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 .
66-463: Like all conventional baryons , Ξ particles contain three quarks . Ξ baryons, in particular, contain either one up or one down quark and two other, more massive quarks. The two more massive quarks are any two of strange , charm , or bottom (doubles allowed). For notation, the assumption is that the two heavy quarks in the Ξ are both strange ; subscripts "c" and "b" are added for each even heavier charm or bottom quark that replaces one of
132-524: A Nobel prize in physics for his work on the Eightfold Way, in 1969. Finally, in 1964, Gell-Mann and George Zweig , discerned independently what the Eightfold Way picture encodes: They posited three elementary fermionic constituents—the " up ", " down ", and " strange " quarks—which are unobserved, and possibly unobservable in a free form. Simple pairwise or triplet combinations of these three constituents and their antiparticles underlie and elegantly encode
198-455: A proton is made of two up quarks and one down quark ; and its corresponding antiparticle, the antiproton , is made of two up antiquarks and one down antiquark. Baryons participate in the residual strong force , which is mediated by particles known as mesons . The most familiar baryons are protons and neutrons , both of which contain three quarks, and for this reason they are sometimes called triquarks . These particles make up most of
264-406: A c quark and some combination of two u and/or d quarks. The c quark has a charge of ( Q = + 2 / 3 ), therefore the other two must be a u quark ( Q = + 2 / 3 ), and a d quark ( Q = − 1 / 3 ) to have the correct total charge ( Q = +1). Valence quark In particle physics , the quark model
330-599: A combination of three u or d quarks. Under the isospin model, they were considered to be a single particle in different charged states. The mathematics of isospin was modeled after that of spin. Isospin projections varied in increments of 1 just like those of spin, and to each projection was associated a " charged state ". Since the " Delta particle " had four "charged states", it was said to be of isospin I = 3 / 2 . Its "charged states" Δ , Δ , Δ , and Δ , corresponded to
396-461: A component of the established quantum field theory of strong and electroweak particle interactions, dubbed the Standard Model . Hadrons are not really "elementary", and can be regarded as bound states of their "valence quarks" and antiquarks, which give rise to the quantum numbers of the hadrons. These quantum numbers are labels identifying the hadrons, and are of two kinds. One set comes from
462-573: A consequence of the quark model classification, when it was appreciated that the spin S = 3 / 2 baryon, the Δ , required three up quarks with parallel spins and vanishing orbital angular momentum. Therefore, it could not have an antisymmetric wavefunction, (required by the Pauli exclusion principle ). Oscar Greenberg noted this problem in 1964, suggesting that quarks should be para-fermions . Instead, six months later, Moo-Young Han and Yoichiro Nambu suggested
528-422: A particle is therefore the combination of intrinsic angular momentum (spin) and orbital angular momentum. It can take any value from J = | L − S | to J = | L + S | , in increments of 1. Particle physicists are most interested in baryons with no orbital angular momentum ( L = 0), as they correspond to ground states —states of minimal energy. Therefore, the two groups of baryons most studied are
594-477: A simple Ξ ; a subscript "c" is added for each constituent charm quark , and a "b" for each bottom quark . Hence Ξ c , Ξ b , Ξ cc , Ξ cb , etc. Unless specified , the non-up/down quark content of Xi baryons is strange (i.e. there is one up or down quark and two strange quarks). However a Ξ b contains one up, one strange, and one bottom quark, while a Ξ bb contains one up and two bottom quarks. In 2012,
660-498: A timely question after new experimental techniques uncovered so many of them that it became clear that they could not all be elementary. These discoveries led Wolfgang Pauli to exclaim "Had I foreseen that, I would have gone into botany." and Enrico Fermi to advise his student Leon Lederman : "Young man, if I could remember the names of these particles, I would have been a botanist." These new schemes earned Nobel prizes for experimental particle physicists, including Luis Alvarez , who
