H. Machner

A liquid hydrogen/deuterium target with very thin windows

Abstract Liquid hydrogen/deuterium targets with a typical size of a few millimeters have been constructed for use in intermediate energy experiments with phase space cooled particle beams. With a purely mechanical pressure stabilization system very thin target windows of 1.5 μm Mylar have been obtained. The main advantage of reduced window thickness is a diminution of background events from the window material. The working pressure of 0.2 bar allows the use of oxygen, nitrogen, and helium without modification of the setup. The design and operational characteristics of the target are described.

Meson production close to threshold

Experimental and theoretical work on meson production close to threshold is reviewed, with emphasis on the recent data from small emittance beams available at accelerators/storage rings at IUCF Bloomington, CELSIUS Uppsala and COSY Julich.

Search for η-mesic nuclei in a recoil-free transfer reaction

We have studied the reaction p+{sup 27}Al {yields} {sup 3}He+p+{pi}{sup -}+X at recoil-free kinematics. An {eta} meson possibly produced in this reaction would be thus almost at rest in the laboratory system and could therefore be bound with high probability, if nuclear {eta} states exist. The decay of such a state through the N*(1535) resonance would lead to a proton-{pi}{sup -} pair emitted in opposite directions. For these conditions we find some indication of such a bound state. An upper limit of {approx_equal}0.5 nb is found.

Emission of helium ions after antiproton annihilation in nuclei

Abstract Spectra of hydrogen and helium ions emitted after stopped antiproton annihilation in nuclei have been measured with a Si-detector telescope. Targets of 12C, 40Ca, 63Cu, 92Mo, 98Mo and 238U were used. The 3He and 4He energy spectra can be fitted with the exponential function e−E/T. The parameter T is essentially independent of the target mass number A. A simple pickup model reproduces the 4He/3He ratios as a function of Z and N (target proton and neutron number). The proton spectra from the 238U target indicate that some protons are also emitted by the fission fragments.

High resolution study of the Λp final state interaction in the reaction p+p→K++(Λp)

The reaction pp ! K + + (�p) was measured at Tp = 1.953 GeV and � = 0 ◦ with a high missing mass resolution in order to study thep final state interaction. The large final state enhancement near thep threshold can be described using the stan- dard Jost-function approach. The singlet and triplet scattering lengths and effective ranges are deduced by fitting simultaneously thep invariant mass spectrum and the total cross section data of the freep scattering.

Simultaneous measurements of the p+d→(A=3)+π reactions

A stack of annular detectors made of high purity germanium was used to measure simultaneously

Charge and isospin symmetry breaking via external π0–η meson mixing

pd\to {^3H} \pi^+

Magnetic spectrometer Big Karl for studies of meson production reactions

and

Cross section and tensor analysing power of the dd→ηα reaction near threshold

pd\to {^3He} \pi^0

Charged-particle spectra from antiproton annihilation at rest in a = 12–238 nuclei

differential cross sections at beam momenta of 750 MeV/c, 800 MeV/c, and 850 MeV/c over a large angular range. The extracted total cross sections for the