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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 field also studies combinations of elementary particles up to the scale of protons and neutrons, while the study of combination of protons and neutrons is called nuclear physics.
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 found in composite subatomic particles called hadrons such as the J/psi meson and the charmed baryons created in particle accelerator collisions. Several bosons, including the W and Z bosons and the Higgs boson, can decay into charm quarks. All charm quarks carry charm, a quantum number. This second-generation particle is the third-most-massive quark, with a mass of 1.27±0.02 GeV/c2 as measured in 2022, and a charge of +2/3 e.
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 field. This coupling yt 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, beauty quark, or b quark, is an elementary particle of the third generation. It is a heavy quark with a charge of −1/3 e.
A pentaquark is a human-made subatomic particle, consisting of four quarks and one antiquark bound together; they are not known to occur naturally, or exist outside of experiments specifically carried out to create them.
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 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 detectors a detection of internally reflected Cherenkov light (DIRC) detector measures the velocity of charged particles and is used for particle identification. It is a design of a ring imaging Cherenkov detector where Cherenkov light that is contained by total internal reflection inside the solid radiator has its angular information preserved until it reaches the light sensors at the detector perimeter.
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.
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.
Luciano Maiani is a Sammarinese physicist best known for his prediction of the charm quark with Sheldon Glashow and John Iliopoulos.
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.
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.
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.
George H. Trilling was a Polish-born American particle physicist. He was co-discoverer of the J/ψ meson which evinced the existence of the charm quark. Trilling joined the Physics Department faculty at the University of California, Berkeley, in 1960, where he was Department Chair from 1968 through 1972. Trilling was on sabbatical leave to CERN in 1973–74, where he worked on the study of the properties of charm particles, their decay modes and excited states. He was also director of the Physics Division at the Lawrence Berkeley National Laboratory from 1984 until 1987. Trilling was a principal proponent of the Superconducting Super Collider project and spokesperson for the Solenoidal Detector Collaboration. After the SSC was cancelled in 1993, Trilling transitioned most of the SDC team to collaborate on the ATLAS experiment at the LHC, which led to the discovery of the Higgs boson in 2012. Trilling was elected vice-president of the American Physical Society, beginning his term on 1 January 1999, and was president of the society in 2001.
References
- ↑ WA76 Archived 2007-08-07 at the Wayback Machine on greybook
- ↑ See the press release by SLAC
- ↑ See also the press release Archived 2006-05-07 at the Wayback Machine 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