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Encyclopedia > Top quark
Composition Elementary particle Fermion Quark Third CDF and D0 collaborations, 1995 t 170.9±1.8 GeV/c2 W boson and bottom quark +2/3 e ½ This box: view • talk • edit
 Flavour in particle physics v • d • e Flavour quantum numbers: Lepton number: L Baryon number: B Strangeness: S Charm: C Bottomness: B' Topness: T Isospin: Iz or I Weak isospin: Tz Electric charge: Q Combinations: For the novel, see The Elementary Particles. ... In particle physics, fermions are particles with half-integer spin, such as protons and electrons. ... For other uses, see Quark (disambiguation). ... In particle physics, a generation is a division of the elementary particles. ... The Collider Detector at Fermilab (CDF) experimental collaboration studies high energy particle collisions at the Tevatron, the worldâ€™s highest energy particle accelerator. ... D0 under construction, the installation of the central tracking system D0s control room The D0 experiment consists of a worldwide collaboration of scientists conducting research on the fundamental nature of matter. ... Year 1995 (MCMXCV) was a common year starting on Sunday. ... The invariant mass or intrinsic mass or proper mass or just mass is a measurement or calculation of the mass of an object that is the same for all frames of reference. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... The bottom quark is a third-generation quark with a charge of -(1/3)e. ... The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... Flavour (or flavor) is a quantum number of elementary particles related to their weak interactions. ... Thousands of particles explode from the collision point of two relativistic (100 GeV per nucleon) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... Quantum numbers describe values of conserved quantity in the dynamics of the quantum system. ... In high energy physics, the lepton number is the number of leptons minus the number of antileptons. ... In particle physics, the baryon number is an approximate conserved quantum number. ... In particle physics, strangeness, denoted as , is a property of particles, expressed as a quantum number for describing decay of particles in strong and electro-magnetic reactions, which occur in a short period of time. ... The charm quark is a second-generation quark with a charge of +(2/3)e. ... The bottom quark is a third-generation quark with a charge of -(1/3)e. ... Isospin (isotopic spin, isobaric spin) is a physical quantity which is mathematically analogous to spin. ... The weak isospin in theoretical physics parallels the idea of the isospin under the strong interaction, but applied under the weak interaction. ... This box:      Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... Hypercharge: Y Y=2(Q-Iz) Weak hypercharge: YW YW=2(Q-Tz) YW=B−L Related topics: In particle physics, the hypercharge (represented by Y) is the sum of the baryon number B and the flavor charges: strangeness S, charm C, bottomness and topness T, although the last one can be omitted given the extremely short life of the top quark (it decays to other quarks before... Weak hypercharge is twice the difference between the electrical charge and the weak isospin. ... In high energy physics, Bâˆ’L (pronounced bee minus ell) is the baryon number minus the lepton number. ... CPT symmetry CKM matrix CP symmetry Chirality

The top quark is the third-generation up-type quark with a charge of +(2/3)e.[1] It was discovered in 1995 by the CDF and D0 experiments at Fermilab, and is by far the most massive of known elementary particles. As of 2007, its mass is measured at 170.9±1.8 GeV/c2.[2] nearly as heavy as a gold nucleus. CPT-symmetry is a fundamental symmetry of physical laws under transformations that involve the inversions of charge, parity and time simultaneously. ... In the standard model of particle physics the Cabibbo-Kobayashi-Maskawa matrix (CKM matrix, quark mixing matrix, sometimes earlier called KM matrix) is a unitary matrix which contains information on the strength of flavour-changing weak decays. ... CP-symmetry is a symmetry obtained by a combination of the C-symmetry and the P-symmetry. ... A phenomenon is said to be chiral if it is not identical to its mirror image (see Chirality (mathematics)). The spin of a particle may be used to define a handedness for that particle. ... In particle physics, a generation is a division of the elementary particles. ... For other uses, see Quark (disambiguation). ... The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... The Collider Detector at Fermilab (CDF) experimental collaboration studies high energy particle collisions at the Tevatron, the worldâ€™s highest energy particle accelerator. ... D0 under construction, the installation of the central tracking system D0s control room The D0 experiment consists of a worldwide collaboration of scientists conducting research on the fundamental nature of matter. ... Aerial view of the Fermilab site. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ...

The top quark interacts primarily by the strong interaction but can only decay through the weak force. It almost exclusively decays to a W boson and a bottom quark. The Standard Model predicts its lifetime to be roughly 1×10−25 s; this is about 20 times shorter than the timescale for strong interactions, and therefore it does not hadronize, giving physicists a unique opportunity to study a "bare" quark. The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). ... The weak nuclear force or weak interaction is one of the four fundamental forces of nature. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... The bottom quark is a third-generation quark with a charge of -(1/3)e. ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... In particle physics, hadronization is the process of the formation of hadrons out of quarks and gluons. ...

