Prof. Yael Shadami from the Faculty of Physics at the Technion focuses on the study of elementary particles including electrons, quarks, photons and gluons, and the interactions, or forces, that act between them. It tries to discover more elementary particles and interactions, beyond those described in the "standard model" of particle physics
What materials, basic building blocks, is the universe made of? The theoretical physicists who deal with this question use theoretical and mathematical tools to describe natural physical systems and predict their behavior. This is how they try to explain physical reality - the one that has been observed and the one that has not yet - and provide predictions that can be tested through experiments and observations.
Prof. Yael Shadami from the Faculty of Physics at the Technion focuses on the study of elementary particles - the building blocks of matter (which are not composed of other particles) - including electrons, quarks, photons and gluons, and the interactions, or forces, that act between them. It tries to discover more elementary particles and interactions, beyond those described in the "standard model" of particle physics.
"The standard model," says Prof. Shadami, "is not a good name because it is a systematic theory, which is based on some basic principles, and describes with amazing precision the set of phenomena that we see and measure. This theory describes almost all known forces: the strong force, the weak force and the electromagnetic force. But it fails to describe gravitation. The elementary particles and their interactions make up everything around us, but we know that's not the end of the story. For example, there is no particle in the standard model that can make up the dark matter in the universe. The Standard Model predicts that neutrinos are massless, but experiments have shown that they have small masses. So it is likely that there are particles, interactions and forms of matter that we do not yet know. Our goal is to expose them."
One of the main places where new particles are searched for are particle accelerators. Two beams of particles, protons for example, are accelerated to high energies and directed so that they collide - head-on - with each other. In a collision, particles of all types can be created, provided that the energy, momentum and general charge is conserved before and after the collision. Advanced detectors are located around the collision area. In most cases, the interesting particles that are created only exist for a fraction of a second, and fade into familiar particles such as electrons, muons, photons, pions, and more. These particles leave characteristic traces in the detector, and thus it is possible to identify which particles were formed in the collision.
In their latest study, which won a research grant from the National Science Foundation, Prof. Shadami and her team sought to examine new and unfamiliar interactions of the Higgs particle and other elementary particles. The Higgs particle is the source of mass of all elementary particles and was discovered in 2012 at the LHC - the world's largest particle accelerator located in the European Complex for the Study of Particle Physics, on the Switzerland-France border.
"The discovery of the Higgs is perhaps the most significant discovery in physics of the last 50 years," says Prof. Shadami, "on the one hand, this is another success of the standard model, which predicts the existence of the Higgs. On the other hand, it is the first elementary particle of its kind that we know of. There is no longer an elementary particle with zero spin (if it is indeed elementary). As such, it poses major new theoretical questions. It should be understood that the discovery of such a particle is only the beginning. We are still in the process of understanding and measuring all its features. And its interactions, especially with the heaviest elementary particles (such as the 'top' quark), are the most interesting for us. The heavier the particle, the stronger its interaction with the Higgs particle. If you want to understand how the mass of the elementary particles is formed - including the Higgs itself - you need to examine the heaviest particles."
In order to discover new and unknown interactions of the Higgs particle and other elementary particles, the researchers in Prof. Shadami's group developed new theoretical tools for calculating physical processes. The existing methods in this field are based on Feynman diagrams, which have an inherent complication, because the calculation is not based on particles, but on fields, and in this description there is a lot of redundancy. "Our goal," says Prof. Shadami, "is to approach the problem in the most general way, without new theoretical assumptions. To this end, we have developed an approach through so-called 'amplitudes' where we only work with the physical degrees of freedom: the particles themselves. This is how we hope to map out all the possibilities for theories that complete the missing parts in the understanding of the Higgs particle."
Later, experimental physicists will be able to examine various phenomena and results in the particle accelerator. "Using the theoretical tools we have developed," says Prof. Shadami, "we are examining a set of particles and looking for all the possible interactions between them, beyond the known ones. This is actually a theoretical stage where we analyze the physical processes that can occur in the accelerator - and in the next stage we will measure them in experiments. In this way we may be able to discover new fundamental interactions, such as collisions between particles and the particles and the amount of energy that is created from them. However, we do not expect to discover many new fundamental interactions. We will be satisfied even if a tiny one appears, which will reveal some additional information about the fundamental structure of matter in the universe."
Prof. Yael Shadami, lives in Haifa, where she moved when she started working at the Technion. Today she thinks it is a wonderful city: beautiful, diverse, interesting and full of surprising corners. She loves traveling, books, music and art, but in practice divides almost all of her time between her two truly great loves: physics, and her family.