A collision recorded by CDF with two high-energy photons produced and no other particles. When a proton and an antiproton collide at very high energy in Fermilab’s Tevatron, about 25 percent of the time they just scatter away from the point of collision at a very small angle without losing any energy. We call that elastic scattering. This can happen in two ways: via the electromagnetic force (a photon is exchanged) or by the strong force if the protons overlap….
DZero tried to faithfully reproduce a CDF result that had the blogosphere buzzing in early April. As is evident from the picture, no bump was observed corresponding to the one seen by CDF. The corresponding CDF figure can be seen here. Things that go bump in the night can send a chill up your spine. They are unexpected, unknown and could be anything. Bumps in data have a very similar effect on physicists. If we see an unexpected bump in…
The outer figure shows the diphoton mass distribution from the CDF data as well as the fit to the data that is used to estimate the background in the search window. The inner figure shows the shape of the Higgs boson signal that physicists expect to see. The main idea is that if the Higgs boson was produced at a large enough rate in the detector, it would be visible as a narrow bump in this distribution. In order to…
In a search for diamonds, one has to learn to how to remove the rest of the gems. Some, like the opal and freshwater pearl are easy to remove from the pile, since they look quite different. However, eventually you are left with gems that are indistinguishable from diamonds and you need to know just how many fakes there are. If the number of predicted fakes is 10 and you have 20 gems, you know you have some diamonds. Nowadays…
A proton contains two up quarks, a down quark and a soup of quark-antiquark pairs, seething below the surface. It is often said that a proton is made of three quarks: two of the same type, called up quarks, and one of a different type called a down quark. But that’s not the whole story. In the space between these three stable quarks there is a boiling soup of quark–antiquark pairs. That is, a quark and an antimatter quark spontaneously…
The points are the measured angular coefficients, A0 and A2, as a function of Z boson transverse momentum. The black curve is the Standard Model prediction which is approximately 70 percent quark-anti-quark (q-qbar in green) and 30 percent quark-gluon (q-G in brown). Z bosons are produced at the Tevatron through collisions of the particles (quarks and gluons) inside the proton and antiproton beams. Once Z bosons are produced they decay into lepton–anti-lepton pairs (e.g. electron-positron or muon–anti-muon). These leptons are…
A new analysis using combined MiniBooNE and SciBooNE data looked for disappearing muon neutrinos building on a MiniBooNE study from 2009. Image credit: Chow.com Kendall Mahn, TRIUMF; and Yasuhiro Nakajima, Kyoto University; were among the experimenters who performed this analysis. When it comes to neutrinos, it’s best to expect the unexpected. Previous Results of the Week have showcased a surprising difference between MiniBooNE electron neutrino appearance and electron antineutrino appearance results. In this special result, we present an analysis done…
We’ve come a long ways since the first Tevatron collisions in 1985. Not only did Fermilab scientists discover the top quark in 1995, but we can now measure its mass to a precision better than 1 percent. In 1985, the first pair of protons and antiprotons collided in the Fermilab Tevatron. One of the main purposes for which the Tevatron was built was to search for the top quark and, after 10 years, DZero and CDF jointly announced the particle’s…
A popular extension of the Standard Model includes the principle of supersymmetry. This extension is called the minimal supersymmetric Standard Model (MSSM) and it predicts not one, but five Higgs bosons, including some with electric charge. This analysis searched for the three electrically neutral Higgs bosons predicted by the MSSM, shown here in red. Fermilab Today readers have heard a lot about the search for the Higgs boson. What might be surprising is that scientists don’t know if it exists….
The transverse mass distribution of electron + missing transverse energy for data and standard model expectation. The red region shows our expectations for a W-prime of mass equal to 800 GeV/c2. In the Standard Model the quarks and leptons communicate with each via the exchange of particles known as bosons. The bosons of the Standard Model are the photon, the gluon and the W and Z particles. It is natural to wonder if there are additional bosons present in nature;…