In 2015, the world's most powerful atom smasher, the
Large Hadron Collider, will restart. The particle accelerator has already
discovered the Higgs boson, the so-called "God particle," and when it
comes back online after two years spent on upgrades, researchers suggest it
could discover other kinds of these God particles, as well as extra dimensions
of reality and the identity of the mysterious dark matter that makes up most of
the mass in the universe.
The Large
Hadron Collider (LHC) is the largest particle collider in the world,
with a ring about 16 miles (27 kilometers) in circumference. It accelerates particles
to nearly the speed of light using close to 9,600 magnets, comprised of about
10,000 tons of iron, more than in the Eiffel Tower. These magnets are made up
of coils of filaments that, if they were unraveled, would stretch to the sun
and back five times with enough left over for a few trips to the moon.
The largest of the LHC's
magnets weigh 35 tons, and are about 50 feet (15 meters) long. They
can generate a magnetic field more than 100,000 times more powerful than
Earth's. These magnets require cooling from liquid helium, making the LHC the
largest refrigerator in the world — the magnets operate at temperatures of
minus 456.3 degrees Fahrenheit (minus 271.3 degrees Celsius), colder than outer
space.
In 2012, the atom smasher helped scientists discover the
long-sought Higgs boson, which helps grant mass to all particles that have
mass, such as protons and electrons. The Higgs boson itself has a mass of 125
billion electron-volts, or more than 130 times the mass of the proton.
Still, as rich as the harvest of results surrounding
the Higgs was, the LHC was designed to be even more powerful than it has yet
been. Just nine days after it first went live in 2008, a faulty electrical
connection between two of its magnets led to several tons of helium escaping
with explosive force, damaging dozens of magnets. [Wacky
Physics: The Coolest Little Particles in Nature]
Now, the LHC is set to return in 2015 nearly twice
as powerful as its first run from 2010 to 2013.
"Doubling the energy will have a huge impact on
the search for new particles at LHC," said experimental particle physicist
Gabriella Sciolla, of Brandeis University in Waltham, Massachusetts, who works
on the ATLAS experiment at the LHC. "The higher the energy, the heavier
the particle one can possibly produce."
One breakthrough the LHC could make after it
restarts is discovering what particles make up dark matter,
one of the greatest mysteries in the universe. Dark matter is thought to be an
invisible, enigmatic substance that makes up about five-sixths of all matter in
the cosmos.
"By going to larger energies at the LHC, we
increase the range of masses of potential dark matter particles that we can
examine," said experimental particle physicist Andrew Lankford at the
University of California, Irvine, who also works on the ATLAS experiment.
The consensus among physicists so far is that dark
matter is made up of new kinds of particles that interact only very weakly with
ordinary matter. Dark matter cannot be explained by any of the particles in the
Standard Model of particle physics, the best description there currently is of
the subatomic world. They must therefore arise from a new understanding of
physics that goes beyond the Standard Model. One possibility lies in an idea
known as supersymmetry, which suggests all known kinds of particles in the
Standard Model have as-yet-undiscovered partners. For example, electrons would
have similar cousins known as selectrons.
"All searches for supersymmetric particles
depend on high-energy collisions between particles," Sciolla said.
Scientists say that the LHC cannot directly detect
any dark matter particles. However, after the LHC smashes protons together, any
energy missing from the aftermath might hint at the creation and existence of
dark matter particles, Sciolla explained.
Another discovery the LHC could make are more kinds
of Higgs bosons. "The LHC proved one kind of Higgs boson exist — no one
says there can't be a second or third or fourth," Sciolla said. "They
could be more Higgs bosons with different masses, and maybe even charge, as is
predicted by supersymmetry."
Learning more about how Higgs bosons interact with
other particles could also illuminate the nature of dark matter. "There
could be very, very rare interactions between Higgs and dark matter particles
that could shed light on what dark matter is," Lankford said. "Higgs
could be a portal into the dark sector."
And last, the LHC may discover the so-called Z-prime
or Z' boson. This particle is theoretically a heavier version of the Z boson, a
particle linked with the weak nuclear force that underlies both nuclear fusion
and radioactive decay.
Nearly any grand unified theory — a theory in
physics that could explain all known forces — would suggest that Z-prime
exists. This includes theories that also suggest the existence of extra
dimensions of reality beyond the three spatial dimensions of length, width and
depth and the fourth dimension of time.
"Z-prime is much heavier than a Z particle,
something like tens of times the mass," Sciolla said. "Z-prime can
decay in a very simple way that yields two very energetic muons, which are
basically heavier versions of electrons. If we can detect the muon signature of
Z-prime, that would support models that predict the existence of Z-prime."
With all this in mind, researchers at the LHC are
greatly looking forward to 2015.
"As the LHC is waking up, a lot of people are
excited right now," Sciolla said. "There's a lot of enthusiasm
here."
soucre:http://www.livescience.com/49265-large-hadron-collider-2015-preview.html
