| 1. |
- Skorodko, Tatiana, et al.
(författare)
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Measurement of the p n ---> p p pi0 pi- reaction in search of the ABC resonance
- 2012
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Ingår i: Proceedings of 12th International Workshop on Production, properties and interaction of mesons (MESON 2012). - Les Ulis Cedex, France : EDP Sciences. ; , s. 09033-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- With pd collisions at T_p = 1.2 GeV exclusive measurements of the quasi-free pn -> pppi^0pi^- reaction have been carried out. Using the WASA detector setup at COSY total and differential cross sections have been obtained for the energy region &radics = 2.35 - 2.48 GeV. Though this includes the region of the ABC effect and its associated resonance structure, no low-mass enhancement (ABC effect) is found in the pi^0pi^--invariant mass spectrum - in agreement with the constraint from Bose statistics demanding the isovector pion pair to be in relative p-wave. Conventional calculations including t-channel processes for Roper, Delta(1600) and DeltaDelta excitations and their decays, which are well-known from the study of the two-pion production in pp collisions, provide a reasonable description of the data at high energies, but fall low at low energies. From this we conclude that a large contribution from a so far unknown isoscalar low-energy process is missed in the calculations. Inclusion of the ABC resonance at m = 2.37 GeV with Gamma = 70 MeV and I(J^P) = 0(3^+), which was recently observed in the pn -> dpi^0pi^0 reaction, leads to a much improved description of the data at low energies.
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| 2. |
- Adlarson, Patrik, et al.
(författare)
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Abashian-Booth-Crowe resonance structure in the double pionic fusion to He-4
- 2012
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 86:3, s. 032201-
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Tidskriftsartikel (refereegranskat)abstract
- Exclusive and kinematically complete high-statistics measurements of the double pionic fusion reaction dd -> He-4 pi(0)pi(0) have been performed in the energy range 0.8-1.4 GeV covering thus the region of the Abashian-Booth-Crowe effect, which denotes a pronounced low-mass enhancement in the pi pi invariant mass spectrum. The experiments were carried out with the WASA detector setup at the cooler synchrotron at Forshungszentrum Julich GmbH. Similar to the observation in the basic pn -> d pi(0)pi(0) reaction, the data reveal a correlation between the ABC effect and a resonancelike energy dependence in the total cross section. The maximum occurs at m = 2.37 GeV + 2m(N), i.e., at the same position as in the basic reaction. The observed resonance width Gamma approximate to 160 MeV can be understood from broadening due to Fermi motion of the nucleons in initial and final nuclei together with collision damping. Differential cross sections are described equally well by the hypothesis of a pn resonance formation during the reaction process.
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| 3. |
- Adlarson, Patrik, et al.
(författare)
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Exclusive measurement of the eta -> pi(+) pi(-) gamma decay
- 2012
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 707:2, s. 243-249
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Tidskriftsartikel (refereegranskat)abstract
- An exclusive measurement of the decay eta -> pi(+) pi(-) gamma has been performed at the WASA facility at COSY. The eta mesons were produced in the fusion reaction pd -> He-3 X at a proton beam momentum of 1.7 GeV/c. Efficiency corrected differential distributions have been extracted based on 13 960 +/- 140 events after background subtraction. The measured pion angular distribution is consistent with a relative p-wave of the two-pion system, whereas the measured photon energy spectrum was found at variance with the simplest gauge invariant matrix element of eta -> pi(+) pi(-) gamma. A parameterization of the data can be achieved by the additional inclusion of the empirical pion vector form factor multiplied by a first-order polynomial in the squared invariant mass of the pi(+) pi(-) system.
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