Pion production by protons on nuclei near the threshold

We propose including in the calculation of the cross section of the process p + N → N + N + π the process of pion production and absorption that proceeds through creation of a Δ-resonance. By taking into account the energy dependence of Δ-resonance width, the contribution of deuteron channel is included in the cross section of π⁰-, π⁺-meson production.     

Elastic and charge exchange scattering of pions on3He in the (3,3)-resonance region

The elastic scattering of pions from³He and the single charge exchange reaction³He(π ^?,π ⁰)³H are calculated in the energy domain of the (3,3)-resonance within the framework of Glauber's theory, including spin and isospin degrees of freedom in all orders. It is pointed out that, from the first minimum on, the differential cross section strongly depends on the parametrization of theπN amplitude, especially on its continuation into the unphysical region of momentum transfer. Single and double spin flip contributions prove to be very important in the charge exchange reaction. Within a modified version of Glauber's formalism, directly usingπN phase shifts rather than amplitudes, the³He charge exchange scattering is reexamined. Whereas the shape of the angle-integrated cross section as a function of pion energy is confirmed, the magnitude is still uncertain within a factor of 2.     

Production of baryon resonances in collisions of 4He nuclei with carbon nuclei at a momentum of 4.2 GeV/c per nucleon

Under conditions of 4π geometry, Δ⁰-and Δ⁺⁺-resonance production in collisions of ⁴He nuclei with carbon nuclei at a momentum of 4.2 GeV/c per nucleon was investigated for the first time. The resonance masses and widths are estimated by analyzing the experimental and background invariant-mass distributions of (pπ ^±) pairs. Contributions to pion production from Δ-resonance decays, as well as from direct pion production, are determined. The results are compared with corresponding data obtained for CC collisions at the same primary momentum of 4.2 GeV/c per nucleon. By and large, the results obtained here comply with the existence of a collective mechanism of delta-isobar excitation in nuclei.     

The N*(1710) as a resonance in the ππN system

We study the ππN system by solving the Faddeev equations, for which the input two-body t-matrices are obtained by solving the Bethe-Salpeter equation in the coupled-channel formalism. The potentials for the ππ, πN sub-systems and their coupled channels are obtained from chiral Lagrangians, which have been earlier used to study resonances in these systems successfully. In this work, we find a resonance in the ππN system with a mass of 1704 ? i375/2MeV and with quantum numbers I = 1/2, J ^π = 1/2⁺. We identify this state with the N ^*(1710). This peak is found where the energies of the ππ sub-system fall in the region of the σ-resonance. We do not find evidence for the Roper resonance in our study indicating a more complex structure for this resonance, nor for any state with total isospin I = 3/2 or 5/2.     

Medium effects in the production and decay of vector mesons in pion-nucleus reactions

The ω-, ϱ-, and φ-resonance production and their dileptonic decay in π⁻ A reactions at 1.1–1.7 GeV/c are calculated within the intranuclear cascade (INC) approach. The invariant mass distribution of the dilepton pair for each resonance can be decomposed in two components which correspond to their decay “inside” the target nucleus and in the vacuum, respectively. The first components are strongly distorted by the nuclear medium due to resonance-nucleon scattering and a possible mass shift at finite baryon density. These medium modifications are compared to background sources in the dilepton spectrum from πN bremsstrahlung as well as the Dalitz decays of ω and η mesons produced in the reaction. Detailed predictions for π⁻Pb reactions at 1.3 and 1.7 GeV/c are made within several momentum bins for the lepton pair.     

Dynamics of f 0(980)-resonance production in the reaction γγ → π + π −

The results of the experiment performed by the Belle Collaboration and aimed at observing the f ₀(980) resonance in the reaction γγ → π ⁺ π ^? are analyzed. It is indicated that these results suggest the presence of mechanisms in this reaction that lead to a strong distortion of the f ₀(980)-resonance line shape in relation to the line shape expected for a solitary Breit-Wigner resonance. It is shown that the K ⁺ K ^?-loop mechanism of f ₀(980) coupling to the γγ system and the destructive interference between the background and f ₀(980)-resonance contributions in the region of the π ⁺ π ^? invariant mass below the K ⁺ K ^? threshold are the main factors responsible for the formation of a specific (stepwise) f ₀(980)-resonance line shape in the cross section for the reaction γγ → π ⁺ π ^?.     

|η+−| and the reaction e+e− → K0K0 at the φ-resonance

|η_+?| can be rather cleanly determined in e⁺e^?→ K⁰$\text{K}$⁰ at the φ-resonance position from the π⁺π^? time-distribution of decays of one of the produced kaons within a suitable angular portion of a hemisphere. Our procedure is better than the existing methods.     

