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DR. RACHIK SOUALAH - FROM A SMALL ALGERIAN VILLAGE TO THE LARGE HADRON COLLIDER
Among the few people responsible for putting the UAE on the particle physics map, Dr. Rachik Soualah researches the unsolved mysteries of our universe. The Assistant Professor at the University of Sharjah explains the value this seemingly impenetrable discipline offers the UAE and the world.
Clarifying some of the lingering mysteries of our universe is one way to make a subtle but significant impact on the country and the wider world and Dr. Rachik Soualah is doing just that. Not only is he an Assistant Professor at the University of Sharjah (UOS), but he’s also a particle physicist in one of the world’s leading large-scale physics collaborations. Dr. Soualah is the region’s only member of ATLAS, one of the four major experiments at the Large Hadron Collider (LHC) near Geneva, Switzerland.
The LHC is a 27-kilometer particle accelerator located in a tunnel 100 meters underground at the European Organization for Nuclear Research, more commonly known as CERN. It’s no ordinary accelerator – it’s the largest and most powerful of its kind. It’s a particle collider – a type of particle accelerator that brings two opposing particle beams together – which speeds up beams of elementary particles to nearly the speed of light and smashes them together inside specialized detectors to recreate the conditions of the early universe. This enables scientists to study how fundamental particles are initially created and describe their interactions, which can provide insights into the fundamental laws of nature and to form visible matter, which represents just 5% of the universe.
As a member of ATLAS, Dr. Soualah is one of nearly 3,000 researchers from 183 institutions in 38 countries. He participates in research that uses the LHC to test predictions of the Standard Model (SM) of particle physics, the theory that describes what we know about the tiny subatomic particles known as the fundamental building blocks of the universe. The SM is a successful theory that continues to describe nature by explaining three of the four known fundamental forces in the universe – electromagnetism, strong nuclear force, and weak nuclear force – and classifies all known elementary particles.
The model illustrates how particles called quarks and leptons make up all known matter, and how force-carrying particles called bosons influence said quarks and leptons. However, despite the SM’s ability to describe so much of the universe, several phenomena remain unclear. For instance, the SM does not account for the material known as dark matter, which is estimated to make up roughly 25% of matter in the universe, but does not interact with the
Among the hundreds of highly cited publications that Dr. Soualah has contributed to as a member of ATLAS, he is particularly proud of a paper published in the Physical Review D journal in 2018, which provided the first evidence of a signal for the production of Higgs boson with the top quark pair. ordinary matter nor reflect or emit light. Additionally, the SM framework does not explain the existence of massive neutrinos, their mixing, and why there is an imbalance in the universe between observable everyday matter known as baryonic and antibaryonic matter.
In order to explain how particles acquire mass, particle physicist Peter Higgs and others proposed a new mechanism in which there must be a field – the Higgs field – whereby fundamental particles gain mass and form atoms and molecules when they interact with it. The Higgs boson is effectively a snapshot of the Higgs field at the moment when particles travel through it and acquire mass. But proof of the Higgs field’s existence in the form of the Higgs boson eluded scientists for decades until 2012, when the particle was finally observed by ATLAS and the Compact Muon Solenoid (CMS) collaborations at CERN. Since then, the Higgs boson has become a core focus for exploration of physics “beyond the standard model,” or BSM, which refers to the theoretical developments needed to define the limitations of the SM.
“There are still so many open questions about our universe. What is the origin of the matter-antimatter asymmetry in the universe? What is the origin of dark matter? What is the origin of the mass hierarchy between particles? Why is gravity weak? Is it possible to unify all forces? All of these questions have shaped the work we do in particle physics,” said Dr. Soualah. In a quest for answers, he works on characterizing the BSM-related issues, like the search for dark matter at colliders and the interplay between the Higgs and dark/hidden sector, which refers to the category of matter that is invisible or undetectable.
Among the hundreds of highly cited publications that Dr. Soualah has contributed to as a member of ATLAS, he is particularly proud of a paper published in the Physical Review D journal in 2018, which provided the first evidence of a signal for the production of Higgs boson with the top quark pair. As mentioned earlier, the Higgs field is theorized to give elementary particles their mass, so an obvious experiment for this mechanism was to study how a pair of the most massive particle – the top quark – interacted with the Higgs boson.
