THE WASHINGTON POST – Don’t lose sight of me. Physicist Abhigyan Dasgupta – Riju to his family and friends – looks over his shoulder to caution our 12-member group as we prepare to descend 300 feet beneath the French countryside into the largest machine on Earth the USD4.7 billion Large Hadron Collider.
Big Science doesn’t get much bigger than the Large Hadron Collider (LHC) on the campus of the European Organisation for Nuclear Research (CERN) facility outside Geneva. The LHC runs in a circular 16.7-mile underground tunnel that crisscrosses the Swiss and French border. More than 1,200 superconducting magnets, each 50 feet long and weighing 35 tonnes and joined end-to-end, make up the collider’s ring. Guided by the magnets, trillions of protons circulate at nearly light speed in opposite directions inside a pair of two-inch-diameter tubes. At four points along the ring, aiming magnets send the two counter-rotating beams crashing into each other.
Our gateway to the collider is the Compact Muon Solenoid (CMS) on the accelerator ring near Cessy, France, a half-hour car ride from downtown Geneva. The CMS detector is one of seven experiments on the collider’s ring and one of the three that visitors may tour.
We enter a cavernous hangarlike room dominated by a 70-foot-high cross-sectional photograph of the CMS detector deep beneath our feet. When the accelerator is running, we are told, this is as close as visitors would get to the CMS.
The Large Hadron Collider is in the first months of a two-year technical shutdown for maintenance and upgrades. During that time, visitors lucky enough to secure a place on a CERN guided tour can go deep underground to visit the cavern that houses the gigantic detectors. When researchers switch the collider back on in early 2021, visitors will receive a more limited underground tour until the next two-year stop in 2025.
You’re extremely lucky, Dasgupta tells us. If you had come here a year ago, you would not have been able to go down.
We round a corner and stop in front of a blocked-off entrance. Dasgupta steps into something that looks like a yellow phone booth. He looks intently at a retinal scanner on the wall of the booth. The doors close behind him as another set opens on the other side. It scans my eyes and it lets me in. The rest get to be cargo and go through the cargo door.
Dasgupta lets us in and we board the freight elevator that will take us 300 feet down to the detector chamber. At the bottom, we pick up orange hard hats fitted with a computer chip so that security can track our precise location. We walk along a long passageway, its walls hung with photos of the collider and informational posters.
Dasgupta, a natural teacher who has just completed his physics PhD at UCLA, switches into data-delivery mode. He explains that, at full power, a proton makes 11,245 trips around the collider ring every second. Instead of a continuous stream, the protons travel in bunches, or packets. Each packet contains 110 billion protons and is spaced 25 nanoseconds apart, an interval of about 25 billionths of a second. Before a proton is annihilated, it will be travelling at 99.9999991 per cent the speed of light, he said.
The next 15 minutes pass as a blur. We must hurry; there are other tours behind us. We pass banks of electronic equipment and computers that tower over our heads, all connected by rivers of wires that snake up to the ceiling.
It is here, Dasgupta said, where electronic hardware and computer software winnow the 40 million collisions that occur every second to the 1,000 most interesting ones. These are stored for further analysis.
We scurry through narrow passageways – banks of overhead lights illuminate our way past danger warning signs and radiation symbols – and descend steep stairs. One more suspended catwalk takes us into the underground cavern that houses the CMS.
The detector is split horizontally in half like a giant melon. The two halves are pulled apart to allow workers access to the detector’s inner workings. They will be inched back together and the proton beam tubes reunited when the work is complete.
It’s anything but compact. The detector measures nearly 70 feet long and 50 feet wide and, at 14,000 tonnes, weighs about twice as much as the Eiffel Tower.
It’s also beautiful. Concentric rings of gold and candy-apple red detectors encircle the proton beam tubes at its centre. Lime-green supports help hold the electronics in place. Shimmering metal that looks like aluminium foil catches the industrial lights. It could be a space station. Or a half-billion-dollar piece of art.
We can almost touch it. It’s so close and so big and so everywhere that it’s hard not to be awed, overwhelmed and a bit intimidated. I can do little more than stare.