Fermilab produced its first high-energy particle beam on March 1, 1972. Since then hundreds of experiments have used Fermilab's accelerators to study matter at ever smaller scales and its detectors to study the universe at great distances. Here is an overview of the top achievements so far.
Discovery of the Higgs boson
The Higgs boson is a particle associated with the Higgs field, the mechanism through which elementary particles gain mass. Without the Higgs field, or something similar, atoms would not form, and there would be no chemistry, no biology and no life.
Physicists first formed the theory of the Higgs field in the 1960s and predicted the existence of the Higgs boson in 1964. On July 4, 2012, scientists on two international experiments at the Large Hadron Collider at CERN laboratory announced the discovery of the Higgs boson by combining signals seen in different types of decays of the new particle.
The discovery was the culmination of nearly five decades of work by thousands of physicists and engineers and included research at the LHC, Fermilab's Tevatron accelerator and CERN's Large Electron-Positron Collider.
Fermilab scientists have played a significant role in the many steps that led to finding the elusive particle. They worked out new ideas and models in the Theory Department; built and ran experiments at the Tevatron, which provided evidence for Higgs boson production; participated in the construction and running of the CMS experiment at CERN, which led to the LHC discovery; and provided computing power and intellectual leadership in data analysis at CMS.
Video: Don Lincoln explains the Higgs boson
Tevatron Experiments: CDF and DZero
Searching for the Higgs required colliding particles at high enough energies to produce other particles, essentially recreating the conditions of the early universe shortly after the big bang. The hunt for the Higgs included experiments at the Large Electron-Positron Collider at European laboratory CERN and continued at Fermilab when its Tevatron accelerator took its turn as the most powerful particle collider in the world.
Two experiments – CDF and DZero, the collaborations for which included more than 1,200 physicists from universities and laboratories around the world – used the Tevatron's high energies to search for the Higgs boson.
Theorists had a good idea about many of the properties of the Higgs boson, but the hardest to predict was its mass. Much of the work conducted at the Tevatron advanced the search for the Higgs boson by eliminating mass ranges not previously excluded at LEP while also looking for signs of where the Higgs might be. On July 2, 2012, scientists on the Tevatron experiments, combining their data, presented strong indications for the production and decay of Higgs bosons based on a decay mode of the Higgs boson that was not seen at the LHC. But it took results from the LHC experiments to establish a discovery.
- Number of countries involved in the CDF experiment: 15.
- Number of countries involved in the DZero experiment: 18.
- At top speeds, particles cycled around the four-mile Tevatron about 48,000 times per second.
- CDF stands for Collider Detector at Fermilab. DZero was named after the detector's location on the accelerator ring.
- Particles collided inside each detector more than 2 million times per second.
The Tevatron was capable of reaching energies as high as 1 TeV (or one trillion electronvolts) in each of the two colliding beams, hence the accelerator's name.
Read the Aug. 4, 2008, press release on the Tevatron and the Higgs boson.
Read the March 11, 2009, press release on a measurement of the W boson constraining the Higgs mass.
Read the July 26, 2010, press release on Fermilab narrowing in on the Higgs boson.
Read the March 7, 2012, press release on the Tevatron seeing hints of the Higgs boson.
Read the July 2, 2012, press release on the Tevatron's final Higgs boson results.
Large Hadron Collider Experiments: CMS
On July 4, 2012, scientists on the CMS and ATLAS experiments at the Large Hadron Collider announced the discovery of the Higgs boson. Fermilab was heavily involved in both the construction of the LHC – designing magnets that focus the particle beams into a collision – and the science conducted with the accelerator that led to the Higgs discovery.
Scientists from the United States, including 100 Fermilab employees, make up approximately a third of the CMS collaboration, one of the two main experiments operating on the LHC. Fermilab serves as the hub for US researchers working on the international experiment. Fermilab is home to the LHC Physics Center, a physics analysis hub for physicists from US institutions on CMS. It also hosts the LHC Remote Operations Center, which allows physicists to help operate the CMS detector and monitor the LHC accelerator from afar.
