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Avraham S. Rinat

Current Research Interests
Inclusive scattering on matter.
One of the universal problems in physics is the description of matter, composed of many particles, when one has information on the nature of the force between two constituents. The quest exists in atomic, molecular, nuclear and astro-physics, and to some extent in particle physics.
As always there are two aspects. Can one develop practical tools to compute matter properties and devise experiments which test those?
The above topic is one approach to the problem. It is a special case of projectiles, which are directed towards a target and where subsequent analysis should provide information. The simplest type is elastic scattering, when the projectile does not loose energy to the target, which remains in the state it was before the scattering. However, the projectile gets deflected from its original path and from it, one distils information on the distribution of particles in matter. Prime examples are x-ray diffraction from crystals and the distribution of protons inside a nucleus.
Occasionally a projectile does loose energy to the target. The probability of occurrence provides specific information on the structure of the target.
Inclusive scattering is a particular kind of inelastic scattering, where a large amount of energy is transferred to a target, enabling the excitation of many modes, without there existing information for a selected one. The same holds for the momentum transferred. In the experiment one deliberately detects only the projectile, or a very limited of other particles. It turns out that the information is nevertheless very rich.
Had the projectile hit only one particle which, due to the large energy imparted to it, had no opportunity to scatter from others, a description of the event must be simple on account of energy-momentum balance in the projectile-particle collision. However, a particle in a medium has no definite momentum. As a result, the experiment gives basic information on the probability that a constituent has a given momentum.
The description above assumes that one knows what the 'constituents' are. What particles does one see if one bombards a complex molecule, a nucleus, or a proton? The answer lies in the energy involved in the encounter. When growing, it will be capable to excite finer details and disclose ever smaller sub-structures. One may thus bombard a nucleus with electrons and in an analysis find that the basic constituents for the given energy are protons and nucleons, undistinguishable from point- particles. Increasing the energy, one will see that those nucleons have finite dimensions. Still increasing the energy discloses that nucleons are composed of quarks and gluons, etc.
In addition to the above, one encounters noise in each energy regime: a hit particle does not leave the target without colliding with others and those modify the simple picture above. That noise can be turned to
information on how 2,3... constituents behave in a medium of many, which is a crucial question in many-body physics.