Th. Walcher

Σ hypernuclear states in (K−, π±) reactions on 12C

Abstract Using negative kaons of momenta 400 and 450 MeV/c, Σ hypernuclear states have been produced in (K−, π−) and (K−, π+) reactions on 12C. The observed states are interpreted as the recoilless production of Σ particles on carbon. The upper limit for the widths of these states is estimated to be 5 MeV, independent of the charge of the Σ particle.

Real-to-imaginary ratio of the pp forward elastic scattering amplitude in the momentum range between 180 and 590 MeV/c

Abstract The real-to-imaginary ratio of the p p forward elastic scattering amplitude has been measured at the LEAR facility of CERN by the Coulomb-nuclear interference method at seven beam momenta between 181 and 590 MeV/c. The ratio is positive at 590 MeV/c, becomes negative below 500 MeV/c, reaches a minimum at 260 MeV/c and then crosses zero again at about 230 MeV/c.

Antiproton-proton elastic cross sections in the momentum range between 180 and 600 MeV/c

Abstract Differential cross sections for pp elastic scattering have been measured in the full angular range for the p momenta between 180 and 600 MeV/ c . It is found that s- and p-wave scattering is dominant below 300 MeV/ c . The s-wave component in the total cross section is 40–60% below 300 MeV/ c , in contrast to the NN scattering where it is about 90%. The s-, p- and d-wave scattering amplitudes are derived.

The (K−, π+) strangeness exchange reaction on 16O

Abstract Using negative kaons of 450 MeV/c momentum, Σ hypernuclear states have been produced in the (K−, π+) reaction on 16O. The observed states are interpreted as the recoilless production of Σ− particles in the p 3 2 and p 1 2 orbits of the Σ16C hypernucleus. Their energy splitting gives a constraint to the magnitude of the spin-orbit coupling for the Σ− particles in the nucleus.

Measurement of the p̄p → n̄n cross section at low p̄ momenta

First measurements of the differential cross section are presented for pp → nn at LEAR in the momentum range between 180 and 600 MeV/c. The differential cross sections show a forward peaking followed by a smooth drop-off. No indication of the “bump-dip” structure reported at higher momenta has been observed. The angle-integrated charge-exchange cross sections are determined down to Enncm = 6.6 MeV.

Fission characteristics of the composite system 32S + 50Ti: (II). Energy and angular dependence

Abstract Angular distributions, mass distributions and excitation functions have been measured for the heavy fragments 35 ≦ A ≦ 60 produced in the bombardment of 50 Ti by 32 S at beam energies between 121 and 166 MeV. The angular distributions are of the form ( sinθ ) −1 for all masses, although slight deviations do occur. The mass distributions exhibit a striking energy dependence with a strong trend towards symmetric mass divisions at high energies. The excitation functions agree qualitatively with the predictions of the rotating liquid drop model.

High resolution inelastic electron scattering and radiation widths of levels in 16O

Abstract Inelastic electron scattering with high energy resolution (FWHM = 30 keV) has been used to study the states at 6.05(0 + ), 6.13(3 − )and 6.92(2 + ) MeV excitation energy in 16 O for momentum transfers q =0.22–0.49 fm −1 . The experiment yields a new determination of reduced transition probabilities and radiative widths for ground-state transitions.

Measurement of αα and αp elastic scattering at the CERN ISR

Abstract Differential cross sections for αα and αp scattering have been measured at √ s =125 and 88 GeV, respectively, in the t range from −0.2 to −0.8 (GeV/ c ) 2 using the Split-Field Magnet detector at the CERN Intersecting Storage Rings. Comparison with theoretical calculations using the Glauber model confirms the importance of including inelastic shadowing effects in very high energy nucleus-nucleus elastic scattering.

A time-of-flight spectrometer using short heavy ion pulses

Abstract A time-of-flight spectrometer consisting of a rebuncher (START signal) and selected surface barrier detectors (STOP signal) has been tested at the Heidelberg post-accelerator. Using the reaction 32 S + 27 Al in an incident energy range of E Lab = 140−320 MeV a time resolution of Δt ∼ 70 ps was routinely achieved. This resulted in a mass resolution for medium-heavy reaction products ( m ≲ 60 u) of Δm ≲ 0.5 u.

Study of high energetic electrons emitted during heavy ion collisions

Double differential cross sectionsd2σ/dΩdE were measured for high energetic electrons emitted in heavy ion collisions. Electrons were detected in the energy range of 60 keV-500 keV for various target projectile combinations 66≦Zu=Zt+Zp≦145 and projectile velocities between 7 % and 10 % of the speed of light. Clear evidence was found that these electrons stem from the united atom formed during the collision. Slope and height of the spectra are discussed with respect to the momentum distribution of strongly bound states (i.e. theL-shell) at momenta far above the mean value. In addition for the systems S, Ni, Br→Pb electrons were detected in coincidence withK x-rays of Pb. By this method the contribution of theK-shell of the combined system to the total spectrum could be separated. Binding energies of theK-shell were estimated by a slope comparison between the coincident and single spectrum. The resulting values are close to the united atom limit.