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In particle physics, a hadron is a subatomic composite particle made of two or more quarks held together by the strong force in a similar way as molecules are held together by the electromagnetic force. Most of the mass of ordinary matter comes from two hadrons: the proton and the neutron.
The omega baryons are a family of subatomic hadron particles that are represented by the symbol
Ω
and are either neutral or have a +2, +1 or −1 elementary charge. They are baryons containing no up or down quarks. Omega baryons containing top quarks are not expected to be observed. This is because the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10−25 s, which is about a twentieth of the timescale for strong interactions, and therefore that they do not form hadrons.
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.
Technicolor theories are models of physics beyond the Standard Model that address electroweak gauge symmetry breaking, the mechanism through which W and Z bosons acquire masses. Early technicolor theories were modelled on quantum chromodynamics (QCD), the "color" theory of the strong nuclear force, which inspired their name.
A tetraquark, in particle physics, is an exotic meson composed of four valence quarks. A tetraquark state has long been suspected to be allowed by quantum chromodynamics, the modern theory of strong interactions. A tetraquark state is an example of an exotic hadron which lies outside the conventional quark model classification.
Exotic baryons are a type of hadron with half-integer spin, but have a quark content different from the three quarks (qqq) present in conventional baryons. An example would be pentaquarks, consisting of four quarks and one antiquark (qqqqq̅).
The
J/ψ
(J/psi) meson or psion 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". 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.
Exotic hadrons are subatomic particles composed of quarks and gluons, but which - unlike "well-known" hadrons such as protons, neutrons and mesons - consist of more than three valence quarks. By contrast, "ordinary" hadrons contain just two or three quarks. Hadrons with explicit valence gluon content would also be considered exotic. In theory, there is no limit on the number of quarks in a hadron, as long as the hadron's color charge is white, or color-neutral.
CLEO was a general purpose particle detector at the Cornell Electron Storage Ring (CESR), and the name of the collaboration of physicists who operated the detector. The name CLEO is not an acronym; it is short for Cleopatra and was chosen to go with CESR. CESR was a particle accelerator designed to collide electrons and positrons at a center-of-mass energy of approximately 10 GeV. The energy of the accelerator was chosen before the first three bottom quark Upsilon resonances were discovered between 9.4 GeV and 10.4 GeV in 1977. The fourth Υ resonance, the Υ(4S), was slightly above the threshold for, and therefore ideal for the study of, B meson production.
The Xi baryons or cascade particles are a family of subatomic hadron particles which have the symbol Ξ and may have an electric charge (Q) of +2 e, +1 e, 0, or −1 e, where e is the elementary charge. Like all conventional baryons, they contain three quarks. Xi baryons, in particular, contain one up or down quark plus two more massive quarks: either strange, charm or bottom. They are historically called the cascade particles because of their unstable state; they decay rapidly into lighter particles through a chain of decays. The first discovery of a charged Xi baryon was in cosmic ray experiments by the Manchester group in 1952. The first discovery of the neutral Xi particle was at Lawrence Berkeley Laboratory in 1959. It was also observed as a daughter product from the decay of the omega baryon observed at Brookhaven National Laboratory in 1964. The Xi spectrum is important to nonperturbative quantum chromodynamics (QCD), such as lattice QCD.
The X(3872) is an exotic meson candidate with a mass of 3871.68 MeV/c2 which does not fit into the quark model because of its quantum numbers. It was first discovered in 2003 by the Belle experiment in Japan and later confirmed by several other experimental collaborations. Several theories have been proposed for its nature, such as a mesonic molecule or a diquark-antidiquark pair (tetraquark).
Z(4430) is a mesonic resonance discovered by the Belle experiment. It has a mass of 4430 MeV/c2. The resonant nature of the peak has been confirmed by the LHCb experiment with a significance of at least 13.9 σ. The particle is charged and is thought to have a quark content of
c
c
d
u
, making it a tetraquark candidate. It has the spin-parity quantum numbers JP = 1+.
In particle physics hexaquarks, alternatively known as sexaquarks, are a large family of hypothetical particles, each particle consisting of six quarks or antiquarks of any flavours. Six constituent quarks in any of several combinations could yield a colour charge of zero; for example a hexaquark might contain either six quarks, resembling two baryons bound together, or three quarks and three antiquarks. Once formed, dibaryons are predicted to be fairly stable by the standards of particle physics.
In particle physics, B mesons are mesons composed of a bottom antiquark and either an up, down, strange or charm quark. The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark's short lifetime. The combination of a bottom antiquark and a bottom quark is not a B meson, but rather bottomonium which is something else entirely.
A strangelet is a hypothetical particle consisting of a bound state of roughly equal numbers of up, down, and strange quarks. An equivalent description is that a strangelet is a small fragment of strange matter, small enough to be considered a particle. The size of an object composed of strange matter could, theoretically, range from a few femtometers across to arbitrarily large. Once the size becomes macroscopic, such an object is usually called a strange star. The term "strangelet" originates with Edward Farhi and Robert Jaffe in 1984. Strangelets can convert matter to strange matter on contact. Strangelets have been suggested as a dark matter candidate.
