We report on the current status of the search for the pi NN-resonance d' with I(J(P)) = 0(0(-... more We report on the current status of the search for the pi NN-resonance d' with I(J(P)) = 0(0(-)) and M = 2.06 GeV in the 2 pi production in pp collisions.
Measurements of the pp --> pppi0 reaction at 310, 320, 340, 360, 400 and 425 MeV, and quasi-fr... more Measurements of the pp --> pppi0 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 --> pppi0 differential cross sections have been parametrised and used to deduce the poorly known sigma01 total cross section through the relation: sigma01 = 2sigma(pn --> pppi-) - sigma(pp --> pppi0). Preliminary results show the sigma01 and sigma11 to be of comparable size for centre-of-mass energies between 8 and 40 MeV.
We report on the first exclusive measurement of the 2 production in NN collisions at Tp = 750 MeV... more We report on the first exclusive measurement of the 2 production in NN collisions at Tp = 750 MeV using aH 2 cluster jet target and the WASA/PROMICE detector at CELSIUS. In the invariant-mass spectrum Mpp we ob- serve a narrow peak at 2.063(2) GeV with a 4 deviation relative to the MC simulations for the conventional nonreso- nant 2 production process. The finding is in agreement with the hypothesis of a narrow NN resonance with I(J P )= even (0 ), called d 0 , postulated recently to describe the pe- culiar resonance-like behavior of the pionic double charge exchange on nuclei.
The first measurement of the quasi-free p+n!p+n+j reaction cross section has been made at the CEL... more The first measurement of the quasi-free p+n!p+n+j reaction cross section has been made at the CELSIUS storage ring using a deuterium internal cluster jet target. The energy dependence of the cross section is extracted using a fixed incident proton energy of T p = 1350 MeV and exploiting the Fermi momentum of the struck neutron. The data cover a range of centre-of-mass excess energies from 16 MeV to 109 MeV. The shape of the excitation function is broadly similar to that of the p+p!p+p+j reaction, though with a cross section about a factor of 6.5 larger. PACS numbers: 13.75.-n 13.60.Le 13.75.cs 13.85.Lg Production of j mesons in nucleon-nucleon collisions, N+N!N+N+j, can be described by two independent partial cross sections oe 0 and oe 1 , where the subscripts refer to the total isospin of the two nucleons (0 or 1) in the initial state. The p+p!p+p+j reaction, which corresponds to a pure oe 1 cross section, is reasonably well measured in the threshold region [1-3]. To learn about th...
The pp→ ppπ0 and pn→ ppπ- reactions have been measured at 310, 320 and 340 MeV using the CELSIUS ... more The pp→ ppπ0 and pn→ ppπ- reactions have been measured at 310, 320 and 340 MeV using the CELSIUS proton beam and 1H and 2H internal cluster-jet targets. The π0 production at 310 MeV has been fully analyzed and a significant deviation from isotropy found in the pion angular distributions. This increases at small excitation energies of the final proton pair, suggesting that d-wave pion production is important even close to threshold. Evidence is also found for some P-wave excitation in the final p--p system.
Recent measurements of the pd --> 3He eta reaction at four beam energies: 930, 965, 1037 and 1... more Recent measurements of the pd --> 3He eta reaction at four beam energies: 930, 965, 1037 and 1100 MeV have shown that the total cross section is nearly constant throughout the whole energy region, despite the CM angular distributions becoming more anisotropic with increasing energy. The data join smoothly onto the results of near-threshold measurements, which are dominated by the
Exclusive measurements of the production of η-mesons in the pp ! ppη reaction have been carried o... more Exclusive measurements of the production of η-mesons in the pp ! ppη reaction have been carried out at excess energies of 16 and 37 MeV above threshold. The deviations from phase space are dominated by the proton-proton final state interaction and this influences particularly the energy distribution of the η meson. However, evidence is also presented at the higher energy
With the PROMICE/WASA detector setup at CELSIUS the reaction {pp --> NNpi pi} has been measure... more With the PROMICE/WASA detector setup at CELSIUS the reaction {pp --> NNpi pi} has been measured in the energy range from 650 to 775 MeV. These data constitute the first exclusive high-statistics measurements on a pure hydrogen target, supplying both differential and integral cross sections. Most of the differential spectra for {pp --> pppi -pi + } are close to phase space predictions (including NN final-state interaction) identifying the production via {N*(1440) --> N(pi pi )I = L = 0 } as the dominant process. However, the measured Mpi +pi --spectrum is strikingly different from phase space simulation pointing to the importance of other processes in this reaction. Possible contributions from dibaryon resonances are discussed.
The status of the search for NN-decoupled resonances in the πNN-system is reviewed. After a short... more The status of the search for NN-decoupled resonances in the πNN-system is reviewed. After a short survey on the history of dibaryon searches reactions suitable for detecting such resonances are discussed. Special emphasis is put on the pionic double charge exchange, where recently evidence for the signature of a narrow πNN resonance, called d′, with I(JP) = even (0−) and m = 2.06 GeV has been quoted. Further reactions discussed in this context are the pion photoproduction on the deuteron and the two-pion production in nucleon-nucleon collisions.
Abstract The two-pion production in nucleon–nucleon collisions has been investigated systematical... more Abstract 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.
