The paper describes modifications of the Jülich magnetic spectrometer Big Karl needed to study meson production and especially to investigate charge symmetry breaking effects—an experiment that requires a high-precision measurement. New elements that have been added to Big Karl have extended the spectrometer capabilities to a much wider momentum range. The new features also facilitate simultaneous detection of particles with very different rigidities. The experimental methods for improving background and determining relative acceptance of the spectrometer at various rigidities are presented.

A stack of annular detectors made of high purity germanium was used to measure pp-->pppi(0) differential cross sections at a beam momentum of 850 MeV/c. A total cross section of sigma=9.1+/-1.1 mub is deduced. The fitted distribution of different partial waves to the world total cross section data and to the present differential cross sections favors an approach without low-energy approximations, with the standard value for the final state interaction scattering length, and an important contribution from an intermediate NDelta state.

A stack of annular detectors made of high-purity germanium was used to measure simultaneously pd --> H-3 pi (+) and pd --> He-3 pi (0) 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 pd --> He-3 pi (0) reactions bridge a gap between near threshold data and those in the resonance region. The ratio of the cross sections for the two reaction channels taken at the same eta = P-pi(cm) / m(pi) yields 2.11 +/- 0.08 indicating that a deviation from isospin symmetry is very small. (C) 2001 Elsevier Science B,V. All rights reserved.

Total and differential cross sections for the reactions p + d → 3He + m 0 with m=π, η and p + d → 3H+π+ were measured with the GEM detector at COSY for beam momenta between threshold and the maximum of the corresponding baryon resonance. For both reactions a strong forward-backward asymmetry was found. The data were compared with model calculations. The aspect of isospin symmetry breaking is studied.

The present data support a large anisotropy in accordance with phase shift predictions and in contrast to another recent experiment.

A. Strzałkowski, 3 R. Tsenov, 6 and K. Zwoll Institut für Kernphysik, Forschungszentrum Ju ̈lich, Jülich, Germany Zentrallabor für Elektronik, Forschungszentrum Ju ̈lich, Germany Institute of Physics, Jagellonian University, Krakow, Poland Institute of Nuclear Physics, Krakow, Poland Institute of Nuclear Physics and Nuclear Energy, Sofia, Bulgaria Physics Faculty, University of Sofia, Sofia, Bulgaria Institut für Strahlenund Kernphysik der Universita ̈t Bonn, Bonn, Germany Institut für Kernphysik, Universita ̈t Münster, Münster, Germany Nuclear Physics Division, BARC, Bombay, India Department of Physics and Astronomy, George Mason University, Fairfax, Virginia 22030-4444 ~Received 3 November 2000; published 19 March 2001 !

We have measured the reaction p + d -> 3He + eta at a proton beam energy of 980 MeV, which is 88.5 MeV above threshold using the new ``germanium wall'' detector system. A missing--mass resolution of the detector system of 2.6% was achieved. The angular distribution of the meson is forward peaked. We found a total cross section of (573 +- 83(stat.) +- 69(syst.))nb. The excitation function for the present reaction is described by a Breit Wigner form with parameters from photoproduction.

A stack of annular detectors made of high purity germanium was used to measure pd --> H-3 pi(+) and pd --> He-3 pi(0) differential cross sections simultaneously at 850 MeV/c over a large angular range. The ratios of the cross sections and for averaged squared matrix elements is constant for large momentum transfer. The mean values are 2.27 +/- 0.05 and 2.23 +/- 0.07, respectively.

We have measured the reaction pd --> He-3 eta at a proton beam energy of 980 MeV, which is 88.5 MeV above threshold using the new 'germanium wall' detector system. A missing-mass resolution of the detector system of 2.6% was achieved. The angular distribution of the meson is forward peaked. We found a total cross section of (573 +/- 83 (stat.) +/- 69 (syst.)) nb. The excitation function for the present reaction is described by a Breit Wigner form with parameters from photoproduction. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

