambda}}_{c}(2593)\ensuremath{\rightarrow}{\ensuremath{\Lambda}}_{c}\ensuremath{\gamma}$ and ${\ensuremath{\Lambda}}_{c}(2625)\ensuremath{\rightarrow}{\ensuremath{\Lambda}}_{c}\ensuremath{\gamma}$ decays are severely suppressed. On the other hand, for their bottom counterparts, which are predicted to have masses of 5900 and 5926 MeV, respectively, they may have significant radiative branching ratios. The ${\ensuremath{\Lambda}}_{b}(5926)\ensuremath{\rightarrow}{\ensuremath{\Lambda}}_{b}\ensuremath{\gamma}$ mode possibly dominates over the strong decay mode, while the ${\ensuremath{\Lambda}}_{b}(5900)$ resonance lies below the strong decay threshold and can only decay radiatively. The isospin allowed ${\ensuremath{\Lambda}}_{Q}^{**}\ensuremath{\rightarrow}{\ensuremath{\Sigma}}_{Q}\ensuremath{\gamma}$ mode is expected to be small.

Particle decay model

Applying a finite color symmetry group, it is shown that every “elementary particle” can be associated with a unique graph. This graph describes the gluon motions and is called the particle's strong graph. One also has an associated weak graph that describes the photon motions. Using the strong (weak) graph, one can exhibit the various strong (weak) decay modes of a particle. Roughly speaking, the particle graph disintegrates into smaller graphs that represent the decay products. The disintegration is dictated by certain decay operations and these operations have specified probability costs. The costs are then used to predict branching ratios and decay probabilities. For the examples presented, these predictions agree with experiment to within 1%.

Exclusive decays of heavy mesons

In order to describe quantitatively the strong or weak decays of heavy particles into two π(K)-mesons one needs to know the behaviour of the π-meson wave function ϕ π ( x) which determines the quark longitudinal momentum distribution inside the π-meson, p 1 = xp π , p 2 = (1 − x) p π , p π → ∞). We calculate the few first moments 〈 ξ 2 n 〉 ≡ ∫ −1 1 d ξξ 2 n ϕ π ( ξ), ξ = 2 x − 1 of the π-meson wave function using the QCD sum rules, and show that sum rules give strong restrictions on the values of the moments 〈 ξ 2 n 〉. Based on these results we discuss the qualitative behaviour of ϕ π ( x) and propose the model wave function. It is shown that this model wave function which fulfills the QCD sum rules gives a good description of the π-meson strong decay modes of the S and P charmonium levels. The two-particle weak decays of the D(F) mesons into π (and/or K) mesons are considered as well. It is shown that the annihilation contributions play an essential role in these decays (because of the earlier found properties of the π(K)-meson wave functions). Estimates of the Cabibbo-allowed and the Cabibbo-suppressed decat widths are presented (D → K π, KK, ππ,…). All the predictions for the strong, electromagnetic and weak two-particle decay widths are consistent with the available experimental data.

Possibility of a ninthJP=12+baryon. II

We demonstrate that the hypothesis of asymptotic level realization of SU(3) in the algebra $[{A}_{i}, {A}_{j}]=i{f}_{\mathrm{ijk}}{V}_{k}$ added to the assumption that a ninth $I=0$, ${J}^{P}={\frac{1}{2}}^{+}$ baryon ${\ensuremath{\Lambda}}^{\ensuremath{'}}$ exists with a mass around 1700 MeV implies that deviations from the good results of SU(6) or SU(6) \ensuremath{\bigotimes} O(3) schemes can be derived theoretically, without invoking the notion of SU(6) symmetry. The Cabibbo angles are determined to be ${sin\ensuremath{\theta}}_{V}=0.227\ifmmode\pm\else\textpm\fi{}0.008$ and ${sin\ensuremath{\theta}}_{A}=0.224\ifmmode\pm\else\textpm\fi{}0.037$. We find that $\frac{D}{(D+F)}\ensuremath{\simeq}0.678$. Hyperon semileptonic decays in the presence of the ${\ensuremath{\Lambda}}^{\ensuremath{'}}$ are analyzed in detail. Partial widths for several ${\frac{3}{2}}^{+}\ensuremath{\rightarrow}{\frac{1}{2}}^{+}+\ensuremath{\pi}$ decays and branching ratios for the strong decay modes of the ${\ensuremath{\Lambda}}^{\ensuremath{'}}$ are discussed.

The 3He( 3He, t)3p reaction at 44 MeV

Triton spectra from the reaction 3He( 3He, t)3p have been measured at a bombarding energy of 44 MeV for lab angles between 6° and 25°. These spectra are quite featureless and show no indication of either a 3p final-state interaction or of a strong sequential decay mode.

Pion-nucleon phase shifts and their implications

We discuss recent π p phase shift analyses and evaluations of dispersion relations. Besides the D 13 resonance, which is much narrower than previously thought, they have revealed P 11 , S 11 and S 31 objects’ in the 500 to 800 MeV region, all with strong inelastic decay modes. The P 11 phase shift reaches 81°. S 11 and S 31 objects were predicted by SU (6), but the behaviour of P 11 is difficult to reconcile either with pure SU (6) or with the reciprocal NN * bootstrap.