Elastic backwardpd-scattering in Δ-resonance region

Contribution ofΔ-resonance mechanism to elastic backwardpd-scattering overT ₀ =0.5–0.8 GeV range of incident energy is analyzed. As distinct from [1–3], the parameters ofNN?NΔ amplitudes in the phenomenology of one-mesonπ- andρ-exchange are determined frompp→pnπ ⁺ reaction immediately in the kinematic region where the processpd→dp occurs. It has been found as a result that in the vicinity of the region whereΔ-isobar is present on-mass-shell, the coherent sum of the amplitudes ofΔ-resonance mechanism, relativistic one-nucleon exchange and single scattering predicts thepd→dp cross-section to be twice smaller than the experimental one and does not describe the tensor polarization oft ₂₀ deuteron. Possible causes of this discrepancy as well as the relation between the mechanisms ofpd→dp process and the data on reactions of quasi-elastic knock-out of fast deuterons by protons (p,pd) from light nuclei, are discussed.     

Testing the nature of the Λ(1520)-resonance in proton-induced production

The Λ(1520)-resonance has been recently studied in a unitarized coupled-channel formalism with πΣ(1385), KΞ(1530), ˉN and πΣ as constituents blocks. We provide a theoretical study of the predictions of this model in physical observables of the pp → pK⁺K^-p and pp → pK⁺π⁰π⁰Λ reactions. In particular, we show that the ratio between the π⁰π⁰Λ and K^-p mass distributions can provide valuable information on the ratio of the couplings of the Λ(1520)-resonance to πΣ(1385) and ˉN than the theory predicts. Calculations are done for energies which are accessible in an experimental facility like COSY at Jülich or the developing CSR facility at Lanzhou.     

Calculation of exclusive processes with baryons

Using the nucleon andΔ ₃₃-resonance wave functions found out in previous papers [14, 15] we calculate the electromagnetic and weak nucleon formfactors, the transition formfactorγ \(\bar N\) Δ and the decay widths of charmonium levels³ S ₁,³ P ₂ and³ P ₁ into \(\bar N\) N and \(\bar \Delta \) Δ.     

Investigation of valence band structures in Cu-Pd alloys

With the use of a HP 5950 A spectrometer X-ray photoelectron spectra (XPS) of valence band were obtained for Cu-Pd alloys and the density of electron states was calculated by the coherent potential method. It is found that d-resonance states of Pd are present in the alloys containing a high percentage of copper but there are no apparant d-resonance states of Cu in the alloys containing a high percentage of palladium.     

The decay of the vacuum in the field of superheavy nuclear systems

In the strong Coulomb field of a nucleus or quasimolecule withZ?172 a change of the QED vacuum has been predicted, signalled by the spontaneous emission of positrons if holes in theK-shell are available. The dynamical semiclassical theory of positron excitation in heavy ion scattering is presented and extended to collisions with nuclear contact. Interference patterns in the energy spectrum of the emitted positrons and, for sufficiently long reaction timeT, the emerging of a characteristic line at the position of the 1sσ-resonance is predicted. The position and width of the 1sσ-resonance is calculated in dependence on the nuclear configuration, the effect of electron screening is taken into account. Recent experimental indications [1, 2] for structures in the spectra of positrons emitted in U-U collisions at energies close to the Coulomb barrier are discussed in terms of spontaneous positron creation. The observed spectra could be explained under the assumption of long lasting nuclear reactions (T?4·10^?20 s) with a cross section in the millibarn region. Various consequences of this interpretation are discussed.     

Coherentπ 0 photoproduction on12C,13C and16O in theΔ (1232) resonance region

π ⁰ photoproduction has been measured on¹²C,¹³C and¹⁶O in theΔ-resonance region. By limiting the acceptance of theπ ⁰ spectrometer to small angles (Θ≦10°), only the coherent channel could contribute. The data show a broadening of the resonance width whereas the peak energy remains essentially unchanged. Theoretical calculations give considerably lower values compared with our data.     

