Discovery of Single Top Quark Production

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After electroweak symmetry breaking when the Higgs acquires a vacuum expectation value , the left- and right-handed components mix, becoming a mass term.

Fermilab collider experiments discover rare single top quark

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 the energy scale distance scale at which they are measured.


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The dynamics of Yukawa couplings are determined by the renormalization group equation. 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. 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. 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.


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  • 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. The top quark Yukawa coupling lies very near the infrared fixed point of the Standard Model. The renormalization group equation is:. Solutions to this equation for large initial values y t cause the right-hand side of the equation to quickly approach zero, locking y t to the QCD coupling g 3. 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 MSSM , there are two Higgs doublets and the renormalization group equation for the top quark Yukawa coupling is slightly modified:.

    Measurement of the t-channel single Top-quark production rates in pp collisions at 7 TeV

    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 antitop quarks.

    From Wikipedia, the free encyclopedia.

    Rare Single Top Quark Discovered In Collider Experiments -- ScienceDaily

    Type of quark. This section needs additional citations for verification.

    Bibliographic Information

    Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. See also: Beta function physics. Tanabashi et al.

    Particle Data Group Physical Review D. The Physics Hypertextbook. Retrieved Quadt European Physical Journal C. Bibcode : EPJC Kobayashi; T. Maskawa Progress of Theoretical Physics. Bibcode : PThPh.. Abe et al. CDF Collaboration Physical Review Letters. Bibcode : PhRvL.. Abachi et al. The Nobel Foundation. Harari Physics Letters B. Only one in every 20 billion proton-antiproton collisions produces a single top quark. Department of Energy. Discovering the single top quark production presents challenges similar to the Higgs boson search in the need to extract an extremely small signal from a very large background.

    Advanced analysis techniques pioneered for the single top discovery are now in use for the Higgs boson search. In addition, the single top and the Higgs signals have backgrounds in common, and the single top is itself a background for the Higgs particle. To make the single-top discovery, physicists of the CDF and DZero collaborations spent years combing independently through the results of proton-antiproton collisions recorded by their experiments, respectively.

    Each team identified several thousand collision events that looked the way experimenters expect single top events to appear. Sophisticated statistical analysis and detailed background modeling showed that a few hundred collision events produced the real thing. On March 4, the two teams submitted their independent results to Physical Review Letters. The two collaborations earlier had reported preliminary results on the search for the single top. Skip to main content Skip to table of contents. Advertisement Hide. Discovery of Single Top Quark Production.

    Front Matter Pages i-xiv. Pages Theoretical Background.