A joint Fermilab/SLAC publication

Burst of LHC collision data a welcome birthday gift


After being blasted in the media for machine problems last year just hours after its turn on and then a power outage this year caused by a rogue bird dropping a baguette onto electrical equipment, physicists have been eager to prove to the world the Large Hadron Collider isn’t a lemon.

This week they did just that.

Attending a symposium at Fermilab in honor of theorist Chris Quigg's 65th birthday, ATLAS experiment co-spokesperson Fabiola Gianotti ended up talking about brand new ATLAS data. It wasn't planned that way, but a burst of beam and steady stream of more than two hours of data in the wee hours before the talk provided a unique and excellently timed opportunity.

Her excited, and proud, utterance to the crowd that they would get "no simulations, no Monte Carlo, just data" in her talk brought booming applause.

On December 8, the four large LHC experiments recorded 3 minutes of world record-breaking energy collisions of 2.36 TeV, the maximum energy threshold for operation in 2009. But the December 14 rush of data was the first time that LHC experimenters got a sustained amount of data at energy levels beyond that of the Tevatron. Monday's data run was the real test for the detectors and collaborators, proving the detectors' quality constructions and the collaborations' speedy communication systems. Within a couple hours of run time, ATLAS was able to record 1200 events and CMS 3600 events.

“It took more than 20 years of effort by the worldwide physics community to get to this fantastic moment,” she said. “I think this is a good sign that things are under control.”

The success took on extra meaning because Quigg has been involved in much of the theory work that defines the LHC research program and he wrote the book Gauge Theories of the Strong, Weak and Electromagnetic Interactions that many physicists, including Gianotti considered “a bible” during their early research years.

“Thank you for this wonderful birthday present and my respect and gratitude to everyone on ATLAS and at CERN for making this happen,” Quigg told Gianotti.

Jet event from ATLAS Dec. 14 at 2.36 TeV

Jet event from ATLAS Dec. 14 at 2.36 TeV

The large dataset points to a finely tuned machine and well laid out data distribution system.

Both experiments have analyzed a multitude of data at the lower 900 GeV energy level and found it agrees with Monte Carlo simulations, meaning the machine is tracking and recording data as expected.  By the time of Gianotti’s talk just seven hours after the 2 a.m. new record breaking collisions, ATLAS also had analyzed some of new data, finding similar agreement.

Physicists were able to record their first photon to electron and positron conversion, the first muon candidates, and to measure the total missing transverse energy, a key sign that researchers are able to mitigate background signals.

Collaborators on ATLAS and CMS have been extremely fast in culling data from their detectors at both low and high energies as well as sending it to universities across the globe through a tiered system of computer grids.

“In some cases, we got results in a few hours,” Gianotti said. “The enthusiasm and team spirit in the collaboration is extraordinary.”

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