RESEARCH IN HIGH ENERGY PHYSICS WITH THE ATLAS EXPERIMENT AT CERN

It has long been established that space is expanding from the very moment after the birth of the Universe, which we call Big Bang.  Indeed, current research in astrophysics, high energy physics and cosmology provide important clues to the Big Bang.  Research in Experimental High Energy Physics is full of new challenges and surprises, often resulting in new exciting discoveries.  High energy physicists today is aiming to take physics to the next step, towards finding a deeper set of physical laws that govern our Universe. No one can say when this will happen, but there is a growing sense within the High Energy Physics community that it is within our reach.  Nowadays, studies in high energy physics also strongly overlap with Astrophysics, Cosmology, and to some extent with Gravitational Physics and Astronomy. 

Take an interactive tour of our universe and view the Milky Way at 10 million light years from the Earth. Then move through space, through the Milky Way Galaxy towards the Solar System and Earth in successive orders of magnitude, until you reach the subatomic particles -- the protons, the electrons, and finally the quarks, which are the fundamental constituent of matter. You can also take the Particle Adventure tour by clicking here. If you want to learn more about latest theoretical advancements in particle physics, then click here.

We have observed that all distant galaxies are moving apart from each other as a result of this expansion.  Whether the expansion of the universe will speed up, slow down, or even possibly reverse, and collapse (close) into itself through gravity will depend on the amount and types of matter and energy contained in the universe.  Ordinary hadronic matter that formed the protons, neutrons, nuclei and the atoms in the early universe can only account for the visible mass in galaxies and clusters, which is only a small fraction (less than 5%) of the total mass/energy of the universe.   So, a new type of matter, not made of atoms must exist, which we call dark matter (since it is non-luminous).  

Even stranger, recent discoveries indicate that most of the matter in the universe is dark energy, unlike any conventional matter we currently know today.  The observations of supernovae from distant galaxies indicate that the empty space in the universe is filled with dark energy, which is pushing the universe to accelerate at an ever-increasing rate, thus overwhelming the pull of gravity, unlike anything we have seen before.  While ordinary and dark matter pulls the universe together, dark energy seem to accelerate the universe.  The nature of dark matter and dark energy are among the two new challenging questions facing high energy physics today.

Indeed, new elementary particles that will be discovered within the next two decades will help us to answer some of the fundamental questions in modern science about the structure of matter and the universe itself.  I believe that within the next decade, research in high energy physics will provide new discoveries that will revolutionize our understanding of the universe and the fundamental structure of matter. Over the past several decades, new experimental discoveries and insights in High Energy Physics have significantly advanced our understanding of the universe. One of my goals is to discover new subatomic particles and phenomena, beyond what is known today.  I am sure there are a lot of surprises awaiting us in the near future, as we attempt to learn more about the Universe through research in high energy physics.  For many research questions, the answers are predictable, but when the question is a challenging one, the answer can be a surprise and somewhat unexpected, often resulting in an exciting discovery.  Today, research in High Energy Physics takes us to the past, back in time, to fractions of a second after the explosive birth of the universe, the Big Bang. 

Since the beginning of history, throughout the ages of all cultures, mankind has marveled at the diversity and complexity displayed by nature. We all at some point have asked many intriguing questions about the universe that for some reason seem quite unanswerable. Research in High Energy Physics attempts to answer some of the most intriguing and challenging questions, such as - (i) how did the universe begin and how did it become the way it is?, (ii) what is the universe made of and what are the smallest constituents of matter?, (iii) what is the origin of the mysterious attribute of matter called mass?, (iv) what is the ultimate fate of the universe? and (v) why does the universe consist of only matter and not antimatter?  Over the past century, high energy physicists have used tools of ever-increasing power and energy to look into the very heart of matter in the continuing quest to find nature's basic building blocks and to discover the simple physical laws that make our universe more understandable. The discoveries made in High Energy Physics help us to understand not just the physical world around us, but also the origin and the ultimate fate of the universe. Through the study of subatomic particles and forces, we are just beginning to unravel how the universe itself developed in the first moments of the Big Bang burst of infinite energy from a single point source of almost negligible dimension.

