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In particle physics, a hadron is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules, which are held together by the electric force. Most of the mass of ordinary matter comes from two hadrons: the proton and the neutron, while most of the mass of the protons and neutrons is in turn due to the binding energy of their constituent quarks, due to the strong force.
Omega baryons are a family of subatomic hadrons which are represented by the symbol
Ω
and are either charge neutral or have a +2, +1 or −1 elementary charge. Additionally, they contain no up or down quarks. Omega baryons containing top quarks are also not expected to be observed. This is because the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10−25 s, which is about a twentieth of the timescale necessary for the strong interactions required for Hadronization, the process by which hadrons form from quarks and gluons.
The charm quark, charmed quark, or c quark is an elementary particle found in composite subatomic particles called hadrons such as the J/psi meson and the charmed baryons created in particle accelerator collisions. Several bosons, including the W and Z bosons and the Higgs boson, can decay into charm quarks. All charm quarks carry charm, a quantum number. This second-generation particle is the third-most-massive quark, with a mass of 1.27±0.02 GeV/c2 as measured in 2022, and a charge of +2/3 e.
A pentaquark is a human-made subatomic particle, consisting of four quarks and one antiquark bound together; they are not known to occur naturally, or exist outside of experiments specifically carried out to create them.
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, 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.
The
J/ψ
(J/psi) meson is a subatomic particle, a flavor-neutral meson consisting of a charm quark and a charm antiquark. Mesons formed by a bound state of a charm quark and a charm anti-quark are generally known as "charmonium" or psions. The
J/ψ
is the most common form of charmonium, due to its spin of 1 and its low rest mass. The
J/ψ
has a rest mass of 3.0969 GeV/c2, just above that of the
η
c, and a mean lifetime of 7.2×10−21 s. This lifetime was about a thousand times longer than expected.
The LHCb experiment is a particle physics detector experiment collecting data at the Large Hadron Collider at CERN. LHCb is a specialized b-physics experiment, designed primarily to measure the parameters of CP violation in the interactions of b-hadrons. Such studies can help to explain the matter-antimatter asymmetry of the Universe. The detector is also able to perform measurements of production cross sections, exotic hadron spectroscopy, charm physics and electroweak physics in the forward region. The LHCb collaborators, who built, operate and analyse data from the experiment, are composed of approximately 1650 people from 98 scientific institutes, representing 22 countries. Vincenzo Vagnoni succeeded on July 1, 2023 as spokesperson for the collaboration from Chris Parkes. The experiment is located at point 8 on the LHC tunnel close to Ferney-Voltaire, France just over the border from Geneva. The (small) MoEDAL experiment shares the same cavern.
In particle physics, quarkonium is a flavorless meson whose constituents are a heavy quark and its own antiquark, making it both a neutral particle and its own antiparticle. The name "quarkonium" is analogous to positronium, the bound state of electron and anti-electron. The particles are short-lived due to matter-antimatter annihilation.
Exotic hadrons are subatomic particles composed of quarks and gluons, but which – unlike "well-known" hadrons such as protons, neutrons and mesons – consist of more than three valence quarks. By contrast, "ordinary" hadrons contain just two or three quarks. Hadrons with explicit valence gluon content would also be considered exotic. In theory, there is no limit on the number of quarks in a hadron, as long as the hadron's color charge is white, or color-neutral.
In particle physics, flavor-changing neutral currents or flavour-changing neutral currents (FCNCs) are hypothetical interactions that change the flavor of a fermion without altering its electric charge.
The Belle experiment was a particle physics experiment conducted by the Belle Collaboration, an international collaboration of more than 400 physicists and engineers, at the High Energy Accelerator Research Organisation (KEK) in Tsukuba, Ibaraki Prefecture, Japan. The experiment ran from 1999 to 2010.
CLEO was a general purpose particle detector at the Cornell Electron Storage Ring (CESR), and the name of the collaboration of physicists who operated the detector. The name CLEO is not an acronym; it is short for Cleopatra and was chosen to go with CESR. CESR was a particle accelerator designed to collide electrons and positrons at a center-of-mass energy of approximately 10 GeV. The energy of the accelerator was chosen before the first three bottom quark Upsilon resonances were discovered between 9.4 GeV and 10.4 GeV in 1977. The fourth Υ resonance, the Υ(4S), was slightly above the threshold for, and therefore ideal for the study of, B meson production.
The Xi baryons or cascade particles are a family of subatomic hadron particles which have the symbol Ξ and may have an electric charge of +2 e, +1 e, 0, or −1 e, where e is the elementary charge.
