Physics

What are Elastic Collisions?

You should be familiar with the concept of elastic collisions, which is characterized by the conservation of linear momentum and of kinetic energy. The total kinetic energy in the two or more colliding objects does not change throughout the entire interaction, in addition to the total momentum remaining constant. An elastic collision between two protons means that, during the interaction, neither of the protons are destroyed, as often happens at high energies, but instead scatter elastically.

How Are They Detected?

The LHC at CERN collides around 600 million protons per second, only a fraction of which scatter elastically. These elastically scattered protons travel 147 or 220 meters past the collision point before hitting the Roman Pots detectors. These detectors are able to localize the trajectory of protons close to the beam within 1 mm (with a precision of around 20 micrometers). Computers then analyze the data to confirm that the detected protons did in fact scatter elastically.

Traveling toward the Roman Pots detectors, the protons are subject to intense magnetic fields which change their scattering path. This, among other variables, needs to be accounted for by the analysis, otherwise no event would appear to be elastic.

The Analysis

In this exercise, the first stage of the analysis has already been completed, and the magnetic fields have been accounted for, allowing the data to be presented as an angular distribution. Simply put, the data is presented as if the protons scattered off each other and traveled unimpeded to the detectors; distinguishing between elastic and inelastic is possible without a computer.