Dark matter: the underground lab searching for wimps

At Gran Sasso National Laboratory, nearly a mile beneath an Italian mountain range, physicists are trying to isolate the particles they believe hold the universe together.

Guardian, By Robin McKie

Drive west along Italy‘s Autostrada 24 and you will come to the Gran Sasso mountain range 80 miles before Rome. This is one of Italy’s most spectacular national parks and includes the 9,554ft (2,912m) Corno Grande, the highest peak in the Apennines. Bears, wildcats, wolves and chamois make their homes here and every summer thousands of tourists gather to holiday in this glorious, rugged landscape.

The mountains hide an intriguing secret, however; one that can be glimpsed from the A24 as it plunges through the 10km tunnel built beneath Gran Sasso. Half way along, another tunnel branches off from the main road. Should you follow it, you will come to a 4m-high, solid stainless steel door manned by guards. You are now at the threshold of the Gran Sasso National Laboratory, a subterranean lair where physicists are probing the structure of matter and the make-up of the universe. With its labyrinth of tunnels, uniformed guards and glittering racks of equipment, it is one of the world’s most spectacular laboratories. All that was lacking from my visit was an appearance from Ernst Blofeld clutching a white Persian cat.

The research centre was built in the 1990s to take advantage of the construction of the A24 Gran Sasso tunnel. Simply add a side entrance and an extra few kilometres of tunnel, scientists told the Italian government, and you will create a unique facility. “And that is what happened,” says Professor Cristian Galbiati, who is based at the laboratory. “About 10km of tunnel were drilled here. Above us there is 1,400m of rock – and that’s what makes this place so important.”

Earth’s upper atmosphere is constantly bombarded by cosmic rays, which create cascades of particles called muons that shower down on the planet’s surface. This background radiation is harmless but it can cause havoc when making delicate measurements of sub-atomic particles. Hence the scientists’ decision to build a laboratory with a 1.4km-thick rock roof. (Gran Sasso translates as “the great stone”.) This rock blocks out nearly all muons that batter the surface, Galbiati adds. “It makes this lab one of the least radioactive places on Earth.”

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