## Contents

In the years leading up to the top quark discovery, it was realized that certain precision measurements of the electro-weak vector boson masses and couplings are very sensitive to the value of the top quark mass. These effects become much larger for higher values of the top mass and therefore could indirectly see the top quark even if it could not be directly produced in any experiment at the time. The largest effect from the top quark mass was on the T parameter and by 1994 the precision of these indirect measurements had led to a prediction of the top quark mass to be between 145 GeV and 185 GeV. It is the development of techniques that ultimately allowed such precision calculations that led to Gerardus 't Hooft and Martinus Veltman winning the Nobel Prize in physics in 1999. In particle physics, the Peskin-Takeuchi parameters are a set of three measurable quantities, called S, T, and U, that parameterize potential new physics contributions to electroweak radiative corrections. ... Gerard t Hooft at Harvard University Gerardus (Gerard) t Hooft [ut-hooft] (The prefix â€™t is pronounced as â€˜utâ€™ and stands for â€˜hetâ€™) (born July 5, 1946) is a professor in theoretical physics at Utrecht University, The Netherlands. ... Martinus J.G. Veltman (Tini for short) (born June 27, 1931) is a 1999 Nobel Prize in Physics laureate for elucidating the quantum structure of electroweak interactions in physics, work done at Utrecht University, The Netherlands. ... The Nobel Prize (Swedish: ) was established in Alfred Nobels will in 1895, and it was first awarded in Physics, Chemistry, Physiology or Medicine, Literature, and Peace in 1901. ...

After the discovery of the first third-generation quark, an attempt was made to name it "beauty" and the predicted sixth quark "truth"; however, this later gave way to the names bottom and top.

The top quark was discovered in 1995 at Fermilab, whose Tevatron accelerator remains the only particle accelerator energetic enough to produce top quarks (until the LHC at CERN comes on-line in 2008). Year 1995 (MCMXCV) was a common year starting on Sunday. ... Aerial view of the Fermilab site. ... Tevatron is a circular particle accelerator (or synchrotron) at the Fermi National Accelerator Laboratory in Batavia, Illinois. ... Atom Smasher redirects here. ... , The Large Hadron Collider (LHC) is a particle accelerator and Hadron collider located at CERN, near Geneva, Switzerland. ... CERN logo The European Organization for Nuclear Research (French: ), commonly known as CERN (see Naming), pronounced (or in French), is the worlds largest particle physics laboratory, situated just northwest of Geneva on the border between France and Switzerland. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ...

## Production and decay

As of 2007, Fermilab's Tevatron is the only place in the world where top quarks can be produced. Tevatron is an accelerator complex which collides protons and antiprotons at center-of-momentum energy of 1.96 TeV. There are two main top-production processes: 2007 is a common year starting on Monday of the Gregorian calendar. ... Aerial view of the Fermilab site. ... Tevatron is a circular particle accelerator (or synchrotron) at the Fermi National Accelerator Laboratory in Batavia, Illinois. ...

• Pair production via strong interactions. This process was first observed simultaneously by two experimental collaboration at Fermilab, CDF and D0 in 1995.
• Single production via weak interactions. As of December 2006, a three-sigma evidence has been observed for this production process by the D0 Collaboration at Fermilab.

The top quark is expected to decay to a W boson and a down-type quark (down, strange or bottom). In the standard model, the branching fraction for t→Wq is predicted to be |Vtq|2, where Vtq is an element in the CKM matrix. The predictions for the branching ratios of the top quark are then B(t→Wd)≈0.006%, B(t→Ws)≈0.17% and B(t→Wb)≈99.8%. Pair production refers to the creation of an elementary particle and its antiparticle, usually from a photon (or another neutral boson). ... The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). ... The Collider Detector at Fermilab (CDF) experimental collaboration studies high energy particle collisions at the Tevatron, the worldâ€™s highest energy particle accelerator. ... D0 under construction, the installation of the central tracking system D0s control room The D0 experiment consists of a worldwide collaboration of scientists conducting research on the fundamental nature of matter. ... The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental interactions of nature. ... In the standard model of particle physics the Cabibbo-Kobayashi-Maskawa matrix (CKM matrix, quark mixing matrix, sometimes earlier called KM matrix) is a unitary matrix which contains information on the strength of flavour-changing weak decays. ...

