Tuesday, December 20, 2011

In the thick of it at the Large Hadron Collider

1112304_36.jpgIn the two weeks leading up to last Wednesday the blogosphere was abuzz with rumours that on December 13, 2011 CERN was going to announce the discovery of the Higgs boson - the elusive particle thought to endow all other particles with mass. Ten days prior to the date, members of CERN had received an internal memo stating that a seminar was to be held, during which the two general purpose experiments, CMS and ATLAS, would report their findings.
Being a member of CMS, I knew well the results we were going to unveil, but I was agog with curiosity as to what ATLAS would announce (I had some idea thanks to intelligence-gathering from my ATLAS friends - something along the lines of: How Bigg is your Higgs? It was all very cloak and dagger and therefore, thoroughly exciting.)
I attended the event via a live webcast from Princeton University, where I have been working since September. A sizable group of us had gathered at 8am, fortified with bagels and coffee, in the hope of witnessing history. There was a palpable feeling of excitement in the auditorium as the seminar began with a presentation from the ATLAS spokesperson, Fabiola Gianotti. This was followed by one from the spokesperson of CMS, Guido Tonelli. Both presented their respective experiments' results on the search for the Higgs. As with any statistical analysis, the results were somewhat open to interpretation but they were best summed up by the Director General of CERN, Rolf Heuer: "These are preliminary results, we're talking small numbers. The window for the Higgs mass gets smaller and smaller but it is still alive. We have not found it yet. Stay tuned for next year."
The broadcast was also exciting for me on a more personal level. Until this summer, I had been at the heart of the action in Geneva. I am still working on the CMS experiment but now do so from thousands of miles away at Princeton. During the webcast when the camera panned out to the audience, I saw many of my CMS colleagues, several of whom I consider friends. I love being at Princeton, teaching the next generation of doctors and scientists but I sometimes miss the experiment and my collaborators at CERN. The fact that I couldn't be with them in person to share this momentous day made me feel rather nostalgic. Plus, the last time there had been such excitement at CERN, back in March 2010, I had been right in the thick of it...
It was the first time we'd witnessed collisions of protons on to protons at the LHC at 7 trillion electron volts, the collision energy the machine will run at until it gets upgraded in 2013. Some of my colleagues had been working for up to 15 years, perhaps even longer, to reach that point. And some of us were complete newbies. I had joined the CMS experiment five months earlier and that day, was fortuitously tasked with the integral job of monitoring the quality of the data captured by the detector.
While many might consider data quality monitoring (DQM) to be a rather mundane task, I beg to differ. The LHC experiments have to catch problems within the highly complex detectors as they arise, on the fly. Bear in mind, "on the fly" means up to 40 million collisions per second. A broken detector means junk data. For us, junk data means no physics and for the taxpayer, it means a waste of money. We take this seriously and DQM is a way of keeping an eye on every tiny bit of the detector, every second it is running. This allows us to fix problems as they occur, sometimes even without interrupting the flow of data. Cool stuff.
Being responsible for the DQM meant that I got to be in the CMS control room on March 30. As on December 13, the world media attention was on us. It was effectively the first opportunity to test the full machinery of the LHC at 7TeV, as well as that of all the experiments. Additionally, after the accident in late 2008, the onus was upon us to show the world that the expense of the LHC and the huge scientific effort put into it weren't for naught. So there was a lot at stake; we had to get it right.
The LHC had been circulating proton beams in the machine all morning so we knew collisions were imminent. About 70 of us watched with bated breath, cramped into the constricted space around the display monitors. By that time, I had been in the control room for 36 hours straight; many had been there even longer, making sure all systems were ready to take data the instant it arrived.
It was at about 1pm when the first proton-proton collision burst onto the event display screens - showing clear tracks and energy deposits left by the collision debris. It looked like fireworks, resplendent in color and light. A short-lived second later, came the second burst, this time human. It was a burst of sheer and utter joy, expressed by ebullient applause and cheers.
It had been quite a 36-hour ride - the anticipation, the tension, eventually the exhilaration and joy, and finally the exhaustion. It felt like a collective delivery of a baby! The sheer hard labour by the LHC machine group and all those working on the experiments had paid off. Some of us celebrated with the requisite cigar.
When I got home, it was a pleasant surprise to find congratulatory emails from many parts of the world - France, Germany, Italy, India and the UK to name just a few. My father, in the US, had watched the whole thing live on CNN. It was touching to learn that the world was engaged and had been able to share the moment.
Particle physics is an experimental science; while the theorists spin and weave their theories with reason and insight, we are the arbiters of what that reality might be. Have we found the Higgs boson? Not quite, but we are close. We will continue to sift through the data and collect more, searching for the Higgs and other signs of exciting new physics. As Rolf Heuer says, stay tuned! 


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