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.