H. R. Amir-Ahmadi

Systematic investigation of the elastic proton-deuteron differential cross section at intermediate energies

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 30degrees and 170degrees . 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 chiPT .

Precision measurement of vector and tensor analyzing powers in elastic deuteron-proton scattering

Abstract.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 Edlab = 130 and 180 MeV were obtained using the RIKEN facility. The beam polarization was unambiguously determined by measuring the ^12C (d, α)^10B(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.

Spin-isospin selectivity in three-nucleon forces

Abstract Precision data are presented for the break-up reaction, H 2 ( p → , p p ) 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 H 2 ( p → , He 2 ) n channel. These results are compared to the H 2 ( 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.

Proton-deuteron break-up measurements with BINA at 135 MeV

High-precision measurements of the proton-deuteron elastic and break-up reaction have been performed in the past at KVI and elsewhere with the aim to study three-nucleon force (3NF) effects. In the present work, we explored 3NF effects in the break-up scattering process by performing a measurement of vector analyzing powers and differential cross sections using a 135 MeV polarized-proton beam impinging on a liquid-deuterium target. For this study, we used a new experimental setup, Big Instrument for Nuclear-polarization Analysis, BINA, which covers almost the entire kinematical phase space of the break-up reaction. The results are interpreted with the help of state-of-the-art Faddeev calculations.

Proton-deuteron radiative capture cross-sections at intermediate energies

Differential cross-sections of the reaction p(d, 3He)γ have been measured at deuteron laboratory energies of 110, 133 and 180 MeV. The data were obtained with a coincidence setup measuring both the outgoing 3He and the photon. The data are compared with modern calculations including all possible meson-exchange currents and two- and three-nucleon forces in the potential. The data clearly show a preference for one of the models, although the shape of the angular distribution cannot be reproduced by any of the presented models.

Measurements of scattering observables for the pd break-up reaction

High-precision measurements of the scattering observables such as cross sections and analyzing powers for the proton-deuteron elastic and break-up reactions have been performed at KVI in the last two decades and elsewhere to investigate various aspects of the three-nucleon force (3NF) effects simultaneously. In 2006 an experiment was performed to study these effects in p+d break-up reaction at 135 MeV with the detection system, Big Instrument for Nuclear polarization Analysis, BINA. BINA covers almost the entire kinematical phase space of the break-up reaction. The results are interpreted with the help of state-of-the-art Faddeev calculations and are partly presented in this contribution.

Quasi-free elastic deuteron-proton scattering in the three-body break-up reaction of deuteron-deuteron scattering

This paper discusses some of the recent results obtained in a deuteron-deuteron scattering experiment using a polarized beam of deuterons with an incident energy of 130 MeV. A 4π detection system allowed to measure cross sections and spin observables for various final-state configurations. Here, we discuss the quasi-free elastic deuteron-proton scattering process in deuteron-deuteron scattering which has been observed by analyzing kinematical configurations for which the target neutron acts as a spectator particle. This part of the data can be compared directly to three-nucleon calculations and with existing data for the elastic deuteron-proton scattering process. The results for the polarization observables iT11 and T22 agree well with elastic scattering data published so-far and measured concurrently using a proton target. Surprisingly, the tensor observable T20 shows significant discrepancies with data taken using a proton target.

Three-body break-up in deuteron-deuteron scattering at 65 MeV/nucleon

We successfully identified several multibody final states in deuteron-deuteron scattering at 65 MeV/nucleon at KVI using a unique and advanced detection system called BINA. This facility enabled us to perform cross sections and polarization measurements with an improved statistical and systematic precision. The analysis procedure and a part of the results of the three-body break-up channel in the deuteron-deuteron scattering at 65 MeV/nucleon are presented.

STUDY OF ALL REACTION CHANNELS IN DEUTERON-DEUTERON SCATTERING

Few-nucleon systems can be used as fundamental laboratories for studying details of the nuclear force effects. We performed a series of deuteron-deuteron scattering experiments at intermediate energies. The experiments exploited BINA and BBS experimental setups and polarized deuteron beams with kinetic energies of 65 and 90 MeV/nucleon. These experiments aim to measure differential cross sections, vector and tensor analyzing powers of all available reaction channels in deuteron-deuteron scattering. With these data we will provide a systematic database, which will be used to test present theoretical approximations and upcoming ab-initio calculations in four-nucleon system.

19TH INTERNATIONAL IUPAP CONFERENCE ON FEW-BODY PROBLEMS IN PHYSICS

We successfully identified several multibody final states in deuteron-deuteron scattering at 65 MeV/nucleon at KVI using a unique and advanced detection system called BINA. This facility enabled us to perform cross sections and polarization measurements with an improved statistical and systematic precision. The analysis procedure and a part of the results of the three-body break-up channel in the deuteron-deuteron scattering at 65 MeV/nucleon are presented.