Produced in a high-energy collision between protons and antiprotons, a top quark-antitop pair (t, t bar) decays into a total of four particles--two W bosons, a bottom quark (b) and an antibottom quark (b bar). In the "all-hadronic" decay mode, pictured above, each W boson decays into a pair of quarks, for a total of four quarks (q1, q2, q3, q4). These quarks, plus the bottom and antibottom quarks, each produce an energetic spray of particles, or "jet," that is detected experimentally. Therefore, in this type of decay the nominally expected signal is six jets. (Illustration by Malcolm Tarlton and Elliot Plotkin, AIP.)
"Dilepton" mode in which each W particle decays into a lepton [such as an electron (e) or muon (µ)] plus a neutrino (). The bottom quark (b) and antibottom quark (b bar) each produce an energetic spray of particles, or "jet" that is detected experimentally.(Illustration by Malcolm Tarlton and Elliot Plotkin, AIP.)
Emerging from the fireball of a proton-antiproton collision, a top quark and its antitop twin quickly decay into a total of four particles--a pair of W bosons, a bottom quark (b), and an antibottom quark (b bar). Discovered in 1995 at the Fermi National Accelerator Laboratory, the top quark continues to be studied by two Fermilab groups, known as D0 and CDF. These groups classify top quark events into three categories according to how the Ws decay:
(1) The most common decay mode, but somewhat difficult to distinguish from non-top particle decays, is the "all-hadronic" mode in which each W decays into a pair of quarks. A new mass measurement (F. Abe et al., 15 Sept. Physical Review Letters) by the CDF group is based on the first identification of all-hadronic top decays.
(2) A rare decay mode is the "dilepton mode" in which each W particle decays into a lepton (such as an electron or muon) plus a neutrino. D0 has reported calculations of the top mass based on the dilepton events. Click here for D0's lay language description of this mass measurement. You can also download a preprint of their scientific paper.
(3) In the "lepton-plus-jets" mode, one W decays into a lepton (such as an electron or a muon) plus a neutrino while the other W decays into two quarks, which subsequently produce a "jet," or spray of particles. The first identified decay mode for the top quark when it was discovered back in 1995, the lepton-plus-jets mode is the basis of a new, record-high-accuracy top mass determination from the D0 experimental group at Fermi National Accelerator Laboratory (S. Abachi et al., Physical Review Letters, 18 August). For an illustration of this decay mode, click here. You can also view D0's lay-language description of this work.
This topic is described in the journal Physical Review Letters by F. Abe et al. (CDF) in the 15 September 1997 issue and by H. Abachi et al. (D0) in the 18 August 1997 issue.
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