The X(3872) is an exotic meson candidate with a mass of 3871.68 MeV/c2 which does not fit into the quark model. It was first discovered in 2003 by the Belle experiment in Japan and later confirmed by several other experimental collaborations. Several theories have been proposed for its nature, such as a mesonic molecule or a diquark-antidiquark pair (tetraquark).
Z(4430) is a mesonic resonance discovered by the Belle experiment. It has a mass of 4430 MeV/c2. The resonant nature of the peak has been confirmed by the LHCb experiment with a significance of at least 13.9 σ. The particle is charged and is thought to have a quark content of
c
c
d
u
, making it a tetraquark candidate. It has the spin-parity quantum numbers JP = 1+.
In particle physics, B mesons are mesons composed of a bottom antiquark and either an up, down, strange or charm quark. The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark's short lifetime. The combination of a bottom antiquark and a bottom quark is not a B meson, but rather bottomonium, which is something else entirely.
The D mesons are the lightest particle containing charm quarks. They are often studied to gain knowledge on the weak interaction. The strange D mesons (Ds) were called "F mesons" prior to 1986.
The Y(4140) particle is an electrically neutral exotic hadron candidate that is about 4.4 times heavier than the proton. It was observed at Fermilab and announced on 17 March 2009. This particle is extremely rare and was detected in only 20 of billions of collisions.
The Y(4260) is an anomalous particle with an energy of 4260 MeV which does not appear to fit into the quark model. It was discovered by the BaBar experiment at Stanford University for the Department of Energy in California and later confirmed by several other experimental collaborations. It being a Charmonium state is unlikely because the Y(4260) is heavier than the threshold for production of two D mesons, yet sits, surprisingly in a dip in the production rate for pairs of D's. It is a possibility that it is a hybrid—a predicted but not-yet-seen type of particle, where a gluon is actually a permanent part of the makeup of the particle, instead of just an ephemeral messenger keeping the quarks bound together.
SooKyung Choi is a South Korean particle physicist at Gyeongsang National University. She is part of the Belle experiment and was the first to observe the X(3872) meson in 2003. She won the 2017 Ho-Am Prize in Science.
References
- ↑ . Powel, D. (2013). "Quark quartet opens fresh vista on matter". Nature . 498 (7454): 280–281. Bibcode:2013Natur.498..280P. doi: 10.1038/498280a . PMID 23783605.
- ↑ Ablikim, M.; BESIII Collaboration; et al. (2013). "Observation of a Charged Charmoniumlike Structure in e+e−→π+π−J/ψ at √s = 4.26 GeV". Physical Review Letters . 110 (25): 252001. arXiv: 1303.5949 . Bibcode:2013PhRvL.110y2001A. doi:10.1103/PhysRevLett.110.252001. PMID 23829729. S2CID 11175322.
- ↑ Liu, Z. Q.; Belle Collaboration; et al. (2013). "Study of e+e−→π+π−J/ψ and Observation of a Charged Charmoniumlike State at Belle". Physical Review Letters . 110 (25): 252002. arXiv: 1304.0121 . Bibcode:2013PhRvL.110y2002L. doi: 10.1103/PhysRevLett.110.252002 . PMID 23829730.
- ↑ Swanson, E. (2013). "Viewpoint: New Particle Hints at Four-Quark Matter". Physics . 6: 69. Bibcode:2013PhyOJ...6...69S. doi: 10.1103/Physics.6.69 .
- 1 2 3 Xiao, T.; Dobbs, S.; Tomaradze, A.; Seth, K. K. (2013). "Observation of the Charged Hadron Z±
c(3900) and Evidence of the Neutral Z0
c(3900) at √s = 4170 MeV". Physics Letters B. 727 (4–5): 366–370. arXiv: 1304.3036 . Bibcode:2013PhLB..727..366X. doi:10.1016/j.physletb.2013.10.041. S2CID 116206390. - ↑ "USTC Play a Role in Discovering New Subatomic Particle". University of Science and Technology of China. 6 April 2013.
- ↑ Ablikim, M.; BESIII Collaboration; et al. (2015). "Observation of Zc(3900)0 in e+ e− to pi0 pi0 J/psi". Physical Review Letters . 115 (11): 112003. arXiv: 1506.06018 . Bibcode:2015PhRvL.115y2003A. doi:10.1103/PhysRevLett.115.112003. PMID 26406823. S2CID 119256995.