Fermilab serves as a Tier-1 computing center, one of two main computing centers in the United States that stores, processes and distributes LHC data from CERN. The United States provides 40 percent of the computing power for the CMS experiment, using high-speed networks to transfer data in real time, and Fermilab is the centerpiece of that effort.
- Number of countries involved in the CMS experiment: 46
- Number of countries involved in the ATLAS experiment: 38
- American institutions make up a quarter of both the CMS and ATLAS collaborations.
- CMS stands for Compact Muon Solenoid, and ATLAS stands for A Toroidal LHC Apparatus. "Toroidal" means donut-shaped.
- The United States provides about 40 percent of the computing power for the CMS experiment.
- The particle beam circles the Large Hadron Collider about 11,245 times per second.
- The LHC produces about 5.8 quadrillion particle collisions each year.
- One out of every 5 billion collisions in the Large Hadron Collider produces a Higgs boson.
Read the Aug. 22, 2011, press release on the LHC eliminating Higgs hiding spots.
Read the Dec. 13, 2011, press release on signs of the Higgs boson at the LHC.
Read the July 4, 2012, press release on the discovery of the Higgs at the LHC.
Discovery of the top quark
On March 2, 1995, physicists at Fermilab's CDF and DZero experiments announced the discovery of the top quark, the last undiscovered quark of the six predicted to exist by current scientific theory. Scientists worldwide had sought the top quark since the discovery of the bottom quark at Fermilab in 1977. Physicists discovered the top quark, as heavy as an entire gold atom but much smaller than a single proton, using particle beams from the Tevatron.
Since the top quark's discovery, scientists at Fermilab have measured its mass to high precision in order to verify the correctness and accuracy of their particle models. Knowing the value of the top quark mass to this high precision allowed physicists to zero in on the mass of the Higgs boson, a crucial component of the theoretical framework of particle physics.
Read the March 2, 1995, press release.
Discovery of the bottom quark
In 1977, an experiment led by physicist and Nobel laureate Leon Lederman at Fermilab provided the first evidence for the existence of the bottom quark, an essential ingredient in the theoretical framework called the Standard Model.
Using a fixed-target experiment, the collaboration discovered a particle that they called an upsilon. It was composed of a previously unobserved kind of quark, the bottom quark, and its antimatter partner, the antibottom quark. The bottom quark was then the heaviest subnuclear particle ever observed, weighing in at 10 times the mass of a proton.
In 1974, physicists at Brookhaven National Laboratory and SLAC National Accelerator Laboratory had discovered particles made of charm quarks and their antimatter partners, anticharm quarks. The discovery of the bottom quark provided important proof that all matter is made up of quarks.
Read the Aug. 7, 1977, press release.
Observation of tau neutrino
On July 21, 2000, the DONUT collaboration at Fermilab announced on July 21, 2000, the first direct evidence for the tau neutrino, the third kind of neutrino known to particle physicists.
Although earlier experiments had produced convincing indirect evidence for the particle's existence, no one had directly observed a tau neutrino, an almost massless particle carrying no electric charge and barely interacting with surrounding matter.
The collaboration reported 12 instances of a neutrino interacting with an atomic nucleus to produce a charged particle called a tau lepton, the signature of a tau neutrino. To make this find, they aimed Fermilab's intense beam of neutrinos across a 3-foot-long target of iron plates sandwiched with emulsion, similar to photographic film, which recorded the particle interactions. In the target, one out of 1 trillion tau neutrinos interacted with an iron nucleus and produced a tau lepton, which left its 1-millimeter-long telltale track in the emulsion. Physicists needed about three years of painstaking work to identify the tracks revealing a tau lepton and its decay, the key to exposing the tau neutrino's secret existence.