726-514: A vector of length S = 1 / 2 with two spin projections ( S z = + 1 / 2 , and S z = − 1 / 2 ). There is another quantity of angular momentum, called the orbital angular momentum ( azimuthal quantum number L ), that comes in increments of 1 ħ, which represent the angular moment due to quarks orbiting around each other. The total angular momentum ( total angular momentum quantum number J ) of
SECTION 10
#1733085970833792-717: Is 6 ⊗ 6 ⊗ 6 = 56 S ⊕ 70 M ⊕ 70 M ⊕ 20 A . {\displaystyle \mathbf {6} \otimes \mathbf {6} \otimes \mathbf {6} =\mathbf {56} _{S}\oplus \mathbf {70} _{M}\oplus \mathbf {70} _{M}\oplus \mathbf {20} _{A}~.} The 56 states with symmetric combination of spin and flavour decompose under flavor SU(3) into 56 = 10 3 2 ⊕ 8 1 2 , {\displaystyle \mathbf {56} =\mathbf {10} ^{\frac {3}{2}}\oplus \mathbf {8} ^{\frac {1}{2}}~,} where
858-492: Is 1 ħ), a single quark has a spin vector of length 1 / 2 , and has two spin projections ( S z = + 1 / 2 and S z = − 1 / 2 ). Two quarks can have their spins aligned, in which case the two spin vectors add to make a vector of length S = 1 and three spin projections ( S z = +1, S z = 0, and S z = −1). If two quarks have unaligned spins,
924-572: Is a vector quantity that represents the "intrinsic" angular momentum of a particle. It comes in increments of 1 / 2 ħ (pronounced "h-bar"). The ħ is often dropped because it is the "fundamental" unit of spin, and it is implied that "spin 1" means "spin 1 ħ". In some systems of natural units , ħ is chosen to be 1, and therefore does not appear anywhere. Quarks are fermionic particles of spin 1 / 2 ( S = 1 / 2 ). Because spin projections vary in increments of 1 (that
990-501: Is a classification scheme for hadrons in terms of their valence quarks —the quarks and antiquarks that give rise to the quantum numbers of the hadrons. The quark model underlies "flavor SU(3)" , or the Eightfold Way , the successful classification scheme organizing the large number of lighter hadrons that were being discovered starting in the 1950s and continuing through the 1960s. It received experimental verification beginning in
1056-490: Is about 3.8 times that of a proton . Isospin and spin values in parentheses have not been firmly established by experiments, but are predicted by the quark model and are consistent with the measurements. Baryon In particle physics , a baryon is a type of composite subatomic particle that contains an odd number of valence quarks , conventionally three. Protons and neutrons are examples of baryons; because baryons are composed of quarks , they belong to
1122-478: Is assumed that the Big Bang produced a state with equal amounts of baryons and antibaryons. The process by which baryons came to outnumber their antiparticles is called baryogenesis . Experiments are consistent with the number of quarks in the universe being conserved alongside the total baryon number , with antibaryons being counted as negative quantities. Within the prevailing Standard Model of particle physics,
1188-421: Is baryonic matter , which includes atoms of any sort, and provides them with the property of mass. Non-baryonic matter, as implied by the name, is any sort of matter that is not composed primarily of baryons. This might include neutrinos and free electrons , dark matter , supersymmetric particles , axions , and black holes . The very existence of baryons is also a significant issue in cosmology because it
1254-417: Is called " intrinsic parity " or simply "parity" ( P ). Gravity , the electromagnetic force , and the strong interaction all behave in the same way regardless of whether or not the universe is reflected in a mirror, and thus are said to conserve parity (P-symmetry). However, the weak interaction does distinguish "left" from "right", a phenomenon called parity violation (P-violation). Based on this, if