## Top quark mass and relationship to the Higgs boson

The Standard Model describes fermion masses through the Higgs mechanism. The Higgs boson has a Yukawa coupling to the left- and right-handed top quarks. After electroweak symmetry breaking (when the Higgs acquires a vacuum expectation value), the left- and right-handed components mix, becoming a mass term. This box:      The Higgs mechanism, also called the Brout-Englert-Higgs mechanism, Higgs-Kibble mechanism or Anderson-Higgs mechanism, was proposed in 1964 by Robert Brout and Francois Englert [1], independently by Peter Higgs [2] and by Gerald Guralnik, C. R. Hagen, and Tom Kibble [3] following earlier work by... The Higgs boson, also known as the God particle, is a hypothetical massive scalar elementary particle predicted to exist by the Standard Model of particle physics. ... In particle physics, Yukawa interaction, named after Hideki Yukawa, is an interaction between a scalar field and a Dirac field of the type (scalar) or (pseudoscalar). ...

$mathcal{L} = y_t h q u^c rightarrow frac{y_t v}{sqrt{2}}( 1 + h^0/v) u u^c$

The top quark Yukawa coupling has a value of $y_t = sqrt{2} m_t/v simeq 1$, where $v=246~{rm GeV}$ is the value of the Higgs vacuum expectation value.

### Yukawa couplings

In the Standard Model, all of the quark and lepton Yukawa couplings are small compared to the top quark Yukawa coupling. Understanding this hierarchy in the fermion masses is an open problem in theoretical physics. Yukawa couplings are not constants and their values change depending on what energy scale (distance scale) at which they are measured. The dynamics of Yukawa couplings are determined by the renormalization group equation. Callan-Symanzik equation exact renormalization group equation Categories: ...

One of the prevailing views in particle physics is that the size of the top quark Yukawa coupling is determined by the renormalization group, leading to the "quasi-infrared fixed point." In theoretical physics, renormalization group (RG) refers to a set of techniques and concepts related to the change of physics with the observation scale. ... In physics, an infrared fixed point is a scale-invariant theory (fixed point) obtained by probing the very long-distance behavior of a quantum field theory or a model of statistical mechanics, as explained in the theory of the renormalization group. ...

The Yukawa couplings of the up, down, charm, strange and bottom quarks, are hypothesized to have small values at the extremely high energy scale of grand unification, 1015 GeV. They increase in value at lower energy scales, at which the quark masses are generated by the Higgs. The slight growth is due to corrections from the QCD coupling. The corrections from the Yukawa couplings are negligible for the lower mass quarks. Quantum chromodynamics (abbreviated as QCD) is the theory of the strong interaction (color force), a fundamental force describing the interactions of the quarks and gluons found in hadrons (such as the proton, neutron or pion). ...

If, however, a quark Yukawa coupling has a large value at very high energies, its Yukawa corrections will evolve and cancel against the QCD corrections. This is known as a (quasi-) infrared fixed point. No matter what the initial starting value of the coupling is, if it is sufficiently large it will reach this fixed point value. The corresponding quark mass is then predicted. In physics, an infrared fixed point is a scale-invariant theory (fixed point) obtained by probing the very long-distance behavior of a quantum field theory or a model of statistical mechanics, as explained in the theory of the renormalization group. ...

The top quark Yukawa coupling lies very near the infrared fixed point of the Standard Model. The renormalization group equation is: In physics, an infrared fixed point is a scale-invariant theory (fixed point) obtained by probing the very long-distance behavior of a quantum field theory or a model of statistical mechanics, as explained in the theory of the renormalization group. ... Callan-Symanzik equation exact renormalization group equation Categories: ...

$mu frac{partial}{partialmu} y_t approx frac{y_t}{16pi^2}left(frac{9}{2}y_t^2 - 8 g_3^2- frac{9}{4}g_2^2 - frac{17}{20} g_1^2 right)$,

where g3 is the color gauge coupling and g2 is the weak isospin gauge coupling. This equation describes how the Yukawa coupling changes with energy scale μ. Solutions to this equation for large initial values yt cause the right-hand side of the equation to quickly approach zero, locking yt to the QCD coupling g3. The value of the fixed point is fairly precisely determined in the Standard Model, leading to a top quark mass of 230  GeV. However, if there is more than one Higgs doublet, the mass value will be reduced by Higgs mixing angle effects in an unpredicted way.

In the minimal supersymmetric extension of the Standard Model (the MSSM), there are two Higgs doublets and the renormalization group equation for the top quark Yukawa coupling is slightly modified: A Minimal Supersymmetric Standard Model is a class of proposed supersymmetric extensions to the Standard Model. ...

$mu frac{partial}{partialmu} y_t approx frac{y_t}{16pi^2}left(6y_t^2 +y_b^2- frac{16}{3} g_3^2- 3g_2^2 -frac{13}{15} g_1^2 right)$,

where yb is the bottom quark Yukawa coupling. This leads to a fixed point where the top mass is smaller, 170–200 GeV. The uncertainty in this prediction arises because the bottom quark Yukawa coupling can be amplified in the MSSM. Some theorists believe this is supporting evidence for the MSSM.

