NEWS | IN DEPTH
By Richard Stone and Pallava Bagla
Naba Mondal began his career 37 years ago snaring elusive subatomic par- ticles called neutrinos in the depths of a gold mine in southern India. Now Mondal, a physicist at the Tata Insti- tute of Fundamental Research (TIFR)
in Mumbai, India, expects to go back underground in a subterranean laboratory of his
own design to answer the next big question
in neutrino physics.
India’s central government this month
approved plans to build the India-based
Neutrino Observatory (INO), a
$244 million facility 1200 meters
under a mountain in southern India.
Its goal—to determine which of
the three types of neutrinos
is heaviest and which is
lightest—may seem esoteric. But it could help
answer other fundamental questions in physics,
including how neutrinos acquire
mass, whether they are their own antiparticles, and why the universe has so much
more matter than antimatter.
INO is competing for the neutrino mass
hierarchy with new facilities in other countries (Science, 7 February 2014, p. 590). “India
has not lost the race,” says Alessandro Bet-tini, director of the Canfranc Underground
Laboratory in Paseo de los Ayerbe, Spain.
But INO is getting a late start after years of
battling environmental concerns, unfounded
radiation fears, and bureaucratic snags.
Even if India falls short, INO—India’s
most expensive basic science facility ever—
will have a profound impact on the nation’s
science. Its opening in 2020 would mark a
homecoming for India’s particle physicists,
many of whom dispersed overseas over the
last quarter-century. And the INO team is lay-
ing plans to propel the facility beyond neu-
trinos into other areas, such as the hunt for
dark matter. INO will “transform physics of
this kind in India and will make a global im-
pact,” says K. VijayRaghavan, secretary of In-
dia’s Department of Science and Technology.
Neutrinos are produced in stars, nuclear
reactors, and particle accelerators, and
when cosmic rays smash into the upper at-
mosphere. They interact with other matter
only through the weak nuclear force, mak-
ing them difficult to detect. And because
cosmic rays swamp any neutrino signal at
Earth’s surface, physicists have to go under-
ground to study the particles, which easily
slip through kilometers of solid rock.
India was once at the forefront of neu-
trino research. In 1964, a TIFR team work-
ing in a mineshaft in southern India’s Kolar
Gold Fields was the first to detect neutrinos
created in the atmosphere. After the mine
closed in 1992, India’s tiny community of
high-energy physicists—fewer than two
dozen at the time—sought havens abroad,
for example at Fermi National Accelera-
tor Laboratory (Fermilab) in Illinois and
CERN, the European laboratory for particle
physics near Geneva, Switzerland.
Mondal and his fellow exiles plotted a
return to India. Around 2001, he says, “we
started thinking about where we could
make an impact.” They opted to return to
their roots by building a supersized version
of the Kolar detector: an iron calorimeter,
which detects charged particles called muons generated when muon neutrinos—one
of the three neutrino types—tangle with nuclei in the iron.
If they can count muon neutrinos gener-
ated in the atmosphere precisely enough,
INO physicists should be able to pin down
the hierarchy of neutrino masses. Neutri-
nos can morph from one type to another
through a process called neutrino oscilla-
tion that depends on the differences in their
masses. From such oscillations, physicists
know that two of the neutrinos are close in
mass and the other is different—but they
don’t know whether there are two heavier
neutrinos and one lighter one or the other
way around. By comparing the morphing of
muon neutrinos and muon antineutrinos as
they zip through the earth, INO physicists
hope to resolve the puzzle.
But it will take a very large detector. At
50,000 tons and 48 meters long, INO’s calorimeter will be the largest of its kind ever
built. Sandwiched between 140 iron plates
will be more than 30,000 thin glass resistive
plate chambers that will detect muons and
measure their properties. Far too bulky to fit
in the shaft of an existing mine, the device
requires a purpose-built cavern.
The Geological Survey of India recommended that the INO team burrow into a
granite mountain in Tamil Nadu state. But
local forestry officials opposed the idea, because the mountain is at the edge of a tiger
reserve (Science, 9 January 2009, p. 197).
After a long standoff, the INO team in 2009
retreated and the geological survey pointed
them to their current site, also in Tamil
Nadu, where they encountered even fiercer
Villagers feared that INO would generate “artificial neutrinos” whose radioactivity
would sicken people and livestock. Then a rumor arose that the government would dump
nuclear waste at INO, Mondal says. His team
mounted an outreach campaign, targeting local professors and high school students. “If
you can convey the concepts to students, they
can talk to their parents,” he says. The scientists also dangled a sweetener: Construction
crews would be mainly local.
After winning hearts in Tamil
Nadu, the physicists still had to
seal the deal in Delhi. Once the central
government signed off in 2011, it became a
matter of slotting the big-ticket item into
India’s budgetary cycle, which revolves
around 5-year plans.
Mondal’s team originally hoped to have
INO up and running by 2012. The 8-year
delay has left the door open to other facilities aiming to work out the mass hierarchy,
including China’s Jiangmen Underground
Neutrino Observatory, which will study
neutrinos from a reactor, and the U.S.-Japanese NOνA experiment, which will
watch for neutrinos from a Fermilab accelerator. But no matter what happens,
Mondal insists, India will win: “Just having
a big science project will get young people
excited about science.” ■
With reporting by Adrian Cho.
The country splurges on a
bid to regain leadership in
A subterranean neutrino snare
Deep under a mountain in southern India. INO
will house the biggest iron calorimeter ever built
and have room to spare for other experiments.