W. Scobel

Double-pionic fusion of nuclear systems and the "ABC" effect: approaching a puzzle by exclusive and kinematically complete measurements.

The ABC effect-a puzzling low-mass enhancement in the pipi invariant mass spectrum, first observed by Abashian, Booth, and Crowe-is well known from inclusive measurements of two-pion production in nuclear fusion reactions. Here we report on the first exclusive and kinematically complete measurements of the most basic double-pionic fusion reaction pn-->dpi;{0}pi;{0} at beam energies of 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a (pipi)_{I=L=0} channel phenomenon associated with both a resonancelike energy dependence in the integral cross section and the formation of a DeltaDelta system in the intermediate state. A corresponding simple s-channel resonance ansatz provides a surprisingly good description of the data.

The WASA Detector Facility at CELSIUS

The WASA 4 pi multidetector system, aimed at investigating light meson production in light ion collisions and eta meson rare decays at the CELSIUS storage ring in Uppsala is presented. A unique fea ...

(n, 2n) Anregungsfunktionen für54Fe,70Ge,74Se,85Rb,8688Sr,89Y,92Mo,204Hg im Neutronenenergiebereich 13–18 MeV

Using the activitation method (n,2n) excitation-functions were measured for54Fe,70Ge,74Se,85Rb,8688Sr,89Y,92Mo, and204Hg in the neutron-energy region 13–18 MeV. The results are checked for consistency by means of a systematic of (n, 2n) cross-sections as a function of the nuclear neutron excess (N-Z)/A. Furthermore the data are compared with results from the statistical nuclear reactions theory which were calculated using optical model absorption cross-sections and the Fermi-gas-model formula for the nuclear level density. In the case of204Hg the influence of preequilibrium nucleon emission was taken into account.

Thepp→ppπ+π−reaction studied in the low-energy tail of the Roper resonance

Exclusive measurements of the p p ->p p pi+ pi- reaction have been carried out at Tp = 775 MeV at CELSIUS using the PROMICE/WASA setup. Together with data obtained at lower energy they point to a dominance of the Roper excitation in this process. From the observed interference of its decay routes N* ->N sigma and N* ->Delta pi ->N sigma their energy-dependent relative branching ratio is determined.

Two-pion production in proton-proton collisions ― experimental total cross sections and their isospin decomposition

The two-pion production in pp-collisions has been investigated at CELSIUS in exclusive measurements from threshold up to T-P = 1.36 GeV. Total and differential Cross sections have been obtained for ...

A Precision Measurement of pp Elastic Scattering Cross Sections at Intermediate Energies

Abstract.We have measured differential cross-sections for \ensuremath{\rm pp} elastic scattering with internal fiber targets in the recirculating beam of the proton synchrotron COSY. Measurements were made continuously during acceleration for projectile kinetic energies between 0.23 and 2.59 GeV in the angular range

Measurement of eta meson decays into lepton-antilepton pairs

30^{\circ} \leq \theta_{\rm c.m.} \leq 90^{\circ}

Delta Delta excitation in proton-proton induced pi(0)pi(0) production

. Details of the apparatus and the data analysis are given and the resulting excitation functions and angular distributions presented. The precision of each data point is typically better than 4%, and a relative normalization uncertainty of only 2.5% within an excitation function has been reached. The impact on phase shift analysis as well as upper bounds on possible resonant contributions in lower partial waves are discussed.

Determination of the thermal neutron flux in a fast neutron beam by use of a boron-coated ionization chamber.

A search for rare lepton decays of the η meson was performed using the WASA detector at CELSIUS. Two candidates for double Dalitz decay η→e+e-e+e- events are reported with a background of 1.3±0.2 e ...

Excitation functions of the analyzing power in elastic proton-proton scattering from 0.45 to 2.5 GeV

Exclusive measurements of the pp -> pp pi(0)pi(0) reaction have been performed at CELSIUS/WASA at energies from threshold up to T-p = 1.3 GeV. Total and differential cross sections have been obt ...