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The higgs, the history, and the grid

Event characteristics expected from decay of Standard Model Higgs boson to a pair of Z bosons.
Event recorded with the CMS detector in 2012 at a proton-proton center-of-mass energy of 8 TeV. The event shows characteristics expected from the decay of the standard model Higgs boson to a pair of Z bosons, one of which subsequently decays to a pair of electrons (green lines and green towers) and the other Z decays to a pair of muons (red lines). The event could also be due to known standard model background processes. Top image courtesy of CMS experiment.

On the morning of the 4 July 2012, from a restaurant screen at CERN, I watched the announcement of the results from the CMS and ATLAS experiments at the Large Hadron Collider (LHC) on the restaurant screens. These two experiments have been competing in the hunt for the Higgs boson particle, the missing piece from the standard model jigsaw. The announcement happened simultaneously at CERN (a bit further away on the site from where I was sitting) and at ICHEP, in Melbourne (a long way from where I was sitting). The result was a discovery of a new particle consistent with the Higgs boson.

As an ex-CERNoise (as they call themselves), I was particularly interested in the announcement. I joined CERN in 2008 to run communications for the Enabling Grids for E-sciencE project, the grid computing infrastructure project that is now the European Grid Infrastructure (EGI). It's a collaboration with the World LHC Computing Grid (WLCG), which provides the distributing computing infrastructure that processes petabytes of data streaming from the four main LHC experiments.

It was good to hear a mention of the contribution that computing has made to this momentous global achievement.

Joe Incandela, spokesperson and physicist, of CMS and Fabiola Gianotti, spokesperson and physicist, of ATLAS said by reducing the time taken to process the individual events results can be announced quicker. No small achievement when the US Tevatron is snapping at their heels.

A little bit of history

While I was at CERN, the LHC started up in September 2008 to astonishing media and global interest; then two short weeks later a faulty electrical connection between two of the accelerator's magnets resulted in a year-long shut-down.

The mood at CERN switched from wild excitement, in physicist terms, to one of pragmatic problem-solving and a collective 'rolling up' of sleeves. Just over a year later, in November 2009, the LHC came back more stable and reliable than before, and has since run pretty much flawlessly, ramping up energy to today's record breaking eight tera-electron volts (TeV).

Physicists are very certain of the results

This diagram shows the new Higgs-like particle appears as the excess of around 126.5 GeV.
Mass distribution for the two-photon channels. The strongest evidence for this new particle comes from analysis of events containing two photons. The smooth dotted line traces the measured background from known processes. The solid line traces a statistical fit to the signal plus background. The new particle appears as the excess around 126.5 GeV. The full analysis concludes that the probability of such a peak is three chances in a million. Top image and front page image courtesy ATLAS experiment.

Back to the morning of 4 July 2012, I happened to be on site in time for the joint announcement from CMS and ATLAS. I watched the auditorium fill up with students, physicists, and a good selection of the world's media. As Peter Higgs arrived to take his seat a round of gentle applause broke out. After a bit of milling about, a rather nervous, Joe Incandela took the podium to run through his slides.

The punchline came out clearly at the end of Incandela's talk: We have found a new boson with mass of 125.3 GeV, + or - 0.6, at 4.9 standard deviations or 'sigma'. A loud and extended round of applause in the auditorium followed. To put it into context, one sigma means the results could be random fluctuations in the data, three sigma counts as an observation and a five sigma result is a discovery. Five sigma means one experiment in three million would see a signal this strong in a universe without the Higgs - so extremely unlikely.

However, the CERN press release reminded us that the results presented today are preliminary, the data from 2012 is still under analysis. The complete analysis is expected to be published around the end of July.

Fabiola Gianotti of the ATLAS experiment followed. "It's tough to talk second, because all the clever things have been said." She then went on to prove that this wasn't the case with a highly technical presentation (despite the comic sans font, which did not go down well online). However, when she got to her conclusion more spontaneous applause started up. The ATLAS experiment results echoed the CMS results - 126.5 GeV for a boson at 5.0 sigma. Gianotti said, "It is very nice for it to be at this energy because we can measure it here at CERN in abundance - thanks nature."

Rolf Heuer, the director general of CERN had a final comment. "It's been a global effort, a global success. It has only been possible because of the extraordinary achievements of the experiments, infrastructure, and the grid computing," Heuer said. "We have a discovery; we have a new particle consistent with the Higgs boson. It's a historic milestone today, but we are only at the beginning. We can all be proud and it has global implications for the future. I think we can be very optimistic." Peter Higgs added his congratulations and announced himself "extraordinarily impressed". I suspect he isn't alone.

A highly significant day for CERN, for the hunt for the Higgs, and for me, as its pretty satisfying to be at CERN, both for the LHC start up, and the announcement of the strongest hints of the famous particle so far. It's 28 years since the idea of the LHC was first suggested at a physics meeting, more than half my life time ago - I feel very lucky to have been here at this time to see the results of the work of over 20 years, thousands of people worldwide, not to mention six director generals - congratulations.

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