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1.
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
2.
The possibilities of extracting parameters of ππ interaction from the experimental data on the πN→ππN reaction are analyzed in detail. The interval 300< Plab<500 MeV/ c is shown to be the smoothness domain of the πN→ππN amplitude. The expression for the background part of the amplitude is developed model-independently. The ππ scattering is described by four parameters to be extracted from experimental data (along with 11 background parameters). 相似文献
3.
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
4.
Elastic and inelastic η-photoproduction from complex nuclei is studied in a distorted-wave impulse approximation (DWIA) framework. The elementary operator is obtained by using a dynamical model which employs the reactions πN→πN, πN→ππN and π −p→ηn to fix the hadronic vertex as well as the isobar propagators and the process γN→πN to constrain the electromagnetic vertex. The nuclear structure input for the inelastic transitions has been extracted from electron-scattering form factors. The η final-state interaction has been included via a simple optical potential using the ηN t-matrix as an input. We find that coherent η-production is dominated by the D 13(1520) isobar while spin-flip transitions to excited nuclear states are sensitive to the S 11(1535) resonance. Predictions are given for coherent production on 4He, 12C and 40Ca, as well as incoherent production on 6Li, 10B and 12C. 相似文献
5.
A stack of annular detectors made of high-purity germanium was used to measure simultaneously pd → 3H π + and pd → 3He π 0 differential cross sections at beam momenta of 750 MeV/ c, 800 MeV/ c, and 850 MeV/ c over a large angular range. The extracted total cross sections for the pd → 3He π 0 reactions bridge a gap between near threshold data and those in the resonance region. The ratio of the cross sections for the two reaction channels taken at the same η= pcmπ/ mπ yields 2.11±0.08 indicating that a deviation from isospin symmetry is very small. 相似文献
6.
A formationstudy of the reaction K −p→Λπ o at 13 c.m. energies between 1915 and 2168 MeV is presented. Experimental differential cross sections and polarizations are given as expansions of Legendre polynomials and associated Legendre polynomials respectively. Partial wave analysis confirms the
assignment of the Σ(2030) and the
assignment of the Σ(1915). The parameters of these resonances are determined. The possible existence of other resonances coupled to this channel is investigated. 相似文献
7.
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
8.
We find that the Callan-Symanzik equation with the intrinsic breaking term omitted suggests ansatz for the differential cross section in the high energy wide angle limit. The agreement with experimental data for the reactions ep → ep, π −p → π −p, pp → pp is very satisfactory. 相似文献
9.
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
10.
The pp → ppη and np → npη reactions at energies near the η production threshold are studied in a non-relativistic one boson exchange model, where the N* (1535 MeV) S11 resonance is excited through the exchange of π, η, and ω mesons and subsequently decays into an η N pair. Energy integrated cross sections and energy spectra of the out going η's are reported. Providing NN and η N final state interactions are taken into account coherently, the model reproduces both the scale and energy dependence of the cross section for the pp → ppη reactions up to 100 MeV. Final state interaction corrections due to the nucleon-nucleon and meson-nucleon forces influence strongly the scale and shape of the cross sections. The shape of the energy spectra of the outgoing η's provides a clear signature of the η N force. 相似文献
11.
Small-angle cross sections are calculated for 6Li(K −, π +) Σ6H at 720 MeV/ c, in order to intepret the data of the preceding paper. Due to the spin-isospin selectivity of ΣN → ΛN conversion, the substitution 1s N → 1s Σ leads to a narrow resonance high in the Σ continuum. Further tests of selectivity with 3,4He targets are suggested. The energy shifts of Σ states which arise from the spin-isospin dependence of the ΣN interaction are discussed. 相似文献
12.
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
13.
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
14.
A high-statistics measurement of the photon spectrum of the reaction π −d → γnn has been performed. The comparison of this spectrum with theoretical spectra folded with the response curve of the spectrometer (measured by the reaction π −p → γn) has provided precise values of the neutron-neutron scattering length, ann = −18.5 ± 0.4 fm, and of the effective range, rnn = 2.80 ± 0.11 fm. Theoretical uncertainties of 0.20 fm and 0.11 fm, respectively, have been evaluated. 相似文献
16.
The differential cross section of the reaction γp→π +n has been measured with the PHOENICS detector at ELSA in Bonn. For the first time this cross section has been determined simultaneously over a large range of photon energies ( Eγ = 220−900 MeV) and pion angles (Θ c.m.pi = 35°−135°) with a tagged photon facility. The experimental set-up allowed a considerable kinematic overdetermination of the investigated reaction. Accordingly, the background contributions have been suppressed to below 1%. The measured differential cross section is in good agreement with existing data. The comparison with different model calculations is presented. 相似文献
17.
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
18.
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
19.
We obtain differential cross sections for the reaction e−+ p→Σ 0+ν e, for incident electron energies from 0.5 GeV to 6.0 GeV. This calculation is phenomenologically based and makes use of SU(3) and SU(2) relations. We obtain contributions of the individual form factors to the differential cross section and show that the vector current form factor dominates in the region of observability. We also obtain reaction rates for a standard set of conditions. Finally we compare this case with that for Λ production and discuss what might be learned from this reaction concerning the structure of the weak, strangeness changing, hadronic current. 相似文献
20.
A spherical harmonic moment analysis of the reactions K −p → K −π +n and K +p → K +π −Δ ++ at 13 GeV/ c demonstrates the existence of a broad K * state with mass in the vicinity of 1800 MeV and spin parity 3 −. 相似文献
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