Isotonic and isobaric dependencies of nuclear charge radii for rare-earth nuclei

Isotonic and isobaric dependencies of nuclear charge radii in the region between Z=54 and Z=70 are obtained from the analysis of isotope shift data r² and muonic and electron scattering data on r². They are compared with the predictions of the droplet model and the Hartree-Fock calculations. The isobaric dependencies of r² have proven to be especially sensitive to the choice of an effective nucleon-nucleon interaction.     

Analysis of the 33-133-133-1final state in photon-photon collisions

The reactione ⁺ e ^- e ⁺ e ^{- 00}e ⁺ e ^- 6 has been analysed using the full data sample taken with the Crystal Ball detector at the DORIS II storage ring at DESY. The ⁰⁰ invariant mass spectrum is dominated by the ', for which we determine the radiative width (') to be (4.5±0.3±0.5)keV. Near 1.9 GeV/c² we observe a second enhancement in the ⁰⁰ mass distribution. Assuming that these events are created by the production and subsequent decay of a wide resonanceX(1900), we have investigated the decay modes, the invariant mass distributions of the ⁰ and ⁰⁰ subsystems and the angular distributions of the final state mesons. We find that the data is best described byJ ^PC=2. For thisJ ^P assignment the resonance parameters are (X) BR(X)=(0.95±0.27±0.20) keV _tot (X)=(221±92±44)MeV, andM(X)=(1881±32±40) MeV/c².Deceased     

Experimental evidence for the box anomaly inη/η′ decays and the electric charge of quarks

Motivated by nearly unanimous claim that the observed mass spectrum ^+- is not that expected from pure ⁰ dominance, we reanalyze all the published data on / ^+- decays. We find non-resonant contributions. In order to evaluate precisely the magnitude of these terms, we also refit the e⁺e^{- +-} data to get reliably the ⁰ parameters and decay amplitude. We show that identifying the non-resonant contribution with the box anomaly predicted by QCD and chiral theories, one achieves a consistent picture. Several checks are performed which show the consistency of our fitted parameters. From four measurements, we determinef ₁,f ₈ and _PS on purely experimental grounds, and we find them in the expected range. Presently available data allow for two solutions, one is consistent with QCD, the other favours integral charge quark models. We show that presently available data do not allow to choose among these two solutions. We discuss the interrelation of uncertainties in e⁺e^{- +-} physics with our two solutions.     

Multi-strange systems in relativistic mean fields

Characteristics of multi- hypernuclei are investigated within the relativistic mean-field theory. Both linear and nonlinear models and a variety of couplings fitted to ordinary hypernuclei have been investigated. All the parametrizations used in the present work predict qualitatively similar dependence of the studied quantities (rms radii, binding energies, densities) on a number of hyperons.Deceased on May 5, 1991     

The Landau-Pomeranchuk effect and soft lepton-pair production in heavy ion collisions

The most general angular decay distribution of the hadronic system in the decay of a polarized into one pseudoscalar plus a vector is calculated. Emphasis is put on decays ine ⁺ e ^– experiments where the neutrino escapes detection and the restframe cannot be reconstructed. We propose a model for the decay intov involving both a vector- and a second class axial vector-current contribution. Then we present numerical results for this decay channel.     

The structure of28Si above 10 MeV excitation energy I: gamma-decay modes and radiative widths of levels

The systematics of-decay modes and radiative widths of highly excited states in²⁸Si has been extended by taking-ray spectra on 60 resonances of the²⁷Al(p,) reaction in the range 1097 keVE _p 4492 keV (12643 keVE _x 15915 keV) and on the²⁴Mg(,) resonances atE =3355, 3431, 4003 keV (E _x =12860, 12925, 13 415 keV). The-decay modes of levels in the sub-resonance region (E _x =10–12.5 MeV) were studied with both the²⁷ A1(p, ) reaction and the²⁷ A1(d, n) reaction at E_d=4,5,6 MeV. Information on radiative widths of levels was obtained by measuring the resonance strengthsS =(2I+1) _p / for 52 resonances of the²⁷Al(p, ) reaction with an emphasis on prospective T=1 states.     

