Standard Model of particle physics |
---|
In particle physics, a tetraquark is an exotic meson composed of four valence quarks. A tetraquark state has long been suspected to be allowed by quantum chromodynamics, [1] the modern theory of strong interactions. A tetraquark state is an example of an exotic hadron which lies outside the conventional quark model classification. A number of different types of tetraquark have been observed. [2] [3]
This article may be better presented in
list format to meet Wikipedia's
quality standards. (July 2022) |
Several tetraquark candidates have been reported by particle physics experiments in the 21st century. The quark contents of these states are almost all qqQQ, where q represents a light ( up, down or strange) quark, Q represents a heavy ( charm or bottom) quark, and antiquarks are denoted with an overline. The existence and stability of tetraquark states with the qqQQ (or qqQQ) have been discussed by theoretical physicists for a long time, however these are yet to be reported by experiments. [4]
In 2003, a particle temporarily called X(3872), by the Belle experiment in Japan, was proposed to be a tetraquark candidate, [6] as originally theorized. [7] The name X is a temporary name, indicating that there are still some questions about its properties to be tested. The number following is the mass of the particle in MeV/c2.
In 2004, the DsJ(2632) state seen in Fermilab's SELEX was suggested as a possible tetraquark candidate. [8]
In 2007, Belle announced the observation of the
Z(4430) state, a
c
c
d
u
tetraquark candidate. There are also indications that the
Y(4660), also discovered by Belle in 2007, could be a tetraquark state.
[9]
In 2009, Fermilab announced that they have discovered a particle temporarily called Y(4140), which may also be a tetraquark. [10]
In 2010, two physicists from
DESY and a physicist from
Quaid-i-Azam University re-analyzed former experimental data and announced that, in connection with the
ϒ
(5S) meson (a form of
bottomonium), a well-defined tetraquark
resonance exists.
[11]
[12]
In June 2013, the BES III experiment in China and the Belle experiment in Japan independently reported on Zc(3900), the first confirmed four-quark state. [13]
In 2014, the Large Hadron Collider experiment LHCb confirmed the existence of the Z(4430) state with a significance of over 13.9 σ. [14] [15]
In February 2016, the
DØ experiment reported evidence of a narrow tetraquark candidate, named X(5568), decaying to
B0
s
π±
.
[16]
In December 2017, DØ also reported observing the X(5568) using a different
B0
s final state.
[17]
However, it was not observed in searches by the LHCb,
[18]
CMS,
[19]
CDF,
[20] or
ATLAS
[21] experiments.
In June 2016, LHCb announced the discovery of three additional tetraquark candidates, called X(4274), X(4500) and X(4700). [22] [23] [24]
In 2020, LHCb announced the discovery of a
c
c
c
c
tetraquark: X(6900).
[2]
[25] In 2022, ATLAS observed X(6900).
[26]
In 2021, LHCb announced the discovery of four additional tetraquarks, including ccus. [3]
In 2022, LHCb announced the discovery of csud and csud. [27]
Standard Model of particle physics |
---|
In particle physics, a tetraquark is an exotic meson composed of four valence quarks. A tetraquark state has long been suspected to be allowed by quantum chromodynamics, [1] the modern theory of strong interactions. A tetraquark state is an example of an exotic hadron which lies outside the conventional quark model classification. A number of different types of tetraquark have been observed. [2] [3]
This article may be better presented in
list format to meet Wikipedia's
quality standards. (July 2022) |
Several tetraquark candidates have been reported by particle physics experiments in the 21st century. The quark contents of these states are almost all qqQQ, where q represents a light ( up, down or strange) quark, Q represents a heavy ( charm or bottom) quark, and antiquarks are denoted with an overline. The existence and stability of tetraquark states with the qqQQ (or qqQQ) have been discussed by theoretical physicists for a long time, however these are yet to be reported by experiments. [4]
In 2003, a particle temporarily called X(3872), by the Belle experiment in Japan, was proposed to be a tetraquark candidate, [6] as originally theorized. [7] The name X is a temporary name, indicating that there are still some questions about its properties to be tested. The number following is the mass of the particle in MeV/c2.
In 2004, the DsJ(2632) state seen in Fermilab's SELEX was suggested as a possible tetraquark candidate. [8]
In 2007, Belle announced the observation of the
Z(4430) state, a
c
c
d
u
tetraquark candidate. There are also indications that the
Y(4660), also discovered by Belle in 2007, could be a tetraquark state.
[9]
In 2009, Fermilab announced that they have discovered a particle temporarily called Y(4140), which may also be a tetraquark. [10]
In 2010, two physicists from
DESY and a physicist from
Quaid-i-Azam University re-analyzed former experimental data and announced that, in connection with the
ϒ
(5S) meson (a form of
bottomonium), a well-defined tetraquark
resonance exists.
[11]
[12]
In June 2013, the BES III experiment in China and the Belle experiment in Japan independently reported on Zc(3900), the first confirmed four-quark state. [13]
In 2014, the Large Hadron Collider experiment LHCb confirmed the existence of the Z(4430) state with a significance of over 13.9 σ. [14] [15]
In February 2016, the
DØ experiment reported evidence of a narrow tetraquark candidate, named X(5568), decaying to
B0
s
π±
.
[16]
In December 2017, DØ also reported observing the X(5568) using a different
B0
s final state.
[17]
However, it was not observed in searches by the LHCb,
[18]
CMS,
[19]
CDF,
[20] or
ATLAS
[21] experiments.
In June 2016, LHCb announced the discovery of three additional tetraquark candidates, called X(4274), X(4500) and X(4700). [22] [23] [24]
In 2020, LHCb announced the discovery of a
c
c
c
c
tetraquark: X(6900).
[2]
[25] In 2022, ATLAS observed X(6900).
[26]
In 2021, LHCb announced the discovery of four additional tetraquarks, including ccus. [3]
In 2022, LHCb announced the discovery of csud and csud. [27]