LHC image via CERN

It's back. Finally. The Large Hadron (LHC) is one of the most powerful scientific tools ever constructed. Ultimately, it stands as the most powerful particle accelerator in the world.

Why is it so special?

Because of its extreme energy output, the LHC allows us to hurl subatomic particles together at amazing speeds, generating conditions similar to what existed shortly after the Big Bang. As a result, the LHC is (potentially) our best hope for solving some of our greatest scientific mysteries, such as figuring out some of the fundamental building blocks of the universe, investigating the elusive nature of dark matter, and maybe even uncovering hidden dimensions in our universe.

It was slated to come back online last month (March, 21015); however, it ran into some problems. Unfortunately, it seems that a little piece of metal fell into the system and created a short circuit.  This delayed the restart for a few weeks because, well, it's not easy to locate a tiny piece of metal in a 17 mile (27 kilometer) ring of helium-cooled magnets.

But at last, after more than two years of intense maintenance, the LHC is back in operation. Today, at 10:41am, a proton beam made its way around the track for the first time in some 700 days.

The technical work done on the LHC was what CERN calls, "a Herculean task." Some 10,000 electrical interconnections between the magnets were consolidated, and the beams were restructured so that they will produce more collisions. The increase in collisions is possible because the updates bunched the proton releases closer together, so the time separating bunches was reduced from 50 nanoseconds to just 25 nanoseconds.

What's more, because of the work that was done over the course of the last two years, the LHC will be operating at unprecedented energy. In fact, it will be working at almost double that of its previous run, which was just at 6.5 TeV per beam. Scientists assert that 13 TeV proton-proton collisions are expected before summer.

"Operating accelerators for the benefit of the physics community is what CERN’s here for,” said CERN Director General Rolf Heuer. "Today, CERN’s heart beats once more to the rhythm of the LHC.” "The return of beams to the LHC rewards a lot of intense, hard work from many teams of people," said Head of CERN’s Beam Department, Paul Collier. "It’s very satisfying for our operators to be back in the driver’s seat, with what’s effectively a new accelerator to bring on-stream, carefully, step by step.”

So the LHC isn't quite up-to-speed just yet. So far, it is only operating at 450 GeV. Scientists are going to run some tests to ensure smooth operations over the coming days before increasing energy of the beams to their full capacity.

"After two years of effort, the LHC is in great shape," said CERN Director for Accelerators and Technology, Frédérick Bordry. "But the most important step is still to come when we increase the energy of the beams to new record levels.”

So, what exactly is on the plate for this run? CERN asserts that the machine (and the scientists operating it) are going to be rather busy:

The Brout-Englert-Higgs mechanism, dark matter, antimatter and quark-gluon plasma are all on the menu for LHC season 2. After the discovery of the Higgs boson in 2012 by the ATLAS and CMS collaborations, physicists will be putting the Standard Model of particle physics to its most stringent test yet, searching for new physics beyond this well-established theory describing particles and their interactions.

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