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.

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

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.

Differential and total cross sections of the p + p → π+ + d reaction close to threshold were measured employing a magnetic spectrograph with track reconstruction, a very thin liquid hydrogen target and an accelerated proton beam with high phase space density. The data resolve a previous discrepancy between the n + p → π0 + d and the π+ + d → 2p reaction close to threshold indicating that isospin symmetry may be broken in the s-wave part of the cross section.

For the first time the reaction pp→ dπ+ was measured close to threshold. A magnetic spectrometer (3Q2DQ) which allows ray tracing was applied to detect the recoiling deuterons and reconstruct their momenta. The measured anisotropies are between 0.008 and 0.29, indicating the importance of p-wave amplitudes even close to threshold. The presented data support the validity of isospin and time reversal symmetries.

The GEM detector, a hybrid system consisting of the Germanium Wall and the magnetic spectrometer BIG KARL, was developed to investigate meson production and meson-nucleus interaction with cooled external proton beams from the COSY accelerator at Jülich. The Germanium Wall is a stack of up to four annular position-sensitive semiconductor detectors made from high-purity germanium. Its special structure allows experiments with high counting rates. Design features and results from first test runs with the uncooled COSY beam are presented.

For hadron physics experiments the combination of a well defined cooled particle beam and a small target volume provides a well defined interaction vertex. With a thin target a precise energy definition is obtained and systematic errors due to Coulomb scattering and secondary interactions with the target material are reduced. A liquid hydrogen/deuterium target of a few millimeter length has been constructed and operated since three years in the external experiments at COSY Julich.A small target together with a wide acceptance of the detectors behind require the diminution of background reactions. Therefore, very thin target windows of 0.9 mu m Mylar foils are realized with the use of a purely mechanical pressure stabilization system. With a fast heating system one can overcome the problem of background reactions with rest gas condensing on the foils.For the precise definition of the incoming beam, veto systems consisting of two annular plastic scintillators are installed before the target in order to detect all particles not passing through the target cell and their reaction products.The improvements of the liquid hydrogen/deuterium target and the design of veto systems are described.

The p + p --> pi(+) + d reaction is studied at excess energies between 0.275 and 3.86 MeV. Differential and total cross section were measured employing a magnetic spectrometer with nearly 4 pi acceptance in the center of mass system; The measured anisotropies between 0.008 and 0.29 indicate that the p wave is not negligible even so close to threshold. The data are compared to other data offering no evidence for charge symmetry breaking or time reversal violation. The s-wave and p-wave contributions at threshold are deduced.

The p+p→π++d reaction is studied at excess energies between 0.275 and 3.86 MeV. Differential and total cross section were measured employing a magnetic spectrometer with nearly 4π acceptance in the center of mass system. The measured anisotropies between 0.008 and 0.29 indicate that the p wave is not negligible even so close to threshold. The data are compared to other data offering no evidence for charge symmetry breaking or time reversal violation. The s-wave and p-wave contributions at threshold are deduced.Received 24 July 1995DOI:https://doi.org/10.1103/PhysRevLett.77.454©1996 American Physical Society

A stack of annular detectors made of high-purity germanium was developed. The detectors are position sensitive with radial structures. The first one (“Quirl”) is double-sided position sensitive defining 40 000 pixels, the following three (E1, E2 and E3) have 32 wedges each. The Quirl acts as tracker while the other three act as calorimeter. The stack was successfully operated in meson production reactions close to threshold.