Have you ever heard about collisions in particle accelerators? PART 2
- Alexa Ines Guido
- May 28
- 3 min read
Updated: Jun 12
Hola! I'm Alexa Guido, a young and curious woman passionate about science. Join me on an exciting journey to explore the wonders of the universe through the lens of physics.
Welcome back! If you haven’t read Part 1 yet, I highly recommend checking it out first to explore the basics of particle accelerators!
Now that we're up to speed, let’s dive deeper into the fascinating inner workings of modern particle colliders, especially the most powerful one ever built: the Large Hadron Collider (LHC).
The Large Hadron Collider is the most powerful accelerator in the world. It boosts particles, such as protons, which form all the matter we know, at speeds nearing that of light, colliding them with other protons to create breathtaking interactions.
These spectacular collisions can produce massive particles, like the Higgs boson and the top quark. By meticulously measuring their properties, scientists deepen our understanding of matter and the very origins of the universe. However, these colossal particles exist only for an instant before they decay into lighter particles, which also rapidly decay. The particles emerging from the successive links in this decay chain are identified in each detector layer.
But how does an accelerator work? How does all this magic happen? Accelerators use electromagnetic fields to accelerate and steer particles with gigantic magnets. Radiofrequency cavities boost the particle beams, while magnets focus the beams and bend their trajectory.
In a circular accelerator, particles repeatedly traverse the same circuit, gaining energy with each lap. Theoretically, this energy can be increased indefinitely. However, as particle energy escalates, the magnetic fields required to maintain their circular trajectory also need to become more powerful.
In a colliding-beam setup, two beams of identical particles (like protons) are directed through separate rings of magnets. One ring guides the particles clockwise, while the other does so counterclockwise, allowing them to collide at designated "interaction regions."
Alternatively, beams of opposite-charge particles (like electrons and positrons) can circulate in opposite directions within the same vacuum chamber, guided by the same magnets, colliding only at specific points.
There’s also the linear accelerator, which consists solely of accelerating structures. Here, particles don’t need to be deflected, so they benefit from a single pass of acceleration. In this case, increasing energy means extending the length of the accelerator.
As physicists have pushed the boundaries of energy, accelerators have grown larger and larger. To study particle interactions effectively, it’s crucial to have the largest possible sample size. This realization inspired physicists to start constructing accelerators as early as the 1920s. The size of an accelerator reflects a balance between energy, curvature radius (if circular), feasibility, and cost.
Now, let’s return to colliders; these accelerators can generate head-on collisions between particles. Thanks to this technique, the collision energy is higher because the energy of the two particles is added together.
The Large Hadron Collider, LHC, with its impressive 27-kilometer circumference, is the largest and most powerful collider in the world. It boosts particles to an energy of 6.5 TeV (teraelectronvolts), generating collisions at an astonishing energy level of 13 TeV. In the LHC, it’s the tiny components within the hadrons that collide, rather than the hadrons themselves.
Energy in particle physics is measured in electronvolts, which represents the energy gained by an electron moving through a one-volt electrical field. As protons race around the LHC, they accumulate an energy of 6.5 trillion electronvolts—6.5 TeV—the highest energy achieved by any accelerator to date.
An accelerator can circulate a lot of different particles, provided that they have an electric charge so that they can be accelerated with an electromagnetic field. The CERN accelerator complex accelerates protons, but also nuclei of ionized atoms (ions), such as the nuclei of lead, argon or xenon atoms. Some LHC runs are thus dedicated to lead-ion collisions. The ISOLDA facility accelerates beams of exotic nuclei for nuclear physics studies.
Yet, in everyday terms, this energy is quite minuscule, akin to the energy of a safety pin dropped from just two centimeters. However, an accelerator can concentrate that energy at an infinitesimal scale, achieving energy levels comparable to those present shortly after the Big Bang.
Finally, luminosity is a crucial metric for an accelerator’s performance, indicating the number of potential collisions per unit area over a specific timeframe. Instantaneous luminosity is expressed in cm⁻²s⁻¹, while integrated luminosity, which represents the total number of collisions possible over a given period, is measured in inverse femtobarn. The higher the luminosity, the greater the chances for physicists to witness rare phenomena.
Thanks for joining me on this journey into the world of particle accelerators. I hope it sparked your curiosity and wonder. See you on the next adventure!
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