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In particle physics, a meson is a type of hadronic subatomic particle composed of an equal number of quarks and antiquarks, usually one of each, bound together by the strong interaction. Because mesons are composed of quark subparticles, they have a meaningful physical size, a diameter of roughly one femtometre (10−15 m), which is about 0.6 times the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few tenths of a nanosecond. Heavier mesons decay to lighter mesons and ultimately to stable electrons, neutrinos and photons.
Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions and bosons. There are three generations of fermions, although ordinary matter is made only from the first fermion generation. The first generation consists of up and down quarks which form protons and neutrons, and electrons and electron neutrinos. The three fundamental interactions known to be mediated by bosons are electromagnetism, the weak interaction, and the strong interaction.
A quark is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. All commonly observable matter is composed of up quarks, down quarks and electrons. Owing to a phenomenon known as color confinement, quarks are never found in isolation; they can be found only within hadrons, which include baryons and mesons, or in quark–gluon plasmas. For this reason, much of what is known about quarks has been drawn from observations of hadrons.
SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center, is a federally funded research and development center in Menlo Park, California, United States. Founded in 1962, the laboratory is now sponsored by the United States Department of Energy and administrated by Stanford University. It is the site of the Stanford Linear Accelerator, a 3.2 kilometer (2-mile) linear accelerator constructed in 1966 that could accelerate electrons to energies of 50 GeV.
The charm quark, charmed quark, or c quark is an elementary particle of the second generation. It is the third-most massive quark, with a mass of 1.27±0.02 GeV/c2 and a charge of +2/3e. It carries charm, a quantum number. Charm quarks are found in various hadrons, such as the J/psi meson and the charmed baryons. There are also several bosons, including the W and Z bosons and the Higgs boson, that can decay into charm quarks.
The top quark, sometimes also referred to as the truth quark, is the most massive of all observed elementary particles. It derives its mass from its coupling to the Higgs Boson. This coupling 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 DØ experiments at Fermilab.
The bottom quark or b quark, also known as the beauty quark, is a third-generation heavy quark with a charge of −1/3 e.
The BaBar experiment, or simply BaBar, is an international collaboration of more than 500 physicists and engineers studying the subatomic world at energies of approximately ten times the rest mass of a proton (~10 GeV). Its design was motivated by the investigation of charge-parity violation. BaBar is located at the SLAC National Accelerator Laboratory, which is operated by Stanford University for the Department of Energy in California.
The
J/ψ
(J/psi) meson is a subatomic particle, a flavor-neutral meson consisting of a charm quark and a charm antiquark. Mesons formed by a bound state of a charm quark and a charm anti-quark are generally known as "charmonium" or psions. The
J/ψ
is the most common form of charmonium, due to its spin of 1 and its low rest mass. The
J/ψ
has a rest mass of 3.0969 GeV/c2, just above that of the
η
c, and a mean lifetime of 7.2×10−21 s. This lifetime was about a thousand times longer than expected.
The DØ experiment was a worldwide collaboration of scientists conducting research on the fundamental nature of matter. DØ was one of two major experiments located at the Tevatron Collider at Fermilab in Batavia, Illinois. The Tevatron was the world's highest-energy accelerator from 1983 until 2009, when its energy was surpassed by the Large Hadron Collider. The DØ experiment stopped taking data in 2011, when the Tevatron shut down, but data analysis is still ongoing. The DØ detector is preserved in Fermilab's DØ Assembly Building as part of a historical exhibit for public tours.
The Xi baryons or cascade particles are a family of subatomic hadron particles which have the symbol Ξ and may have an electric charge of +2 e, +1 e, 0, or −1 e, where e is the elementary charge.
In particle physics, a B-factory, or sometimes a beauty factory, is a particle collider experiment designed to produce and detect a large number of B mesons so that their properties and behavior can be measured with small statistical uncertainty. Tau leptons and D mesons are also copiously produced at B-factories.
Neutral B meson oscillations are one of the manifestations of the neutral particle oscillation, a fundamental prediction of the Standard Model of particle physics. It is the phenomenon of B mesons changing between their matter and antimatter forms before their decay. The
B
s meson can exist as either a bound state of a strange antiquark and a bottom quark, or a strange quark and bottom antiquark. The oscillations in the neutral B sector are analogous to the phenomena that produce long and short-lived neutral kaons.
The timeline of particle physics lists the sequence of particle physics theories and discoveries in chronological order. The most modern developments follow the scientific development of the discipline of particle physics.
Nigel Stuart Lockyer is a British-American experimental particle physicist. He is the current director of the Cornell Laboratory for Accelerator-based ScienceS and Education (CLASSE) as of May 1, 2023. He was the Director of the Fermi National Accelerator Laboratory (Fermilab), in Batavia, Illinois, the leading particle physics laboratory in the United States, from September 2013 to April 2022.
Richard K. Yamamoto (1935–2009) was an elementary particle physicist and professor of physics at MIT focusing primarily on the study of leptons and quarks and their interactions. To this end he was involved with experiments at Brookhaven, Fermilab, and SLAC, including the BaBar Experiment. He was also known for his expertise in building experimental hardware, which he shared with students.
Richard Edward Taylor,, was a Canadian physicist and Stanford University professor. He shared the 1990 Nobel Prize in Physics with Jerome Friedman and Henry Kendall "for their pioneering investigations concerning deep inelastic scattering of electrons on protons and bound neutrons, which have been of essential importance for the development of the quark model in particle physics."
Mohammad Sajjad "Saj" Alam was a Bengali Pakistani and a naturalized American particle physicist. His work focused on particle physics and computational physics. He played a significant role in several major particle physics experiments that led to new discoveries in the area of high-energy particle physics.
The INFN National Laboratory of Frascati (LNF) was founded in 1954 with the objective of furthering particle physics research, and more specifically to host the 1.1 GeV electrosynchrotron, the first accelerator ever built in Italy. The Laboratory later developed the first ever electron-positron collider: from the first prototype AdA, which demonstrated the feasibility, to the ring ADONE and later on to DAΦNE, still operative today (2022). LNF was also the proposed site of the cancelled particle accelerator SuperB.
Vera G. Lüth is an experimental particle physicist and professor emerita at Stanford Linear Accelerator Center (SLAC), Stanford University, in the United States. A senator of the Helmholtz Association, she has worked in particle physics at SLAC since 1974. She is a fellow of the American Physical Society.
References
- ↑ WA76 Archived 2007-08-07 at the Wayback Machine on greybook
- ↑ See the press release by SLAC
- ↑ See also the press release by INFN.
- ↑ Whitehouse, David (30 April 2003). "Physicists find 'rebel' particle". BBC News Online. Retrieved 21 March 2011.
- ↑ Observation of a Narrow Meson Decaying to Ds+π0 at a mass of 2.32 GeV/c2, Phys. Rev. Lett.90 (2003) 242001