To the Higgs Particle and Beyond: U.Va. Physicists are Part of an International Team Searching for the Last Undiscovered Aspect of the Standard Model of Physics

Nov. 8, 2006 -- For more than three decades, physicists have been trying to find the Higgs particle — sometimes called the “God particle” — the theoretical underlying particle that possibly is the ultimate basis of everything in the universe.

U.Va. physicists are part of this search.

U.Va.’s High Energy Physics Group is a member of a major international physics undertaking, the Compact Muon Solenoid Detector (CMS) experiment, which will start taking data next year at the new $3.2 billion Large Hadron Collider (LHC). Using a huge international computer grid, U.Va. physicists will gain access to massive amounts of data from what will be the highest energy interactions ever produced by humans.

The researchers will be seeking a high level of understanding of the most basic structure of matter and the evolution of the universe. They will look for physical evidence beyond the “Standard Model” (the current theory of fundamental particles and how they interact), such as supersymmetric particles (possibly the mysterious “dark matter” of the universe), extra dimensions beyond the four of space-time and micro black holes.

“This experiment will be at the forefront of experimental particle physics for the next decade or two,” said Brad Cox, a physics professor and a principal investigator in the High Energy Physics Group. “The discovery of the Higgs particle in particular would make profound differences in the way we think about the physical world. The LHC will help us unravel the next layer of the onion of nature by moving us to the next frontier of our understanding of matter and energy.”

The Large Hadron Collider is a new particle accelerator at the European Organization for Nuclear Research (known as CERN – Center for European Research Nucleare). The machine, which is 14 miles in circumference (the largest particle accelerator in the world), works by colliding beams of high energy. The collisions break apart protons, producing new particles, the most basic elements of all things.

The LHC will smash together 7 trillion electron volt beams and produce 14 trillion electron volts of energy.

“These interactions will in effect take us back to the very brink of the universe, just 10- to 35-seconds after the Big Bang,” Cox said. “We are essentially looking for the grand unified theory of everything, but until now we didn’t have the technology in place to produce the high energy interactions needed to do this science.”

Construction for the LHC began in 1994 and is nearly complete. It is located near Geneva, straddling the border of Switzerland and France. The first experiments will begin by the middle of 2007. Cox says scientists will immediately begin gathering reams of data.

Cox likens the LHC to the first use of microscopes — with the right tools, things that are there but not visible can suddenly be revealed. The experiments will allow physicists to recreate, so to speak, the formation of the early universe, and glean new information about how it all happened, and where it’s going.

Scientists will attempt to detect the Higgs particle; the last undiscovered aspect of the “Standard Model,” and they will search for supersymmetric particles, which go “beyond” the Standard Model.

“These particles are thought to be the mysterious ‘dark matter’ that astronomers see evidence of in the galaxies,” Cox said. “There may be five to eight times more dark matter than ordinary matter in the universe.”

Cox and his colleagues also will try to detect evidence of extra dimensions beyond the four of space and time; and other “exotic phenomena” such as micro black holes.

Development of the LHC and the design of the experiments is an international effort involving the 19 European member nations of CERN, as well as 42 U.S. universities and institutes, and research groups in Japan, China, Brazil and other non-European nations.

“We all will have a significant job to do for the next two decades,” Cox said.

The collider will produce 1 billion “interactions” per second.

“The electromagnetic particle detectors in the collider must sort through all these interactions and find the one event in 10 trillion that has new physics,” Cox said. “And the detectors must be able to function property for one to two decades with very little maintenance. It’s a huge technical

The $800 million electromagnetic particle detectors in the accelerator have been in development since the start of the project in 1994. Cox and a team of U.Va. physicists (including
Professors Sergio Conetti, Robert Hirosky and Richard Imlay), scientists Alexander Ledovskoy and Michael Arenton, postdocs, technicians and graduate students have helped develop and test components for the detectors. Colleagues in computer science, electrical engineering, the ITC division and the radiology department also have contributed time and expertise.

Cox notes that basic knowledge gained from the LHC experiments will likely result in new technologies in the future, such as superconductivity links for power grids, advanced forms of software, “currently unimagined technologies,” and a “more sophisticated understanding of the

“A greater understanding of energy gleaned from the LHC experiments will possibly someday make nuclear power seem equivalent to a caveman throwing logs on a fire,” he said.

Researchers' goal: Completing the Standard Model of Physics

The Standard Model of particle physics that has been developed over the last 60 years incorporates all known facts about the fundamental constituents of matter, the six quarks (whimsically named up, down, strange, charm, beauty and top) and the six leptons (the electron, muon, and tau leptons and their associatedneutrinos) and their electromagnetic,weak, strong nuclear and gravitational interactions with each other. The Standard Model has stood the test of
time and no exceptions to it have been found other than the recent discovery that neutrinos have mass.

However at a fundamental level, the Standard Model is incomplete. It contains no explanation for the pattern masses of the quarks and leptons,which range from less than three electron volts of an electron volt for the neutrino masses, to 171 billion electron volts for the top quark. In addition, the couplings (or charges) of the quarks and leptons to the photon,Wand Z particles, gluons and gravitons that are the carriers of the electromagnetic, weak, strong and gravitational
forces respectively, are not predicted in the Standard Model. For example, while the charge of the electron can be measured very precisely, physicists have no idea why it has its value. Moreover the quarks and leptons seem to be point like which leads to several paradoxes beyond the physics of the present day. Finally,while the Higgs particle is predicted to exist and is a key to the Standard Model (as yet undetected), its mass cannot be predicted within the Standard Model. There is obviously a deeply layer of physics, another layer of the onion to peel away to get at the fundamental nature of the world.

The experiments at the LHC propose first to detect the Higgs particle and measure its properties to make certain that the ideas underlying the Standard Model are correct. With this assured, the search for new particles will go on with special emphasis on detection of the supersymmetric partners of the quarks and leptons. If these new particles are detected, it is expected that they will give clues to the strange structure of the quarks and leptons and their interactions. Moreover,
the dark matter of the universe (which is much larger than the luminous matter) will be composed of the lightest of these new particles.

Even more exotic discoveries may be within the reach of the LHC. In particular, the LHC experiments may be able to detect effects of new dimensions of nature beyond the familiar three of space and one of time. Also, it is possible that micro black holes may be generated in the very high energy interactions, leading to a chance to study these fundamental objects of gravitational physics in a laboratory setting.

Brad Cox, professor of physics