The single top t-channel fiducial cross section at 8 TeV measured with the ATLAS detector
Daniël Alphonsus Adrianus Geerts · CERN Document Server (European Organization for Nuclear Research) · 2015
QuarksAt the top left, the three generations of quark doublets are listed (pairs) horizontally.The first generation is the lightest one, with mass increasing with each generation.The quarks (anti-quarks) on the first row have a charge of +⅔ (-⅔), while the second row of quarks (anti-quarks) have charge -⅓ (+⅓).The quarks also carry color charge: red, green or blue for quarks, and anti-red, anti-green or anti-greenfor anti-quarks.The force particle of the strong interaction is the gluon that exchanges color charge between the quarks, and it's denoted by g in the figure.This massless boson carries one color and one anti-color charge. Decay channel Percentage [%]Electron 10.71 ± 0.16 Muon 10.63 ± 0.15 Tau 11.38 ± 0.21 Hadrons 67.41 ± 0.27Table 1.1:The percentages of each decay channel for the W-boson.[12] the weak interaction: the W ± and Z 0 .Their masses are quite significant ( for the W-bosons, and for the Z-boson).The weak interaction is responsible for the radioactive decay of nuclei, and allows for the flavor violation in electroweak theory. Higgs bosonWithout mass, there would not be three generations of quarks and leptons.For instance, a top-quark would be exactly the same particle as an up-quark.To endow particles with mass, the Higgs mechanism was proposed by Higgs et all.[7][8] Through the interaction with the Higgs field the particles acquire their mass and the mass difference between top-and upquarks becomes as large as the mass difference between a tennis ball and a truck.The SM does not predict the magnitude of the mass of each particle.The Higgs boson's discovery was recently announced by CERN.[9][10] It is the particle associated with the Higgs field.Its discovery has drawn a lot of attention, and François Englert and Peter W. Higgs were awarded the Nobel price in 2013.[11] -Why top-quarks?The top-quark is the heaviest quark in the SM.In fact, it is the heaviest fundamental particle known, with a mass of 173.21 ± 0.51 ± 0.71 .[12] It was experimentally verified to exist only in 1995 by the CDF and D0 collaboration at the Tevatron accelerator at Fermilab.[13][14] The top-quark almost exclusively decays to a W-boson and a b-quark.It has a short lifetime of τ t = 1 Γ t = ∼5•10 -25 sec.At this time scale no hadronization takes place.Hadronization is the formation of hadrons, which will be explained in more detail in section 2.4.3, and it takes place in a typical hadronization time τ had = ∼ 1 Λ QCD = ∼3•10 -24 sec.The final decay mode of the top-quark is determined by the decay of the W-boson it produces.The percentages are given in table 1.1.