A. Moalem

Comparison of eta and eta ' production in the pp -g pp eta(eta ') reactions near threshold

Abstract The total cross section of the p p→p p η′ reaction has been measured at two energies near threshold by detecting the final protons in a magnetic spectrometer. The values obtained are about a factor of 70 less than for the corresponding η production, in good agreement with the predictions of a one-pion-exchange model.

Excitation of giant resonances by inelastic

Inelastic /sup 3/He scattering at 71 MeV on twelve nuclei ranging from / sup 27/Al to /sup 209/Bi shows an enhancement of the continuum very similar to that observed in electron and proton scattering. The effect is ascribed to a giant multipole state. The strength of the excitation indicates an E2 character for thc state. (auth)

sup 3

Abstract The ground state differential cross sections for the (n, p) reaction at 0° on 6 Li, 12 C and 13 C have been measured for 198 MeV neutrons with a precision of about 4% relative to the corresponding value for the H(n, p) reaction. These data, together with the accurately known ft values for the β- decay of 6 He, 12 B and 13 B provide three calibrations of the (n, p) reaction as a probe of Gamow-Teller strength for isospin raising transitions.

He scattering

Abstract The mass of the η meson has been measured through the study of the d p→ 3 He η reaction near threshold, the beam having been calibrated through comparison with three other nuclear reactions. The value obtained is m η =547.30±0.15 MeV/ c 2 , where the error bar includes both systematic and statistical effects. This is much more precise and significantly lower than the Particle Data Group average, through it is consistent with a previous counter experiment.

The (n, p) reaction as a probe of Gamow-Teller strength

Abstract The pp → ppη reaction at energies near threshold is studied in a nonrelativistic one-boson exchange model, where the S11 (1535 MeV) nucleon isobar is excited through the exchange of π, η and ϱ mesons. Providing NN and ηN final state interactions are taken into account, our predictions reproduce the energy dependence as well as the scale of the total production cross section near threshold, and thus enforce the validity of the S11 mechanism and perturbative approaches applied to η production in hadronic collisions.

The η-meson mass

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, ϱ and ω mesons and subsequently decays into an ηN pair. Energy integrated cross sections and energy spectra of the out going ηs are reported. Providing NN and ηN 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 ηs provides a clear signature of the ηN force.

Threshold production cross section of the pp → ppη reaction in a nonrelativistic OBE model

Abstract The angular distributions of states excited in the reaction 94 Mo(p,t) 92 Mo at E p = 40 MeV are measured. Values of the angular momentum transfers L and the spectroscopic enhancement factors are extracted by means of a zero-range DWBA calculation. Several new J π assignments are made. The strongly excited states are attributed to 1p-1h and 2p-2h neutron states. Lower-lying proton configuration states are weakly excited. Good agreement is obtained with a calculation which describes the excitation of these proton states through particular components in the 94 Mo g.s. wave function. The long predicted 0 + state in 92 Mo at 2.5 MeV is identified. A 0 + pairing vibrational state has been located at 3.85 MeV. The possible existence of 2 + , 4 + , 3 − and 5 − pairing vibrational states is discussed.

The NN → NNη reaction close to threshold

Abstract: The total cross section of the pd→pdη reaction has been measured at two energies near threshold by detecting the final proton and deuteron in a magnetic spectrometer. The values are somewhat larger than expected on the basis of two simple theoretical estimates.

A nuclear structure study with the 94Mo(p, t)92Mo reaction

Abstract A relativistic covariant one boson exchange model, previously applied to describe elastic nucleon-nucleon scattering, is extended to study η production in NN collisions. The transition amplitudes for the elementary BN → ηN processes with B being the meson exchanged ( B = π , σ , η , ϱ , ω and δ ) are taken to be the sum of four terms corresponding to s and u-channels with a nucleon or a nucleon isobar N ∗ (1535 MeV) in the intermediate states. Taking the relative phases of the various exchange amplitudes to be +1, the model reproduces the cross sections for the NN → Xη reactions in a consistent manner. In the limit where all ηs are produced via N ∗ excitations, interference terms between the overall contribution from the exchange of pseudoscalar and scalar mesons with that of vector mesons cancel out. Consequently, much of the ambiguities in the model predictions due to unknown relative phases of different vector and pseudoscalar exchanges are strongly reduced.A relativistic covariant one boson exchange model, previously applied to describe elastic nucleon-nucleon scattering, is extended to study

Near-threshold η production in the pd→pdη reaction

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