“these are results that have been awaited for 50 years.” — PE TEr Car GIll
Particle physicists chasing ghosts
By Devin Powell
Two experiments on different continents have found hints that particles
called neutrinos can shape-shift in an
unexpected way.
This behavior may be the key to
understanding why these particles
are so weird, says neutrino physicist
Jennifer Raaf of the Fermi National
Accelerator Laboratory in Batavia, Ill.,
the nation’s largest particle physics lab.
Raaf presented an overview
of recent neutrino findings
on August 9.
The ne w results also bode
well for future neutrino
experiments that may one
day help scientists understand why the universe contains vastly
more matter than antimatter. These
experiments are part of the changing
landscape of U.S. particle physics: With
Fermilab’s Tevatron, once the most
powerful particle collider in the world,
shutting down soon, the government
laboratory is reconfiguring itself to
focus on projects that require particularly intense beams and look for
extremely rare events.
“Neutrinos will play a big role moving
forward,” says Young-Kee Kim, deputy
director at Fermilab.
In the bestiary of particle physics,
each of the three charged leptons — the
familiar electron and the heavier muon
and tau particle — have electrically neutral neutrino counterparts. Neutrinos
are loners by nature, rarely interacting
with the rest of the universe. But they do
occasionally change form. That process,
called oscillation, may offer clues about
why the universe contains so little antimatter.
In June the T2K experiment in Japan
reported evidence that muon neutri-
nos occasionally oscillate into electron
neutrinos. Six electron neutrinos
appeared in a nearly pure beam of muon
neutrinos traveling from an accelerator
at the J-PARC facility to an underground
detector 295 kilometers away.
Days later, physicists at the MINOS
experiment announced finding traces
of this oscillation in neutrinos traveling
735 kilometers from Fermilab to a mine
in Minnesota. Those results, presented
August 9, help to narrow T2K’s estimate
of how often this changeup happens.
Taken together, the
chance that both sightings
are flukes is less than one
in a thousand, according to
a recent analysis by a team
of physicists in Italy and
Germany. That’s below the
standard for claiming a discovery but
good enough to warrant further study,
says Ed Kearns, a Boston University
neutrino physicist and a member of the
T2K team.
“This helps us justify future experiments,” he says. “It makes a big difference in our confidence going forward.”
Another project, called LBNE (for
Long-Baseline Neutrino Experiment), also hopes to extend this line
of research. LBNE would send beams
of neutrinos and antineutrinos from
Fermilab to a detector 1,300 kilometers
away, giving the particles more time to
change identity — and the scientists a
better shot at understanding whether
neutrinos behave differently than their
antimatter counterparts.
“Neutrinos
will play a big
role moving
forward.”
YOuNG-KEE KIM
Dark energy camera getting
ready for first light
Scientists have finished testing a
camera that could sharpen up their
picture of dark energy, a mysteri-
ous phenomenon thought to be
pushing the universe apart. in late
September, the 570-megapixel
dark energy Camera will be boxed
up, flown to Chile and mounted
on the victor m. Blanco telescope
at the Cerro tololo inter-american
observatory perched in the andes,
Jiangang hao of the fermi national
accelerator Laboratory in Batavia,
ill., reported august 11. there, the
device will survey a broad area of
the sky, taking snapshots of galax-
ies and supernovas to measure
how the rate of the expansion of
the cosmos has changed over time.
more than 120 researchers from
the united States, Brazil, Spain,
Germany and the united Kingdom
are involved in the project.
— Devin Powell
Gravity, meet antigravity
Like a prospective presidential can-
didate, gravity may flip-flop—trans-
forming into antigravity that pushes
instead of pulls. this new predic-
tion comes from two-time physics,
a theory developed by physicist
itzhak Bars of the university of
Southern California in Los angeles.
in this theory, time is not linear
but more like a flat sheet with two
dimensions, and space contains
an extra hidden dimension beyond
the usual three. a universe moving
through this six-dimensional space-
time would experience multiple Big
Bangs and alternate between peri-
ods of gravity and antigravity, Bars
reported august 12.
— Devin Powell
www.sciencenews.org
September 10, 2011 | SCIENCE NEWS | 9