The quasi-infrared fixed point has subsequently formed the basis of top quark condensation theories of electroweak symmetry breaking in which the Higgs boson is composite at extremely short distance scales, composed of a pair of top and anti-top quarks. In physics, an infrared fixed point is a scale-invariant theory (fixed point) obtained by probing the very long-distance behavior of a quantum field theory or a model of statistical mechanics, as explained in the theory of the renormalization group. ...

## Properties

• At the current Tevatron energy of 1.96 TeV, top/anti-top pairs are produced with a cross section of about 7 picobarns. The Standard Model prediction (at next-to-leading order with mt = 175 GeV) is 6.7–7.5 picobarns.
• Combining measurements from both CDF and D0, the most recent estimation of the top quark mass is 170.9±1.8 GeV/c2.[2]
• Production of single top quarks through weak vector bosons is predicted in the Standard Model and has a cross section of 0.9 picobarns in the s-channel and 2.0 picobarns in the t-channel. Neither experiment at the Tevatron has observed this process with statistical significance. However, on 8 December 2006, the D0 collaboration announced it had seen evidence for single top production at the 3 sigma level, measuring an s+t channel cross section of 4.9 picobarns.[3] A preprint article submitted to Physical Review Letters is available from the arXiv.org preprint server.[4]
• The W bosons from top quark decays carry polarization from the parent particle, hence pose themselves as a unique probe to top polarization.
• In the Standard Model, top quark is predicted to have a spin of ½ and charge ⅔. A first measurement of the top quark charge has been published, resulting in approximately 90% confidence limit that the top quark charge is indeed ⅔.[5]

In nuclear and particle physics, the concept of a cross section is used to express the likelihood of interaction between particles. ... A barn (symbol b) is a unit of area. ... A GEV (or Ground Effect Vehicle) is vehicle that takes advantage of the aerodynamic principle of ground effect (or Wing-in-ground). ... A line showing the speed of light on a scale model of Earth and the Moon, taking about 1â…“ seconds to traverse that distance. ... In theoretical physics, the Mandelstam variables are numerical quantities that encode the energy, momentum, and angles of particles in a scattering process in a Lorentz-invariant fashion. ... In probability and statistics, the standard deviation of a probability distribution, random variable, or population or multiset of values is a measure of the spread of its values. ... Physical Review Letters is one of the most prestigious journals in physics. ... The title given to this article is incorrect due to technical limitations. ...

## References

1. ^ H B Prosper and B Danilov (eds.) Scott Willenbrock (author) (2003). The standard model and the top quark; in Techniques and concepts of high-energy physics XII. Dordrecht: NATO Science Series Vol. 123; Kluwer Academic, Chapter 1. ISBN 1402015909.
2. ^ a b A Combination of CDF and D0 Results on the Mass of the Top Quark, arXiv:hep-ex/0703034
3. ^ Fermilab press release, 13 Dec 2006, DZero finds evidence of rare single top quark
4. ^ Evidence for production of single top quarks and first direct measurement of |Vtb|, arXiv:hep-ex/0612052
5. ^ Experimental discrimination between charge 2e/3 top quark and charge 4e/3 exotic quark production scenarios, arXiv:hep-ex/0608044

arXiv (pronounced archive, as if the X were the Greek letter Ï‡) is an archive for electronic preprints of scientific papers in the fields of physics, mathematics, computer science and quantitative biology which can be accessed via the Internet. ... arXiv (pronounced archive, as if the X were the Greek letter Ï‡) is an archive for electronic preprints of scientific papers in the fields of physics, mathematics, computer science and quantitative biology which can be accessed via the Internet. ... arXiv (pronounced archive, as if the X were the Greek letter Ï‡) is an archive for electronic preprints of scientific papers in the fields of physics, mathematics, computer science and quantitative biology which can be accessed via the Internet. ...

Results from FactBites:

 Quarks (1357 words) Quarks are observed to occur only in combinations of two quarks (mesons), three quarks (baryons), and the recently discovered particles with five quarks (pentaquark). Quarks undergo transformations by the exchange of W bosons, and those transformations determine the rate and nature of the decay of hadrons by the weak interaction. Convincing evidence for the observation of the top quark was reported by Fermilab 's Tevatron facility in April 1995.
 Vertices Fall94: Top Quark (2931 words) The top quark, for which experimenters have been searching for 17 years, is a subatomic particle whose existence is necessary to corroborate a theory that seeks to explain how matter and energy interact at the most basic, subatomic level. The top quark, sometimes called "truth," is one of six different types or "flavors" of quarks, which are subatomic particles that serve as the basic building blocks for hadrons, which encompass all particles that interact by means of the strong nuclear force. If quarks and leptons prove to be truly elementary, then the discovery of the top quark (when and if its existence is finally confirmed) will represent the culmination of a 2400-year-old struggle to identify the fundamental building blocks of matter.
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