The Reason for Mass
by Michael Campbell
Several
University of Kansas physicists are part of a team that got $1.5 million
late last year to look for a subatomic particle that may answer a deceptively
tough question:
Why do you weigh as much as you do?
KU physics professors Philip Baringer, Alice Bean and
Graham Wilson, along with scientists from around the world, will use
the grant from the National Science Foundation to build a detector to
find the elusive particle, known as the Higgs boson.
The Higgs is one of the fundamental particles predicted
by scientists to make up everything that exists.
It is the only one that scientists have not found.
"We've been looking for it for many years," Bean said,
"It's like the Holy Grail."
The NSF grant will fund construction of a new particle
detector for the atom smasher at the Fermi National Accelerator Laboratory
outside Chicago.
The current detector should burn out by 2004, Bean
said.
Bean described the detector as a four-foot long tube
the diameter of a medium pizza. Inside the tube, a million mini-computers
monitor an array of hair-thin wires etched onto silicon. The computers
sit in six concentric rings to detect any passing particles.
The fact that the Higgs is missing interests scientists.
So, too, does the fact that they believe that Higgs
particles are what ultimately determine the weight of everything in
the universe.
In the visible world, weight results from gravity pulling
on an object. The strength of gravity's pull is determined by an object's
mass. And its mass is a measurement of how much material an object contains.
Something large, like a whale, has more mass than something
smaller, like a fly. Something dense, like lead, has more mass than
something airy, like foam.
According to Bean, though scientists have long understood
how mass works in the world of whales, lead and flies, the rules change
for things smaller than atoms.
There, mass may not reflect how much material is inside
a particle.
"The electron is 2,000 times lighter than the proton,"
Bean said, "Why? There is no concept of that."
In the 1960's, a physicist named Peter Higgs theorized
that mass comes from an interaction between atoms and an energy field,
now named the Higgs Field, surrounding everything.
The Higgs Field contains swarms of Higgs bosons.
"It's this field around you that slows you down like
you're trying to move through water," Baringer said, "It's analogous
to friction."
The more the field slows a particle down, the more
mass it has, he said.
The new boson detector will allow the researchers to
locate and track particles with lifetimes as short as one-trillionth
of a second -- some of which should be Higgs bosons.
The researchers fire protons and anti-protons in opposite
directions around an underground ring two-and-a-half times larger than
the track at the Kansas Speedway. Powerful magnets along the ring accelerate
the particles until they smash into each other with great force.
According to Baringer, the collisions create very hot,
very energetic conditions that mimic those seen at the beginning of
the universe. Under these conditions, the scientists can detect particles
that are normally difficult to observe.
By tracing the paths of all the particles flying loose
after the collisions, the researchers can reconstruct what happened
like state troopers investigating a very tiny, very powerful accident,
Bean said.
And if they reconstruct enough collisions, the researchers
say, they should eventually find the Higgs boson.
