Alpha-gamma decay studies of 255Rf, 251No and 247Fm

The decay of the isotopes ²⁵⁵Rf, ²⁵¹No and ²⁴⁷Fm produced in the reactions , and was investigated by means of α-γ spectroscopy. Previously observed γ transitions in coincidence with α decays of ²⁵⁵Rf were confirmed, their energies and line intensities were measured more precisely, and their multipolarities were determined as E1. In ²⁵¹No a new isomeric state at E ^* > 1700keV with a half-life of ≈ 2μs was identified. The decay of ²⁴⁷Fm was measured more precisely. A partial level scheme of the daughter nucleus ²⁴³Cf could be established.     

Lowest- Q2 measurement of the γp → Δ reaction: Probing the pionic contribution

To determine nonspherical angular-momentum amplitudes in hadrons at long ranges (low Q²), data were taken for the p(ˉe, e'p)π⁰ reaction in the Δ region at Q ² = 0.060 (GeV/c)² utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios at W = 1232 MeV are , Re( )%, and Re( )%. These disagree with predictions of constituent quark models but are in reasonable agreement with lattice calculations with nonlinear (chiral) pion mass extrapolations, with chiral effective field theory, and with dynamical models with pion cloud effects. These results confirm the dominance, and general Q² variation, of the pionic contribution at large distances.     

New information on the T1/2 = 47 s isomer in the 136I nucleus

The ¹³⁶I nucleus, populated in the spontaneous fission of ²⁴⁸Cm, was studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. The observation in this work of the 42.6keV prompt-γ, M1 + E2 transition de-exciting the 7^- level in ¹³⁶I indicates that this level, interpreted as the configuration, does not correspond to the T = 47s, β-decaying isomer in ¹³⁶I. The isomer is placed 42.6keV below the 7^- level. It has spin 6^- and is interpreted as the configuration. This and other members of both multiplets can be reproduced properly only if one assumes that the πd_5/2 orbital in ¹³⁶I is located 400keV lower than in ¹³³Sb. Possible mechanisms causing this effect are discussed.     

ω- πγtransition form factor in proton-proton collisions

Dalitz decays of ω and ρ mesons, and , produced in pp collisions are calculated within a covariant effective meson-nucleon theory. We argue that the ω transition form factor is experimentally accessible in a fairly model-independent way in the reaction pp → ppπ⁰ e ⁺ e ^- for invariant masses of the π⁰ e ⁺ e ^- subsystem near the ω pole. Numerical results are presented for the intermediate-energy kinematics of envisaged HADES experiments.     

Di-electrons from η -meson Dalitz decay in proton-proton collisions

The reaction is discussed within a covariant effective meson-nucleon theory. The model is adjusted to data of the subreaction . Our focus is on di-electrons from Dalitz decays of η -mesons, , and the role of the corresponding transition form factor . Numerical results are presented for the intermediate-energy kinematics of HADES experiments.     

Alpha-gamma decay studies of 255No

The decay of ²⁵⁵No was investigated by means of α-γ spectroscopy. The isotope was produced in the reactions ²⁰⁸Pb(⁴⁸Ca, n)²⁵⁵No, , and $²³⁸U(²²Ne, 5n)²⁵⁵No$. Levels of the daughter nucleus ²⁵¹Fm were assigned by α-γ coincidence measurements and on the basis of systematics. Level energies were determined precisely using measured γ-rays. The results are compared with the known level schemes of the lighter isotones ²⁴⁷Cm and ²⁴⁹Cf as well as with data for ²⁵³No.     

