When two protons collide at almost the speed of light inside the Large Hadron Collider (LHC), several things occur. Let's break down the process step by step:
Acceleration: Protons are accelerated to high speeds using electromagnetic fields within the LHC. They are guided around a circular path by a series of powerful magnets, gradually gaining energy until they reach nearly the speed of light.
Bunching: The protons are organized into bunches to increase the chances of collisions. These bunches are separated by gaps to minimize the probability of unwanted collisions between protons.
Collision: The bunches of protons are made to intersect at specific interaction points within the LHC. When two protons from different bunches pass through each other at the same location, there is a chance of interaction and collision.
Quantum Interactions: At the subatomic level, protons are not solid particles but rather quantum objects with wave-like properties. When two protons approach each other, there is an electromagnetic interaction between their constituent particles (quarks and gluons), mediated by fundamental forces such as electromagnetism and the strong nuclear force.
Gluon Exchange and Quark Interactions: The strong nuclear force, carried by particles called gluons, acts between the quarks within the colliding protons. During the collision, the gluons exchange energy and momentum, causing the quarks to interact strongly. This interaction leads to the creation of new particles, such as mesons or heavier particles like W or Z bosons.
Decay and Detection: The newly formed particles can decay into other particles almost instantaneously. These subsequent particles are detected by sophisticated detectors surrounding the interaction points within the LHC. The detectors record the energies, momenta, and types of particles produced, allowing scientists to study the fundamental properties of matter and investigate various phenomena, such as the Higgs boson or possible new particles beyond the Standard Model.
Now, addressing your second question, protons do not pass through each other without colliding due to the electromagnetic forces between them. Protons have positive electric charges, and like charges repel each other. When protons approach each other, the electromagnetic repulsion prevents them from passing through each other unimpeded. The high speeds achieved in the LHC allow the protons to overcome the repulsive forces and come close enough for the strong nuclear force to come into play, leading to collisions and subsequent interactions as described above.