Exclusive measurements of the two-pion production channel \(pp \rightarrow pp\pi^ + \pi^-\) have been carried out near threshold at CELSIUS with the PROMICE/WASA detector. They reveal \(pp \rightarrow pp^*(1440)\rightarrow pp\sigma \rightarrow pp(\pi^ + \pi^-)_{I = \ell = 0}\) as the dominant process at these energies, however, the data exhibit also significant contributions from \(p^*(1440) \rightarrow \Delta \pi \rightarrow p(\pi^ + \pi^-)_{I = \ell = 0}\). From the observed interference of these Roper decay routes their relative branching ratio is derived. The status on the search for NN-decoupled \(NN\pi\)-resonances is reviewed with regard to recent experimental searches in the pionic double charge exchange in nuclei, the two-pion production in nucleon-nucleon collisions, the photo pion-production on the deuteron and the electro pion-production in nuclei.

Physikalisches Institut der Universita ̈t Tübingen, Morgenstelle 14, D-72076 Tu ̈bingen, Germany The Svedberg Laboratory, S-751 21 Uppsala, Sweden Department of Radiation Sciences, Uppsala University, S-751 21 Uppsala, Sweden Institut für Experimentalphysik der Universita ̈t Hamburg, Hamburg, Germany IKP—Forschungszentrum Ju ̈lich GmbH, D-52425 Ju ̈lich, Germany Joint Institute for Nuclear Research Dubna, 101000 Moscow, Russia Institute for Theoretical and Experimental Physics, 117218 Moscow, Russia Soltan Institute for Nuclear Studies, PL-00681 Warsaw, Poland Institute of Experimental Physics, Warsaw University, PL-0061 Warsaw, Poland Soltan Institute for Nuclear Studies, PL-90137 Lo ́dz, Poland ~Received 30 January 2003; published 28 May 2003 !

Exclusive measurements of the pp → ppπ + π -reaction have been carried out at Tp = 775 MeV at CELSIUS using the PROMICE/WASA setup.Together with data obtained at lower energy they point to a dominance of the Roper excitation in this process.From the observed interference of its decay routes N * → N σ and N * → ∆π → N σ their energy-dependent relative branching ratio is determined.

Exclusive measurements of the pp-->pppi(+)pi(-) reaction have been carried out at T-p=775 MeV at CELSIUS using the PROMICE/WASA setup. Together with data obtained at lower energy, they point to a dominance of the Roper excitation in this process. From the observed interference of its decay routes N-*-->Nsigma and N-*-->Deltapi-->Nsigma, their energy-dependent relative branching ratio is determined.

Exclusive measurements of the two-pion production channel pp → ppπ+π− have been carried out near threshold at CELSIUS with the PROMICE/WASA detector. They reveal \(pp \to pp*\left( {1440} \right) \to pp\sigma \to pp\left( {{\pi ^ + }{\pi ^ - }} \right)I = \ell = 0\) as the dominant process at these energies, however, the data exhibit also significant contributions from \({p^*}\left( {1440} \right) \to \Delta \pi \to p\left( {{\pi ^ + }{\pi ^ - }} \right)I = \ell = 0\) \({p^*}\left( {1440} \right) \to \Delta \pi \to p\left( {{\pi ^ + }{\pi ^ - }} \right)I = \ell = 0\) From the observed interference of these Roper decay routes their relative branching ratio is derived. The status on the search for N N-decoupled N N π-resonances is reviewed with regard to recent experimental searches in the pionic double charge exchange in nuclei, the two-pion production in nucleon-nucleon collisions, the photo pion-production on the deuteron and the electro pion-production in nuclei.

The two-pion production in nucleon–nucleon collisions has been investigated systematically by exclusive and kinematically complete measurements at CELSIUS/WASA and more recently at COSY-TOF and particularly WASA@COSY. The data for all p p -induced isovector production channels in the energy range from threshold up to T p = 1.4 GeV can be well understood by t -channel Roper, Δ Δ and possibly Δ ( 1600 ) excitation. In contrast to that the purely isoscalar reaction channel p n → d π 0 π 0 exhibits a narrow resonance-like structure with m = 2.37 GeV and Γ = 70 MeV in the total cross section, which is correlated with an intriguing low-mass enhancement in the π π invariant mass spectrum (ABC effect) as well as with the formation of a Δ Δ system in the intermediate state. From the angular distributions the spin and parity of this structure have been derived resulting in I ( J P ) = 0 ( 3 + ) . The consequences of the resonance hypothesis for other reaction channels are discussed. The fact that also the double-pionic fusion reactions to 3He and 4He exhibit a corresponding resonance-like structure in the total cross section correlated with the ABC effect suggests that the underlying conjectured p n resonance is obviously robust enough to survive in nuclei.

Experimental results of the dp --> dp gamma reaction are presented for several observables with deuteron projectile energies between 437 MeV and 559 MeV. The kinematically complete measurements were performed at the CELSIUS storage ring with the PROMICE/WASA setup. Angular and spectral distributions of the charged ejectiles are decomposed into fractions that can be attributed to a quasifree np --> dgamma process with a spectator proton and to a process involving all three nucleons. Within the acceptance of the detector, about two thirds of the events are associated to the quasifree process; the remainder are characterized by substantial transverse momentum components transferred to a participating outgoing proton.

