Xi (particle) - AbsoluteAstronomy.com

The Xi baryons or cascade particles are a family of subatomic

Subatomic particle

In physics or chemistry, subatomic particles are the smaller particles composing nucleons and atoms. There are two types of subatomic particles: elementary particles, which are not made of other particles, and composite particles...

hadron

Hadron

In particle physics, a hadron is a composite particle made of quarks held together by the strong force...

particles which have the symbol and have a +2, +1 or -1 elementary charge

Elementary charge

The elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...

or are neutral

Neutral particle

In physics, a neutral particle is a particle with no electric charge. This is not to be confused with a real neutral particle, a neutral particle that is also identical to its own antiparticle.-Stable or long-lived neutral particles:...

. They are baryon

Baryon

A baryon is a composite particle made up of three quarks . Baryons and mesons belong to the hadron family, which are the quark-based particles...

s containing three quarks: one up

Up quark

The up quark or u quark is the lightest of all quarks, a type of elementary particle, and a major constituent of matter. It, along with the down quark, forms the neutrons and protons of atomic nuclei...

or down

Down quark

The down quark or d quark is the second-lightest of all quarks, a type of elementary particle, and a major constituent of matter. It, along with the up quark, forms the neutrons and protons of atomic nuclei...

quark, and two heavier quarks. They are sometimes 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 particle is also known as the cascade B particle and contains quarks from all three families. It was discovered by DØ and CDF

Collider Detector at Fermilab

The Collider Detector at Fermilab experimental collaboration studies high energy particle collisions at the Tevatron,the world's former highest-energy particle accelerator...

experiments at Fermilab

Fermilab

Fermi National Accelerator Laboratory , located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics...

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

Subatomic particle

made of quarks from all three quark generations

Generation (particle physics)

In particle physics, a generation is a division of the elementary particles. Between generations, particles differ by their quantum number and mass, but their interactions are identical....

—namely, a down quark

Down quark

, a strange quark

Strange quark

The strange quark or s quark is the third-lightest of all quarks, a type of elementary particle. Strange quarks are found in hadrons, which are subatomic particles. Example of hadrons containing strange quarks include kaons , strange D mesons , Sigma baryons , and other strange particles...

, and a bottom quark

Bottom quark

The bottom quark, also known as the beauty quark, is a third-generation quark with a charge of − e. Although all quarks are described in a similar way by the quantum chromodynamics, the bottom quark's large bare mass , combined with low values of the CKM matrix elements Vub and Vcb, gives it a...

. The DØ collaboration reported mass of the new state to be ; while the CDF collaboration measured the mass at . The two results are consistent with each other. The Particle Data Group

Particle Data Group

The Particle Data Group 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 results that are phenomenologically relevant, including...

world average mass is .

When unspecified, the non-up/down quark content of Xi baryons is strange. Thus a is contains one up, one strange, and one bottom quark, while a contains one up and two bottom quarks.

Xi Baryons
Particle	Symbol	Rest mass MeV/c Speed of light The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time... ²	Isospin Isospin In physics, and specifically, particle physics, isospin is a quantum number related to the strong interaction. This term was derived from isotopic spin, but the term is confusing as two isotopes of a nucleus have different numbers of nucleons; in contrast, rotations of isospin maintain the number... I Isospin In physics, and specifically, particle physics, isospin is a quantum number related to the strong interaction. This term was derived from isotopic spin, but the term is confusing as two isotopes of a nucleus have different numbers of nucleons; in contrast, rotations of isospin maintain the number...	Spin Spin (physics) In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,... (Parity Parity (physics) In physics, a parity transformation is the flip in the sign of one spatial coordinate. In three dimensions, it is also commonly described by the simultaneous flip in the sign of all three spatial coordinates:... ) J Spin (physics) In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,... ^{PParity (physics) In physics, a parity transformation is the flip in the sign of one spatial coordinate. In three dimensions, it is also commonly described by the simultaneous flip in the sign of all three spatial coordinates:...}	Q Charge (physics) In physics, a charge may refer to one of many different quantities, such as the electric charge in electromagnetism or the color charge in quantum chromodynamics. Charges are associated with conserved quantum numbers.-Formal definition:...	S Strangeness In particle physics, strangeness S is a property of particles, expressed as a quantum number, for describing decay of particles in strong and electromagnetic reactions, which occur in a short period of time...	C	B Bottomness In physics, bottomness also called beauty, is a flavour quantum number reflecting the difference between the number of bottom antiquarks and the number of bottom quarks that are present in a particle: B^\prime = -Bottom quarks have a bottomness of −1 while bottom antiquarks have a...	Mean lifetime s Second The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....	Decays to
Xi		1 314.86 ± 0.20		^{+^*}	0	−2	0	0	2.90 ±
Xi		1321.31 ± 0.13		^{+^*}	−1	−2	0	0
Xi resonance	(1530)	1 531.80(32)		⁺	0	−2	0	0
Xi resonance	(1530)	1 535.0(6)		⁺	−1	−2	0	0
charmed Xi		2 467.9 ± 0.4		* ^{+^*}	+1	−1	+1	0		See Decay Modes
charmed Xi		2 471.0 ± 0.4		* ^{+^*}	0	−1	+1	0		See Decay Modes
charmed Xi resonance		2 575.7±3.1		⁺†	+1	−1	+1	0
charmed Xi resonance		2 578.0±2.9		⁺†	0	−1	+1	0
double charmed Xi^†			*	* ^{+^*}	+2	0	+2	0
double charmed Xi^[a]		3 518.9 ± 0.9^[c]	*	* ^{+^*}	+1	0	+2	0	<^[a]	^[e] or ^[e]
bottom Xi		5 792 ± 3	*	* ⁺*	0	−1	0	−1	^[b]	See Decay Modes
bottom Xi or Cascade B		5 792.9 ± 3.0	*	* ^{+^*}	−1	−1	0	−1		See Decay Modes ( was also seen)
double bottom Xi^†			*	* ^{+^*}	0	0	0	−2
double bottom Xi^†			*	* ^{+^*}	−1	0	0	−2
charmed bottom Xi^†			*	* ⁺	+1	0	+1	−1
charmed bottom Xi^†			*	* ^{+^*}	0	0	+1	−1

^[a] Some controversy exists about this data. See references

^[b] This is actually a measurement of the average lifetime of b-baryons that decay to a jet containing a same sign ^±^± pair. Presumably the mix is mainly , with some .

† Particle (or quantity, i.e. spin) has neither been observed nor indicated.

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

See also

External links