Particles are the smallest known objects in the universe, and are intangible like light. So how is it that scientists can observe, study, and manipulate them? But particles are so small that no visible light bounces back, even when using the most powerful microscopes.
All particles behave differently when passing through matter. Electrons and photons rapidly lose their energy by continuously colliding with other material atoms until they get trapped. Protons travel through matter almost unnoticed until they are close to the end of their journey, when they lose all their energy in a burst and immediately stop.
Muons, on the other hand, can travel through layers and layers of any material, even through hundreds of meters of solid rock, without losing much of their energy.
Scientists build labs, like the Gran Sasso laboratory in Italy , deep under mountains to shield sensitive experiments from cosmic muons. Neutrinos, another fundamental particle, interact extremely weakly with all other objects: they can pass through entire planets without stopping. It has been built under the Gran Sasso, the highest mountain of the Italian Appennini. Thousands of meters or rock shield the experiments conducted underground from most of the effects of the cosmic rays.
Source : Wikipedia. Physicists leverage these different behaviors to develop detectors that catch and measure each type of particle. When a particle passes through a material it leaves a certain amount of its energy behind. By layering different detectors, physicists can reconstruct particle trajectories, and, under certain circumstances, measure the exact energy of a particle. Many particles have an electric charge. Charged particles, like electrons or protons, are influenced by electromagnetic fields.
An electric field can be used to push charged particles forward, while a magnetic field can make a particle move to one side or another, depending on the charge of the particle. In , Carl Anderson discovered the positron , an electron with positive charge. The discovery proved the existence of anti-matter. References :  and . Arrow symbols by Freepik.
You can freely read it online. Also, if you like, you can take photos of cosmic rays too! In , while photographing cosmic rays with a Wilson chamber , Carl Anderson took a photograph of a particle passing through a thin film of photographic emulsion. The particle behaved almost exactly like an electron, except for the way a magnetic field around the film bent its trajectory. If it were an electron, the magnet would have bent the path in the opposite direction. What he observed was a positron , the anti-electron, and the first proof of the existence of anti-matter. Electromagnetic fields influence the speed and trajectories of charged particles.
An electromagnetic field can always be divided into two distinct components: an electric field and a magnetic field. The force exerted by the field on a charged particle is called the Lorentz force :. In the above formula, q q q is the charge of the particle and v v v its velocity, E E E is the electric field, and B B B is the magnetic field.
For a given electric and magnetic field, the particle experiences a force F F F from the field dependent on its charge and speed. The expression describes the velocity of a particle, v v v , given the potential difference of an electric field. The particle in the diagram has been drastically slowed down. Also notice how much more energy is needed to push a proton, which has the same electric charge as an electron, but contains a much higher mass.
You have to choose the highest voltage setting to make it move! Using these two principles, physicists started building particle accelerators. By using accelerating modules one after another, we can build linear accelerators where the energy that these accelerators can produce is governed by their length.
By combining accelerating and bending modules, we can build circular accelerators, in which particles are injected and forced to move in a circular path. Each time a particle goes around it is accelerated. After a given amount of cycles the particles attains their maximum energy and can be used for experiments.
Circular accelerators can be further divided into two main groups: cyclotrons , which were the first to be invented around , and synchrotrons. The former can be seen in hospitals today. Physicists designed accelerators to study the basic characteristics of particles, but it quickly became clear that they could have many other scientific and industrial applications.
For example, old television sets were driven by cathode-ray tubes, which are nothing more than compact particle accelerators!
Electrons are produced and subjected to an electric field, causing them to fly towards a certain end of the tube. This end is covered by a layer of phosphorescent material that becomes luminescent when hit by electrons. The trajectory of the electrons is bent by a variable magnetic field, which forces electrons to hit the luminescent screen at different points.
By modulating the intensity of the magnetic field, the electron beam paints an image on the screen. So far, we have talked about particles produced in natural sources, but there are many more natural phenomena involving particles. All fundamental phenomena involving the electromagnetic force, for example, depend on the characteristics of electrons and photons—the elementary particle which is responsible for light. The stability of atoms, which compose all matter, depend on the interaction between two fundamental particles: quarks and gluons.
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This creates a number of interesting questions for modern physicists. For example, how did the universe form? At the beginning of time, in a fraction of a second, quarks and gluons bounced and smashed, interacting and recombining until creating the first glimpse of the matter we see today. Is gravity carried by a particle like the other fundamental forces? And how are high-energetic cosmic rays that hit our planet generated, if there are no known sources for them near Earth? To answer these questions, and others not yet asked, we need particles interacting at much higher energies and with a much higher flux than those we can obtain from natural sources like radioactive elements or cosmic rays.
To make progress, we would need bespoke particle factories, to create large fluxes of particles at the desired energy to study interactions and effects. In , Albert Einstein proposed a theory about the equivalence of mass and energy. Conversely, if we create the exact amount of energy that corresponds to the mass of a specific particle, we can then create that particle and study it.
Modern particle colliders are built for this: they accelerate particles up to the highest possible velocities and make them collide.
Acceleration of quasi-mono-energetic electron bunches to 5 MeV at 1 kHz with few-cycle laser pulses
The energy involved in the impact is used to create new particles which are caught by detectors and studied. The particles created in colliders are not to be considered artificial: they are naturally found under specific conditions in other places, like stars, or confined in microscopic objects, like the nuclei of atoms. Using particle colliders, we are simply creating the right conditions for them to be observed in a laboratory.
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In a circular collider, two beams of accelerated particles smash into one another at a collision point. From the energy of that collision, new particles arise, which physicists can catch and measure. By identifying and measuring these particles, physicists can infer how they were generated. For that, particle physics experiments use many layers of different types of detectors placed around the collision point, since different particles require different detectors different particles act differently when traveling through matter!
Detect a particle and measure its trajectory By measuring the curve taken by the charged particle in the magnetic field we can infer its energy.
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Reset Start! In the simplified visualization above, three layers of detectors are placed one after the other. A magnetic field permeates the space around them. When a charged particle comes, the magnetic field bends its trajectory, as seen above, and makes it traverse the three detectors at different position.
The detectors record the passage of the particle and send the information to the computers which handle the experimental data. From those data, scientists can reconstruct the trajectory of the particle in the experiment and, by knowing the strength of the magnetic field, the energy of the particle.
Modern particle physics experiments can be very large due to the amount of energy involved smashing particles together. When a collision occurs, many new particles are created which move outward from the collision at extremely fast speeds in all directions. To catch and measure these particles properly, scientists use layers of detectors and magnets placed around the collision point, so that they can reconstruct the particle trajectory after the collision for analysis.