Narrow structures in the range of a few MeV have been searched for in pppi(+) and pppi(-) invariant mass spectra (Mpppi+ and Mpppi-) obtained from exclusive measurements of the pp --> pppi(+)pi(-) reaction at T-p = 725,750 and 775 MeV using the PROMICE/WASA detector at CELSIUS. The selected reaction is particularly well suited for the search for dibaryon resonances decoupled from NN and/or NDelta. In the mass range 2020 MeV/c(2) < m(dibaryon) < 2085 MeV/c(2) no narrow structures could be identified on the 3sigma level of statistical significance neither in Mpppi- nor in Mpppi+ giving an upper limit (95% C.L.) for dibaryon production in this reaction of sigma < 20 nb. (C) 2002 Elsevier Science B.V All rights reserved.

The pp-->pp pi(+) pi(-) reaction has been measured exclusively near threshold at CELSIUS. The total cross sections are nearly an order of magnitude lower than expected from previous inclusive measurements. The differential cross sections reveal pp-->pp(*)(1440)-->pp sigma = pp(pi(+)pi(-))(I = l = 0) as the dominant process as well as significant contributions from p(*)-->Delta(++)pi(-)-->psigma. The observed anisotropy in the proton angular dependence is consistent with heavy-meson exchange. In the invariant mass spectra, no narrow structures of statistical relevance (3sigma) are found.

Extensive kinematically complete measurements of the pp→ppπ0 reaction have been made at six beam energies: 310, 320, 340, 360, 400, and 425 MeV. Angles and energies of both final-state protons are extracted from the forward detector system of the WASA-CELSIUS apparatus. Projected one-parameter distributions of the centre-of-momentum pion angle and the angle of the two-proton relative momentum show significant deviations from isotropy. The slope in the pion angular distribution changes from being negative at 310 MeV to positive at 425 MeV. These distributions, and that of the two-proton relative momentum, are described in terms of partial waves corresponding to the Ss,Ps,Pp,Sd and Ds final states. Commonly used amplitudes, derived from their simple threshold behaviour, fail to reproduce the data at the higher energies. However, in a DWBA treatment, assuming interaction ranges related either to π or ρ exchange, we find acceptable agreement, though the longer range of pion exchange provides significantly better description of the Ps and Pp waves.

The two-pion production in proton-proton collisions in vacuum has been measured for the first time exclusively in the energy range T-1 = 650 - 750 MeV with the WASA/PROMICE detectorat CELSIUS. The differential cross sections reveal pp --> pp*(1440) --> ppsigma --> pp(pi(-)pi(+))(/=/=0) to be the dominant process with a significant contribution from the path pp --> pp*(1440) --> pDeltapi --> pp(pi(-)pi(+))(/=/=0). Hence this reaction is very well suited for studying the still poorly known Roper resonance and may also provide in ideal sigma source to study effects of the chiral restauration in the nuclear medium.

Mesurements of the pp-->pppi(0) reaction at 310, 320, 340, 360, 400 and 425 MeV and quasi-free pn-->pppi(+) production in pd collisions at 320 MeV have been carried out at the PROMICE/WASA facility at CELSIUS. The pp-pppi(0) cross sections have been parameterized and used to extract the poorly known sigma(01) cross section through the relation: sigma(pp-->pppi(0)). The results obtained show the sigma(01) and sigma(11), to be of comparable size for CM energies between 3 and 48 MeV.

Extensive kinematically complete measurements of the pp→ppπ0 reaction have been made at six beam energies: 310, 320, 340, 360, 400, and 425 MeV. Angles and energies of both final-state protons are extracted from the forward detector system of the WASA-CELSIUS apparatus. Projected one-parameter distributions of the centre-of-momentum pion angle and the angle of the two-proton relative momentum show significant deviations from isotropy. The slope in the pion angular distribution changes from being negative at 310 MeV to positive at 425 MeV. These distributions, and that of the two-proton relative momentum, are described in terms of partial waves corresponding to the Ss,Ps,Pp,Sd and Ds final states. Commonly used amplitudes, derived from their simple threshold behaviour, fail to reproduce the data at the higher energies. However, in a DWBA treatment, assuming interaction ranges related either to π or ρ exchange, we find acceptable agreement, though the longer range of pion exchange provides significantly better description of the Ps and Pp waves.

High power buried heterostructure 1.55 mum tunable DBR lasers have been designed, fabricated and characterized. The laser consists of a gain section, a distributed Bragg reflector, a semiconductor optical amplifier and front photodetector for automated power control. The heterostructures were grown by MOCVD with the help of selective area growth techniques and dual waveguide heterostructure. Several advantages stem from this integration scheme which include simplicity of design and fabrication, increased reliability and low cost. The laser exhibits output power of 13dBm in the fiber and is tunable over 30 (50GHz) ITU channels. The laser exhibits excellent performance and long-term control and reliability. The laser/transmitter also demonstrates significant increase of its functionality while its size remains small.