Physics in a nutshell

The Main Injector is the flagship accelerator at Fermilab. Over the coming months, this column will review how machines such as this one achieve high-energy particle beams. Photo: Reidar Hahn Much of the information we gather from the physical world comes to us by a scattering process. Scattering occurs when a beam consisting of light or charged particles strikes a target. The incident particle and target can simply recoil from the interaction, or other additional particles can materialize out of…

A shower produces dozens of particles that could be observed individually (inset figure) or collectively in a calorimeter (bottom). The previous Physics in a Nutshell introduced tracking, a technique that allows physicists to see the trajectories of individual particles. The biggest limitation of tracking is that only charged particles ionize the medium that forms clouds, bubbles, discharges or digital signals. Neutral particles are invisible to any form of tracking. Calorimetry, which now complements tracking in most particle physics experiments, takes…

Happy trails

This shows a particle identified in a photograph of a bubble chamber (left) and a computer reconstruction of signals from a silicon tracker (right). Much of the complexity of particle physics experiments can be boiled down to two basic types of detectors: trackers and calorimeters. They each have strengths and weaknesses, and most modern experiments use both. This and the next Physics in a Nutshell are about trackers and calorimeters, to kick off a series about detectors in general. The…

The purpose of particle physics is to better understand the rules that govern the universe. Long before the papers are written, accelerators and detectors must be designed, built and operated. It is technology that makes it all possible. Readers of Fermilab Today have read many articles on many experiments: CDF and DZero, LHC, the neutrino program, the muon program, astrophysics studies. These articles focus on the outcome of the measurements and what they tell us about the physical world. But…

How many forces?

Unlike in Star Wars, where there was but one force with a light and dark side, the number of fundamental forces is a much murkier question. If you’ve read many of my columns, you know quite a bit about the Standard Model. You know that there are quarks and leptons. You’ve heard about the gluon, the W and Z bosons, the photon and the graviton. And you know that this means that there are four fundamental forces: the strong and…

A photograph from the day that Sweden switched from driving on the left to driving on the right. A physicist might call this a change in chirality, since one driving pattern was replaced by its mirror image. Photo courtesy of rarehistoricalphotos.com One morning in 1967, all cars in Sweden had to stop, move over to the right side of the road, wait 10 minutes and then resume driving. From that day forward, Sweden has been a drive-on-the-right country, like its…

Electromagnets

Electromagnets are made by wrapping wire in a coil and attaching it to a battery. The same technology is used to make the magnets used in large particle accelerators. Magnets are something most of us are familiar with, but you may not know that magnets are an integral part of almost all modern particle accelerators. These magnets aren’t the same as the one that held your art to your parent’s refrigerator when you were a kid. Although they have a…

This spiderweb was overtaken by a sudden frost. The last few days have been cold. Really cold. It prompted me to make some comparisons: cold as outer space, cold as laser beams, cold as an electron — but most of these are nonsensical. The concept of temperature only makes sense in settings with large numbers of particles and a diffuse distribution of energy, such as our everyday world. A single particle doesn’t have a temperature, and the temperature of a…

Ingredients for a neutrino beam: speedy protons, target, magnetic horn, decay pipe, absorbers. Image adapted from Fermilab Fermilab is in the middle of expanding its neutrino program and is developing new detectors to study these ghostly particles. With its exquisite particle accelerator complex, Fermilab is capable of creating very intense beams of neutrinos. Our neutrino recipe starts with a tank of hydrogen. The hydrogen atoms are fed an extra electron to make them negatively charged, allowing them to be accelerated….

Bandwidth, or the spreading of a radio station onto multiple, neighboring frequencies, is related to uncertainty in quantum mechanics. When I first started teaching, I was stumped by a student who asked me if quantum mechanics affected anything in daily life. I said that the universe is fundamentally quantum mechanical and therefore it affects everything, but this didn’t satisfy him. Since then, I’ve been noticing examples everywhere. One surprising example is the effect of Heisenberg’s uncertainty principle on Wi-Fi communication…