共查询到20条相似文献,搜索用时 296 毫秒
1.
The process η → π 0π 0γγ is discussed in Chiral Perturbation Theory (ChPT). Special attention is deveted to one-loop corrections, η-η′ mixing effects and vector-meson dominance of ChPT counter-terms. The less interesting η → π +π −γγ transition is briefly discussed too. 相似文献
2.
The theoretical mechanisms for the decays ψ′ → ψπ 0 and ψ′ → ψη, which violate SU 2 and SU 3, respectively discussed. It is argued that symmetry breaking in the decay amplitudes may be as important as π 0 −η −η′ mixing. The π 0 −η mechanism ψ′ → ψν → ψπ 0 leads to Γ(ψ′ → ψπ 0) = (3.3±1.0) × 10 −3 Γ(ψ′ → ψν), but this number may be enhanced by a factor as large as 12 by π 0−η′ mixing and isospin violation in the decay amplitude. The related decays ψ → ηγ and ψ → η′γ are also discussed. 相似文献
3.
We analyze the supersymmetric contributions to direct– CP–violating observables in K→ππγ decays induced by gluino–mediated magnetic–penguin operators. We find that ε′ +−γ and the differential width asymmetry of K±→π ±π 0γ decays could be substantially enhanced with respect to their Standard Model values, especially in the scenario where ε′/ε is dominated by supersymmetric contributions. These observables could therefore provide a useful tool to search for New Physics effects in |Δ S|=1 transitions, complementary to ε′/ε and rare decays. 相似文献
4.
We calculate the amplitude of the decays η → π 0π +π − and η → π 0π 0π 0 to first non-leading order in the low-energy expansion. It is shown that the infrared singularities of chiral perturbation theory strongly enhance the perturbation generated by the quark mass term. The corrections of order ms increase the current algebra prediction for the rate by more than a factor of two and remove the well-known discrepancy between the low-energy theorems of current algebra and experiment. 相似文献
5.
Using the quark-meson coupling (QMC) model, we investigate whether ω, η, η′ and D− mesons form meson-nucleus bound states. Our results suggest that one should expect to find η- and ω-nucleus bound states in all the nuclei considered. Furthermore, it is shown that the D− meson will form quite narrow bound states with 208Pb. 相似文献
6.
The time-dependence of the decay rate of initially pure K 0 into the final state (π +π −π 0) has been studied in search for the decay k S0→π +π −π 0. No evidence is found in a sample of 384 observed events. The ratio of the CP -violating K S0 amplitude and the K L0 amplitude is η +−0 = (0.13 −0.20+0.17) + i(0.17 −0.26+0.27); the ratio of the CP-conserving K S0 amplitude and the K L0 amplitude is < 0.4. The energy dependence of the K 0→π +π −π 0 matrix element is found to be a+−0 = −0.31 ± 0.03. 相似文献
7.
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. 相似文献
8.
We study the ρ 0 and φ decays into π +π −γ, π 0π 0γ and φ into π 0ηγ using a chiral unitary approach to deal with the final state interaction of the MM system. The final state interaction modifies only moderately the large momenta tail of the photon spectrum of the ρ 0→π +π −γ decay. In the case of φ decay the contribution to π +π −γ and π 0π 0γ decay proceeds via kaonic loops and gives a distribution of ππ invariant masses in which the f0(980) resonance shows up with a very distinct peak. The spectrum found for φ→π 0π 0γ decay agrees with the recent experimental results obtained at Novosibirsk. The branching ratio for φ→π 0ηγ, dominated by the a0(980), is also in agreement with recent Novosibirsk results. 相似文献
9.
The production rate for η′ in pp → ppη′ at rest is calculated in a covariant one boson exchange model, previously applied to study π 0 and η production in NN collisions. The transition amplitudes for the elementary BN → η′ N processes with B being the meson exchanged ( B = π, σ, η, , ω and a0) are taken to be the sum of s- and u-channels with a nucleon in the intermediate states, and an a0 meson pole in a t-channel. The couplings of the η′ to hadrons are a factor 0.4 weaker than the respective η-hadron couplings, as suggested by a quark model and a singlet-octet mixing angle θ = −23°. The model reproduces near threshold cross sections for the quasielastic processes π −p → nη(η′) and pp → ppη(η′) reactions. 相似文献
10.
The production of η mesons has been observed at high momentum transfer in the reaction π −p → nη. The ratio between this cross-section and that for backward charge exchange yields a value for the relative couplings g2ηNN/ g2πNN. 相似文献
11.
In an analysis of 1114 events of the type K −d → pΛ 0π −+ neutrals with ‘spectator’ proton momentum in excess of 0.11 GeV/ c we have found that the number of protons having a momentum in the range 0.25–1.2 GeV/ c exceeds that predicted on the basis of the impulse model using the Hulthén distribution by 3 : 1. Final-state interactions in which the proton does not form resonances with the other final-state particles are mainly held responsible for this effect. 相似文献
12.
We present an amplitude analysis of the process π −p→π +π −n at 15 GeV/ c assuming spin and phase coherence of the production amplitude. The bearing of the results on aspects of dipion production phenomenology is discussed. 相似文献
13.