1320-700: Is not generally accepted. The particle physics community as a whole did not view their existence as likely in 2006, and in 2008, considered evidence to be overwhelmingly against the existence of the reported pentaquarks. However, in July 2015, the LHCb experiment observed two resonances consistent with pentaquark states in the Λ b → J/ψK p decay, with a combined statistical significance of 15σ. In theory, heptaquarks (5 quarks, 2 antiquarks), nonaquarks (6 quarks, 3 antiquarks), etc. could also exist. Nearly all matter that may be encountered or experienced in everyday life
1386-410: Is symmetric in flavor, the singlet antisymmetric and the two octets have mixed symmetry. The space and spin parts of the states are thereby fixed once the orbital angular momentum is given. It is sometimes useful to think of the basis states of quarks as the six states of three flavors and two spins per flavor. This approximate symmetry is called spin-flavor SU(6) . In terms of this, the decomposition
SECTION 20
#17330859708331452-472: Is thought to be due to non- conservation of baryon number in the very early universe, though this is not well understood. The concept of isospin was first proposed by Werner Heisenberg in 1932 to explain the similarities between protons and neutrons under the strong interaction . Although they had different electric charges, their masses were so similar that physicists believed they were the same particle. The different electric charges were explained as being
1518-678: The CMS experiment at the Large Hadron Collider detected a Ξ b baryon (reported mass 5945 ± 2.8 MeV/ c ). (Here,"*" indicates a baryon decuplet .) The LHCb experiment at CERN discovered two new Xi baryons in 2014: Ξ′ b and Ξ b . In 2017, the LHCb researchers reported yet another Xi baryon: the double charmed Ξ cc baryon, consisting of two heavy charm quarks and one up quark. The mass of Ξ cc
1584-428: The Eightfold Way classification, invented by Gell-Mann, with important independent contributions from Yuval Ne'eman , in 1961. The hadrons were organized into SU(3) representation multiplets, octets and decuplets, of roughly the same mass, due to the strong interactions; and smaller mass differences linked to the flavor quantum numbers, invisible to the strong interactions. The Gell-Mann–Okubo mass formula systematized
1650-555: The Gell-Mann–Nishijima formula : where S , C , B ′, and T represent the strangeness , charm , bottomness and topness flavour quantum numbers, respectively. They are related to the number of strange, charm, bottom, and top quarks and antiquark according to the relations: meaning that the Gell-Mann–Nishijima formula is equivalent to the expression of charge in terms of quark content: Spin (quantum number S )
1716-2279: The Omega ( Ω ). For example, the constituent quark model wavefunction for the proton is | p ↑ ⟩ = 1 18 [ 2 | u ↑ d ↓ u ↑ ⟩ + 2 | u ↑ u ↑ d ↓ ⟩ + 2 | d ↓ u ↑ u ↑ ⟩ − | u ↑ u ↓ d ↑ ⟩ − | u ↑ d ↑ u ↓ ⟩ − | u ↓ d ↑ u ↑ ⟩ − | d ↑ u ↓ u ↑ ⟩ − | d ↑ u ↑ u ↓ ⟩ − | u ↓ u ↑ d ↑ ⟩ ] . {\displaystyle |{\text{p}}_{\uparrow }\rangle ={\frac {1}{\sqrt {18}}}[2|{\text{u}}_{\uparrow }{\text{d}}_{\downarrow }{\text{u}}_{\uparrow }\rangle +2|{\text{u}}_{\uparrow }{\text{u}}_{\uparrow }{\text{d}}_{\downarrow }\rangle +2|{\text{d}}_{\downarrow }{\text{u}}_{\uparrow }{\text{u}}_{\uparrow }\rangle -|{\text{u}}_{\uparrow }{\text{u}}_{\downarrow }{\text{d}}_{\uparrow }\rangle -|{\text{u}}_{\uparrow }{\text{d}}_{\uparrow }{\text{u}}_{\downarrow }\rangle -|{\text{u}}_{\downarrow }{\text{d}}_{\uparrow }{\text{u}}_{\uparrow }\rangle -|{\text{d}}_{\uparrow }{\text{u}}_{\downarrow }{\text{u}}_{\uparrow }\rangle -|{\text{d}}_{\uparrow }{\text{u}}_{\uparrow }{\text{u}}_{\downarrow }\rangle -|{\text{u}}_{\downarrow }{\text{u}}_{\uparrow }{\text{d}}_{\uparrow }\rangle ]~.} Mixing of baryons, mass splittings within and between multiplets, and magnetic moments are some of
1782-510: The Particle Data Group . These rules consider the up ( u ), down ( d ) and strange ( s ) quarks to be light and the charm ( c ), bottom ( b ), and top ( t ) quarks to be heavy . The rules cover all the particles that can be made from three of each of the six quarks, even though baryons made of top quarks are not expected to exist because of