Electro-excitation amplitudes of the Δ-isobar in the Skyrme model

Electro magnetic transition form factors for the excitation of the Δ33-resonance are evaluated in the Skyrme model. They crucially rely on rotationally induced deformations of the hedgehog soliton which are suppressed by two N _C-orders as compared to the leading parts of the isovector current. Partial photon coupling through vector mesons is included in a schematic way. Recoil corrections are approximated by a boost to the equal-velocity frame. The results for the photodecay amplitudes agree with experimental numbers and the shapes of M1, E2, C2— transition form factors show essential features as observed in electro-excitation experiments.     

On the role of Δ-resonance in the pion production in collisions of heavy intermediate-energy ions in the hydrodynamic approach

Pion production in heavy-ion collisions is considered within the hydrodynamic approach. It is shown that consideration of pion production as a result of Δ-resonance decay (Δ → N + π) leads to hardening of the high-energy “tails” of subthreshold pions.     

Pionic charge exchange on the proton from 40 to 250 MeV

The total cross sections for pionic charge exchange on hydrogen were measured using a transmission technique on thin CH₂ and C targets. Data were taken for π⁻${\pi }^{-}$ lab energies from 39 to 247 MeV with total errors of typically 2% over the Δ-resonance and up to 10% at the lowest energies. Deviations from the predictions of the SAID phase shift analysis in the 60–80 MeV region are interpreted as evidence for isospin-symmetry breaking in the s-wave amplitudes. The charge dependence of the Δ-resonance properties appears to be smaller than previously reported.     

Pion scattering from a bound nucleon at medium energies

In order to examine the validity of the impulse approximation for pion-nucleus scattering in the 33-resonance energy region, we consider pion-scattering from a “nucleus” which consists of a single nucleon bound in a harmonic oscillator potential. A separable πN interaction is assumed. The oscillator parameter is chosen such that the nuclear sizes are fitted for ⁴He ～ ¹⁶O. The binding effect is found to result in a downward shift of the resonance energy (by about 20 MeV), and an increase (by 50 ～ 70%) of the total cross section near the resonance. The angular distribution is also strongly modified. In connection with the binding effect, the importance of a careful treatment of nucleon recoil is emphasized. It is pointed out that the closure approximation which is often used to sum over intermediate nuclear states leads to very misleading results. The effect of the Pauli principle is also examined by excluding some intermediate states.     

The rotational spectrum of trichlorofluoromethane

The microwave and millimetre-wave spectra of CF³⁵Cl₃ have been measured in the ground and first excited doubly degenerate (E) vibrational states. Rotational, centrifugal distortion, and quadrupole parameters were obtained for both states. In the E state, strong l-resonance was observed, enabling some rotation-vibration parameters to be accurately determined. In addition, there was a splitting of the (kl − 1) = ± 1 lines due to the asymmetry of the individual quadrupole coupling tensors with respect to the principal inertial axes.     

On the enhancement of M1-transitions from neutron resonances in the Ba and Ce isotopes

The M1-strength functions for transitions from the ground states of ^136,138Ba and ¹⁴⁰Ce to the states lying near the neutron binding energy B_n are calculated within the quasiparticle-phonon nuclear model. The calculated M1-strength functions describe well the relevant experimental data. It is shown that a notable enhancement of the M1-transitions is caused by the proximity of the maximum of the M1-resonance to B_n. As a result the intensities of the E1 and M1-transitions appear to be close to each other.     

Three-body hadronic structure of low-lying 1/2+ Σ and Λ resonances⋆

We discuss the dynamical generation of some low-lying 1/2⁺ Σ 's and Λ 's in two-meson one-baryon systems. These systems have been constructed by adding a pion in the S -wave to the ˉN pair and its coupled channels, where the 1/2^- Λ(1405) -resonance gets dynamically generated. We solve Faddeev equations in the coupled-channel approach to calculate the T -matrix for these systems as a function of the total energy and the invariant mass of one of the meson-baryon pairs. This squared T -matrix shows peaks at the energies very close to the masses of the strangeness -1 , 1/2⁺ resonances listed in the particle data book.