Modern particle accelerators create the feeble imitations of the Big Bang - for very short times, when the fundamental particles and the forces that govern them were beginning to form.  We see that the pattern of particles uncovered in accelerators influenced the initial conditions of the universe so as to produce the world we live in.  Particle accelerators and their detectors are designed to re-create and re-produce for a fleeting instant, in a smaller volume, the Universe, as it existed a few micro-seconds after the Big Bang.  At that time, six type of quarks (up, down, strange, charm, beauty, and top) were produced, but only the up and the down quarks along with the strong force carrier, gluons combined to form protons and neutrons, which then bound together to form the nuclei of the Atom of ordinary matter.  The other four types of quarks (strange, charm, beauty, and top) can be re-created using particle accelerators, through a series of events that will eventually decay into the stable up and down quarks.   

We all notice that the universe contains a preponderance of over antimatter. But, the early universe was made up of an almost exactly equal number of matter (particle) and antimatter (antiparticle). Most of these particles quickly paired up and annihilated each other.  However, a very tiny excess of matter over anti-matter in the early universe has persisted until the present time, allowing everything in the universe to exist.  Thus we suspect that the laws of nature must somehow discriminate between the opposite forms, otherwise we would not exist, and matter which forms the stars and everything in the universe would have annihilated.  In the past few years, striking new progress in understanding the distinction between matter and antimatter has come from the accelerator-based high energy physics experiments.

According to some new theories in high energy physics, extra higher dimensions have been predicted.  We live in a world that has the usual 3 space dimensions and one time dimension.  Therefore, at the macroscopic level, any space dimensions beyond 3, seems unphysical; so, we tend to regard higher extra space dimensions beyond 3 as a science-fictional entity.  It is predicted by some of the current theories that such new extra space dimensions are compactified at smaller distances at the sub-microscopic level.   We however do not quite know the range of this sub-microscopic distance. Indeed, any evidence of new extra higher dimensions will revolutionize the science of space and time.  It is quite possible that due to the some peculiar properties of gravitons (the carrier of gravitational force), the universe extends in a 4 + n dimensional space, while we are trapped inside the 4 dimensions (3 of space and one of time).   Therefore, we are certainly on the threshold of another new era of discoveries as we step into the 21^st century.    

Scientific studies in High Energy Physics have also enriched society by the new understanding and applications of matter at the quantum level.  For example, the ability to produce new materials in nature, are the results of the information gained from the understanding to the proton, neutrons, electrons, and other fundamental particles. Our computer based information age rests upon the intellectual foundation of the quantum revolution early this century. The subatomic particle, electron, is a vital component of matter and has triggered the 20^th century revolutions of electronics and computing.

Advances in High Energy Physics depend on the advancing technology of the tools of research. An important part of the science of experimental High Energy Physics is the never-ending development of accelerator and detector technology to reach ever higher energies.  Indeed, the search for the challenging questions of nature makes extreme demands on experimental techniques. In meeting these challenges, new instruments and technologies are created with enormous potential for other sciences, and for practical applications.  Hence, there are many spin-offs of High Energy Physics research.

The challenge of rapidly analyzing vast amounts of data from accelerator-based experiments has contributed to advances in cost-effective high–performance computing and internet communications. This need for rapid and effective communication among high energy physicists, led to the invention of the tool known as the World Wide Web (WWW) in the early 1990s.  The Web was originally developed as a data communication tool for experimental high energy physicists around the world.  Since then, the Web has indeed revolutionized the entire world, as far as information technology is concerned. Particle physicists have constantly been finding more and more effective ways of making measurements, faster ways of recording and analyzing data, and better ways of sharing and distributing information.  To address the new challenges of large-scale multi-institutional collaborative data analysis tasks and due to the rapidly growing experimental datasets, global grid computing projects have recently been proposed. 