Production properties of K^\star(892)^\pm vector mesons and their spin alignment as measured in the NOMAD experiment

First measurements of mesons production properties and their spin alignment in charged current (CC) and neutral current (NC) interactions are presented. The analysis of the full data sample of the NOMAD experiment is performed in different kinematic regions. For and mesons produced in CC interactions and decaying into we have found the following yields per event: and respectively, while for the and mesons produced in interactions the corresponding yields per event are: and . The results obtained for the parameter, and for and produced in CC interactions, are compared to theoretical predictions tuned on LEP measurements in annihilation at the pole. For mesons produced in interactions the measured parameter is . PACS 13.15.+g, 13.60.Le, 13.87.Fh, 13.88.+e, 14.40.Ev     

Exotic baryons and monopole excitations in a chiral soliton model

We compute the spectra of exotic pentaquarks and monopole excitations of thelow-lying and baryons in a chiral soliton model. Once the low-lying baryon properties are fit, the other states are predicted without any more adjustable parameters. This approach naturally leads to a scenario in which the mass spectrum of the next to lowest-lying states is fairly well approximatedby the ideal mixing pattern of the representation of flavor SU(3). We compare our results to predictions obtained in other pictures for pentaquarks and speculate about the spin-parity assignment for and .Received: 21 April 2004, Revised: 19 May 2004, Published online: 23 July 2004PACS: 12.39.Dc Skyrmions - 14.20.-c Baryons (including antiparticles) - 14.80.-j Other particles (including hypothetical)     

Hyperon-nucleon single-particle potentials with low-momentum interactions

Single-particle potentials in Hartree-Fock approximation for different hyperon-nucleon (YN channels are calculated in the framework of the effective low-momentum YN interaction . In contrast to the nucleon-nucleon interaction, the available experimental data for the YN interaction are scarce. As a consequence, no unique YN low-momentum potential can be predicted from the various bare potentials. The resulting momentum- and density-dependent single-particle potentials for several different bare OBE models and for chiral effective field theory are compared to each other.     

Hadronic η and $ \eta{^\prime}$ decays

The hadronic decays η, ↦3π and ↦ηππ are investigated within the framework of U(3) chiral effective field theory in combination with a relativistic coupled-channels approach. Final state interactions are included by deriving s- and p-wave interaction kernels for meson-meson scattering from the chiral effective Lagrangian and iterating them in a Bethe-Salpeter equation. Very good overall agreement with currently available data on decay widths and spectral shapes is achieved.     

Improving bounds on flavor changing vertices in the two Higgs doublet model from B^0-\bar{B}^0 mixing

We find some constraints on the flavor changing vertices of the two Higgs doublet model, from the measurement. Although bounds from this observable have already been considered, this paper takes into account the role of a new operator not included previously, as well as the vertices , and . Using the Cheng–Sher parametrization, we find that for a relatively light charged Higgs boson (200–300 GeV), we obtain , while the parameter could have values up to about 50. In addition, we use bounds for and obtained from at next to leading order, and study the case where the only vanishing vertex factors are the ones involving quarks from the first family. We obtain that is not sensitive to the change of the parameter , while .     

Spin- {\frac{{3}}{{2}}} beyond the Rarita-Schwinger framework

We employ the two independent Casimir operators of the Poincaré group, the squared four-momentum, p², and the squared Pauli-Lubanski vector, W², in the construction of a covariant mass m, and spin- projector in the four-vector spinor, ψ_μ. This projector provides the basis for the construction of an interacting Lagrangian that describes a causally propagating spin- particle coupled to the electromagnetic field by a gyromagnetic ratio of .     

Study of spectator tagging in the reaction np → ppπwith a deuteron beam

The reaction has been studied in a kinematically complete experiment at a single beam momentum GeV/c (T = 759MeV). All four ejectiles have been detected in the large-acceptance time-of-flight spectrometer COSY-TOF. We analyzed the data along the lines of the spectator model as a means to isolate the quasi-free reaction. The spectator proton was identified by its momentum and flight direction thus yielding access to the associated Fermi motion of the bound neutron. A comparison is carried out with Monte Carlo simulations based on two different parameterizations of the deuteron wave function. Up to a Fermi momentum of roughly 150MeV/c no significant deviations between experimental and simulated data of various observables were found from which we conclude that the deuteron can indeed be taken as a valid substitute for the neutron.     

