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R. Engels

Publications and source records attributed to R. Engels.

67 records · Page 4Linked to original sources
arXiv2013

Characterization of the JUDIDT Readout Electronics for Neutron Detection

The Group for the development of neutron and gamma detectors in the Central Institute of Engineering, Electronics and Analytics (ZEA-2) at Forschungszentrum Juelich (FZJ) has developed, in collaboration with European institutes, an Anger Camera prototype for improving the impact point reconstruction of neutron tracks. The detector is a chamber filled with $^3He+CF_4$ gas for neutron capture and subsequent production of a tritium and a proton. The energy deposition by the ions gives rise to drifting electrons with an avalanche amplification as they approach a micro-strip anode structure. The scintillating light, generated during the electron drift and avalanche stage, is collected by four vacuum photomultipliers. The position reconstruction is performed via software algorithms. The JUDIDT readout electronics was modified at ZEA-2 to cope with the data acquisition requirements of the prototype. The results of the commissioning of the electronics are here presented and commented.

physics.ins-det↗
arXiv2012

Isospin Decomposition of the Basic Double-Pionic Fusion in the Region of the ABC Effect

Exclusive and kinematically complete high-statistics measurements of the basic double pionic fusion reactions pn -> dpi0pi0, pn -> d pi+pi- and pp -> dpi+pi0 have been carried out simultaneously over the energy region of the ABC effect using the WASA detector setup at COSY. Whereas the isoscalar reaction part given by the dpi0pi0 channel exhibits the ABC effect, i.e. a low-mass enhancement in the pipi-invariant mass distribution, as well as the associated resonance structure in the total cross section, the isovector part given by the dpi+pi0 channel shows a smooth behavior consistent with the conventional t-channel Delta Delta process. The dpi+pi- data are very well reproduced by combining the data for isovector and isoscalar contributions, if the kinematical consequences of the isospin violation due to different masses for charged and neutral pions are taken into account.

nucl-ex↗
arXiv2012

The neutron-proton charge-exchange amplitudes measured in the dp -> ppn reaction

The unpolarised differential cross section and the two deuteron tensor analysing powers A_{xx} and A_{yy} of the pol{d}p -> (pp)n charge-exchange reaction have been measured with the ANKE spectrometer at the COSY storage ring. Using deuteron beams with energies 1.2, 1.6, 1.8, and 2.27 GeV, data were obtained for small momentum transfers to a (pp) system with low excitation energy. The results at the three lower energies are consistent with impulse approximation predictions based upon the current knowledge of the neutron-proton amplitudes. However, at 2.27GeV, where these amplitudes are far more uncertain, agreement requires a reduction in the overall double-spin-flip contribution, with an especially significant effect in the longitudinal direction. These conclusions are supported by measurements of the deuteron-proton spin-correlation parameters C_{x,x} and C_{y,y} that were carried out in the pol{d}pol{p} -> (pp)n reaction at 1.2 and 2.27GeV. The values obtained for the proton analysing power also suggest the need for a radical re-evaluation of the neutron-proton elastic scattering amplitudes at the higher energy. It is therefore clear that such measurements can provide a valuable addition to the neutron-proton database in the charge-exchange region.

nucl-ex↗
arXiv2012

The Polarized H and D Atomic Beam Source for ANKE at COSY-Jülich

A polarized atomic beam source was developed for the polarized internal storage-cell gas target at the magnet spectrometer ANKE of COSY-Jülich. The intensities of the beams injected into the storage cell, measured with a compression tube, are $7.5\cdot 10^{16}$ hydrogen atoms/s (two hyperfine states) and $3.9\cdot 10^{16}$ deuterium atoms/s (three hyperfine states). For the hydrogen beam the achieved vector polarizations are $p_{\rm z}\approx\pm0.92$. For the deuterium beam, the obtained combinations of vector and tensor ($p_{\rm zz}$) polarizations are $p_{\rm z}\approx\pm 0.90$ (with a constant $p_{\rm zz}\approx +0.86$), and $p_{\rm zz}=+0.90$ or $p_{\rm zz}=-1.71$ (both with vanishing $p_{\rm z}$). The paper includes a detailed technical description of the apparatus and of the investigations performed during the development.

physics.ins-det↗
arXiv2012

ABC Resonance Structure in the Double-Pionic Fusion to 4He

Exclusive and kinematically complete high-statistics measurements of the double pionic fusion reaction $dd \to ^4$He$π^0π^0$ have been performed in the energy range 0.8 - 1.4 GeV covering thus the region of the ABC effect, which denotes a pronounced low-mass enhancement in the $ππ$-invariant mass spectrum. The experiments were carried out with the WASA detector setup at COSY. Similar to the observation in the basic $pn \to d π^0π^0$ reaction, the data reveal a correlation between the ABC effect and a resonance-like energy dependence in the total cross section. The maximum occurs at m=2.37 GeV + 2$m_N$, i.e. at the same position as in the basic reaction. The observed resonance width $Γ\approx$ 160 MeV can be understood from broadening due to Fermi motion of the nucleons in initial and final nuclei together with collision damping. Differential cross sections are described equally well by the hypothesis of a $pn$ resonance formation during the reaction process.