Thomas Carlos Mehen is an American physicist. His research has consisted of primarily Quantum chromodynamics (QCD) and the application of effective field theory to problems in hadronic physics. He has also worked on effective field theory for non-relativistic particles whose short range interactions are characterized by a large scattering length, as well as novel field theories which arise from unusual limits of string theory.
In particle physics, W′ and Z′ bosons refer to hypothetical gauge bosons that arise from extensions of the electroweak symmetry of the Standard Model. They are named in analogy with the Standard Model W and Z bosons.
Modern searches for Lorentz violation are scientific studies that look for deviations from Lorentz invariance or symmetry, a set of fundamental frameworks that underpin modern science and fundamental physics in particular. These studies try to determine whether violations or exceptions might exist for well-known physical laws such as special relativity and CPT symmetry, as predicted by some variations of quantum gravity, string theory, and some alternatives to general relativity.
The Zc(3900) is a hadron, a type of subatomic particle made of quarks, believed to be the first tetraquark that has been observed experimentally. The discovery was made in 2013 by two independent research groups: one using the BES III detector at the Chinese Beijing Electron Positron Collider, the other being part of the Belle experiment group at the Japanese KEK particle physics laboratory.
References
- ↑ "Oddball Particle Surprises Physicists at Fermilab". redOrbit. 19 March 2009. Retrieved 2009-03-21.
- ↑ Handwerk, Brian (20 March 2009). "Strange Particle Created; May Rewrite How Matter's Made". National Geographic News . Retrieved 2009-03-21.
- ↑ Minard, Anne (18 March 2009). "New Particle Throws Monkeywrench in Particle Physics". Universe Today .
- ↑ Riesselmann, Kurt (December 4, 2012). "Experiment confirms existence of odd particle". Phys.Org.
- ↑ Hidalgo-Duque, C; Nieves, J; Pavón Valderrama, M (2012). "Heavy Quark Spin Symmetry and SU(3)-Flavour Partners of the X(3872)". Nuclear Physics A. 914: 482–487. arXiv: 1211.7004 . Bibcode:2013NuPhA.914..482H. doi:10.1016/j.nuclphysa.2013.01.025.
- ↑ Dorigo, Tommaso (September 26, 2013). "DZERO Confirms The Y(4140) And Its Excitation"
- ↑ D0 Collaboration; Abbott, B; Acharya, B. S; Adams, M; Adams, T; Agnew, J. P; Alexeev, G. D; Alkhazov, G; Alton, A; Askew, A; Atkins, S; Augsten, K; Avila, C; Badaud, F; Bagby, L; Baldin, B; Bandurin, D. V; Banerjee, S; Barberis, E; Baringer, P; Bartlett, J. F; Bassler, U; Bazterra, V; Bean, A; Begalli, M; Bellantoni, L; Beri, S. B; Bernardi, G; Bernhard, R; et al. (2013). "Search for the X(4140) state in B+→J/ψφK+ decays with the D0 detector". Physical Review D. 89 (12004): 012004. arXiv: 1309.6580 . Bibcode:2014PhRvD..89a2004A. doi:10.1103/PhysRevD.89.012004.
- ↑ Shen, C. P.; et al. (2010). "Evidence for a New Resonance and Search for the Y(4140) in the γγ→ϕJ/ψ Process". Physical Review Letters . 104 (11): 112004. arXiv: 0912.2383 . Bibcode:2010PhRvL.104k2004S. doi:10.1103/PhysRevLett.104.112004. PMID 20366468.
- ↑ LHCb collaboration; Aaij, R; Adeva, B; Adinolfi, M; Ajaltouni, Z; Akar, S; Albrecht, J; Alessio, F; Alexander, M; Ali, S; Alkhazov, G; Alvarez Cartelle, P; Alves Jr, A. A; Amato, S; Amerio, S; Amhis, Y; An, L; Anderlini, L; Andreassi, G; Andreotti, M; Andrews, J. E; Appleby, R. B; Aquines Gutierrez, O; Archilli, F; d'Argent, P; Arnau Romeu, J; Artamonov, A; Artuso, M; Aslanides, E; et al. (2016). "Observation of J/ψφ structures consistent with exotic states from amplitude analysis of B+→J/ψφK+ decays". Physical Review Letters. 118 (2): 022003. arXiv: 1606.07895 . Bibcode:2017PhRvL.118b2003A. doi:10.1103/PhysRevLett.118.022003. PMID 28128595.
- ↑ LHBc collaboration; Aaij, R; Adeva, B; Adinolfi, M; Ajaltouni, Z; Akar, S; Albrecht, J; Alessio, F; Alexander, M; Ali, S; Alkhazov, G; Alvarez Cartelle, P; Alves Jr, A. A; Amato, S; Amerio, S; Amhis, Y; An, L; Anderlini, L; Andreassi, G; Andreotti, M; Andrews, J. E; Appleby, R. B; Aquines Gutierrez, O; Archilli, F; d'Argent, P; Arnau Romeu, J; Artamonov, A; Artuso, M; Aslanides, E; et al. (2016). "Amplitude analysis of B+→J/ψφK+ decays". Physical Review D. 95 (12002): 012002. arXiv: 1606.07898 . Bibcode:2017PhRvD..95a2002A. doi:10.1103/PhysRevD.95.012002.
