| 1. |
- Schonning, K., et al.
(author)
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The pd -> He-3 eta pi(0) reaction at T-p=1450 MeV CELSIUS/WASA Collaboration
- 2010
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In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 685:1, s. 33-37
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Journal article (peer-reviewed)abstract
- The cross section for the pd -> He-3 eta pi(0) reaction has been measured at a beam energy of 1450 MeV using the WASA detector at the CELSIUS storage ring. The He-3 was detected in coincidence with four photons from the decays of the two mesons. The data indicate that the production mechanism involves the formation of the Delta(1232) isobar. Although the beam energy does not allow the full peak of this resonance to be seen, the invariant mass distributions Of all three pairs of final particles are well reproduced by a phase space Monte Carlo simulation weighted with the p-wave factor of the square of the pi(0) momentum in the He-3 pi(0) system.
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| 2. |
- Schönning, Karin, et al.
(author)
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Production of eta and 3 pi mesons in the pd -> (HeX)-He-3 reaction at 1360 and 1450 MeV
- 2010
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In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 45:1, s. 11-21
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Journal article (peer-reviewed)abstract
- The cross-sections of the pd -> He-3 eta, pd -> He-3 pi(0)pi(0)pi(0) and pd -> He-3 pi(+)pi(-)pi(0) reactions have been measured at the beam kinetic energies T-p = 1360 MeV and T-p = 1450 MeV using the CELSIUS/WASA detector setup. At both energies, the differential cross-section d sigma/d Omega of the eta meson in the pd -> He-3 eta reaction shows a strong forward-backward asymmetry in the CMS. The ratio between the pd -> He-3 pi(+)pi(-)pi(0) and pd -> He-3 pi(0)pi(0)pi(0) cross-sections has been analysed in terms of isospin amplitudes. The reconstructed invariant-mass distributions of the pi pi, He-3 pi and (3)He2 pi systems provide hints on the role of nucleon resonances in the 3 pi production process.
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| 3. |
- Schönning, Karin, et al.
(author)
-
The pd →3Heηπ0 reaction at Tp = 1450 MeV
- 2010
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 685:1, s. 33-37
-
Journal article (peer-reviewed)abstract
- The cross section for the pd→3Heηπ0 reaction has been measured at a beam energy of 1450 MeV using the WASA detector at the CELSIUS storage ring and detecting one 3He and four photons from the decays of the two mesons. The data indicate that the production mechanism involves the formation of the Δ(1232) isobar. Although the beam energy does not allow the full peak of this resonance to be seen, the invariant masses of all three pairs of final particles are well reproduce dby a phase space Monte Carlo simulation weighted with the p-wave factor of the square of the π0 momentum in the 3He π0 system.
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| 4. |
- Kren, F., et al.
(author)
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Exclusive measurements of pp -> d pi(+)pi(0) : Double-pionic fusion without ABC effect
- 2010
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 684:2-3, s. 110-113
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Journal article (peer-reviewed)abstract
- Exclusive measurements of the reaction pp -> d pi(+)pi(0) have been carried out at T-p = 1.1 GeV at the CELSIUS storage ring using the WASA detector. The isovector pi(+)pi(0) channel exhibits no enhancement at low invariant pi pi masses, i.e. no ABC effect. Therefore this most basic isovector double-pionic fusion reaction qualifies as an ideal test case for the conventional t-channel Delta Delta excitation process. Indeed, the obtained differential distributions reveal the conventional t-channel Delta Delta mechanism as the appropriate reaction process, which also accounts for the observed energy dependence of the total cross section.
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| 5. |
- Skorodko, T., et al.
(author)
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Delta Delta excitation in proton-proton induced pi(0)pi(0) production
- 2011
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In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 695:1-4, s. 115-123
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Journal article (peer-reviewed)abstract
- Exclusive measurements of the pp -> pp pi(0)pi(0) reaction have been performed at CELSIUS/WASA at energies from threshold up to T-p = 1.3 GeV. Total and differential cross sections have been obtained. Here we concentrate on energies T-p >= GeV. where the Delta Delta excitation becomes the leading process. No evidence is found for a significant ABC effect beyond that given by the conventional t-channel Delta Delta excitation. This holds also for the double-pionic fusion to the quasibound He-2. The data are compared to model predictions, which are based on both pi- and rho-exchange. Total and differential cross sections are at variance with these predictions and call for a profound modification of the rho-exchange. A phenomenological modification allowing only a small rho-exchange contribution leads to a quantitative description of the data.
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| 6. |
- Skorodko, T., et al.
(author)
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Exclusive measurement of the pp -> nn pi(+)pi(+) reaction at 1.1 GeV
- 2011
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In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 47:9, s. 108-
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Journal article (peer-reviewed)abstract
- First exclusive data for the pp -> nnp(+)pi(+) reaction have been obtained at CELSIUS with the WASA detector setup at a beam energy of T(p) - 1.1 GeV. Total and differential cross-sections disagree with theoretical calculations, which predict the Delta Delta excitation to be the dominant process at this beam energy. Instead, the data require the excitation of one of the nucleons to a higher-lying Delta state, preferably the Delta(1600)P(33), to be the leading process.
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| 7. |
- Skorodko, T, et al.
(author)
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Two-pion production in proton-proton collisions : experimental total cross sections and their isospin decomposition
- 2009
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In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 679:1, s. 30-35
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Journal article (peer-reviewed)abstract
- The two-pion production in pp-collisions has been investigated at CELSIUS in exclusive measurements from threshold up to T-P = 1.36 GeV. Total and differential Cross sections have been obtained for the channels pn pi(+)pi(0), pp pi(+)pi(-), pp pi(0)pi(0) and also nn pi(+)pi(+). For intermediate incident energies T-P > 1GeV, i.e. in the region which is beyond the Roper excitation but at the onset of Delta Delta excitation, the total pp pi(0)pi(0) cross section falls behind theoretical predictions by as much as all order of magnitude near 1.2 GeV, whereas the nn pi(+)pi(+) cross section is a factor of five larger than predicted. An isospin decomposition of the total cross sections exhibits a s-channel-like energy dependence in the region of the Roper excitation as well as a significant contribution of an isospin 3/2 resonance other than the Delta(1232). As possible candidates the Delta(1600) and the Delta(1700) are discussed. (C) 2009 Elsevier B.V. All rights reserved.
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