Thesis

The evolution of the total cross-section: from LHC to Auger

• Call:

  FCT / IDPASC call 2010

• Academic Year:

  2010 / 2011

• Domain:

  Theoretical Particle Physics

• Supervisor:

  Jorge Dias de Deus

• Co-Supervisor:

  Mário Pimenta

• Institution:

  Instituto Superior Técnico

• Host Institution:

  Laboratório de Instrumentação e Física Experimental de Partículas

• Abstract:

  Fundamental principles of quantum field theory tell us that total cross sections are bound by a (ln s)**2 behaviour ( Froissard-Martin bound). The bound seems to be saturated in the energy dependence of the cross section, but not in the magnitude: it is bellow a factor of the order of 10**-3. This means that unexpected increases of the cross- section may occur.n At the LHC. in CERN. the total cross -section in pp collisions will be measured, at center of mass energies of the order of 10 TeV. These values, extrapolated to the Auger energies - a factor of two orders of magnitude above - may be crucial to explain the slow increase in the average length and the decrease of the root mean square of the cosmic ray shower penetration with the energy.n The main objective of this work is to solve an old puzzle: is there an increase in the total cross-section, or a change in the nature of the primary beam ( nucliei instead of protons) in cosmic rays?