Exclusive and kinematically complete high-statistics measurements of quasifree polarized np scattering have been performed in the energy region of the narrow resonance-like structure d * with 2 I(J P ) = 0(3 + ), M ≈ 2380 MeV and Γ ≈ 70 MeV observed recently in the double-pionic fusion channels pn → dπ 0 π 0 and pn → dπ + π − . The experiment was carried out with the WASA detector setup at COSY having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process dp → np + pspectator. This allowed the np analyzing power, Ay, to be measured over a broad angular range. The obtained Ay angular distributions deviate systematically from the current SAID SP07 NN partial-wave solution. Incorporating the new Ay data into the SAID analysis produces a pole in the 3 D3 − 3 G3 waves in support of the d * resonance hypothesis.
Exclusive measurements of the quasi-free np → npπ 0 π 0 reaction have been performed by means of dp collisions at T d = 2.27 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region √ s = (2.35-2.46) GeV, which includes the region of the ABC effect and its associated d * (2380) resonance. Adding the d * resonance amplitude to that for the conventional processes leads to a reasonable description of the data. The observed resonance effect in the total cross section is in agreement with the predictions of Fäldt and Wilkin as well with those of Albadajedo and Oset. The ABC effect, i.e. the low-mass enhancement in the π 0 π 0 -invariant mass spectrum, is found to be very modest -if present at all, which might pose a problem to some of its interpretations.
New data on quasifree polarized neutron-proton scattering, in the region of the recently observed d * resonance structure, have been obtained by exclusive and kinematically complete high-statistics measurements with WASA at COSY. This paper details the determination of the beam polarization, 2 checks of the quasifree character of the scattering process, on all obtained Ay angular distributions and on the new partial-wave analysis, which includes the new data producing a resonance pole in the 3 D3-3 G3 coupled partial waves at (2380±10−i40±5) MeV -in accordance with the d * dibaryon resonance hypothesis. The effect of the new partial-wave solution on the description of total and differential cross section data as well as specific combinations of spin-correlation and spin-transfer observables available from COSY-ANKE measurements at T d = 2.27 GeV is discussed.
Observables in elastic proton-deuteron scattering are sensitive probes of the nucleon-nucleon interaction and three-nucleon force effects. The present experimental data base for this reaction is large, but contains a large discrepancy between data sets for the differential cross section taken at 135 MeV/nucleon by two experimental research groups. This paper reviews the background of this problem and presents new data taken at KVI. The nucleon-nucleon potential (NNP) has been studied extensively by investigating the properties of bound nuclear systems, and, in more detail, via a comparison of high-precision two-nucleon scattering data with modern potentials based on the exchange of bosons [1,2,3]. A few of the modern NNPs were facilitated by a partialwave analysis (PWA), that provides a nearly modelindependent analysis of the available scattering data [4]. The modern NNPs reproduce the world data base with a reduced chi-square close to one and have, therefore, been accepted as high-quality benchmark potentials. The precision of modern NNPs has given confidence to study in detail the three-nucleon potential (3NP) which was already predicted in 1939 by Primakoff and Wilson [5]. Compelling evidence of 3NP effects came from various recent theoretical and experimental studies. For example, for light nuclei, Green's function Monte-Carlo calculations employing the high-quality NNPs clearly underestimate the experimental binding energies [2], and, therefore, show that NNPs are not sufficient to describe the three-nucleon and heavier systems accurately. In the last decade, high-precision data at intermediate energies in elastic Nd and dN scattering [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23] for a large energy range together with rigorous Faddeev calculations [24] * Electronic address: ramazani@kvi.nl † Electronic address: messchendorp@kvi.nl for the three-nucleon system have proven to be a sensitive tool to study the 3NP. In particular, a large sensitivity to 3NP effects exists in the minimum of the differential cross section [25,26]. Precision data for a large energy interval for the differential cross section and analyzing power came from recent experimental studies at KVI [7,8,9], RIKEN [10] and RCNP [12]. All these experiments had one common energy of 135 MeV/nucleon. Strikingly, the cross sections obtained at KVI were found to be significantly larger than those measured at RIKEN and at RCNP. The KVI data show significant deviation from predictions of state-of-the-art Faddeev calculations incorporating modern NNPs and 3NPs at this energy, whereas the results obtained at RIKEN and RCNP imply that the cross section can be described reasonably well exploiting the same potentials.This paper presents the results of a new measurement of the differential cross sections of the reaction 2 H( p, d)p at a proton-beam energy of 135 MeV, taken to provide additional data at 135 MeV/nucleon. These results are compared with the previously published data taken at intermediate energies. The data are obtained at KVI using a ne...
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