nucl-ex↗
arXiv2011

Exclusive Measurement of the eta --> pi+ pi- gamma Decay

An exclusive measurement of the decay eta --> pi+ pi- gamma has been performed at the WASA facility at COSY. The eta mesons were produced in the fusion reaction pd --> 3He X at a proton beam momentum of 1.7 GeV/c. Efficiency corrected differential distributions have been extracted based on 13340\pm140 events after background subtraction. The measured pion angular distribution is consistent with a relative p-wave of the two-pion system, whereas the measured photon energy spectrum was found at variance with the simplest gauge invariant matrix element of eta --> pi+ pi- gamma. A parameterization of the data can be achieved by the additional inclusion of the empirical pion vector form factor multiplied by a first-order polynomial in the squared invariant mass of the pi+ pi- system.

nucl-ex↗
arXiv2011

Hydrogen Spectroscopy with a Lamb-shift Polarimeter - An Alternative Approach Towards Anti-Hydrogen Spectroscopy Experiments

A Lamb-shift polarimeter, which has been built for a fast determination of the polarization of protons and deuterons of an atomic-beam source and which is frequently used in the ANKE experiment at COSY-Jülich, is shown to be an excellent device for atomic-spectroscopy measurements of metastable hydrogen isotopes. It is demonstrated that magnetic and electric dipole transitions in hydrogen can be measured as a function of the external magnetic field, giving access to the full Breit-Rabi diagram for the $2^2S_{1/2}$ and the $2^2P_{1/2}$ states. This will allow the study of hyperfine structure, $g$ factors and the classical Lamb shift. Although the data are not yet competitive with state-of-the-art measurements, the potential of the method is enormous, including a possible application to anti-hydrogen spectroscopy.

physics.atom-ph↗
arXiv2011

ABC Effect in Basic Double-Pionic Fusion --- Observation of a new resonance?

We report on a high-statistics measurement of the basic double pionic fusion reaction $pn \to dπ^0π^0$ over the energy region of the so-called ABC effect, a pronounced low-mass enhancement in the $ππ$-invariant mass spectrum. The measurements were performed with the WASA detector setup at COSY. The data reveal the ABC effect to be associated with a Lorentzian shaped energy dependence in the integral cross section. The observables are consistent with a resonance with $I(J^P) =0(3^+)$ in both $pn$ and $ΔΔ$ systems. Necessary further tests of the resonance interpretation are discussed.

nucl-ex↗
arXiv2009

Measurement of the Spin-Dependence of the pbar-p Interaction at the AD-Ring

We propose to use an internal polarized hydrogen storage cell gas target in the AD ring to determine for the first time the two total spin-dependent pbar-p cross sections sigma_1 and sigma_2 at antiproton beam energies in the range from 50 to 450 MeV. The data obtained are of interest by themselves for the general theory of pbar-p interactions since they will provide a first experimental constraint of the spin-spin dependence of the nucleon-antinucleon potential in the energy range of interest. In addition, measurements of the polarization buildup of stored antiprotons are required to define the optimum parameters of a future, dedicated Antiproton Polarizer Ring (APR), intended to feed a double-polarized asymmetric pbar-p collider with polarized antiprotons. Such a machine has recently been proposed by the PAX collaboration for the new Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany. The availability of an intense stored beam of polarized antiprotons will provide access to a wealth of single- and double-spin observables, thereby opening a new window on QCD spin physics.

nucl-ex↗
arXiv2009

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.

nucl-ex↗
arXiv2009

Machine studies for the development of storage cells at the ANKE facility of COSY

We present a measurement of the transverse intensity distributions of the COSY proton beam at the target interaction point at ANKE at the injection energy of 45 MeV, and after acceleration at 2.65 GeV. At 2.65 GeV, the machine acceptance was determined as well. From the intensity distributions the beam size is determined, and together with the measured machine acceptance, the dimensions of a storage cell for the double-polarized experiments with the polarized internal gas target at the ANKE spectrometer are specified. An optimum storage cell for the ANKE experiments should have dimensions of 15mm x 20mm x 390mm (vertical x horizontal x longitudinal), whereby a luminosity of about 2.5*10^29 cm^-2*s^-1 with beams of 10^10 particles stored in COSY could be reached.

nucl-ex↗
arXiv2006

Determination of Deuteron Beam Polarizations at COSY

The vector and tensor polarizations of a deuteron beam have been measured using elastic deuteron-carbon scattering at 75.6 MeV and deuteron-proton scattering at 270 MeV. After acceleration to 1170 MeV inside the COSY ring, the polarizations of the deuterons were checked by studying a variety of nuclear reactions using a cluster target at the ANKE magnet spectrometer placed at an internal target position of the storage ring. All these measurements were consistent with the absence of depolarization during acceleration and provide a number of secondary standards that can be used in subsequent experiments at the facility.

nucl-ex↗