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...

The question, whether the high-quality nucleon-nucleon potentials can successfully describe the three-nucleon system, and to what extent three-nucleon forces (3N Fs) play a role, has become very important in nuclear few-body physics. One kinematic region where effects because of 3N Fs show up is in the minimum of the differential cross section of elastic nucleon-deuteron scattering. Another observable, which could give an indication about the contribution of the spin to 3N Fs, is the vector analyzing power. To investigate the importance of 3N Fs systematically over a broad range of intermediate energies, both observables of elastic proton-deuteron scattering have been measured at proton bombarding energies of 108, 120, 135, 150, 170, and 190 MeV, covering an angular range in the center-of-mass system between 30 • and 170 •. The results show unambiguously the shortcomings of calculations employing only two-body forces and the necessity of the inclusion of 3N Fs. They also show the limitations of the results of the present day models for few-nucleon systems at backward angles, especially at higher beam energies. New calculations based on chiral perturbation theory are also presented and compared with the data at the lowest energy.

Precision data are presented for the break-up reaction, 2 H( p, pp)n, within the framework of nuclear-force studies. The experiment was carried out at KVI using a polarized-proton beam of 190 MeV impinging on a liquid-deuterium target and by exploiting the detector, BINA. Some of the vector-analyzing powers are presented and compared with state-of-the-art Faddeev calculations including three-nucleon forces effect. Significant discrepancies between the data and theoretical predictions were observed for kinematical configurations which correspond to the 2 H( p, 2 He)n channel. These results are compared to the 2 H( p, d)p reaction to test the isospin sensitivity of the present three-nucleon force models. The current modeling of two and three-nucleon forces is not sufficient to describe consistently polarization data for both isospin states. Understanding the exact nature of the nuclear force is one of the long-standing questions in nuclear physics. In 1935, Yukawa successfully described the pair-wise nucleon-nucleon (NN) interaction as an exchange of a boson [1]. Current NN models are mainly based on Yukawa's idea and provide an excellent description of the high-quality database of proton-proton and neutron-proton scattering [2] and of the properties of the deuteron. However, for the simplest three-nucleon system, triton, three-body calculations employing NN forces clearly underestimate the experimental binding energies [3], demonstrating that NN forces are not sufficient to describe the three-nucleon system accurately. Some of the discrepancies between experimental data and calculations solely based on the NN interaction can be resolved by introducing an additional three-nucleon force (3NF). Most of the current models for the 3NF are based on a refined version of Fujita-Miyazawa's 3NF model [4], in which a 2π-exchange mechanism is incorporated by an intermediate ∆ excitation of one of the nucleons [5,6].The structure of the 3NF can be studied via a measurement of observables in three-nucleon scattering processes. More detailed information on the spin dependence of the 3NF can be obtained by measuring polarization observables such as the analyzing powers. For this, a series of * Electronic address: messchendorp@kvi.nl extensive studies of 3NF effects in elastic-scattering reactions have been performed at KVI and other laboratories. Precision measurements of the vector analyzing power of the proton in elastic proton-deuteron scattering have been performed at various beam energies ranging from 90 to 250 MeV [7,8,9,10,11]. Also, vector and tensor analyzing powers in elastic deuteron-proton scattering have been obtained at various beam energies ranging from 75 to 270 MeV [12,13,14,15,16,17]. In these measurements, systematic discrepancies between data and theoretical predictions which rigorously solve the Faddeev equations and using only NN potentials were observed. A large part of the discrepancies were removed by adding a 3NF to the NN potentials. Nevertheless, there are still unresolved problems specially at higher...

High precision vector and tensor analyzing powers of elastic deuteron-proton (d + p) scattering have been measured at intermediate energies to investigate effects of three-nucleon forces. Angular distributions in the range of 70 • -120 • in the center-of mass frame for incident-deuteron energies of E lab d = 130 and 180 MeV were obtained using the RIKEN facility. The beam polarization was unambiguously determined by measuring the 12 C(d, α) 10 B(2 + ) reaction at 0 • . Results of the measurements are compared with state-of-the-art three-nucleon calculations. The present modeling of nucleon-nucleon forces and its extension to the three-nucleon system is not sufficient to describe the high precision data consistently and requires, therefore, further investigation.

To investigate the importance of three-nucleon forces (3NF) systematically over a broad range of intermediate energies, the differential cross sections of elastic proton-deuteron scattering have been measured at proton bombarding energies of 108, 120, 135, 150, 170, and 190 MeV at c.m. angles between 30°and 170°. Comparisons with Faddeev calculations show unambiguously the shortcomings of calculations employing only two-body forces and the necessity of including 3NF. They also show the limitations of the latest few-nucleon calculations at backward angles, especially at higher beam energies. Some of these discrepancies could be partially due to relativistic effects. Data at lowest energy are also compared with a recent calculation based on PT.