Excitations in208Pb nearE x=5683 keV

A search for the recently proposed two-phonon octupole vibrational (2-POV) 4⁺ or 6⁺ state in²⁰⁸Pb at an excitation energy of 5683 keV has been performed using the²⁰⁷Pb(d,p),²⁰⁸Pb (p,p) and (,) reactions at high energy resolution. No evidence for a two-phonon excitation at this energy is found.This work was supported in part by the DFG under contract nr. II C4-Gr 894/2-1 and by the DFG-Graduiertenkolleg Struktur der Hadronen und Kerne under contract nr. Mu 705/3-1.     

Extended operator expansion method for neutrinoless double beta decay

Reliable calculations of nuclear matrix elements are a prerequisite for the determination of the effective neutrino mass and other particle physics parameters from neutrinoless double beta decay. Here, the operator expansion method is improved by including Coulomb, tensor and central interactions simultaneously. Furthermore, the formalism of the OEM is extended to those matrix elements necessary to extract the right-handed parameters and from 0 decay. OEM includes the dependence of the nuclear matrix elements on the intermediate states implicitly and can therefore be understood as a step beyond the closure approximation. Numerical studies are carried out for the isotope⁷⁶Ge combining the OEM expressions with ground-state wave functions calculated within a proton-neutron quasiparticle Random Phase Approximation (pn-QRPA) model. The influence and relative importance of central, tensor and Coulomb interactions is investigated. Within the OEM, contributions from the Coulomb force are found to be negligible in 0 decay, while the tensor force leads to a moderate change of the results, of the order of (10–30)%, giving a better agreement between sets of calculations which employ different NN-interactions. Generally, results of the OEM+QRPA calculation are similar to previous calculations of 0 decay matrix elements, indicating that 0 decay is not sensitive to model approximations and might therefore be more accurately calculated than the strongly suppressed 2 decay matrix elements.     

Two-proton multiplets in theN=82 nucleus 62 144 Sm82 from in-beamγ-measurements

In a high sensitivity (,2n) in-beam study of ₆₂ ¹⁴⁴ Sm₈₂, with the Kölner Würfel OSIRIS -detector array including a Compton polarimeter, we have identified the complete two-proton multiplets d ₅ ^2/–2 , d ₅ ^2/–1 g ₇ ^2/–1 , g ₇ ^2/–2 , h_11/2d ₅ ^2/–1 and the 9^– to 4^– members of the h_11·/2g ₇ ^2/–1 multiplet.Work partially supported by CICYT (Spain).     

An analysis of dibaryon resonance spectra by GSAP,AUTSPAN and SAMPO-80 codes

Narrow dibaryon resonances observed in elastic and inelastic hadron scattering channels atM _NN ^* =1875–2300 MeV/c² are characterized by the relative resolution (FWHM/M _pp ^* ) 10^–3 comparable to that provided by Ge(Li) detectors in the case of gamma-ray spectroscopy. The gamma-ray spectrum analysis codes GSAP, AUTSPAN and SAMPO-80 have been used to analyse the effective mass distributions of dibaryons from the reactions dp (pn) p, dp (pp) n, np pp^–, and pppp studied at the Dubna synchrophasotron. The produced results suggest these codes to be reliable software tools in the new spectroscopic region of interest.On leave fromNuclear Physics Institute, Czechosl. Acad. Sci., 250 68 e near Prague, Czechoslovakia.     

