The Xi baryons or cascade particles are a family of subatomic hadron particles which have the symbol and may have an electric charge () of +2 , +1 , 0, or −1 , where is the

elementary charge The elementary charge, usually denoted by is the electric charge carried by a single proton or, equivalently, the magnitude of the negative electric charge carried by a single electron, which has charge −1 . This elementary charge is a fundame ...

. Like all conventional baryons, particles contain three quarks. baryons, in particular, contain either one up or one

down Down most often refers to: * Down, the relative direction opposed to up * Down (gridiron football), in American/Canadian football, a period when one play takes place * Down feather, a soft bird feather used in bedding and clothing * Downland, a ty ...

quark and two other, more massive quarks. The two more massive quarks are any two of

strange Strange may refer to: Fiction * Strange (comic book), a comic book limited series by Marvel Comics * Strange (Marvel Comics), one of a pair of Marvel Comics characters known as The Strangers * Adam Strange, a DC Comics superhero * The title char ...

charm Charm may refer to: Social science * Charisma, a person or thing's pronounced ability to attract others * Superficial charm, flattery, telling people what they want to hear Science and technology * Charm quark, a type of elementary particle * Ch ...

, or bottom (doubles allowed). For notation, the assumption is that the two heavy quarks in the are both

; subscripts "c" and "b" are added for each even heavier

or bottom quark that replaces one of the two presumed

strange quark The strange quark or s quark (from its symbol, s) is the third lightest of all quarks, a type of elementary particle. Strange quarks are found in subatomic particles called hadrons. Examples of hadrons containing strange quarks include kaons ( ...

s. 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 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 In mathematics and physics, a non-perturbative function (mathematics), function or process is one that cannot be described by perturbation theory. An example is the function : f(x) = e^, which does not have a Taylor series at ''x'' = 0. Every c ...

quantum chromodynamics In theoretical physics, quantum chromodynamics (QCD) is the theory of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type ...

(QCD), such as

lattice QCD Lattice QCD is a well-established non-perturbative approach to solving the quantum chromodynamics (QCD) theory of quarks and gluons. It is a lattice gauge theory formulated on a grid or lattice of points in space and time. When the size of the ...

History

The 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 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

, and a bottom quark. The DØ and CDF collaborations reported the consistent masses of the new state. The

Particle Data Group The Particle Data Group (or PDG) is an international collaboration of particle physicists that compiles and reanalyzes published results related to the properties of particles and fundamental interactions. It also publishes reviews of theoretical r ...

world average mass is . For notation, the assumption is that the two heavy quarks are both

, denoted by a simple ; a subscript "c" is added for each constituent charm quark, and a "b" for each bottom quark. Hence , , , , 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 contains one up, one strange, and one bottom quark, while a contains one up and two bottom quarks. In 2012, the

CMS CMS may refer to: Computing * Call management system * CMS-2 (programming language), used by the United States Navy * Code Morphing Software, a technology used by Transmeta * Collection management system for a museum collection * Color managem ...

experiment at the

Large Hadron Collider The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundred ...

detected a baryon (reported mass ). (Here,"*" indicates a

baryon decuplet In particle physics, a baryon is a type of composite particle, composite subatomic particle which contains an odd number of valence quarks (at least 3). Baryons belong to the hadron list of particles, family of particles; hadrons are composed o ...

.) The LHCb experiment at

CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in a northwestern suburb of Gene ...

discovered two new Xi baryons in 2014: and . In 2017, the LHCb researchers reported yet another Xi baryon: the double charmed baryon, consisting of two heavy charm quarks and one up quark. The mass of is about 3.8 times that of a

proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

List of Xi baryons

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. ^{/sup> or
}^{/sup>
, -
, bottom Xi

, align="center",
, align="center",
, align="center",
, align="center", ()
, align="center", (⁺)
, align="center", 0
, align="center", −1
, align="center", 0
, align="center", −1
, align="center",
, align="center", Se
decay modes
, -
, bottom Xi or
Cascade B
, align="center",
, align="center",
, align="center",
, align="center", ()
, align="center", (⁺)
, align="center", −1
, align="center", −1
, align="center", 0
, align="center", −1
, align="center",
, align="center", Se
decay modes

( was also seen)
, -
,
, align="center",

, align="center",
, align="center",
, align="center",
, align="center", 1/2+
, align="center", −1
, align="center", −1
, align="center", 0
, align="center", −1
, align="center", >
, align="center",
, -
,
, align="center",
, align="center",
, align="center",
, align="center",
, align="center", 3/2+
, align="center", −1
, align="center", −1
, align="center", 0
, align="center", −1
, align="center",
, align="center",
, -
,
, align="center", (6227)⁻

, align="center",
, align="center",
, align="center",
, align="center",
, align="center", −1
, align="center", −1
, align="center", 0
, align="center", −1
, align="center", 3.64±0.36×10⁻²³
, align="center",

, -
, double bottom Xi
, align="center",
, align="center",
, align="center",
, align="center", ()
, align="center", (⁺)
, align="center", 0
, align="center", 0
, align="center", 0
, align="center", −2
, align="center",
, align="center",
, -
, double bottom Xi
, align="center",
, align="center",
, align="center",
, align="center", ()
, align="center", (⁺)
, align="center", −1
, align="center", 0
, align="center", 0
, align="center", −2
, align="center",
, align="center",
, -
, charmed bottom Xi
, align="center",
, align="center",
, align="center",
, align="center", ()
, align="center", ()⁺
, align="center", +1
, align="center", 0
, align="center", +1
, align="center", −1
, align="center",
, align="center",
, -
, charmed bottom Xi
, align="center",
, align="center",
, align="center",
, align="center", ()
, align="center", (⁺)
, align="center", 0
, align="center", 0
, align="center", +1
, align="center", −1
, align="center",
, align="center",

;Table notes:

See also

* Delta baryon
* Hyperon
* Lambda baryon
* List of baryons

Baryons are composite particles made of three quarks, as opposed to mesons, which are composite particles made of one quark and one antiquark. Baryons and mesons are both hadrons, which are particles composed solely of quarks or both quarks and a ...

* List of mesons
* List of particles
This is a list of known and hypothesized particles.
Elementary particles

Elementary particles are particles with no measurable internal structure; that is, it is unknown whether they are composed of other particles. They are the fundamental ob ...

* Nucleon
* Omega baryon
* Sigma baryon
* Timeline of particle discoveries

This is a timeline of subatomic particle discoveries, including all particles thus far discovered which appear to be elementary (that is, indivisible) given the best available evidence. It also includes the discovery of composite particles and an ...

References

External links

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{{DEFAULTSORT:Xi Baryon
Baryons
Nuclear physics}}