We study semileptonic decays B→η (′)lν, taking into account the flavor-singlet contribution ( Fsinglet+) to the B→η (′) form factors, which arises from the two-gluon emission in a decaying B meson. It has been recently pointed out that, in addition to large weak annihilation effects, the unknown value of Fsinglet+ prevents accurate theoretical estimates in the analysis of B→η′ K decays in QCD factorization. We present a certain method to determine Fsinglet+ with a reasonable accuracy, using B→η (′)lν and B→π lν decays. We also investigate the possible effect of Fsinglet+ on the estimated branching ratios (BRs) for B→η (′)lν and find that the BR for B→η′ lν is particularly sensitive to the effect of Fsinglet+. 相似文献
14.
The arguments are put forward that the many pion decays ω→2π +2π −π 0 and π +π −3π 0 provide an ideal test site for testing the predictions of chiral models of the vector meson decays into many pions. Using the approach based on the Weinberg Lagrangian or, in a new language, the Lagrangian of hidden local symmetry added with the term induced by the anomalous Lagrangian of Wess and Zumino, the partial widths of these decays are evaluated, and their excitation curves in e +e − annihilation are obtained. The discussed are the perspectives of the experimental study of the decays ω→5π in e +e − annihilation and photoproduction. 相似文献
15.
The s-wave η self-energy in the nuclear medium is calculated in a chiral unitary approach. A coupled channel Bethe–Salpeter equation is solved to obtain the effective η N interaction in the medium. The base model reproduces well the free space π N elastic and inelastic scattering at the η N threshold or N*(1535) region. The Pauli blocking on the nucleons, binding potentials for the baryons and self-energies of the mesons are incorporated, including the η self-energy in a self-consistent way. Our calculation predicts about −54− i29 MeV for the optical potential at normal nuclear matter for an η at threshold but also shows a strong energy dependence of the potential. 相似文献
16.
We report on the observation of an ηη′ threshold enhancement produced in
p annihilations at rest into π 0ηη′, which we identify with the recently discovered ƒ 0(1500). 相似文献
17.
The inclusive production of η mesons at CM energies around 34 GeV has been studied for e +e − annihilation into hadrons. The average number of η-mesons per event is found to be 0.72 ± 0.10 (stat.) ± 0.18 (syst.). The abundance of η's is studied as a function of event shape parameters and it is compared to the corresponding π 0 rates. 相似文献
18.
We report on I– V characteristics for in situ formed Nb/Au/(1 1 0)YBa 2Cu 3O 7−δ (YBCO) Josephson junction, where the homoepitaxial (1 1 0)YBCO film shows ultra-smooth surface morphology. The field dependence of critical supercurrent Ic shows anisotropic large junction behavior with normal Fraunhofer patterns expected from BCS model of d x2−y2 wave superconductors. This strongly suggests that the Nb/Au/(1 1 0)YBCO junctions cannot be regarded as atomic scaled corner junctions, in contrast with (0 0 1)/(1 1 0)YBCO grain boundary junctions to show “π-junction” with a pronounced dip near zero fields in field modulation of Ic. 相似文献
19.
The reactions π −p → 2π −π +p, π −p → 2π −π +π op and π −p → 2π −2π +n are analysed at 11 and 16 GeV/ c using longitudinal phase space (LPS) plots. The weighted LPS distributions for π −p → 2π −π +p is dominated by two well separated structures corresponding to single diffraction dissociation of the pion, π −p → (2π −π +)p, and of the proton, π −p → π −(π −π +p). The former is more abundant than the latter, and both are approximately constant with energy. In contrast, processes of type π −p → (2π)(πp) decrease with increasing energy. In the five-body reactions the weighted LPS distribution reveals especially at 16 GeV/c a maximum for single dissociation of the proton into 3πp, namely π−p → π−(π−π+πop); this process is likely to be diffractive. The neutron channel has a corresponding maximum displaced toward a multiperipheral configuration π−p → π−(π−2π+)n. Another strong maximum corresponds to the pion dissociation π−p → (2π−π+πo)p. This is interpreted to be an ω-exchange process because no analogous structure occurs in π−p → (2π−2π+)n. Finally, a broad structure reveals double dissociation of both incident particles; it occurs in the two channels π−p → (2π−π+)(πop) and π−p → (2π−π+)(π+n), being stronger in the latter. Further analysis of this process in terms of isospin exchange suggests that it is partially diffractive. Factorization is also discussed. An appendix gives general aspects of the LPS analysis for the asymptotic study of n-body collisions at very high energy. 相似文献
20.
The reaction γ p → π °γ′ p has been measured with the TAPS BaF 2 calorimeter at the Mainz Microtron accelerator facility MAMI for energies between √2 = 1221–1331 MeV. Cross sections differential in angle and energy have been determined for the photon γ′ in three bins of the excitation energy. This reaction channel provides access to the magnetic dipole moment of the Δ +(1232) resonance and, for the first time, a value of μ Δ+ = (2.7 +1.0−1.3( stat) ± 1.5( syst) ± ( theor)) π N has been extracted. 相似文献
|