The top quark, sometimes also referred to as the truth quark, (symbol: t) is the most massive of all observed elementary particles. It derives its mass from its coupling to the Higgs Boson. This coupling









y



t









{\displaystyle y_{t}}

is very close to unity; in the Standard Model of particle physics, it is the largest (strongest) coupling at the scale of the weak interactions and above. The top quark was discovered in 1995 by the CDF and D experiments at Fermilab.

Like all other quarks, the top quark is a fermion with spin 1/2 and participates in all four fundamental interactions: gravitation, electromagnetism, weak interactions, and strong interactions. It has an electric charge of +2/3 e. It has a mass of 172.760.3 GeV/c2, which is close to the rhenium atom mass. The antiparticle of the top quark is the top antiquark (symbol: t, sometimes called antitop quark or simply antitop), which differs from it only in that some of its properties have equal magnitude but opposite sign.

The top quark interacts with gluons of the strong interaction and is typically produced in hadron colliders via this interaction. However, once produced, the top (or antitop) can decay only through the weak force. It decays to a W boson and either a bottom quark (most frequently), a strange quark, or, on the rarest of occasions, a down quark.

The Standard Model determines the top quark's mean lifetime to be roughly 51025 s. This is about a twentieth of the timescale for strong interactions, and therefore it does not form hadrons, giving physicists a unique opportunity to study a "bare" quark (all other quarks hadronize, meaning that they combine with other quarks to form hadrons and can only be observed as such).

Because the top quark is so massive, its properties allowed indirect determination of the mass of the Higgs boson (see § Mass and coupling to the Higgs boson below). As such, the top quark's properties are extensively studied as a means to discriminate between competing theories of new physics beyond the Standard Model. The top quark is the only quark that has been directly observed due to the fact that it decays faster than the hadronization time.



Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been operated by the Fermi Research Alliance, a joint venture of the University of Chicago, and the Universities Research Association (URA). Fermilab is a part of the Illinois Technology and Research Corridor.

Fermilab's Tevatron was a landmark particle accelerator; until the startup in 2008 of the Large Hadron Collider (LHC) near Geneva, Switzerland, it was the most powerful particle accelerator in the world, accelerating protons and antiprotons to energies of 980 GeV, and producing proton-proton collisions with energies of up to 1.96 TeV, the first accelerator to reach one "tera-electron-volt" energy. At 3.9 miles (6.3 km), it was the world's fourth-largest particle accelerator in circumference. One of its most important achievements was the 1995 discovery of the top quark, announced by research teams using the Tevatron's CDF and DØ detectors. It was shut down in 2011. Since then Fermilab's Main Injector, two miles (3.3 km) in circumference, has been the laboratory's most powerful particle accelerator. The construction of the first building for the new PIP-II linear accelerator began in 2020.Fermilab hosts neutrino experiments, such as MicroBooNE (Micro Booster Neutrino Experiment), ICARUS (Imaging Cosmic and Rare Underground Signals), NOνA (NuMI Off-Axis νe Appearance) and Muon g-2. Completed neutrino experiments include MINOS (Main Injector Neutrino Oscillation Search), MINOS+, MiniBooNE and SciBooNE (SciBar Booster Neutrino Experiment) as well as the SeaQuest fixed-target experiment. The MiniBooNE detector was a 40-foot (12 m) diameter sphere containing 800 tons of mineral oil lined with 1,520 phototube detectors. An estimated 1 million neutrino events were recorded each year. SciBooNE sat in the same neutrino beam as MiniBooNE but had fine-grained tracking capabilities. The NOνA experiment uses, and the MINOS experiment used, Fermilab's NuMI (Neutrinos at the Main Injector) beam, which is an intense beam of neutrinos that travels 455 miles (732 km) through the Earth to the Soudan Mine in Minnesota and the Ash River, Minnesota, site of the NOνA far detector. In 2017, the ICARUS neutrino experiment was moved from CERN to Fermilab, with plans to begin operation in 2020.Fermilab also pursues research in quantum information science. It founded the Fermilab Quantum Institute in 2019. Since 2020, it also is home to the SQMS (Superconducting Quantum and Materials Science) center.In the public realm, Fermilab is home to a native prairie ecosystem restoration project and hosts many cultural events: public science lectures and symposia, classical and contemporary music concerts, folk dancing and arts galleries. Ordinarily, the site is open from dawn to dusk to visitors who present valid photo identification, although it has been temporarily closed to the public since March 2020 because of the COVID-19 pandemic.

Asteroid 11998 Fermilab is named in honor of the laboratory.