We have measured the reaction pdTMHe h at a proton beam energy of 980 MeV, which is 88.5 MeV above threshold using the new ‘germanium wall’ detector system. A missing-mass resolution of the detector system of 2.6% was achieved. Ž Ž . Ž .. The angular distribution of the meson is forward peaked. We found a total cross section of 573 " 83 stat. " 69 syst. nb. The excitation function for the present reaction is described by a Breit Wigner form with parameters from photoproduction. q 2000 Published by Elsevier Science B.V. All rights reserved. 1 Also at National Accelerator Centre, Faure, South Africa. 2 E-mail: h.machner@fz-juelich.de 3 On leave from IUCF, Bloomington, Indiana, USA. 0370-2693r00r$ see front matter q 2000 Published by Elsevier Science B.V. All rights reserved. Ž . PII: S0370-2693 99 01456-2 ( ) M. Betigeri et al.rPhysics Letters B 472 2000 267–272 268 The production of h-mesons is interesting because it opens the possibility of studying the interaction between the lightest isoscalar particle and the nuclear environment. Haider and Liu were the first to show that even bound h-nucleus systems, i.e. h-mesic w x nuclei, could be possible 1 . Based on the results of w x Bhalerao and Liu 2 they found an attractive h-N interaction which in their calculations leads to bound w x states for nuclei with mass number A G 10 3 . w x Rakityanski et al. 4 even relaxed this condition to A G 2. The widths of such states were predicted to be narrow enough to be observable for nuclei with A G w x 4. Wycech et al. 5 also predicted the formation of mesic nuclei in ddTM 4 He,h, but not in pdTM He h. w x In contrast, Abaev and Nefkens 6 , as well as Wilkin w x 3 7 showed that the formation of quasi-bound hHe states in the reaction pdTM He h should indeed be possible. In addition, the reaction pdTM He h is of interest due to its surprisingly large cross section close to threshold making this reaction a prime candidate for w x the source of h-mesons in tagged h-facilities 8 . w x A detector system called the ‘germanium wall’ 9 Ž . was built at the COSY facility in Julich see Fig. 1 . In its complete setup, the germanium wall is a stack of four position sensitive high-purity germanium detectors having a conical acceptance with an opening angle of "287.5 mrad. In the centre of each detector is a hole with a size of "28 mrad allowing the primary beam to pass through. Two types of detecŽ . tors are used, one 1.3 mm thin diode ‘quirl-detector’ for determining the reaction vertices through its good position resolution given by the crossing of two counterrotating spirals and three 17 mm thick diodes Ž for measuring the particle energies ‘energy-detec. w x tors’ . For further details see Ref. 9 . The setup used for the present measurement consisted of one quirl Ž and two energy-detectors Quirl, E1 and E3, see Fig. . 1 . First measurements with the ‘germanium wall’ showed the good missing-mass resolution of the system. The reaction pdTM He h was studied at a Ž proton beam energy of 980 MeV 88.5 MeV above . threshold leading to almost 4p acceptance of the detector system for the product He-particles. We performed two runs at different times. The target was a cell filled with liquid deuterium with 6 mm diameter and thicknesses of 2.4"0.2 Ž . Ž . mm run A and 4.4"0.2 mm run B , respectively w x 10 . The COSY extracted proton beam was focussed onto the target yielding a spot with a radius ss 0.5 mm and a divergence of 6 mrad. These parameters together with the short distance between target to detector yields a total angular uncertainty of 16 mrad, where the individual contributions are linearly added. This uncertainty is much larger than that resulting from the position resolution of the detector, which is in the order of 2 mrad. The beam had a y4 w x momentum spread of Dprps8=10 11 . The energy and direction of the emerging Heparticles were measured by the ‘germanium wall’. Fig. 2 shows a DE–E spectrum demonstrating the capability of the detector system for particle identification. Through energy and emission direction measurement of He-particles, the missing-mass was calculated. A missing-mass spectrum for run B is shown in Fig. 3. The h-peak is clearly visible with a Ž . 2 resolution of ss 6.1"0.5 MeVrc . Background Fig. 1. The detector system ‘germanium wall’. In the present measurement detector E2 was removed. ( ) M. Betigeri et al.rPhysics Letters B 472 2000 267–272 269 Fig. 2. Particle identification using a DE–E spectrum measured with the first two detectors of the ‘germanium wall’. Protons, deuterons, tritons and He-particles can be identified as indicated

We studied the absorption cross section for light ions at hundreds of MeV energy. For such particles solid state detectors have a reduced detection efficiency due to nuclear interactions. The results for the efficiency are condensed to simple formulae with only one parameter.

A Reply to the Comment by J. Blomgren and N. Olsson.Received 18 February 1999DOI:https://doi.org/10.1103/PhysRevLett.83.1693©1999 American Physical Society

We present a method to determine precisely the absolute momentum of the external proton beam from the Jülich Cooler Synchrotron COSY near 1930 MeV/c. In the pp→dπ+ reaction at 1930.477 MeV/c incident beam momentum, the forward going pions (θc.m.=0°) and the backward going deuterons (θc.m.=180°) have the same laboratory momentum. Such coincident pion–deuteron events are detected in the focal plane of the magnetic spectrometer BIG KARL located at θlab=0°. Using the nearly linear dependence of the difference between the measured pion and deuteron momenta as a function of the proton beam momentum, the absolute momentum of the external proton beam from COSY near 1930 MeV/c was determined with a precision of 5.2×10−5.

Measurements of proton induced meson production on hydrogen and deuterium targets using the GEM-detector at COSY are described. Preliminary estimates of the total cross section are presented. Results of the pp --> d pi(+) and pp --> pp pi(o) cross section are in agreement with previous findings. The total cross section of pd --> He-3 pi(o) is consistent with results from pion absorption but a surprisingly large value was found at a beam momentum of 750 MeV/c. The reaction pd --> He-3 eta was measured at two beam energies and was identified by missing mass technique.

The magnetic spectrometer BIG KARL is used to get energy calibration fix-points for the external beam of COSY-Julich. These fixpoints were obtained by measuring the meson-production reaction pp --> d pi(+) close to threshold and at the beam momentum, where the forward pions and the backward deuterons have the same momentum.