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LHC smashes high-energy record
By Laura Sanders
By all accounts, the Large Hadron Col-lider’s record-setting day of proton bashing was a smashing success. The powerful
machine at CERN, Europe’s high-energy
physics lab near Geneva, got off to a rocky
start on March 30. But by early afternoon
(Geneva time), two 3.5-trillion-electron-
volt beams were colliding head-on.
The collisions in the 27-kilometer-
around accelerator set a new record for
highest-energy particle crashing.
“Today, we opened the door and put our
nose through it,” says Jürgen Schukraft,
a physicist with CERN’s ALICE experi-
ment, which will explore new types of
matter produced in the collisions.
“Already it looks like we are entering
new territory,” Schukraft says. But it will
take “years, not days or weeks,” he adds, to
answer physicists’ questions about theoretical predictions like the elusive Higgs
particle, dark matter and supersymmetry.
A morning collision attempt was
aborted when a piece of overly sensitive
equipment detected errant electromagnetic radiation. Scientists resolved the
issue, and by early afternoon, “it was all
OK,” Schukraft says. “It works perfectly.”
CERN plans to run the accelerator at
3. 5 TeV per beam for the next 18 months
to two years, with a brief maintenance
break at the end of 2010. Then the LHC
will be shut down and prepared to run at
its maximum energy of 7 TeV per beam.
Gamma-ray data from blazars
favor ‘top-down’ hypothesis
By Alexandra Witze
Astronomers have detected evidence of
how strong the magnetic fields between
galaxies must be. The finding illuminates
how magnetism arose in the cosmos and
could one day serve as a probe for understanding processes that happened soon
after the Big Bang, 13. 7 billion years ago.
The study, published online April 1 in
Science, “may be a clue that there was
some fundamental process in the intergalactic medium that made magnetic fields,”
says Ellen Zweibel, an astrophysicist at
the University of Wisconsin–Madison,
who was not associated with the work.
All galaxies contain magnetic fields;
the Milky Way’s field is most intense
near its center, where its strength is about
1/10,000th of Earth’s. Magnetic fields also
permeate intergalactic space, but until
now astronomers haven’t known how
strong those fields are or how they arose.
One “top-down” idea is that all of space
was imbued with a slight magnetic field
soon after the Big Bang, and this field
grew in strength as stars and galaxies
amassed. A “bottom-up” possibility is
that magnetic fields formed first by the
motion of plasma in small objects, such
as stars, and then propagated outward
into space. The new work suggests that
the top-down option is right and puts a
lower limit on the intensity of the fields.
Andrii Neronov and Ievgen Vovk, of the
Geneva Observatory, reached this conclusion by studying blazars, the bright hearts
of active galaxies that spew jets of energized particles toward Earth. The orbiting Fermi Gamma-ray Space Telescope
Blazars, active galactic nuclei that beam
near–light-speed particles at Earth, offer
clues to magnetic fields in space.
has spotted a number of these objects.
But blazars are more than cosmic
beauties; they also provide information
about the space the gamma rays have traversed. Gamma-ray photons are electrically neutral and so zoom through empty
space unperturbed by magnetic fields.
But occasionally a gamma ray will collide with another photon of much lower
energy, generating an electron and a positron. Because those two new particles are
charged, they are subject to deflection by
a magnetic field. They later recombine to
form a gamma ray again, which proceeds
unharmed, but with a lower intensity.
Neronov’s team looked at Fermi data
for gamma rays with the intensity expected if they hadn’t been converted into
charged particles and then deflected by
magnetic fields. The researchers spotted
no such rays. That lack of detection, says
Neronov, “tells us that electrons and positrons were deflected. There is nothing
else to deflect them but a magnetic field.”
That means magnetic fields must exist
in intergalactic space with a strength of
at least one ten-million-billionth the
strength of Earth’s. That lower bound suggests that “there really was some process
that acted on very wide scales throughout
the universe,” Zweibel says.
Goddard Space FliGht center/naSa