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

subatomic In physical sciences, a subatomic particle is a particle that composes an atom. According to the Standard Model of particle physics, a subatomic particle can be either a composite particle, which is composed of other particles (for example, a pro ...

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 e ...

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 respe ...

() of +2 , +1 , 0, or −1 , where is the elementary charge. 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 classif ...

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

bottom Bottom may refer to: Anatomy and sex * Bottom (BDSM), the partner in a BDSM who takes the passive, receiving, or obedient role, to that of the top or dominant * Bottom (sex), a term used by gay couples and BDSM * Buttocks or bottom, part of th ...

(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 charm or

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 The omega baryons are a family of subatomic hadron (a baryon) particles that are represented by the symbol and are either neutral or have a +2, +1 or −1 elementary charge. They are baryons containing no up or down quarks. Omega baryons co ...

() observed at Brookhaven National Laboratory in 1964. The Xi spectrum is important to nonperturbative quantum chromodynamics (QCD), such as lattice QCD.

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 national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been opera ...

. 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, from ...

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 up ...

, 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 containin ...

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

LHCb The LHCb (Large Hadron Collider beauty) experiment is one of eight particle physics detector experiments collecting data at the Large Hadron Collider at CERN. LHCb is a specialized b-physics experiment, designed primarily to measure the paramet ...

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 c ...

* Hyperon

In particle physics, a hyperon is any baryon containing one or more strange quarks, but no charm, bottom, or top quark. This form of matter may exist in a stable form within the core of some neutron stars. Hyperons are sometimes generically re ...

* Lambda baryon

The lambda baryons (Λ) are a family of subatomic hadron particles containing one up quark, one down quark, and a third quark from a higher flavour generation, in a combination where the quantum wave function changes sign upon the flavour of a ...

* List of baryons
* List of mesons

:''This list is of all known and predicted scalar, pseudoscalar and vector mesons. See list of particles for a more detailed list of particles found in particle physics.''

This article contains a list of mesons, unstable subatomic particles ...

* List of particles
* 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 were ...

* Omega baryon

The omega baryons are a family of subatomic hadron (a baryon) particles that are represented by the symbol and are either neutral or have a +2, +1 or −1 elementary charge. They are baryons containing no up or down quarks. Omega baryons co ...

* Sigma baryon
Sigma (; uppercase Σ, lowercase σ, lowercase in word-final position ς; grc-gre, σίγμα) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. In general mathematics, uppercase Σ is used a ...

* Timeline of particle discoveries

References

External links

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{{DEFAULTSORT:Xi Baryon
Baryons
Nuclear physics}}