Measured values of the differential cross sections for pion-nucleon charge exchange, pi- p --> pi0 n, are presented for pi- momenta of 103, 112, 120, 130, 139, 152, and 178 MeV/c. Complete angular distributions were obtained by using the Crystal Ball detector at the Alternating Gradient Synchrotron at Brookhaven National Laboratory. Statistical uncertainties of the differential cross sections vary from 3% to 6% in the backward angle region, and from 6% to about 20% in the forward region with the exception of the two most forward angles. The systematic uncertainties are estimated to be about 3% for all momenta.

The experimental program "Baryon spectroscopy with the Crystal Ball" was under way in 1998–2002 at the Alternating Gradient Synchrotron AGS of Brookhaven National Laboratory, USA. The main goal of this program was to map up the existence of all baryon resonances and to study their characteristics with a high precision. The program has been carried out with the team, the Crystal Ball Collaboration, including 14 institutions from 5 countries. Physicists of PNPI participated in this collaboration playing an essential role. Almost all our information on the N and Δ resonances comes from πN data, mainly from elastic scattering, in the form of cross section and polarization measurements. The data are synthesized by a partialwave analysis. The end products are the various partial waves; the Argand diagram and speed plot of each wave are used to identify the resonances. Till starting the experiments at BNL, the πN data sets in certain energy regions were incomplete and it was easy for a resonance with a small elasticity to be missed. One of the most evident shortcomings of the existed data-base was a lack of precise and systematic data on πp reaction with neutral particles in the final state: πp → γn, πp → πn, πp → ππn, πp → ηn. The experiment E913 at the AGS was concerned with the systematic measurement of neutral final states in πp interactions in the region of low-lying πN resonances; the experiment covered the N and Δ resonances using π-beams. The multi-photon Crystal Ball detector was used for registering photons and neutral mesons in this experiment. This detector has a good energy and angular resolution. The Crystal Ball made it possible to study neutral baryon spectroscopy on a scale not seen before.

Measured values of the differential cross section for pion-nucleon charge exchange, pi(-)p --> pi(0)n, are presented at pi- momenta of 148, 174, 188, 212, 238, 271, 298, and 323 MeV/c, a region dominated by the A(1232) resonance. Complete angular distributions were obtained using the Crystal Ball detector at the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL). Statistical uncertainties of the differential cross sections are typically 2-6%, exceptions being the results at the lowest momentum and at the most forward measurements at the five lowest momenta. We estimate the systematic uncertainties to be 3-6%.

V. Koptev,1 M. Büscher,2 H. Junghans,2 M. Nekipelov,1,2 K. Sistemich,2 H. Ströher,2 V. Abaev,1 H.-H. Adam,3 R. Baldauf,4 S. Barsov,1 U. Bechstedt,2 N. Bongers,2 G. Borchert,2 W. Borgs,2 W. Bräutigam,2 W. Cassing,5 V. Chernyshev,6 B. Chiladze,7 M. Debowski,8 J. Dietrich,2 M. Drochner,4 S. Dymov,9 J. Ernst,10 W. Erven,4 R. Esser,11,* P. Fedorets,6 A. Franzen,2 D. Gotta,2 T. Grande,2 D. Grzonka,2 G. Hansen,12 M. Hartmann,2 V. Hejny,2 L. v. Horn,2 L. Jarczyk,13 A. Kacharava,9 B. Kamys,13 A. Khoukaz,3 T. Kirchner,8 S. Kistryn,13 F. Klehr,12 H. R. Koch,2 V. Komarov,9 S. Kopyto,2 R. Krause,2 P. Kravtsov,1 V. Kruglov,9 P. Kulessa,2,15 A. Kulikov,9,14 V. Kurbatov,9 N. Lang,3 N. Langenhagen,8 I. Lehmann,2 A. Lepges,2 J. Ley,11 B. Lorentz,2 G. Macharashvili,7,9 R. Maier,2 S. Martin,2 S. Merzliakov,9 K. Meyer,2 S. Mikirtychiants,1 H. Müller,8 P. Munhofen,2 A. Mussgiller,2 V. Nelyubin,1 M. Nioradze,7 H. Ohm,2 A. Petrus,9 D. Prasuhn,2 B. Prietzschk,8 H. J. Probst,2 D. Protic,2 K. Pysz,15 F. Rathmann,2 B. Rimarzig,8 Z. Rudy,13 R. Santo,3 H. Paetz gen. Schieck,11 R. Schleichert,2 A. Schneider,2 Chr. Schneider,8 H. Schneider,2 G. Schug,2 O. W. B. Schult,2 H. Seyfarth,2 A. Sibirtsev,2 J. Smyrski,13 H. Stechemesser,12 E. Steffens,16 H. J. Stein,2 A. Strzalkowski,13 K.-H. Watzlawik,2 C. Wilkin,17 P. Wüstner,4 S. Yashenko,9 B. Zalikhanov,9 N. Zhuravlev,9 P. Zolnierczuk,13 K. Zwoll,4 and I. Zychor18 1High Energy Physics Department, Petersburg Nuclear Physics Institute, 188350 Gatchina, Russia 2Institut für Kernphysik, Forschungszentrum Jülich, D-52425 Jülich, Germany 3Institut für Kernphysik, Universität Münster, W.-Klemm-Strasse 9, D-48149 Münster, Germany 4Zentralinstitut für Elektronik, Forschungszentrum Jülich, D-52425 Jülich, Germany 5Institut für Theoretische Physik, Universität Gießen, H.-Buff-Ring 16, D-35392 Gießen, Germany 6Institute for Theoretical and Experimental Physics, Cheremushkinskaya 25, 117259 Moscow, Russia 7High Energy Physics Institute, Tbilisi State University, University Street 9, 380086 Tbilisi, Georgia 8Institut für Kernund Hadronenphysik, Forschungszentrum Rossendorf, D-01474 Dresden, Germany 9Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, 141980 Dubna, Russia 10Institut für Strahlenund Kernphysik, Universität Bonn, Nußallee 14, D-53115 Bonn, Germany 11Institut für Kernphysik, Universität zu Köln, Zülpicher Strasse 77, D-50937 Köln, Germany 12Zentralabteilung Technologie, Forschungszentrum Jülich, D-52425 Jülich, Germany 13Institute of Physics, Jagellonian University, Reymonta 4, 30059 Cracow, Poland 14Dubna Branch, Moscow State University, 141980 Dubna Moscow Region, Russia 15The Henryk Niewodniczanski Institute of Nuclear Physics, Radzikowskiego 152, PL-31342, Cracow, Poland 16Physikalisches Institut II, Universität Erlangen-Nürnberg, Erwin-Rommel-Strasse 1, D-91058 Erlangen, Germany 17Physics Department, UCL, Gower Street, London WC1 6BT, United Kingdom 18The Andrzej Soltan Institute for Nuclear Studies, PL-05400 Swierk, Poland (Received 3 April 2001; published 21 June 2001)

