Experimental Investigations of Discrepancies in Three-Nucleon Reactions

Abstract

Experiments on pd scattering, pd capture and pd breakup performed by our Kyushu University group since 1988 are reviewed. Various discrepancies between the experimental results and 3N Faddeev calculations have been found, and systematical measurements of the discrepancies have been made. From discrepancies in pd scattering cross section and in 3N binding energy, 2π-exchange 3N force was determined, and the discrepancies were satisfactorily diminished. There are, however, still many discrepancies awaiting theoretical investigation, as described in this report. IntroductionA precise experimental study of three-nucleon (3N) reactions at Kyushu University Tandem Accelerator Laboratory (KUTL) was started in 1988. Before the 3N experiments, high-intensity polarized p-and d-beams had been already developed at KUTL to measure ( d, p) polarization transfer coefficients. These beams were used to obtain high-statistics 3N data. To obtain high-precision and reliable 3N data, experimental facilities were improved.Beam polarization and beam position on the target should be stable in order to obtain reliable data. Also beam intensity should be stable to correctly estimate counting efficiency of detectors. Beam polarization, integrated beam charge, and target thickness (gas pressure and length along the beam axis) should be accurately measured. To obtain high-statistic data, data acquisition speed should be fast enough to accumulate many counts with low counting loss. These requirements were not easily satisfied in a university laboratory.Our purpose for starting 3N experiments at that time was to find 3N forces and to solve A y puzzle. Numerical calculations of Faddeev equations were greatly developed in 1980's. Speeds of computers became faster every year. Koike and Heidenbauer pointed out presence of A y puzzle (1986) [1]. Faddeev calculations with realistic NN potentials instead of separable potentials were made first by Takemiya [2], then by Bochum group [3,4].We decided therefore, to obtain precise and systematic experimental data of 3N reactions. When the precise data were compared with reliable Faddeev calculations, shortage of 2N force (2NF) might appear as a discrepancy between the data and the calculations. The discrepancy might indicate effects of 3NF or other origins which we were looking for. If a discrepancy was confirmed, theoretical investigations would reveal its origin(s), which would be 3NF or others. On this thought, we started precise and systematic experiments on pd system at KUTL in 1988.By 2009 we have made many experiments on (a) pd scattering in a beam energy range of 2-18 MeV,

Elastic nucleon-deuteron scattering and breakup with chiral forces

“…The two nd data sets come from different measurements and both reveal the similar disagreement to data. The pd data set shown in Figure 8a is supported by other SST pd breakup measurements [28] at this energy range. The calculations of the pd breakup with inclusion of the pp Coulomb force [29] revealed only very small Coulomb force effects for this configuration.…”

Dynamics of Three-Nucleon System Studied in Deuteron–Proton Breakup Experiments

“…Further verification of the role of the 3NF has been carried out on the basis of scattering experiments: the measurements of observables for elastic nucleondeuteron scattering and for the breakup of a deuteron in its collision with a nucleon. The extensive discussions of the present status of our understanding of the 3N system dynamics, based on modern calculations and many precise and rich data sets, can be found in recent reviews [9][10][11]. The 3NF turned out to be very important for improving the description of the cross section for nucleon-deuteron elastic scattering.…”

Experimental tests of nuclear interaction models in few-nucleon systems

“…Similarly to the elastic scattering, in addition to differential cross section for the breakup reaction, observables related to nuclear polarization are studied, like vector and tensor analyzing powers and higher-rank polarization observables: spin-correlation coefficients and polarization transfer coefficients. For the systematic reviews of the data of the 3N breakup see [20,21,22]. The goal of measurements in the domain of few-nucleon systems is to validate the existing calculations or, alternatively, to point out the regions of missing dynamical ingredients.…”