Accelerators designed for research to collide subatomic particles have now become instruments for medical diagnosis and treatment. Particle accelerators are used to treat cancerous tumors that are inoperable or resistant to traditional radiation therapies.  The technological base of cancer radiation therapy is the electron linear accelerator. Particle beams and detectors used in High Energy Physics research have also led to the development of new proton cancer therapies. At present, medical studies have shown that one in three of us will have an encounter with cancer, and in developed countries, about one in eight will have this treated by a linear accelerator.

Also the R&D of superconducting magnet designs used in accelerators has substantially improved the sensitivity, speed and resolution of MRI machines. In hospitals and medical centers, the very detectors built to produce fine images of subatomic particle tracks are now being used for visualizing the human body by using these particle imaging techniques. Thus medical imaging is a spin-off of experimental High Energy Physics research, which has led to the development of PET (Positron Emission Tomography). All these spin-off applications have greatly benefited society. 

High Energy Physics therefore plays an important part in advancing our scientific knowledge about inventing hi-tech applications as well as enriching technical education. X-rays and ultraviolet light from the particle accelerators known as synchrotron light sources provide valuable information about chemical composition, the dynamics of structural transition, and the magnetic properties of matter, which benefits the petrochemical, pharmaceutical, semiconductor and computer industries.  Indeed, the R&D in high energy physics pushes the state of art in many directions, and has benefits well beyond the field of high energy physics.  Indeed, High Energy Physics today is an exciting and vibrant field that is poised to make new discoveries in the next two decades and beyond.

Twenty years of precision tests of this Standard Model have resulted in an enormous number of successful comparisons of data and theory, with no verified departure from the Standard Model.   However, current results in HEP hints that new physics, and answers to some of the most profound questions of our times lie at energies around 1 TeV. Despite the successes of the Standard Model, it is widely believed not to be the final word.  And despite this impressive predictive power and the successes, we now believe that Standard model is a low-energy approximation to a more general theory, the one that explains our world in its completeness. Although, that the standard model of High Energy Physics has been studied with very high precision over the course of the past two decades without significant deviations, our understanding of the origin of the electroweak symmetry breaking is still incomplete.  This arises in large part because the only remaining undetected standard model particle is the SM Higgs boson, which mediates electroweak symmetry breaking in the standard model. 

Supersymmetry (SUSY) offers a possible cure for many of the shortcomings of the Standard Model. Space-time symmetries such as those of translation or rotations of coordinates lead to momentum and energy conservation.  Supersymmetry postulates a further symmetry between bosons (integer-spin particles) and fermions (half-integer-spin particles), thereby generalizing the Poincare group describing space and time. This radical reshaping of our understanding of space-time is also a key ingredient in the theory of strings in multiple dimensions.  When used as a phenomenological ingredient of physics at the scale of present-day experiments, it provides a natural solution to the shortcomings of the SM involving the instability of the mass of the Higgs boson, and permits the unification of the strong and electroweak forces.   Supersymmetry predicts that each known fermion and boson should have a mirror "superpartner" of the opposite type.   Clearly, supersymmetry is broken, since there is no spin-zero superpartner for the electron at 0.511 MeV.  But to be self-consistent, supersymmetry predicts that the superpartners should be found with masses below 1000 GeV, which will be within the reach of discovery at the LHC. 

According to SUSY, similar to the quarks and gluons which make up protons, squarks and gluinos should be readily produced, and if it does exist, it ought to be found at LHC. While most squarks are anticipated to be heavy, according to some SUSY models, there could be lighter bottom and top squarks. While it seems like a paradox, according to these SUSY models, the higher masses of bottom and top quarks could lead to smaller masses for their superpartners.  The models predict that left and right helicity states of the third generation squarks can have large mixing, leading to one of their masses eigenstates to be substantially lighter that other squarks. These SUSY particles can be produced at LHC, as bottom and anti-bottom squark pairs. Indeed the next research instrument in HEP that will answer some of the outstanding questions in HEP will be the LHC.  There is an almost agreed expectation that the new upcoming experiments in LHC will make the next generation of breakthrough discoveries.