We report a measurement of charge symmetry breaking in the NN eta system. We have measured the ratio of the differential cross sections of the charge-symmetric reactions pi (+) d-->pp eta and pi (-) d-->nn eta in the energy region of the eta threshold. Our result is R = d sigma(pi (+) d-->pp eta)/d sigma(pi (-) d-->nn eta) = 0.938+/-0.009 after a phase- space correction is made for the difference in the threshold energies of the two reactions. The deviation of R from unity is an indication of charge symmetry breaking, which is mostly due to pi (0)- eta mixing. A theoretical model for eta production which includes pi (0) - eta mixing was used to fit the data and yields a mixing angle of (1.5+/-0.4)degrees. Our result is consistent with the mixing angle determined in particle decay and isospin-forbidden processes as well as predictions by several theoretical analyses which yield approximate to1 degrees and another which yields approximate to2 degrees.

R. J. Sutter, 5 A. Švarc, and D. B. White University of California, Los Angeles, Los Angeles, California 90095-1547 Petersburg Nuclear Physics Institute, Gatchina, Leningrad District, 188350, Russia Rudjer Boskovic ́ Institute, Zagreb 10000, Croatia George Washington University, Washington, D.C. 20052 Brookhaven National Laboratory, Upton, New York 11973 Abilene Christian University, Abilene, Texas 79699 Los Alamos National Laboratory, Los Alamos, New Mexico 87545 Forschungszentrum, Ju ̈lich D-52425, Ju ̈lich, Germany ~Received 16 June 2000; published 6 February 2001 !

The near-forward cross section for the pp ->pn pi^+ reaction has been measured at 492 MeV by using the large acceptance ANKE magnetic spectrometer placed at an internal target position of the storage ring COSY-Juelich. Protons and pions emitted near zero degrees were detected in coincidence, and those with theta_pi<= 2 degrees and theta_p<= 2.5degrees were subjected to detailed analysis. Under these conditions, the excitation energy in the np system was below 3 MeV over the measured momentum range. This is the region of the np final-state-interaction peak, which was measured with a resolution of a fraction of an MeV. The shape of the peak allows one to conclude that the fraction of final spin-singlet np pairs is below about 10%. By using the results of scattering theory, this limit is confirmed through a comparison with the cross section for pp ->d pi^+. The smallness of the singlet contribution is consistent with trends seen in lower energy data.

K+ meson production in pA (A = C, Cu, Au) collisions has been studied using the ANKE spectrometer at an internal target position of the COSY-Juelich accelerator. The complete momentum spectrum of kaons emitted at forward angles, theta<12 degrees, has been measured for a beam energy of T(p)=1.0 GeV, far below the free NN threshold of 1.58 GeV. The spectrum does not follow a thermal distribution at low kaon momenta and the larger momenta reflect a high degree of collectivity in the target nucleus.

A universal facility is in preparation for the study of particle production in proton-nucleus reactions below the nucleon-nucleon threshold. The device will be located at the internal target position TP2 at COSY-Jülich and will consist of three dipole magnets. This 0° Facility will separate ejectiles from the circulating proton beam and allow momentum and angle analysis both for positively and negatively charged particles. A major goal of the experimental program is the investigation of the K+-meson production at projectile energies below the NN threshold. The detector concept for these studies is described and also an overview over further planned experiments is given.

First measurement of the spin rotation parameters R and A in {pi}-p elastic scattering in the region of pion-nucleon resonances has been performed at the Leningrad Nuclear Physics Institute. The experiment was carried out on a pion channel of the LNPI synchrocyclotron using a polarized target with LNPI synchrocyclotron using a polarized target with horizontally oriented polarization vector and a multi-plate carbon polarimeter consisting of optical spark chambers with television read-out. Results at the energies 450 and 560 MeV are given in comparison with the predictions of phase-shift analyses.