This plot shows the mjet1 versus mjet2 distribution for the data taken in this experiment. At CDF, protons of energy 1 TeV, or 1 trillion electronvolts, collided with antiprotons of equal energy. In many of these events, we observe a phenomenon called a jet. A jet is a spray of particles all moving in the same direction and typically originating from a practically massless subatomic particle, which is why it is also expected to have a low mass. It is…
N is the number of events determined by a fit for each decay mode. The first uncertainty is statistical, and the second is systematic. In 1957 Lev Landau postulated that the laws of physics are symmetric under charge parity. This means that a mirror reflection of a particle with a particular charge and handedness would yield a particle of opposite charge and handedness. For example, a left-handed electron is transformed under charge parity to a right-handed antielectron. In 1964 Cronin,…
This plot shows the number of events observed in the data and expected various values of R as a function of identified b jets. One of the most intriguing elementary particles physicists study is the top quark. Discovered at Fermilab in 1995, it is as heavy as a tungsten atom, and its large mass implies that it decays before joining with lighter quarks to form hadrons. This gives scientists the opportunity to study its properties in detail. Our understanding of…
This plot shows the dijet mass distribution in W/Z + 2 jets, overlaid, in the combined electron and muon data sets. The plot incorporates improved jet energy scale corrections for simulated quark and gluon jets and tunings of the multijet-background modeling. The bottom panel shows data with all fit background contributions subtracted, except those from diboson production. Three years ago, CDF saw an excess of events containing a W boson and two jets — a peak in the 140 GeV/c2…
The asymmetry of the leptons from top decays as a function of the lepton rapidity from the CDF data. The fit (red curve) is in good agreement with the data and provides for a measurement of the inclusive asymmetry. Since the discovery of the top quark in 1995, physicists at the Tevatron have been probing the properties of this mysterious elementary particle to see whether it behaves the way we expect it to. One of these properties is called forward-backward…
An illustration of the final state used in the reconstruction of the Ξb0 baryon. The data was collected by imposing requirements on the tracks in magenta. In addition to the wide program of top quark studies performed at hadron colliders, scientists have obtained many results on the physics of particles containing bottom quarks, also known as b quarks, at these machines over the years. Baryons are particles with three quarks, similar to protons and neutrons. The study of b baryons…
This diagram shows the s-channel single-top quark production mechanism sought in this analysis, which selects signal events in which the lepton is not identified. In collisions of high-energy beams, new, heavy particles are usually produced in pairs: a matching antiparticle for every particle. That’s the case for the bottom quark and the top quark, both discovered at Fermilab. But every now and then, the weak force is responsible for the collision, and so particles can be transmuted from one kind…
Comparisons of the world’s average of direct measurements of the mass of the W boson (TeV and LEP-2, in black), with the recent CDF indirect measurements extracted from the forward-backward asymmetry of Z bosons (in red and blue). The W boson is one of the particles that mediates electroweak interactions. Scientists have put forth great effort to determine its mass, and a recent column related CDF’s documentation of the single most precise direct measurement. This column summarizes an indirect determination…
This shows a Feynman diagram for s-channel single top quark production. The top quark decays into a W boson and a b-jet. This week, a combined effort from the CDF and DZero experiments reported the observation of a new top quark process. This article discusses the contribution to that result from the CDF experiment. The top quark was discovered almost 20 years ago by the CDF and DZero experiments through a process in which it is produced in pairs. Events…
The six input σ{tt } measurement from the CDF and DZero experiments, along with the CDF-only and DZero-only combination results and their combination for the Tevatron result. Fermilab Today has recently reported on several combined measurements. Today we look closely at one of them: the production cross section of a top quark and antiquark by a collision of a proton beam with an antiproton beam, where the energy in the center-of-mass frame is 1.96 TeV. The aim of combining six…