A meson-theoretical explanation of the f 0 (980)-production puzzle in the reaction π− p → π0π0 n

A meson-theoretical model for the reaction π^? p → π⁰π⁰ n for large π^? momenta is developed which treats the final-state interaction between the two produced pions microscopically. For small momentum transfers, the squares of the S-wave amplitudes of the produced two-pion system show a dip for invariant twopion masses in the vicinity of the f ₀(980) meson, while for momentum transfers ?t>0.2(GeV/c)², the f ₀(980) meson appears as a bump. The model provides a microscopic explanation of the long-standing puzzle seen by both the GAMS and the BNL experimental collaborations.     

Cluster-model calculations of the electrodisintegration of lithium

Extending previously derived cluster-model treatments of the lithium isotopes to continuum states, we calculate (longitudinal) electrodisintegration cross-sections in the energy loss range 1.5 to 7.5 MeV, for momentum transfers q² = 0 to 1.5 fm^?2.     

The structure of the high-momentum parts of the deuteron spectra from d-d collisions at 4.3, 6.3 and 8.9 GeV/c

The experimental data on d-d collisions at 4.3, 6.3 and 8.9 GeV/c, exhibiting the two-peak structure in the high-momentum parts of the secondary deuteron spectra at momentum transfers |t| ≈ 0.4–0.8 (GeV/c)², are presented. An analysis of the results in terms of the multiple nucleon-nucleon scattering model is given. Some conclusions about the mechanism of the elastic and quasielastic d-d scattering at the above-mentioned momentum transfers are made.     

Relations between the electroexcitation of nucleon resonances and the deep inelastic continuum for proton and deuteron targets

New data of the electroexcitation cross section on protons and deuterons in the resonance region are compared with the results in the deep inelastic region for four-momentum transfers q² ? 1.5 (GeV/c)². The Bloom-Gilman sum rule is shown to hold for q² ? 1.2 (GeV/c) while the Rittenberg-Rubinstein sum rule is saturated for q² ? 0.4 (GeV/c)². It is shown that the sum rules do not saturate in a local way.     

Excitation of the Δ resonance in inclusive ed scattering

The parameters of the pion-electroproduction peak in the cross section for inclusive electron scattering on ¹H and d target nuclei are determined for various kinematical conditions of measurements. It is shown that, for low 4-momentum transfers, 0.030≤Q ²≤0.086 (GeV/c)², the Q ² dependence of the shift of the pion-electroproduction peak in the πN invariant mass for a deuteron target with respect to that for a free proton does not exhibit a universal behavior that is characteristic of complex nuclei.     

Form factors for exotic baryons of isospin <Emphasis Type="Italic">I</Emphasis> = 5/2

Electric form factors for exotic baryons are calculated within the relativistic quark model in the region of low and intermediate momentum transfers, Q ² ≤ 1 GeV². The charge radii of E ⁺⁺⁺ baryons are determined.     

Interplay of valence-shell clusters and the vibrational field in205Pb and206Pb

The properties of²⁰⁵Pb and²⁰⁶pb are described in the cluster vibrational field coupling model. Excitation energies, strengths for one-particle transfers,E2 andM1 observables are compatible with the available experimental data. Other theoretical approaches for these nuclei are discussed and compared with the results of the present investigation.     

Comparison of inelastic electron and positron scattering cross sections on 12C and 27Al

The ratio R = σ⁺/σ^? of the cross sections for inelastic and electron scattering on ¹²C and ²⁷Al has been measured for four momentum transfers 0.08 (GeV/c)² ?q² ?0.45 (GeV/c)² of the virtual photon and invariant masses 0.95 GeV ? W ? 3.3GeV of the hadronic system. The mean value of the ratio is R = (1.005 ± 0.027). No q², respectively, W dependence of the ratio is observed.     

The total cross section for π+ electroproduction on hydrogen near threshold

The total cross section for the reaction ep → enπ⁺ at momentum transfers |k²| between 0.08 and 0.32 ($\text{GeV}\text{c}$)² and for centre of mass energies between threshold, at W = 1.078 GeV, and W = 1.106 GeV has been measured by detecting the electron and neutron in coincidence. Comparisons are made with both current algebra and dispersion relation theoretical models.     

Inelastic electron scattering from 6Li near the α-d threshold

The form factor for the alpha-deuteron continuum in ⁶Li has been measured in the excitation region within 2 MeV of threshold, for momentum transfers q < 1.2 fm^?1. The results are interpreted in terms of an α-d cluster model. The monopole breakup appears to be predominant near threshold, but the influence of the J = 2⁺ (4.31 MeV) quadrupole resonance becomes important a few MeV above threshold. The form factor for the C2 transition to the 3⁺ (2.185 MeV) state is also presented.     

Probing lepton and quark substructure in polarized e∓N scattering

If leptons and quarks are composite objects their non-elementary nature would emerge clearly from deep inelastic scattering at momentum transfers of the order of the compositeness scale Λ_H. On the other hand, residual lepton-quark interactions induced by the new binding force would indicate the existence of a further layer of substructure already at considerably smaller momentum transfers. The effects of such non-standard interactions on various cross sections and asymmetries in polarized e^?N scattering are studied in detail. It is shown that, if Λ_H < 5 TeV, one should encounter rather striking deviations from the standard model expectations in the Q²-range accessible at future ep colliders like HERA.     