Read the July 20, 2000, press release.
Discovery of a quasar at a distance of 27 billion light-years
On April 13, 2000, scientists of the Sloan Digital Sky Survey announced the observation of the most distant object ever observed, a quasar at a red shift of 5.8, a distance of 27 billion light-years from Earth. The SDSS ultimately surveyed more than 10,000 square degrees, or one quarter of the sky, and 200 million celestial objects. Fermilab scientists were involved in managing and analyzing this large amount of data. These astrophysical studies complement Fermilab's quest to understand the structure and evolution of the universe.
Read the April 13, 2000, press release.
Observation of direct CP violation in kaon decays
On February 24, 1999, physicists from Fermilab's KTeV collaboration announced results establishing the existence of direct CP violation in the decay of kaons, particles containing a strange quark. The observation is a significant step in understanding why the universe displays an abundance of matter, while antimatter disappeared at an early stage in the evolution of the universe.
When certain subatomic particles called kaons decay, they break into a charged pion, a neutrino and either an electron or its antimatter counterpart, a positron. In the absence of CP violation, the number of electrons and positrons created in these decays would be equal. However, scientists observed that the scales tip slightly toward decay into electrons. This provides proof that CP violation can lead to an excess of matter over antimatter. If this process occurred in the early universe, all of the positrons would annihilate upon encountering electrons. But after all of the positrons had disappeared, some matter would remain.
This result gives credence to the theory that CP violation allowed all of us to exist. But the effects of the process that causes an excess of matter from kaon decays are too small to complete the picture. The observed difference is orders of magnitude away from explaining asymmetry in the universe. This is one of the reasons that scientists are so interested in observing CP violation in other places, like neutrinos.
Read the March 1, 1999, press release.
Confirming evidence of dark energy
Scientists found the first evidence of dark energy in 1998 when they discovered through the observation of distant supernovae that the universe was expanding at an increasing rate. They had expected to find a slowing rate of expansion due to the force of gravity. The observation to the contrary led them to theorize that another force was pushing the universe apart.
Fermilab researchers found a way to test the finding with the Sloan Digital Sky Survey. Through SDSS, scientists could observe large clusters of galaxies and connect them to fluctuations in the cosmic microwave background, mapped by a separate satellite called WMAP. The cosmic microwave background gives astrophysicists a picture of the universe as it was about 300,000 years afterthe big bang. Objects in space have left imprints on the cosmic microwave background in the form of areas of concentrated particles and energy. Imagine those hot spots as the light areas left on an old carpet when a sofa that has sat in one place for years is put in another room. SDSS measured the deflection light from the background hotspots, or the light spots on the carpet, as it passed by the foreground galaxy clusters, or furniture. From this, researchers deduced that the accelerating expansion of the universe was real.
Scientists compared the intensities of the hot spots left in the cosmic microwave background to the locations and sizes of clusters of galaxies they observed with the SDSS to determine how the universe has expanded since a time shortly after the Big Bang. The experiment confirmed that the universe has expanded at an increasing rate. This offered independent confirmation of the study that suggested the existence of dark energy.
Observation of the origins of high-energy cosmic rays
In 1993, Fermilab physicists proposed the construction of the world's largest cosmic ray detector, the Pierre Auger Observatory, to address the question of the origin of high-energy cosmic rays. Researchers previously had assumed that cosmic rays approach the Earth uniformly from random directions. However, in 2007, researchers at Pierre Auger announced that the most energetic cosmic rays to impact the Earth generally come from the direction of active galactic nuclei.
Many large galaxies, including our own Milky Way, have a supermassive black hole in their centers. While most black holes will sit quietly in the nucleus of a galaxy for billions of years, if a galaxy's black hole happens to be surrounded and fed by a steady stream of gas and stars, it creates what is called an active galactic nucleus. An active galactic nucleus releases high-energy radiation observable by radio, X-ray and gamma ray telescopes on earth.
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