The event display shows the Higgs boson generation associated with the two top quarks, a process that is critical to understanding the Higgs boson and a major challenge in accuracy calculations. **Atlas Collaboration.
There are many unanswered questions about the Standard Model (SM) of particle physics, which is currently our best description of the world of particle physics. Experimental physicists and theoretical physicists compete against each other in a virtuous race to scrutinize SM and identify parts of it that require further explanation, rather than the model's well-known shortcomings, such as neutrino mass.
Experiments carried out at the Large Hadron Collider and other facilities of CERN can detect specific features where the data deviate slightly from the theory**. It is crucial to continue to explore whether this potential bias can reveal new physics or be explained by SM.
In order to distinguish the signal from the background in an experiment, theoretical physicists need to calculate all complex processes with extreme precision. This involves examining fine details, including observable quantities, such as the number of events or the kinematic details of a particular process, that can reveal the footprint of unknown phenomena.
For example, this calculation improves the accuracy of mass measurements of w bosons and top quarks, as well as the strong coupling constant.
The powerful forces and their coupling are the least known of the SM, but they control almost every process of the LHC. In addition, accuracy calculations help to develop new techniques to describe the scattering process and how to effectively model it.
These calculations were already challenging in the LEP era, but the Large Hadron Collider took them to the next level, leading to a surge in computational complexity that required new methods to calculate the scattering process.
In modern experiments, aspects of precision calculations have become necessary for data analysis: for example, they need to be used to calculate complex scattering amplitudes that describe the final state immediately after a collision, such as two protons colliding to produce three particles.
A striking example is the generation of the Higgs boson, specifically associated with the two top quarks. New physics can enter in many different ways due to the many possible production mechanisms and end states. As a result, theoretical physicists must calculate each mode of production with high accuracy.
Calculating scattering amplitude is only a small part of the broader field of accuracy calculations. The other is the Monte Carlo Event Generator. These calculations are designed to describe all stages of the scattering process, from the few particles produced in the collision to the hundreds of particles observed in the detector. At each stage, the Monte Carlo method is used to probabilistic interpretation and simulation of the fundamental physics, which is essential for the simulations that can be adopted experimentally as a robust control of the uncertainty of the system in the analysis.
A key example is vector boson fusion, in which two quarks scatter and exchange a weak boson, resulting in the creation of a Higgs boson and other particles. Calculating this process with a Monte Carlo generator is a very complex but important task, as the new physics may be hidden in the details of the final state.
A few decades ago, this would not have been possible. Our ability to describe data with up to 5% or more accuracy now demonstrates the power of first-principles calculations and their ability to accurately reflect the complexity of the Hadron Collider environment, such as LHC. I'm really looking forward to what the era of the high-brightness Large Hadron Collider and the future collider will bring," said Pier Monni, a theoretical physicist at CERN.