Leo Bellantoni

The nature of the strong nuclear force is such that the energy of its field is concentrated in long thin tubes, or strings, that pull on quarks. Thinking of our two goats as a bottom quark-antiquark pair produced in a Tevatron collision, the strong nuclear force strings will pull them in certain specific directions. The other ends of the strings are connected to the outgoing fragments of the colliding proton and antiproton (not shown). Image courtesy of Megan Brain Disponible…

The top diagram shows one of several ways to create a Z along with a bottom quark-antiquark pair. The initial quark and antiquark on the left are partons in the proton-antiproton collisions of the Tevatron.The bottom diagram shows a similar process without the Z. Because the Z is so massive, the gluon, shown in bright blue, will have different energy and momenta in the two cases. The force that holds a proton together also makes it more difficult to figure…

Sea quarks and gluons, the nonvalence parts of the proton, are continuously interacting with each other, as shown here. Gluons (the springy lines) can split into quark-antiquark pairs that nearly instantly merge again to reform gluons. But if another proton or antiproton collides with this constantly changing system, one of these sea quarks can be broken off and fly out of the proton with great energy. That sea quark might be a bottom flavored quark, or it might be a…

This plot shows the probabilities of finding up and down quarks with different fractions of a proton’s momentum. The vertical axis is arbitrary and different for the two curves. Disponible en español The parts inside of a proton are called, in a not terribly imaginative terminology, partons. The partons that we tend to think of first and foremost are quarks — two up quarks and a down quark in each proton — but there are other kinds of partons as…

Mixing tops

This Feynman diagram shows the mixing of a b (bottom) quark into a t (top) quark. Time flows from left to right. A b enters as one of the ephemeral quarks of the “quark sea” that is the proton or antiproton. It interacts with a W boson emanating from a quark or antiquark in the other colliding particle. In fiction, a common plot device is the police’s confusion about the identity of the perpetrator of some crime. In physics, a…

A visualization of a force field created by a stationary object. The massive object at the center of the system creates a stationary force field; one has to determine only how a relatively light object’s motion responds to the force.  Photo courtesy University of New Mexico Department of Physics and Astronomy Physicists who remember the past are delighted to repeat it. Nicolaus Copernicus and Galileo Galilei both realized that the sun is pretty much stationary at the center of the…

Which way did it go? On the left, it went south. On the right, it went nowhere. Disponible en español In the DZero detector, the direction in which a particle travels — the direction of its momentum — is often easier to measure precisely than its energy or, equivalently, its amount of momentum. This is the key idea behind a recent result. Put a flat piece of paper on your desktop. This is what particle physicists call the transverse plane….

A particle can take a number of different decay paths to arrive at the same result. Click to enlarge. Disponible en español Q: When is 3 plus 4 not 7? A: When the 3 and the 4 are in different directions. Walk 3 miles due east, say, then 4 miles due north. You are not 7 miles from your starting point; you are 5 miles from your starting point. To be fair, telling someone to go “3 miles due east”…

How many electroweak symmetry-breaking doublets are in that hand? Photo: Leo Bellantoni Disponible en español With all the discussion about “the Higgs,” it is worth remembering that what Peter Higgs (and Robert Brout, François Englert, Gerald Guralnik, Carl Hagen and Tom Kibble) gave us was not at first a particle. Originally, it was a trick. Specifically, it was a mathematical trick to solve a particular physics problem — the problem of how to retain a lovely property called gauge invariance…

At left is the apparatus used by Robert Millikan and his student to measure the charge of the electron in the early 20th century. At right is the apparatus used by more than 300 physicists — including students — to measure the charge of the top quark in the early 21st century. Disponible en español In 1909, Robert Millikan and Harvey Fletcher performed a Nobel Prize-winning experiment that showed that elementary particles always have a specific amount of electric charge…