1848-466: The Poincaré symmetry — J , where J , P and C stand for the total angular momentum , P-symmetry , and C-symmetry , respectively. The other set is the flavor quantum numbers such as the isospin , strangeness , charm , and so on. The strong interactions binding the quarks together are insensitive to these quantum numbers, so variation of them leads to systematic mass and coupling relationships among
1914-591: The S = 1 / 2 ; L = 0 and S = 3 / 2 ; L = 0, which corresponds to J = 1 / 2 and J = 3 / 2 , respectively, although they are not the only ones. It is also possible to obtain J = 3 / 2 particles from S = 1 / 2 and L = 2, as well as S = 3 / 2 and L = 2. This phenomenon of having multiple particles in
1980-1254: The circumgalactic medium , and the remaining 30 to 40% could be located in the warm–hot intergalactic medium (WHIM). Baryons are strongly interacting fermions ; that is, they are acted on by the strong nuclear force and are described by Fermi–Dirac statistics , which apply to all particles obeying the Pauli exclusion principle . This is in contrast to the bosons , which do not obey the exclusion principle. Baryons, alongside mesons , are hadrons , composite particles composed of quarks . Quarks have baryon numbers of B = 1 / 3 and antiquarks have baryon numbers of B = − 1 / 3 . The term "baryon" usually refers to triquarks —baryons made of three quarks ( B = 1 / 3 + 1 / 3 + 1 / 3 = 1). Other exotic baryons have been proposed, such as pentaquarks —baryons made of four quarks and one antiquark ( B = 1 / 3 + 1 / 3 + 1 / 3 + 1 / 3 − 1 / 3 = 1), but their existence
2046-504: The hadron family of particles . Baryons are also classified as fermions because they have half-integer spin . The name "baryon", introduced by Abraham Pais , comes from the Greek word for "heavy" (βαρύς, barýs ), because, at the time of their naming, most known elementary particles had lower masses than the baryons. Each baryon has a corresponding antiparticle (antibaryon) where their corresponding antiquarks replace quarks. For example,
Xi baryon - Misplaced Pages Continue
2112-412: The top quark 's short lifetime. The rules do not cover pentaquarks. It is also a widespread (but not universal) practice to follow some additional rules when distinguishing between some states that would otherwise have the same symbol. Quarks carry a charge, so knowing the charge of a particle indirectly gives the quark content. For example, the rules above say that a Λ c contains
2178-570: The wavefunction for each particle (in more precise terms, the quantum field for each particle type) were simultaneously mirror-reversed, then the new set of wavefunctions would perfectly satisfy the laws of physics (apart from the weak interaction). It turns out that this is not quite true: for the equations to be satisfied, the wavefunctions of certain types of particles have to be multiplied by −1, in addition to being mirror-reversed. Such particle types are said to have negative or odd parity ( P = −1, or alternatively P = –), while
2244-693: The wavefunction of a baryon must be antisymmetric under the exchange of any two quarks. This antisymmetric wavefunction is obtained by making it fully antisymmetric in color, discussed below, and symmetric in flavor, spin and space put together. With three flavors, the decomposition in flavor is 3 ⊗ 3 ⊗ 3 = 10 S ⊕ 8 M ⊕ 8 M ⊕ 1 A . {\displaystyle \mathbf {3} \otimes \mathbf {3} \otimes \mathbf {3} =\mathbf {10} _{S}\oplus \mathbf {8} _{M}\oplus \mathbf {8} _{M}\oplus \mathbf {1} _{A}~.} The decuplet
2310-535: The Eightfold Way classification, in an economical, tight structure, resulting in further simplicity. Hadronic mass differences were now linked to the different masses of the constituent quarks. It would take about a decade for the unexpected nature—and physical reality—of these quarks to be appreciated more fully (See Quarks ). Counter-intuitively, they cannot ever be observed in isolation ( color confinement ), but instead always combine with other quarks to form full hadrons, which then furnish ample indirect information on
