The Xi baryons or ''cascade particles'' are a family of subatomic

hadron In particle physics, a hadron (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the ele ...

particles which have the symbol and may have an

electric charge Electric charge is the physical property of matter that causes charged matter to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried by protons and electrons respecti ...

() 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 funda ...

. Like all conventional

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

s, particles contain three

quarks 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 ...

. 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,

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 * Cha ...

, or bottom (doubles allowed). For notation, the assumption is that the two heavy quarks in the are both strange; subscripts "c" and "b" are added for each even heavier

bottom quark The bottom quark or b quark, also known as the beauty quark, is a third-generation heavy quark with a charge of − ''e''. All quarks are described in a similar way by electroweak and quantum chromodynamics, but the bottom quark has exce ...

that replaces one of 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 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 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 ty ...

(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 D0 and CDF experiments at

Fermilab Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy United States Department of Energy National Labs, national laboratory specializing in high-energy parti ...

. The discovery was announced on 12 June 2007. It was the first known

particle In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass. They vary greatly in size or quantity, fro ...

made of

from all three quark generations – namely, a

down quark The down quark or d quark (symbol: d) is the second-lightest of all quarks, a type of elementary particle, and a major constituent of matter. Together with the up quark, it forms the neutrons (one up quark, two down quarks) and protons (two u ...

, a strange quark, and a

. The D0 and CDF collaborations reported the consistent masses of the new state. The Particle Data Group world average mass is . For notation, the assumption is that the two heavy quarks are both strange, denoted by a simple ; a subscript "c" is added for each constituent

charm quark The charm quark, charmed quark or c quark (from its symbol, c) is the third-most massive of all quarks, a type of elementary particle. Charm quarks are found in hadrons, which are subatomic particles made of quarks. Examples of hadrons containi ...

, and a "b" for each

. 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 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 hundr ...

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

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

.) The LHCb experiment at CERN 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.

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

The Delta baryons (or baryons, also called Delta resonances) are a family of subatomic particle made of three up or down quarks (u or d quarks), the same constituent quarks that make up the more familiar protons and neutrons.
Properties
Four ...

* 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

In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number (nucleon number).

Until the 1960s, nucleons w ...

* 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 ...

References

External links

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*
*
*
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{{DEFAULTSORT:Xi Baryon
Baryons
Nuclear physics}}