Andrew Beretvas

Comparisons of the world’s average of direct measurements of the mass of the W boson (TeV and LEP-2), with the recent CDF indirect measurement extracted from the forward-backward asymmetry of Z bosons (CDF ee 2 fb-1). In the Standard Model of particle physics, the masses of the Z and W bosons (MZ, MW) are related to another parameter of the theory, namely the electroweak mixing angle sin2(θW). The parameter sin2(θW) defines the relative strengths of the weak interaction (which causes…

This plot shows the final data in the exclusive (photon + missing energy) final state, along with the backgrounds as modeled from data. The signal region for this analysis is from 2 to 7 nanoseconds. The CDF collaboration has just completed a new search for “delayed” photons, this time in the exclusive photon-plus-missing-energy final state. Delayed photons are a smoking-gun signature of heavy, long-lived particles that are often predicted in gauge-mediated supersymmetry-breaking scenarios. If produced in a collision, a long-lived…

Dominant production of top quark and lepton-plus-jets decay mode is shown. CDF physicists recover these events even though a charged lepton is missed. The top quark is the most massive of the currently known elementary particles. Of the six quarks, the top quark has the largest mass, which is a whopping 40 times more massive than that of the next most-massive quark, the bottom quark. Because of the top’s very large mass, it may play a special role in our…

Distribution of the transverse-energy values for the two jets with the largest transverse energy in each event (black points) for the signal sample. The lower panel shows the observed data yield divided by the predicted yield. An important part of the Tevatron’s legacy is the discovery of the top quark and subsequent determinations of its intrinsic properties. Here we make the first measurement of the top-antitop cross section using the full Run II data set. The top-antitop cross sections give…

Shown is the product of the charge of the W boson and the associated b quark jet. An excess of data in the exotic-model-like right-hand side would indicate that the top quark is not what we think it is. Since the discovery of the top quark, several of its properties have been measured to confirm the Standard Model predictions. As the top quark decays, one can study its decay products, which are a W boson and a b quark. Determining…

Proton and antiproton collide to produce a top-antitop pair. R is the ratio of the branching fraction of top → W+b to top → W+q, where q is any quark (d, s, b). If there is no background, the number of events with one tag is proportional to 2R(1-R), and the number of events with two tags is proportional to R2. By studying the properties of known particles and comparing their actual measurements to calculated predictions, scientists can investigate whether…

The measured differential cross sections of events with a photon and a heavy b quark as a function of photon energy. The data are compared to four theoretical predictions. A simple picture of the proton is that it is made out of three quarks: one down quark and two up quarks. The quarks are “glued” together by gluons. However, this picture is incomplete. The so-called “sea” in the proton plays an essential role. The sea is produced by the gluons…

A comparison of current limits from ATLAS, DZero, CMS, CDF (this paper) and LHCb at 95 percent confidence limit. The SM prediction, at 68 percent confidence limit, is shown as a gray vertical band. You may remember the excitement in July 2011 surrounding searches by CDF for extremely rare decays of Bs mesons. Bs mesons are composed of an anti-b quark and an s quark. Their decays into pairs of muons (Bs → μ+μ–) are predicted in the Standard Model…

The energy imbalance (represented by ET with a slash through it) occurs whenever a Z boson decays into two neutrinos at the same time that a Higgs boson decays into two quarks (represented by the two jets). We can search for the Higgs boson in various ways. To search for it directly, particle physicists look for its decays into pairs of particles such as W+W–, ZZ or two photons. The combined mass of the pair is that of its parent…

Distribution of events, in the signal region. The horizontal axis shows bb invariant mass. The figure shows the data, the signal and four different backgrounds. The signal hypothesis is: a total cross section of 250 femtobarns, a heavy neutral Higgs boson of mass 500 GeV/c2 and lighter charged Higgs boson H± of mass 300 GeV/c2 along with the Standard Model Higgs boson. An exciting part of the much-celebrated particle discovery recently made at the Large Hadron Collider is that it…