2376-506: The Gell-Mann–Nishijima formula individually, so any additive assembly of them will as well. Mesons are made of a valence quark–antiquark pair (thus have a baryon number of 0), while baryons are made of three quarks (thus have a baryon number of 1). This article discusses the quark model for the up, down, and strange flavors of quark (which form an approximate flavor SU(3) symmetry ). There are generalizations to larger number of flavors. Developing classification schemes for hadrons became
2442-458: The application of this decomposition to the mesons. If the flavor symmetry were exact (as in the limit that only the strong interactions operate, but the electroweak interactions are notionally switched off), then all nine mesons would have the same mass. However, the physical content of the full theory includes consideration of the symmetry breaking induced by the quark mass differences, and considerations of mixing between various multiplets (such as
2508-495: The existence of a hidden degree of freedom, they labeled as the group SU(3)' (but later called 'color). This led to three triplets of quarks whose wavefunction was anti-symmetric in the color degree of freedom. Flavor and color were intertwined in that model: they did not commute. The modern concept of color completely commuting with all other charges and providing the strong force charge was articulated in 1973, by William Bardeen , Harald Fritzsch , and Murray Gell-Mann . While
2574-457: The four Deltas and the two nucleons were thought to be the different states of two particles. However, in the quark model, Deltas are different states of nucleons (the N or N are forbidden by Pauli's exclusion principle ). Isospin, although conveying an inaccurate picture of things, is still used to classify baryons, leading to unnatural and often confusing nomenclature. The strangeness flavour quantum number S (not to be confused with spin)
2640-470: The hadrons in the same flavor multiplet. All quarks are assigned a baryon number of 1 / 3 . Up , charm and top quarks have an electric charge of + 2 / 3 , while the down , strange , and bottom quarks have an electric charge of − 1 / 3 . Antiquarks have the opposite quantum numbers. Quarks are spin- 1 / 2 particles, and thus fermions . Each quark or antiquark obeys
2706-444: The isospin projections I 3 = + 3 / 2 , I 3 = + 1 / 2 , I 3 = − 1 / 2 , and I 3 = − 3 / 2 , respectively. Another example is the "nucleon particle". As there were two nucleon "charged states", it was said to be of isospin 1 / 2 . The positive nucleon N (proton)
Xi baryon - Misplaced Pages Continue
2772-429: The late 1960s and is a valid and effective classification of them to date. The model was independently proposed by physicists Murray Gell-Mann , who dubbed them "quarks" in a concise paper, and George Zweig , who suggested "aces" in a longer manuscript. André Petermann also touched upon the central ideas from 1963 to 1965, without as much quantitative substantiation. Today, the model has essentially been absorbed as
2838-519: The mass of the visible matter in the universe and compose the nucleus of every atom ( electrons , the other major component of the atom, are members of a different family of particles called leptons ; leptons do not interact via the strong force). Exotic baryons containing five quarks, called pentaquarks , have also been discovered and studied. A census of the Universe's baryons indicates that 10% of them could be found inside galaxies, 50 to 60% in
2904-411: The number of baryons may change in multiples of three due to the action of sphalerons , although this is rare and has not been observed under experiment. Some grand unified theories of particle physics also predict that a single proton can decay , changing the baryon number by one; however, this has not yet been observed under experiment. The excess of baryons over antibaryons in the present universe
2970-432: The octet and the singlet). N.B. Nevertheless, the mass splitting between the η and the η′ is larger than the quark model can accommodate, and this " η – η′ puzzle " has its origin in topological peculiarities of the strong interaction vacuum, such as instanton configurations. Mesons are hadrons with zero baryon number . If
