The Large Hadron Collider (LHC) determines which particles to collide using a complex process involving several components and considerations. Here's a general overview:
Particle Beams: The LHC accelerates and collides beams of particles, typically protons or heavy ions. These beams circulate in opposite directions in separate beam pipes, which are maintained in a near-vacuum environment to minimize interactions with other particles.
Particle Sources: Particle sources, such as hydrogen or lead sources, provide the initial particles for the accelerator. For protons, hydrogen gas is ionized to create a beam of positively charged protons. For heavy ions, atoms are stripped of their electrons to produce the desired ions.
Particle Acceleration: The initial particles are injected into a series of pre-accelerators, which gradually increase their energy before they enter the LHC. The pre-accelerators include linear accelerators (LINACs), circular accelerators, and smaller colliders.
Particle Bunching and Colliding: Once inside the LHC, the particles are grouped into bunches to maximize the collision rate. Radiofrequency cavities provide the necessary energy to accelerate the particles and keep them in circular orbits. These bunches of particles circulate in opposite directions and cross paths at designated collision points.
Particle Detectors: Around the collision points, particle detectors are positioned to observe and record the resulting particle interactions. These detectors, such as the ATLAS and CMS detectors at the LHC, are massive and complex instruments designed to measure the properties of the particles produced in the collisions.
Trigger Systems: To handle the immense amount of data produced by the collisions, the LHC employs sophisticated trigger systems. These systems quickly analyze the initial collision events and decide which events are worth recording for further analysis based on specific criteria. This helps filter out less interesting or common collisions, allowing scientists to focus on the most relevant data.
The selection of particles to collide primarily depends on the research goals of the scientists operating the LHC. They design experiments and adjust the LHC parameters accordingly to study specific phenomena, such as the search for new particles, the investigation of the Higgs boson, or the study of quark-gluon plasma, among others. The LHC's flexibility allows for different types of particles, energies, and collision modes to be explored to advance our understanding of fundamental physics.