145 research outputs found

    Exclusive Measurements of pp -> dpi+pi0: Double-Pionic Fusion without ABC Effect

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    Exclusive measurements of the reaction pp -> dpi+pi0 have been carried out at T_p = 1.1 GeV at the CELSIUS storage ring using the WASA detector. The isovector pi+pi0 channel exhibits no enhancement at low invariant pipi masses, i. e. no ABC effect. The differential distributions are in agreement with the conventional t-channel Delta-Delta excitation process, which also accounts for the observed energy dependence of the total cross section. This is an update of a previously published version -- see important note at the end of the article

    Measurement of the Slope Parameter for the eta->3pi0 Decay in the pp->pp eta Reaction

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    The CELSIUS/WASA setup is used to measure the 3pi0 decay of eta mesons produced in pp interactions with beam kinetic energies of 1.36 and 1.45 GeV. The efficiency-corrected Dalitz plot and density distributions for this decay are shown, together with a fit of the quadratic slope parameter alpha yielding alpha = -0.026 +/- 0.010(stat) +/- 0.010(syst). This value is compared to recent experimental results and theoretical predictions.Comment: 4 pages, 7 Postscript figures, uses revtex4.st

    Study of the nucleon-induced preequilibrium reactions in terms of the Quantum Molecular Dynamics

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    The preequilibrium (nucleon-in, nucleon-out) angular distributions of 27^{27}Al, 58^{58}Ni and 90^{90}Zr have been analyzed in the energy region from 90 to 200 MeV in terms of the Quantum Moleculear Dynamics (QMD) theory. First, we show that the present approach can reproduce the measured (p,xp') and (p,xn) angular distributions leading to continuous final states without adjusing any parameters. Second, we show the results of the detailed study of the preequilibrium reaction processes; the step-wise contribution to the angular distribution, comparison with the quantum-mechanical Feshbach-Kerman-Koonin theory, the effects of momentum distribution and surface refraction/reflection to the quasifree scattering. Finally, the present method was used to assess the importance of multiple preequilibrium particle emission as a function of projectile energy up to 1 GeV.Comment: 22pages, Revex is used, 10 Postscript figures are available by request from [email protected]

    Study of the p p -> p p pi+ pi- Reaction in the Low-Energy Tail of the Roper Resonance

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    Exclusive measurements of the p p -> p p pi+ pi- 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 sigma and N* -> Delta pi -> N sigma their energy-dependent relative branching ratio is determined

    Double-Pionic Fusion of Nuclear Systems and the ABCEffect -- Aproaching a Puzzle by Exclusive and Kinematically Complete Measurements

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    The ABC effect - a puzzling low-mass enhancement in the ππ\pi\pi invariant mass spectrum - is well-known from inclusive measurements of two-pion production in nuclear fusion reactions. Here we report on first exclusive and kinematically complete measurements of the most basic double pionic fusion reaction pndπ0π0pn \to d \pi^0\pi^0 at 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a (ππ)I=L=0(\pi\pi)_{I=L=0} channel phenomenon associated with both a resonance-like energy dependence in the integral cross section and the formation of a ΔΔ\Delta\Delta system in the intermediate state. A corresponding simple s-channel resonance ansatz provides a surprisingly good description of the data

    Production of eta and 3pi mesons in the pd->3HeX reaction at 1360 and 1450 MeV

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    The cross sections of the pd -> 3He eta, pd -> 3He pi0 pi0 pi0 and pd -> 3He pi+ pi- pi0 reactions have been measured at 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 dsigma/dOmega of the eta meson in the pd -> 3He eta reaction shows a strong forward-backward asymmetry in the CMS. The ratio between the pd -> 3He pi+ pi- pi0 and the pd -> 3He pi0 pi0 pi0 cross sections has been analysed in terms of isospin amplitudes. The reconstructed invariant mass distributions of the pi-pi, 3He-pi and 3He-2pi systems provide hints on the role of nucleon resonances in the 3pi production process.Comment: Shorter version accepted to EPJA 10 pages 14 figure
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