Few-Body Experimental Group studies the short-range, Strong Nuclear interactions in the system of three and four nucleons at intermediate energies (few tens to few hundreds MeV).The strong nuclear force is one of the four fundamental forces known in Nature. The other three (Gravity, Electromagnetic and Weak Nuclear) are understood relatively well.
Yukawa, in 1935, was the first to give theory of interactions between two nucleons, as a Meson exchange picture, analogous to the electromagnetic force (where photons are exchanged between two charged particles). After more than a decade , in 1947, British physicist Powell and his team found the mesons experimentally. Yukawa received Noble Prize in Physics of 1949 for the discovery of mesons.
Today, after more than 6 decades of consistent hard work, theoreticians have been able to model the strong nucleon-nucleon interactions, with high accuracy. Some of these important ‘realistic‘ NN-potential models (NN) are; Argonne V18, Nijmegen I, Neimegen II, Charge-Dependent (CD) Bonn. But when the number of nucleons increases (e.g. three nucleon system), the models fail to describe the systems dynamics (or at least some discrepancy remains). Recently researchers have introduced an idea of Three-Nucleon Force (3NF), the force that comes into action (along with the NN-force) when a third nucleon is present in the system. Most widely used 3NF are Tucson-Melbourn 99 (TM-99) and Urbana XI (UXI). Inclusion of 3NF in the original pairwise NN intersections have shown great improvement in understanding the nuclear systems with A>2. Our recent publications will give more detail on 3NF studies. Recently these models have been updated with the inclusion of coulomb effects and relativistic corrections.
At most fundamental level of quantum chromodynamics (QCD), the strong force between the nucleons is understood as residual color force (quark interaction). A direct description of few-nucleon systems at low energy from first principles would require the solution of QCD in the non-perturbative regime, which is not possible. However, the low energy dynamics of QCD can be studied in the chiral effective field theory (EFT) framework. This was first done by Weinberg, he gave chiral perturbation theory (ChPT) for application to the interactions between two and more nucleon system. The result of ChPT may be viewed as an effective nuclear potential. Application of ChPT is very recent and has been studied up to N3LO (next-to-next-to-next leading order) for 2N system, and three or more nucleon system have been studied only up to NNLO (next-to-next leading order). The ChPT approach is very unique and provides a strongly consistent model since the NN and 3N interactions are produced withing ChPT framework.
Our aim is to prepare experimental data-base covering large phase-space region with different observables (differential cross sections and analyzing powers) in order make a full test and reliability of the present nucleon nucleon models.
READ MORE :: http://www.scholarpedia.org/article/Nuclear_Forces
[The group photo above was taken during the last experimental collaboration with the group from KVI, The Netherland]