We report on the current status of the search for the pi NN-resonance d' with I(J(P)) = 0(0(-... more We report on the current status of the search for the pi NN-resonance d' with I(J(P)) = 0(0(-)) and M = 2.06 GeV in the 2 pi production in pp collisions.
Measurements of the pp --> pppi0 reaction at 310, 320, 340, 360, 400 and 425 MeV, and quasi-fr... more Measurements of the pp --> pppi0 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 --> pppi0 differential cross sections have been parametrised and used to deduce the poorly known sigma01 total cross section through the relation: sigma01 = 2sigma(pn --> pppi-) - sigma(pp --> pppi0). Preliminary results show the sigma01 and sigma11 to be of comparable size for centre-of-mass energies between 8 and 40 MeV.
We report on the first exclusive measurement of the 2 production in NN collisions at Tp = 750 MeV... more We report on the first exclusive measurement of the 2 production in NN collisions at Tp = 750 MeV using aH 2 cluster jet target and the WASA/PROMICE detector at CELSIUS. In the invariant-mass spectrum Mpp we ob- serve a narrow peak at 2.063(2) GeV with a 4 deviation relative to the MC simulations for the conventional nonreso- nant 2 production process. The finding is in agreement with the hypothesis of a narrow NN resonance with I(J P )= even (0 ), called d 0 , postulated recently to describe the pe- culiar resonance-like behavior of the pionic double charge exchange on nuclei.
The first measurement of the quasi-free p+n!p+n+j reaction cross section has been made at the CEL... more The first measurement of the quasi-free p+n!p+n+j reaction cross section has been made at the CELSIUS storage ring using a deuterium internal cluster jet target. The energy dependence of the cross section is extracted using a fixed incident proton energy of T p = 1350 MeV and exploiting the Fermi momentum of the struck neutron. The data cover a range of centre-of-mass excess energies from 16 MeV to 109 MeV. The shape of the excitation function is broadly similar to that of the p+p!p+p+j reaction, though with a cross section about a factor of 6.5 larger. PACS numbers: 13.75.-n 13.60.Le 13.75.cs 13.85.Lg Production of j mesons in nucleon-nucleon collisions, N+N!N+N+j, can be described by two independent partial cross sections oe 0 and oe 1 , where the subscripts refer to the total isospin of the two nucleons (0 or 1) in the initial state. The p+p!p+p+j reaction, which corresponds to a pure oe 1 cross section, is reasonably well measured in the threshold region [1-3]. To learn about th...
The pp→ ppπ0 and pn→ ppπ- reactions have been measured at 310, 320 and 340 MeV using the CELSIUS ... more The pp→ ppπ0 and pn→ ppπ- reactions have been measured at 310, 320 and 340 MeV using the CELSIUS proton beam and 1H and 2H internal cluster-jet targets. The π0 production at 310 MeV has been fully analyzed and a significant deviation from isotropy found in the pion angular distributions. This increases at small excitation energies of the final proton pair, suggesting that d-wave pion production is important even close to threshold. Evidence is also found for some P-wave excitation in the final p--p system.
Recent measurements of the pd --> 3He eta reaction at four beam energies: 930, 965, 1037 and 1... more Recent measurements of the pd --> 3He eta reaction at four beam energies: 930, 965, 1037 and 1100 MeV have shown that the total cross section is nearly constant throughout the whole energy region, despite the CM angular distributions becoming more anisotropic with increasing energy. The data join smoothly onto the results of near-threshold measurements, which are dominated by the
Exclusive measurements of the production of η-mesons in the pp ! ppη reaction have been carried o... more Exclusive measurements of the production of η-mesons in the pp ! ppη reaction have been carried out at excess energies of 16 and 37 MeV above threshold. The deviations from phase space are dominated by the proton-proton final state interaction and this influences particularly the energy distribution of the η meson. However, evidence is also presented at the higher energy
With the PROMICE/WASA detector setup at CELSIUS the reaction {pp --> NNpi pi} has been measure... more With the PROMICE/WASA detector setup at CELSIUS the reaction {pp --> NNpi pi} has been measured in the energy range from 650 to 775 MeV. These data constitute the first exclusive high-statistics measurements on a pure hydrogen target, supplying both differential and integral cross sections. Most of the differential spectra for {pp --> pppi -pi + } are close to phase space predictions (including NN final-state interaction) identifying the production via {N*(1440) --> N(pi pi )I = L = 0 } as the dominant process. However, the measured Mpi +pi --spectrum is strikingly different from phase space simulation pointing to the importance of other processes in this reaction. Possible contributions from dibaryon resonances are discussed.
The status of the search for NN-decoupled resonances in the πNN-system is reviewed. After a short... more The status of the search for NN-decoupled resonances in the πNN-system is reviewed. After a short survey on the history of dibaryon searches reactions suitable for detecting such resonances are discussed. Special emphasis is put on the pionic double charge exchange, where recently evidence for the signature of a narrow πNN resonance, called d′, with I(JP) = even (0−) and m = 2.06 GeV has been quoted. Further reactions discussed in this context are the pion photoproduction on the deuteron and the two-pion production in nucleon-nucleon collisions.
Abstract The two-pion production in nucleon–nucleon collisions has been investigated systematical... more Abstract 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.
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Papers by Wolfram Brodowski