R. Gebel

Parity violation in proton-proton scattering at 13.6 MeV

Abstract Parity nonconservation in proton-proton scattering has been studied by measuring the angle-integrated longitudinal analyzing power A z . We found A z (13.6 MeV)=(−1.5±0.5)×10 −7 . The error includes uncertainties due to statistics and corrections, as well as upper limits on systematic effects. The experimental result is discussed with respect to recent theoretical calculations.

The polarized ion source for COSY

The polarized ion source for COSY‐Julich has been set in operation. The source produces H− or D− ion beams by means of a charge exchange reaction. For the first time beam acceleration in the injector cyclotron and a first measurement of the beam polarization downstream of the cyclotron took place. The working scheme of this colliding‐beam source and the latest results are discussed.

Position sensitivity by light splitting in scintillator arrays

Abstract A novel detector design of overlapping plastic scintillator elements in cylindrical geometry has been developed for detection of low multiplicity events of fast protons and other light charged particles: each particle traversing the detector from the axis outwards will produce light in several elements. The relative amounts of energy deposited in those elements allow one to interpolate on the particle trajectory beyond the resolution given by the granularity. The detector covers the angular range 10° ≤ Θ lab ≤ 72° and 0° ≤ ϕ ≤ 360° with an inner layer of scintillator bars of triangular cross section and an outer layer of rings. The material is BC408. Tests with minimum ionizing electron beams show that spatial resolutions of ΔΘ lab ≈ 1.5° and Δϕ 12 ≈ 1.5° (FWHM) can be obtained for electrons or proton pairs with energies in the GeV range. In the EDDA experiment the ultimate spatial resolution is then determined by the size of the interaction area rather than by the intrinsic pulse height resolution of the detector.

STATUS OF THE EDDA EXPERIMENT AT COSY

The EDDA experiment is designed to study p + p excitation functions with high energy resolution and narrow step size in the kinetic energy range from 250 MeV to 2500 MeV at the Cooler Synchrotron COSY. Measurements during the accelertion phase in conjunction with internal targets will allow to achieve a fast and precise energy variation. Prototypes of the detector elements and the fiber target have been extensively tested with proton and electron beams; the detector performance and trigger efficiency have been studied in Monte Carlo simulations. In this contribution, results concerning detector design, prototype studies, Monte Carlo simulations and the anticipated detector resolutions will be reported.

Depolarization in proton-6Li elastic scattering

We have measured the differential cross section dσ/dΩ, the analyzing power Ay and the depolarization parameter D for p-6Li elastic scattering at 72 MeV. The spin/isospin character of this transition and the large spinflip effects observed make p-6Li elastic scattering a good case to study the isoscalar spinflip component of the effective force. The data were fitted by a conventional optical-model potential which included a real, spherical spin-spin potential with surface form factor and Vss = 5.3 ± 1.0 MeV. A qualitative description of the data was also achieved with a “semi-microscopic” folding calculation based on the density-dependent Paris effective force, shell-model wave functions and a phenomenological optical-model potential.

Studies on scintillating fiber response

Scintillating fibers of type Bicron BCF-12 with 2 × 2 mm2 cross section, up to 600 mm length, and PMMA cladding have been tested, in conjunction with the multi-channel photomultiplier Hamamatsu R 4760, with minimum ionizing electrons. The impact of cladding, extramural absorbers and/or wrapping on the light attenuation and photoelectron yield is studied in detail. Fibers have been circularly bent with radii of 171 mm and arranged in two layers to bundles forming granulated scintillator rings. Their performance in the EDDA experiment at COSY for detection of high energy protons revealed typically more than 9 (6) photoelectrons per fiber from bundles with (without) mirror on the rear side, guaranteeing detection efficiencies >99% and full compatibility with corresponding solid scintillator rings. The time resolution of 3.4 ns FWHM per fiber read out is essentially due to the R 4760.

A hadron-nucleus collision event generator for simulations at intermediate energies

Abstract Several available codes for hadronic event generation and shower simulation are discussed and their predictions are compared to experimental data in order to obtain a satisfactory description of hadronic processes in Monte Carlo studies of detector systems for medium energy experiments. The most reasonable description is found for the intra-nuclear-cascade (INC) model of Bertini which employs microscopic description of the INC, taking into account elastic and inelastic pion–nucleon and nucleon–nucleon scattering. The isobar model of Sternheimer and Lindenbaum is used to simulate the inelastic elementary collisions inside the nucleus via formation and decay of the Δ 33 -resonance which, however, limits the model at higher energies. To overcome this limitation, the INC model has been extended by using the resonance model of the HADRIN code, considering all resonances in elementary collisions contributing more than 2% to the total cross-section up to kinetic energies of 5xa0GeV. In addition, angular distributions based on phase shift analysis are used for elastic nucleon–nucleon as well as elastic and charge exchange pion–nucleon scattering. Also kaons and antinucleons can be treated as projectiles. Good agreement with experimental data is found predominantly for lower projectile energies, i.e. in the regime of the Bertini code. The original as well as the extended Bertini model have been implemented as shower codes into the high energy detector simulation package GEANT-3.14, allowing now its use also in full Monte Carlo studies of detector systems at intermediate energies. The GEANT-3.14 here have been used mainly for its powerful geometry and analysing packages due to the complex EDDA detector system.

Reduction of space charge effects and tests of larger samples of photomultipliers for the EDDA experiment

Abstract For the EDDA experiment at COSY, the response of the small, linear focused photomultipliers Hamamatsu R 1450 and R 1355 has been studied with fast light pulses generating yields up to 2 × 10 3 photoelectrons/cm 2 or peak currents of 24 mA. Linearity was obtained with a tapered bleeder chain at a tolerable loss of gain. The serial test of altogether 140 photomultipliers revealed the close correlation between single electron and amplitude resolution. The influence of the photoelectron statistics on this correlation is discussed.

Status of the polarized source for the cooler synchrotron COSY‐Jülich

A polarized ion source of the colliding‐beams type is presently installed at the cooler synchrotron COSY‐Julich. The source provides pulsed H↘−‐ or D↘−‐beams. The working scheme, the relations which control the resulting intensity, emittance, and polarization of the source and its status is discussed.

Precise position- and angle-control of a proton beam☆

Abstract For a parity experiment at the Bonn Cyclotron the alignment of the polarized proton beam was stabilized to a precision of less than a μm and μrad, respectively. This stabilization was achieved using fast position pick-ups, fast automatic and low-noise control electronics, and fast steerer devices. Special attention has been payed to neutralize mutual couplings of position signals in space- and time-domain by means of a matrix decoupler.