Andrew Beretvas

Uncertainties in units of MeV/c2 on the latest result for the mass of the W boson, which was determined to be 80,387 ± 19 MeV/c2. The total uncertainty amounts to 0.02 percent. On Feb. 29, 2012, CDF submitted to the journal Physical Review Letters the world’s most precise measurement of the W boson mass. More recently, on Nov. 4, 2013, we submitted a long paper to Physical Review D documenting this measurement in detail. This has long been a practice…

Distribution of B**+ candidates is shown with black squares, and a smooth curve in blue shows the result of a fit. The mass is measured as a mass difference Q to improve the mass resolution. In the last century, physicists discovered that the proton-electron system of a hydrogen atom has discrete energy levels that depend on the relative position, angular momentum and spin orientation of the two constituents. This meant that electromagnetic force that bound them would permit the electron to live…

The diphoton mass distribution of the Drell-Yan and non-resonant (γγ,γ-jet and jet-jet) backgrounds is compared to the data for the region 60 < mγγ < 120 GeV/c2, which includes part of the fit region along with the signal region. The Z boson, one of the particles responsible for weak interactions, has been studied extensively since its discovery at CERN in 1983. We now know that the Z boson decays into quark-antiquark pairs about 70 percent of the time, into neutrino-antineutrino...

Dijet invariant mass distribution with fit results overlaid for events passing all selection criteria (top) and the same background-subtracted distribution with the fitted diboson contribution overlaid (bottom). In an older Fermilab Today article, CDF reported the observation of an unusual excess of events in which a W boson appeared together with two jets (which are among the most commonly produced particles at the Tevatron). The jets appeared to match well with the possibility of being produced through a totally unexpected…

The dilepton mass distribution of electron- or muon-pair + lepton events for the Standard Model background, CDF data and a SUSY benchmark (stacked on top of the Standard Model background) in the signal region. One way physicists try to make the big discovery is by searching for the unexpected — unexpected by the current accepted theories and, very often, even unexpected by new theories. The question they face is, “Where do we look for the unexpected?”. The answer is usually,…

This shows the asymmetry of the leptons from top decays as a function of the lepton rapidity. This is fit to a functional form, allowing the recovery of the inclusive lepton asymmetry. For several years, physicists at the Tevatron — both at CDF and DZero — have been studying a mystery in the production of top quarks: Outgoing top quarks prefer to go in the direction of the incoming proton beam (forward), while anti-top quarks prefer the opposite direction (backward)….

The figure shows the inclusive invariant pT differential cross section distributions for Ks, K*± and φ measured in this experiment. The predictions from PYTHIA are shown as dotted lines. Physicists currently have a very good understanding of the Standard Model. Thus many of the results presented in this column can be understood in terms of the Standard Model theory of the strong interactions, called quantum chromodynamics. But the particle production from soft interactions — collisions usually referred to as minimum-bias…

The figure shows the limits on the top quark width at the 68 percent and 95 percent confidence levels and the result of a fit to the data. The top quark is the heaviest currently known elementary particle. The only way the top quark can decay is through the weak interaction, which is the only interaction that allows quarks to change flavor (t → W + b). Its large mass endows it with the largest so-called decay width, and hence,…

This shows part of the mass spectrum for the Λb*0 candidates. The projection of the corresponding unbinned likelihood fit is superimposed. Physicists from the CDF collaboration have observed the Λb*0 baryon. This state is made of two light quarks (up and down) and a heavy (bottom) quark. It has exactly the same quark content as the ground state Λb0 baryon. The intriguing difference between the newly observed state and the well-known Λb0 is that the pair of light quarks (u,…

The differential cross section for top-antitop production is measured. The observed forward-backward asymmetry is described by an expansion in Legendre polynomials. The polynomials from a1 to a7 are measured. For several years, CDF and DZero physicists have been studying a puzzle in the production of top quarks at the Tevatron: The outgoing top quarks prefer to travel in the same direction as the incoming protons (forward) and the top antiquarks prefer to go in the opposite direction (backward). The Standard…