3036-720: The other particles are said to have positive or even parity ( P = +1, or alternatively P = +). For baryons, the parity is related to the orbital angular momentum by the relation: As a consequence, baryons with no orbital angular momentum ( L = 0) all have even parity ( P = +). Baryons are classified into groups according to their isospin ( I ) values and quark ( q ) content. There are six groups of baryons: nucleon ( N ), Delta ( Δ ), Lambda ( Λ ), Sigma ( Σ ), Xi ( Ξ ), and Omega ( Ω ). The rules for classification are defined by
3102-446: The other quantities that the model predicts successfully. The group theory approach described above assumes that the quarks are eight components of a single particle, so the anti-symmetrization applies to all the quarks. A simpler approach is to consider the eight flavored quarks as eight separate, distinguishable, non-identical particles. Then the anti-symmetrization applies only to two identical quarks (like uu, for instance). Then,
3168-462: The proton wavefunction can be written in a simpler form: and the If quark–quark interactions are limited to two-body interactions, then all the successful quark model predictions, including sum rules for baryon masses and magnetic moments, can be derived. Color quantum numbers are the characteristic charges of the strong force, and are completely uninvolved in electroweak interactions. They were discovered as
3234-405: The quantification of these small mass differences among members of a hadronic multiplet, controlled by the explicit symmetry breaking of SU(3). The spin- 3 / 2 Ω baryon , a member of the ground-state decuplet, was a crucial prediction of that classification. After it was discovered in an experiment at Brookhaven National Laboratory , Gell-Mann received
3300-399: The quarks lie in the fundamental representation , 3 (called the triplet) of flavor SU(3) . The antiquarks lie in the complex conjugate representation 3 . The nine states (nonet) made out of a pair can be decomposed into the trivial representation , 1 (called the singlet), and the adjoint representation , 8 (called the octet). The notation for this decomposition is Figure 1 shows
3366-400: The quark–antiquark pair are in an orbital angular momentum L state, and have spin S , then If P = (−1) , then it follows that S = 1, thus PC = 1. States with these quantum numbers are called natural parity states ; while all other quantum numbers are thus called exotic (for example, the state J = 0 ). Since quarks are fermions , the spin–statistics theorem implies that
SECTION 50
#17330859708333432-438: The result of some unknown excitation similar to spin. This unknown excitation was later dubbed isospin by Eugene Wigner in 1937. This belief lasted until Murray Gell-Mann proposed the quark model in 1964 (containing originally only the u, d, and s quarks). The success of the isospin model is now understood to be the result of the similar masses of u and d quarks. Since u and d quarks have similar masses, particles made of
3498-482: The same number then also have similar masses. The exact specific u and d quark composition determines the charge, as u quarks carry charge + 2 / 3 while d quarks carry charge − 1 / 3 . For example, the four Deltas all have different charges ( Δ (uuu), Δ (uud), Δ (udd), Δ (ddd)), but have similar masses (~1,232 MeV/c ) as they are each made of
3564-401: The same total angular momentum configuration is called degeneracy . How to distinguish between these degenerate baryons is an active area of research in baryon spectroscopy . If the universe were reflected in a mirror, most of the laws of physics would be identical—things would behave the same way regardless of what we call "left" and what we call "right". This concept of mirror reflection
3630-463: The same way to the strong interaction. Since quarks do not have the same mass, they do not interact in the same way (exactly like an electron placed in an electric field will accelerate more than a proton placed in the same field because of its lighter mass), and the symmetry is said to be broken . It was noted that charge ( Q ) was related to the isospin projection ( I 3 ), the baryon number ( B ) and flavour quantum numbers ( S , C , B ′, T ) by
