from the editor
The enlightening transition from stuff to stuff
In practice, much of particle physics involves looking at how stuff turns into other stuff. When high-energy particles decay into new particles, the properties of those decays tell you all sorts of things about the original particles. Conversely, some of the properties of the new particles can be deduced from how they came into being. The process of change is just as important as the characteristics of the stuff involved in that change when it comes to understanding the laws of nature.
In many cases, the process is obscured; physicists see only the start or the end of it. When all of the energy that goes into a particle collision can’t be accounted for in the aftermath, it means physicists are not seeing some of the end products—neutrinos, perhaps, or something more exotic that their detectors aren’t picking up. In other cases, only the end products are visible, such as in experiments where physicists see light coming from high-energy muons that were created as neutrinos hit the detector. Astrophysicists may look for gamma rays that are the end product of dark-matter annihilation, which we can’t see directly.
But in the best cases, when both the initial and end products are visible, physicists can often close loopholes involving exotic particles or unknown physical phenomena. One example recently is the OPERA experiment’s observation of muon neutrinos turning into tau neutrinos in a process called oscillation. This marked the first time that the second half of the process—the tau neutrino appearing out of the oscillation—had been captured. (See the May 31 post in symmetry breaking online for more details of that experiment.)
A planned experiment called Mu2e, in which muons might be seen turning into electrons, is another example of capturing both the initial components and end products of a change. (See The Muon Guys: On the Hunt for New Physics.) Physicists don’t yet know if this process actually exists, but the question of whether it does or not (see “Explain it in 60 Seconds”) has big implications for the fundamental structure of the laws of the universe, especially as scientists try to unify all the particles and forces into a sensible, consistent framework.
Particle physics, or at least the news reports
of it, often seems concerned only with the existence
and characteristics of various particles.
However, physicists are just as interested in what
happens as those particles turn into each other.
The universe is not merely a zoo of strange stuff. It
is an oddly behaved, mysterious, and intriguing
dance of evanescent players, with an everchanging
choreography, and new performers
appearing on the floor as it progresses. It is the
dance of the universe that enlivens us and
drives us, gradually revealing its steps to those
persistent enough to watch closely.
David Harris, Editor-in-chief
Click here to download the pdf version of this article.
Email Update List
Receive email notifications of the release of future issues of symmetry:
In this artwork, Braniac, John Zaklikowski used every last
mother board, cell phone and floppy disk he had collected—and an array
of low-tech goods ranging from old-fashioned telephone
bells to a kitchen-sink strainer. He began with a rigid
plywood armature and used screws to attach hundreds
of components. A thick blue ring made of wax mixed
with pigment added coherence to the intricate result,
a juxtaposition of high and low tech. See more of his
work in the Gallery.
Photo: Bradley Plummer, SLAC
Shrink Wrap
Oct 2009
If you buy a Butterball turkey this Thanksgiving, you have particle accelerators to thank for its freshness. For decades now, industry has used particle accelerators to produce the sturdy, heat-shrinkable film...
Solar Neutrinos
May 2005
Ray Davis' experiments in a gold mine led him to solve the solar neutrino puzzle and win the 2002 Nobel Prize in Physics...
Positron
Apr 2007
A positron is the antimatter equivalent of an electron, with the same mass but opposite electric charge. When the two meet, they annihilate into a flash of energy...