Fixed exciton number level density for a finite potential well

We present a calculation of the nuclear level density _ph(E) for a fixed number of particlesp and holesh, taking into account the energy dependence of the singleparticle level densityg(). We demonstrate the significant effects of the finite depth of the potential well (continuum effect) and the finite surface thickness of the nucleus on the value of _ph(E).Communicated by: X. Campi     

Λ-Hypernucleus formation in proton-nucleus reactions

We study the production of hyperons inp + A reactions within the BUU transport approach including elastic N rescattering and extract the sticking probabilities and hypernucleus formation cross sections as a function of bombarding energy and target mass. At 1.5 GeV about 25% of the hyperons are found to be bound in case of heavy nuclei like²³⁸U leading to large cross sections for-hypernuclei. The respective hypernuclei show broad distributions in excitation energy, momentum and angular momentum. The decay of the hyperon in case of heavy targets is found to be almost entirely due to nonmesonic decay channels, i.e.N NN processes.Supported by BMFT, GSI, Forschungszentrum Jülich and the Polish Committee for Scientific Research under Grant no. PB2593/2/91     

K s →π+π−γ: a laboratory for meson dynamics

We discuss the decayK _{s +–} in the framework of chiral perturbation theory. The direct emission in this decay can be an useful test of meson dynamics.     

AssociateJ/ψ+γ production: a clean probe of gluon densities

Production of strange and charm particles by hadron-proton collisions is analyzed in terms of a fire-ball (FB) model assuming the multiplicity of secondaries of a given massm, to be proportional to the FB mass: n(m)M ^*, the FB kinematics being determined by the Feynman-Yang scaling, as in the case of production. It is found that (m)1/m ² and that, using this property together with the scaling, no-free-parameter fits to currently available data of strange and charm particles frompp and p collisions are satisfactory, as well as for the photoproduction of charm mesonD and charm hyperon _c .     

A simple model of resonance-dominated quasi-elastic scattering

We examine a highly simplified model of projectile-nucleus scattering in which the elementary interactions are resonance dominated. The essential element introduced into the nuclear dynamics is a shift of spectral strength to an energy comparable with or greater than the resonance half-width. The interplay of the energy dependences yields strong sensitivity to the underlying dynamics. Phenomenological treatments based on simplified nuclear dynamics, such as the -hole model, are seen to reproduce inclusive observables. They do less well on more exclusive observables and can be misleading in their implications for the underlying physics.Communicated by F. Lenz     

Shell model high-spin states in 67 151 Ho84

In an in-beam study of ₆₇ ¹⁵¹ Ho₈₄ we have established its high-spin states up to 10 MeV and have suggested spin assignments up to (49/2) at 6.2 MeV. The main decay-cascade proceeds through the yrast states of the h³ _11/2f² _7/2 and h³ _11/2f_7/2h_9/2 5-particle configurations, which are predicted with good accuracy in parameter-free shell-model calculations. States with one proton in d_3/2, or involving i_13/2 or f_7/2×3^– excitations were also identified.     

The droplet in the tube: A case of phase transition in the canonical ensemble

We consider the 2-dimensional Ising model with ferromagnetic nearest neighbour interaction at inverse temperature. LetS _N = _t be the total magnetization inside anN×N square box, ^per be the Gibbs state in with periodic b.c., andm() be the spontaneous magnetization. We show the existence of the limit

Energy inversion of thef 7/2 andh 9/2 neutrons in yrast states of154Yb

The N=84 nucleus¹⁵⁴Yb was investigated through the¹⁰⁶Cd(⁵⁴Fe,2p) reaction. We found the 16⁺ yrast level in this nucleus to be formed by the (h_11/2 ² f_7/2h_9/2) configuration, in contrast to the lower-Z isotones where (h_11/2 ² f_7/2 ²)16⁺ is the yrast state. Manybody shell model calculations with empirical two-body interactions support our conclusion.Dedicated to Prof. Dr. O. Schult on the occasion of his 60^th birthday     

A search for the lepton-flavour violating decays τ → eα, τ → μα

Lepton spectra in decays have been studied with the ARGUS detector at thee ⁺ e ^– storage ring DORIS II at DESY using the pseudo-rest-frame technique. We have improved upper limits for two-body -decays into a lepton and an unobservable particle.Supported by the German Bundesministerium für Forschung und Technologie, under contract number 054DO51P