Study of spin and decay-plane correlations of W bosons in the e + e$^-\rightarrow$ W + W- process at LEP

Data collected at LEP at centre-of-mass energies GeV are used to study correlations of the spin of W bosons using events. Spin correlations are favoured by data, and found to agree with the Standard Model predictions. In addition, correlations between the W-boson decay planes are studied in and events. Decay-plane correlations are measured to be consistent with the Standard Model predictions.Received: 26 October 2004, Revised: 15 January 2005, Published online: 3 March 2005     

Photo-induced nucleosynthesis: Current problems and experimental approaches

Photon-induced reactions play a key role in the nucleosynthesis of rare neutron-deficient p -nuclei. The paper focuses on , , and reactions which define the corresponding p -process path. The relation between stellar reaction rates and laboratory cross-sections is analyzed for photon-induced reactions and their inverse capture reactions to evaluate various experimental approaches. An improved version S _C(E) of the astrophysical S -factor is suggested which is based on the Coulomb wave functions. S _C(E) avoids the apparent energy dependence which is otherwise obtained for capture reactions on heavy nuclei. It is found that a special type of synchrotron radiation available at SPring-8 that mimics stellar blackbody radiation at billions of kelvins is a promising tool for future experiments. By using the blackbody synchrotron radiation, sufficient event rates for and reactions in the p -process path can be expected. These experiments will provide data to improve the nuclear parameters involved in the statistical model and thus reduce the uncertainties of nucleosynthesis calculations.     

Measurement of the LT-asymmetry in πelectroproduction at the energy of the Δ(1232)-resonance

The reaction p(e, e'p)π⁰ has been studied at Q² = 0.2 (GeV/c)² in the region of W = 1232MeV. From measurements left and right of , cross-section asymmetries ρ_LT have been obtained in forward kinematics ρ_LT( = 20^°) = (- 11.68±2.36_stat±2.36_sys) and backward kinematics ρ_LT( = 160^°) = (12.18±0.27_stat±0.82_sys) π⁰. Multipole ratios {S₁₊ ^* M₁₊}/| M₁₊|² and {S₀₊ ^* M₁₊}/| M₁₊|² were determined in the framework of the MAID2003 model. The results are in agreement with older data. The unusally strong negative {S₀₊ ^* M₁₊}/| M₁₊|² required to bring also the result of Kalleicher et al. in accordance with the rest of the data is almost excluded.     

Absolute resonance strengths in the $^{6,7}Li(\alpha, \gamma)^{10,11}B$ reactions

The absolute strengths of the keV resonance in the reaction and of the keV resonance in the reaction have been measured to meV and meV, respectively, in good agreement with previous values. These resonances can be used to measure the absolute acceptance of the recoil separator ERNA to a precision of about 10%.Received: 12 December 2003, Revised: 10 February 2004, Published online: 3 August 2004PACS: 24.30.-v Resonance reactions - 25.40.Lw Radiative capture - 26.20. + f Hydrostatic stellar nucleosynthesis     

Investigation of the a 0 + (980)-resonance with ANKE

Two experiments on the production of the a ₀ ⁺ (980)-resonance in the reaction were performed with the ANKE spectrometer at COSY-Jülich. The decay channels and were measured simultaneously at energies T = 2.65 GeV and T = 2.83 GeV. For the reaction a total production cross-section of nb has been deduced for T = 2.65 GeV. Further goals of the data analysis are to determine differential cross-sections like angular distributions and the branching ratio .Received: 30 September 2002, Published online: 22 October 2003PACS: 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 25.40.Ve Other reactions above meson production thresholds (energies > 400 MeV)P. Fedorets: For the ANKE Collaboration: Complete collaboration list available via: http: //www.fz-juelich.de/ikp/ankeV. Kleber: For the ANKE Collaboration: Complete collaboration list available via: http: //www.fz-juelich.de/ikp/anke