Large Hadron Collider restarts after 2 years of maintenance

Scientific Method / Science & Exploration

Large Hadron Collider restarts after 2 years of maintenance

"Operators will check all systems before increasing energy of the beams."

by Cyrus Farivar - Apr 5, 2015 9:57am EDT

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Particle "splashes" occur when protons hit the collimator, resulting in a shower of particles.

CERN

Further Reading

A rare LHC tour—avoiding radiation to see scientific history up close

With hardware still disassembled for service, Ars snuck underground to see LHC up close.

After being shut down for two years, the Large Hadron Collider (LHC) is back online, CERN announced Sunday. "Today at 10:41am [local time], a proton beam was back in the 27-kilometer ring, followed at 12:27pm by a second beam rotating in the opposite direction," the European Organization for Nuclear Research reported in a statement.
"These beams circulated at their injection energy of 450 GeV. Over the coming days, operators will check all systems before increasing energy of the beams."
The LHC is set to ramp up its energy capacity over the coming months, reaching 6.5 Tera-electron Volts (TeV) per beam.
Ars Science Editor John Timmer toured the facility, which straddles the French-Swiss border, while it was under repairs:

The two general purpose detectors are a bit like an onion, with a layered structure. The inner-most layers house silicon-based particle detectors, which have very high spatial resolution. Outside of those sits a calorimeter, which measures the energies carried by electrons and photons. Beyond that, magnets cause charged particles to take a curved trajectory through the hardware, aiding in identification. Large areas of the detector are iron plates that help shape the resulting magnetic fields.

Further Reading

Large Hadron Collider shuts down for two years of upgrades

Renovations will allow LHC to reach its full design energy, improve detectors.

Next comes the hadron calorimeter, which measures the energy carried by particles composed of quarks—protons, neutrons, and their more exotic relatives. Muon detectors make up the outside, and these can be kept at some distance simply because muons are relatively stable particles (their 2.2 microsecond half-life is stretched out by relativity, since they're moving quickly relative to the detector hardware). By tracking particles through the various detectors, it's possible to reproduce the tracks of everything that comes out of a collision and quickly figure out something about the physics. This is done at the detectors themselves, which have "triggers" that dictate whether collision data gets saved or not, based on whether it represents familiar behavior or something potentially interesting. Out of roughly 40 million collisions a second, the triggers ensure roughly 100 are kept, preventing a flood of data from overwhelming the entire system. Even with this heavy filtering, the LHC saves 15,000TB of data each year.
But aside from the Higgs, interesting phenomena have been hard to come by. Ohio State University's Carl Vuosalo, a post-doctoral researcher, is part of what's called the "exotica working group," a team looking for previously undiscovered particles. Sadly, there haven't been any hints of anything, he told Ars.
"It's a bit scary that all we have is the Higgs," he said.
His hope is that we just haven't seen enough collisions yet—something the upgraded collider is intended to fix.