A measurement of the proton structure function F2(x,Q2)

A measurement of the proton structure function F₂(x, Q²) is reported for momentum transfers squared Q² between 4.5 GeV² and 1600 GeV² and for Bjorken x between 1.8 × 10⁻¹⁴ and 0.13 using data collected by the HERA experiment H1 in 1993. It is observed that F₂ increases significantly with decreasing x, confirming our previous measurement made with one tenth of the data available in this analysis. The Q² dependence is approximately logarithmic over the full kinematic range covered. The subsample of deep inelastic events with a large pseudo-rapidity gap in the hadronic energy flow close to the proton remnant is used to measure the “diffractive” contribution to F₂.     

π+-electroproduction above the resonance region

The reaction e + p → e' + n + π⁺ was studied detecting e' and e' and π⁺ in coincidence at an invariant hadronic mass of 2.19 GeV. The measurements were performed at electron four-momentum transfers squared of Q² = 0.06, 0.28, 0.70, and 1.35 GeV² in the range of t = (γ_v?π)² between tmin and ?1.0 GeV². The cross section d²σ/dtd was found to be roughly independent of Q² for Q² > 0.7 GeV² and ∥t∥ > 0.2 GeV².     

Inelastic electron scattering from hydrogen at 50° and 60°

Inelastic electron scattering cross sections have been measured for four-momentum transfers between 4.1 GeV² and 30.5 GeV². At the large scattering angles of this experiment, the dominant contribution to the cross section comes from the W₁ structure function. In the conventional scaling variables, x and x′, this structure function does not exhibit scaling behavior, and at fixed x or x′ it is found to decrease with increasing four-momentum transfer.     

On the scale dependence of the dimension of hadronic matter

We advance the notion of a dynamical, scale-dependent Hausdorff dimension for hadronic matter. The physical motivations behind such a concept are explained. For very small scales, we relate this dimension to the anomalous dimension of the product of two momentum densities. For hadrons, we rely on the precocious onset of Bjorken scaling in e-p inelastic scattering and a heuristic parton model to obtain the Hausdorff dimensional profile for the proton d(q²) as a function of the probing photon momentum q². We find that d reaches a maximum around d = 1 for a range of low q² values. This feature is indicative of a string-like structure of the hadrons at low momentum transfers.     

On the longitudinal charge response in the quasielastic peak region

The nuclear charge response in the quasielastic peak region is calculated in a semiclassical approach for moderate momentum transfers (q ≅ 1.5 fm⁻¹). Using the Gogny force and taking full account of the antisymmetrisation, reasonable agreement is found with (e, e′) experimental data in the case of ¹²C. This situation is, however, degrading as one goes to heavier nuclei. Arguments that this is due to the increasing influence of 2p-2h states are given.     

The transverse electron scattering response function of 3He

Results on the transverse response function R _T (q,ω) of ³He obtained within the Lorentz integral transform [LIT] [1] method are presented. The response is calculated using the BonnRA nucleon-nucleon potential [2], the Tucson-Melbourne [3] three-body force, and the Coulomb potential for various momentum transfers. The results are compared with available data.     

Electron scattering from some even fp- and N50-shell nuclei with implanting the influence of short-range correlation functions

The influence of two body short range correlations on elastic electron scattering charge form factors, charge densities as well as root mean square charge radii of some fp-shell nuclei (for example, ⁴⁸Ca, ⁵⁰Cr, ⁵⁴Fe, ⁵⁸Ni, ⁷⁰Ge and ⁷⁴Se) and some N50-shell nuclei (for example, ⁸⁸Sr and ⁹⁰Zr) is analyzed using the one- and two-body terms in the cluster expansion together with the single particle harmonic oscillator wave functions. The Jastrow-type correlation function is utilized to embed the effect of short range correlations into elastic charge form factors F(q) and charge densities ρ(r). Both F(q) and ρ(r) depend upon the harmonic oscillator parameter b and the correlation parameter β (which initiates from the Jastrow correlation function). Here, the parameters b and β are determined via the fitting to the measured charge form factors. The embedding of short range correlations imitates the measured charge form factors at the high momentum transfers (q ≥ 2 fm⁻¹). It is noticed that the implanting of short range correlations is required for obtaining a remarkable alteration in the computed elastic charge form factors which in turn leads to explain the data of electron scattering astonishingly throughout the entire range of considered momentum transfers.     

A measurement of the azimuthal angle dependence of the process ep → enπ+ near threshold

The azimuthal angle dependence of the process ep → enπ⁺ has been measured by detecting the electron and neutron in coincidence. Data are presented for momentum transfers (?k²) between 0.08 and 0.32 $\text{(}\text{GeV}\text{c}\text{)}{}^2$ and at energies close to threshold. Fixed-t dispersion relation models give predictionsin good qualitative agreement with the data.     

Single Regge pole model for large angle elasticp-p scattering at high energies

The elastic proton-proton angular distribution at large momentum transfers (?t?8 (GeV/c)²) and energies above 10 GeV laboratory momentum can be understood in the framework of a single Regge pole model.