“It is known that the Higgs boson cannot decay directly into top quarks due to their high mass. We measured the coupling of the associated production of a Higgs boson with a pair of top quarks, which could either confirm the SM or possibly reveal new physics,” he revealed. “A dedicated analysis was performed with the LHC data to better understand how the Higgs boson interacts with heavy particles, like the top quark.”
This initial research has led to insights about the recent breakthrough of the Higgs boson, including the first observation of the Higgs boson produced simultaneously with a top quark pair – known as the ttH production. The resulting projects have further helped prove the SM’s explanation of the link between the Higgs boson and elementary particles and provide a new direction with new hypotheses for physics BSM through new exclusion limit regions.
When asked what inspires him to tackle so many weighty scientific mysteries, Dr. Soualah paraphrased noted physicist Richard Feynman, saying, “It doesn’t matter how beautiful your theory is, it doesn’t matter how smart you are. If it doesn’t agree with experiment, it’s wrong.” It was that determination to understand and explain the unknown that led Dr. Soualah through his advanced education and professional development, taking him from a small village in Algeria to the world’s biggest physics center in Switzerland.
CERN
He studied at the Paris-based Pierre and Marie Curie University in 2003 before being selected for the High Energy Physics program at the International Centre for Theoretical Physics (ICTP) in Italy, where he received a diploma in 2005. Dr. Soualah followed up this achievement with a PhD in Physics from Heidelberg University in Germany as a fellow of Development and Application of Intelligent Detectors, a joint research group between Germany and Norway. It was there that Dr. Soualah realized that in order to achieve the level of research he desired, he should tackle more deep physics problems with advanced technologies at the particle detectors.
“I learned a lot about the SM and its beauty during my diploma – more importantly on what not to do to reach a solid understanding. In my PhD program, I was involved in the search for the Quark-Gluon Plasma (QGP) state that occurred right after the Big Bang. This accumulated expertise pushed me to study fundamental questions, like the top quark physics with more precision measurements, which led me to eventually join ATLAS,” he recalled. After working as a post-doctorate researcher at ICTP for about five years, Dr. Soualah was awarded an international fellowship at the Italian National Institute for Nuclear Physics (INFN) and CERN. He worked there for several years before moving to the UAE to join UOS in 2016.
- Dr. Rachik Soualah, Assistant Professor in the Department of Applied Physics and Astronomy University of Sharjah
Since joining UOS, Dr. Soualah has had a tremendous impact on formalizing and deepening the UAE’s participation in the international high energy physics community, particularly through CERN and the ICTP. He has also helped developed the UAE’s CERN Summer Student Program through which selected students spend eight to 13 weeks at the organization. Once there, they work with some of the world’s top particle physicists to deepen their understanding and develop their technical skills while contributing to important research. A total of 11 students from the UAE have benefitted from the program during the past five years.
“I’ve been working to promote particle physics as a cutting-edge research direction at the University of Sharjah and the UAE in general. That is why I involve university students in research from an early stage, as I believe it helps raise awareness on the value of particle physics in the education sector,” explained Dr. Soualah. He says that while it can sometimes be hard to communicate particle physics’ value to young students – particularly where applied science is more highly regarded for its tangible outcomes – the field’s impact is undeniable.
“Research in particle physics does not produce fruit as quickly as applied sciences. It is a long-term investment, but it can produce major innovations and spillover technologies. We at CERN don’t just study phenomena – we often end up developing entirely new technologies to observe, analyze, and perform measurements. For example, the World Wide Web was invented by Sir Timothy Berners-Lee at CERN. Fundamental physics research has a huge impact on technologies that serve us in our daily lives. Without it, we would miss out on so many innovations,” he added.
Going forward, Dr. Soualah hopes to continue to guide and inspire young people into particle physics while focusing his research more on new physics in order to clarify the neutrino and DM interplay. “By working in this field, we hope to contribute to increasing our understanding of the universe. Along the way, I hope our research can help in explaining or answering any of the lingering mysteries, like Higgs and dark matter physics,” he concluded.
