P. Thörngren Engblom

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 ...

A small size zero-degree spectrometer with germanium detectors

Abstract A small size spectrometer for detecting heavy reaction products emitted at small angles has been developed. It is installed at the synchrotron storage ring CELSIUS in Uppsala. It uses the focussing and bending magnetic elements of the storage ring itself in combination with a detector telescope, made of high-purity germanium, inserted into the ring vacuum. The spectrometer has been used for studies of pion production reactions close to threshold. The spectrometer is described together with results of ray-trace calculations and experimental tests.

New method for a continuous determination of the spin tune in storage rings and implications for precision experiments

A new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the spin tune-defined as the number of spin precessions per turn-is given by ν(s)=γG (γ is the Lorentz factor, G the gyromagnetic anomaly). At 970u2009u2009MeV/c, the deuteron spins coherently precess at a frequency of ≈120u2009u2009kHz in the Cooler Synchrotron COSY. The spin tune is deduced from the up-down asymmetry of deuteron-carbon scattering. In a time interval of 2.6 s, the spin tune was determined with a precision of the order 10^{-8}, and to 1×10^{-10} for a continuous 100 s accelerator cycle. This renders the presented method a new precision tool for accelerator physics; controlling the spin motion of particles to high precision is mandatory, in particular, for the measurement of electric dipole moments of charged particles in a storage ring.

Polarizing a Stored Proton Beam by Spin-Flip?

We discuss polarizing a proton beam in a storage ring, either by selective removal or by spin flip of the stored ions. Prompted by recent, conflicting calculations, we have carried out a measurement of the spin-flip cross section in low-energy electron–proton scattering. The experiment uses the cooling electron beam at COSY as an electron target. The measured cross sections are too small for making spin flip a viable tool in polarizing a stored beam. This invalidates a recent proposal to use co-moving polarized positrons to polarize a stored antiproton beam.

Exclusive measurement of two-pion production in the dd -g He-4 pi pi reaction

The results from the first kinematically complete measurement of the dd -> He-4 pi pi reaction are reported. The aim was to investigate a long standing puzzle regarding the origin of the peculia ...

Isospin resolved double pion production in the reaction p+d→3He+2π

Abstract Neutral and charged two-pion production in p+d→ 3 He+2 π reactions has been studied at CELSIUS at a proton beam energy of 477 MeV. The total cross section for double pion production is 0.22±0.03 μ b. The ratio of the cross sections for the production of charged pion pairs with isospin T =1 and T =0 was determined to be σ ( π + π − ; T =1)/ σ ( π + π − ; T =0)=1.4±0.4.

The inclusive reaction d + d → 4He + X 29 MeV above the 2π0 threshold☆

Abstract The momentum spectrum of 4 He particles from d + d reactions at E lab = 569 MeV has been measured at zero degrees in the laboratory. The missing-mass spectrum is consistent with a pure phase space behaviour for the isospin zero channel of two pions, corresponding to a total cross section of 43 ± 5 nb.

Facility for studying spin dependence in pion production near threshold

Abstract We describe an experimental setup for the measurement of polarization observables in pion production near threshold. Experiments carried out with this facility use a polarized proton beam in the Indiana University Cooler storage ring, and an internal, polarized hydrogen target. The detector system measures energy, direction and velocity of multiple outgoing charged particles that are within a forward cone of about 32° opening angle. An array of scintillators also allows the detection of neutrons. In addition to the technical details of the apparatus, we describe the procedure for data acquisition, as well as some aspects of the analysis.

The pp→ppπππ reaction channels in the threshold region

The cross section for direct neutral and charged three pion production in pp interactions was measured at excess energies in the range 160–216 MeV. That comprises the first measurement of the pp→ppπ0π0π0 reaction and the direct comparison with the pp→ppπ+π−π0 process. The experiment was performed above the η meson production threshold and the cross section could be directly normalized to the cross section of the pp→ppη reaction, with the η decaying into 3 pions. Since the same final states are selected, the measurement has a low systematical error. The measured cross section ratio σ(pp→ppπ+π−π0)/σ(pp→ppπ0π0π0) is compared to predictions of dominance of different isobars in the intermediate state.

Faddeev Calculations of Breakup Reactions with Realistic Experimental Constraints

Abstract.We present a method to integrate predictions from a theoretical model of a reaction with three bodies in the final state over the region of phase space covered by a given experiment. The method takes into account the true experimental acceptance, as well as variations of detector efficiency, and eliminates the need for a Monte-Carlo simulation of the detector setup. The method is applicable to kinematically complete experiments. Examples for the use of this method include several polarization observables in dp breakup at 270u2009MeV. The calculations are carried out in the Faddeev framework with the CD Bonn nucleon-nucleon interaction, with or without the inclusion of an additional three-nucleon force.