3696-521: The spin vectors add up to make a vector of length S = 0 and has only one spin projection ( S z = 0), etc. Since baryons are made of three quarks, their spin vectors can add to make a vector of length S = 3 / 2 , which has four spin projections ( S z = + 3 / 2 , S z = + 1 / 2 , S z = − 1 / 2 , and S z = − 3 / 2 ), or
3762-486: The superscript denotes the spin, S , of the baryon. Since these states are symmetric in spin and flavor, they should also be symmetric in space—a condition that is easily satisfied by making the orbital angular momentum L = 0 . These are the ground-state baryons. The S = 1 / 2 octet baryons are the two nucleons ( p , n ), the three Sigmas ( Σ , Σ , Σ ),
3828-406: The trapped quarks themselves. Conversely, the quarks serve in the definition of quantum chromodynamics , the fundamental theory fully describing the strong interactions; and the Eightfold Way is now understood to be a consequence of the flavor symmetry structure of the lightest three of them. The Eightfold Way classification is named after the following fact: If we take three flavors of quarks, then
3894-497: The two Xis ( Ξ , Ξ ), and the Lambda ( Λ ). The S = 3 / 2 decuplet baryons are the four Deltas ( Δ , Δ , Δ , Δ ), three Sigmas ( Σ , Σ , Σ ), two Xis ( Ξ , Ξ ), and
3960-491: The two presumed strange quarks . They are historically called the cascade particles because of their unstable state; they are typically observed to decay rapidly into lighter particles, through a chain of decays (cascading 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
4026-404: The u and d mass are similar, this description of particle mass and charge in terms of isospin and flavour quantum numbers works well only for octet and decuplet made of one u, one d, and one other quark, and breaks down for the other octets and decuplets (for example, ucb octet and decuplet). If the quarks all had the same mass, their behaviour would be called symmetric , as they would all behave in
SECTION 60
#17330859708334092-471: Was also observed as a daughter product from the decay of the omega baryon ( Ω ) observed at Brookhaven National Laboratory in 1964. The Xi spectrum is important to nonperturbative quantum chromodynamics (QCD), such as lattice QCD . The Ξ b particle is also known as the cascade B particle and contains quarks from all three families. It was discovered by DØ and CDF experiments at Fermilab . The discovery
4158-433: Was announced on 12 June 2007. It was the first known particle made of quarks from all three quark generations – namely, a down quark , a strange quark , and a bottom quark . The DØ and CDF collaborations reported the consistent masses of the new state. The Particle Data Group world average mass is 5.7924 ± 0.0030 GeV/ c . For notation, the assumption is that the two heavy quarks are both strange , denoted by
4224-533: Was at the forefront of many of these developments. Constructing hadrons as bound states of fewer constituents would thus organize the "zoo" at hand. Several early proposals, such as the ones by Enrico Fermi and Chen-Ning Yang (1949), and the Sakata model (1956), ended up satisfactorily covering the mesons, but failed with baryons, and so were unable to explain all the data. The Gell-Mann–Nishijima formula , developed by Murray Gell-Mann and Kazuhiko Nishijima , led to
4290-404: Was identified with I 3 = + 1 / 2 and the neutral nucleon N (neutron) with I 3 = − 1 / 2 . It was later noted that the isospin projections were related to the up and down quark content of particles by the relation: where the n' s are the number of up and down quarks and antiquarks. In the "isospin picture",
4356-418: Was noticed to go up and down along with particle mass. The higher the mass, the lower the strangeness (the more s quarks). Particles could be described with isospin projections (related to charge) and strangeness (mass) (see the uds octet and decuplet figures on the right). As other quarks were discovered, new quantum numbers were made to have similar description of udc and udb octets and decuplets. Since only
#832167