At CERN's Super Proton Synchrotron, scientists have observed fixed lines induced by a nonlinear resonance. The invisible structure measured and quantified by the accelerator can divert the course of the particles therein, creating problems for particle research.
(Photo: Wikimedia Commons/ x70tjw)
Resonance in Particle Physics
In particle physics, resonance refers to the peak located around a specific energy found in differential cross-sections of scattering experiments. In quantum field theory, resonances are associated with unstable particles. These particles are made in some collisions, live briefly, and decay back to the original particles.
Resonance also occurs due to the interaction and syncing up of two systems. It can happen on a large scale, such as between planetary orbits that gravitationally interact in their journey around the star, or on a small scale, like a tuning fork that starts to ring sympathetically when sound waves from another tuning fork hit its tines.
Elusive Ghost Particle
In accelerator physics, understanding resonances and nonlinear dynamics is important to avoid the loss of beam particles. In a recent study, researchers confirmed the theoretical dynamics prediction for a single two-dimensional coupled resonance. By observing the so-called fixed lines, the scientists discovered the specter that haunts the tunnels of a CERN particle accelerator.
The structure was found to occur in phase space, representing one or more states of a moving system. The experts view it as four-dimensional since four states are required to describe the structure.
The 4D structure was created by a phenomenon called resonance. By quantifying and measuring it, physicists are a step closer to solving a problem universal to magnetic particle accelerators.
According to physicist Giuliano Franchetti, the particles do not precisely follow the path they want because of resonance, so they fly away and get lost. This results in beam degradation, making it challenging to achieve the required beam parameters.
Particle accelerators typically use powerful magnets that generate electromagnetic fields to guide and accelerate beams of particles in the direction the scientists want them to go. However, due to the magnets' imperfections, resonance can occur in the accelerator, creating a magnetic structure that interacts with particles in problematic ways.
Understanding the impact of resonance on a particle beam took a few years and some heavy computer simulations. However, Franchetti used this information to finally measure the magnetic anomaly.
The Super Proton Synchrotron is the second-largest machine in CERN's accelerator complex. The research team used beam monitors along this machine to measure the position of the particles for approximately 3,000 beams. After carefully measuring where the particles were centered, the physicists could generate a map of the resonance that haunts the accelerator.
This finding is remarkable because it shows how individual particles behave in a coupled resonance. The researchers were able to demonstrate that the experiment's findings agree with what had been predicted based on theory and simulation.
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