This summer, as the global physics community holds its breath in anticipation, three Brown physics professors will play an integral role in the most ambitious experiment in history.
By racing tiny particles around a track nearly 250 football fields long – and colliding them at just under the speed of light - scientists are hoping to find the final piece of the Standard Model of particle physics, an as yet unobserved particle only theorized to exist. The experiment promises to shed light on the very foundation of the universe.
Physics professors David Cutts, Greg Landsberg and Meenakshi Narain will be some of the first to analyze the data from the Large Hadron Collider, an $8.7-billion particle accelerator on the France-Switzerland border that will be completed this summer. In preparation, they are constructing different components of a detector that will look for traces of the Higgs boson, an unstable particle predicted by the 1960s work of, among others, a current Brown physicist.
The Standard Model is a widely accepted theory of how the universe’s smallest particles interact with one another. The existence of the Higgs boson is predicted by and necessary for the model, but has not yet been proven experimentally. Confirmation will answer the question of what mass is and where it comes from.
This is “physics at a very fundamental level,” said Professor of Physics Chung-I Tan, who chairs the department. He said the experiment “tests the very foundation of modern physics.”
Cutts said the research is exciting “because it provides a way to get close to the fundamental question of nature” and “recreate an early time.”
The Large Hadron Collider, or LHC, which is part of the European Organization for Nuclear Research, collides protons at just under the speed of light to create conditions similar to those less than a trillionth of a second after the Big Bang, the explosion believed to have created the universe. These collisions create new, unstable particles that decay into other particles called hadrons and muons. Layers of specific detectors that encircle the collider record these particles’ signatures, which scientists use to infer what unstable particles were formed in the collision. It’s a bit like arriving at the scene of a car crash and determining what car was in the accident by re-assembling its parts, Narain said.
The two speeding beams of protons cross paths at four locations, with a detector at each point. The Brown team is working on a general detector called the Compact Muon Solenoid, a 12,500 ton machine that Narain said is like a camera that takes 40 million three-dimensional pictures per second. The data is then heavily filtered by a computer program that selects the times at which Higgs boson decay is most likely to occur.
Currently, the most powerful particle accelerator in the world is the Tevatron at the Fermi National Accelerator Laboratory in Illinois, but it isn’t as well-suited to detect the Higgs boson. The LHC, however, is seven times more powerful than the Tevatron.
The LHC, which has taken eight years to build, is now mostly complete. It is 27 kilometers around and 100 meters underground, near Geneva. The world’s longest superconducting installation, the accelerator and track are cooled to -271 degrees Celsius, just above absolute zero, in a vacuum simulating interplanetary space.
Because of the sheer magnitude of the project, Landsberg and Narain said collaboration among scientists is necessary, and the work is divided up across the globe. Approximately 10,000 scientists from 60 countries have helped construct LHC and its detectors. The Brown team has worked specifically on the CMS’s momentum tracker and the actual hadron detector.
Because of the large amount of information that will be produced, the data from the experiments will be distributed and stored on computers around the globe via a system called The Grid. The magnitude of the project and the amount of data to analyze provides a “tremendous opportunity” for graduate and undergraduate students interested in physics, Cutts said.
The theory behind the Higgs boson comes from work done by Peter Higgs and others, and was developed independently in 1964 by then-graduate student Gerald Guralnik along with C. R. Hagen and T. W. B. Kibble. Guralnik, now a professor of physics at Brown, said it is “fantastic that we are finally in a position to test this theory in its simplest form.”
“The theory for this experiment is very well understood, yet if not found, there are many ways to explain SM,” or the Standard Model, “without the Higgs boson,” Guralnik added. Still, “this model it too beautiful not to be the route that is chosen.”
Theoreticians like Guralnik and Tan accepted the Standard Model about 30 years ago and have now moved on to other theories, such as the currently popular string theory.
But in the back of their minds they are still thinking, the Standard Theory “had better be right,” Tan said. “We must expect all possibilities,” Landsberg said, adding that evidence that the Higgs boson doesn’t exist “would be even more interesting.” Then, scientists would have to seek alternative solutions to the Standard Model, such as extra-dimensional space and dark matter.
But two men from Hawaii are fearing the worst. They recently filed a lawsuit to suspend the LHC experiments, arguing that the particle collisions could create a black hole that could potentially engulf the Earth, the New York Times reported March 29.
Narain dismissed the concerns. “It’s a lawsuit that doesn’t have much merit,” she said. “If you really understand what is going on, (a black hole) is such a remote possibility it will have zero impact.”
Though technically complicated, the LHC has recently entered the public eye. It and CERN, the facility where it’s located, played a role in Dan Brown’s best seller “Angels and Demons,” in which terrorists steal dark matter from the facility. The science in the book is largely unfounded.
Landsberg said the LHC capitvates people for several reasons. “LHC machines (are) pushing the frontier of modern technology,” he said. “Technology is being pushed by the needs of particle physicists.”
He also said CERN has a history of pushing man to his limit and riding on the cutting edge of technology – in 1989, CERN scientist Tim Berners-Lee invented the World Wide Web.
Landsberg added that the experiments themselves are very beautiful from a scientific perspective. CMS is a “piece of modern art,” he said, adding that people want to understand the most fundamental aspects of the universe. “If satisfied, then we would never make progress,” Landsberg said.
Narain also stressed the importance of these questions.
“We are getting so close to figuring out where we came from,” Narain said. “Maybe we will be able to solve the mysteries of mass.”
But the experiment is most philosophical for Guralnik, whose previous work is the foundation for the current project at the LHC. “You really want a theory that explains everything,” he said. “The essence of being human is to be able to ask questions like this.”