Underneath a few quiet little towns on the French-Swiss border sits the Large Hadron Collider (LHC). It’s here that we ask the biggest questions about the smallest and most fundamental things. The LHC is a machine designed to recreate the conditions of the Universe fractions of a second after the Big Bang, to look for answers to questions like “what is mass?” and “just how strong is gravity?” This is the first time in human history we have a machine powerful enough to test the amazingly precise Standard Model of physics at the mysterious TeV-scale, and I get to analyse the first LHC data for my PhD thesis. That’s why, for my birthday last November, all I really wanted was LHC collisions.

We live in a cold Universe, which is getting colder all the time.  The average temperature of outer space today, roughly 15 thousand million years after the Big Bang, is -270.4°C (2.75 K). At this temperature, we have the planets, stars and galaxies we have been looking up at for all of human history. According to Big Bang theory and the cosmological evidence supporting it, when the Universe was a little younger, around a thousand million years old or so, the average temperature was closer to -255.15°C (18 K), but it was still cold enough for atoms to come together to form stars and stars to come together and form galaxies. When the Universe was a mere 300,000 years old, the average temperature was closer to 5,726.85°C (6000 K). This is where it starts getting difficult to recognize the universe we call home. The Universe at this tender age is too hot for complex structures to form; heating up the matter in the Universe that much meant we would have very few stars, let alone galaxies. When the Universe was just three minutes old, the average temperature was 109 K. That’s too hot for protons and neutrons to stay close enough to each other for long enough to make the atoms we know and love.

This is where things get interesting: when the Universe was just one second old, protons and neutrons were starting to form. Before that, between 10^-32 seconds (less than a billionth of a billionth of a billionth of a second) and one second after the Big Bang, or between 1027 K and 1010 K, most of the universe was just a superhot plasma, or a soup of quarks and gluons. As we go up in temperature and back in time, we delve deeper into the understanding of the early Universe and its evolution to today. 

In the LHC, proton beams are accelerated to 99.9999% of the speed of light and collide at an interaction point ten times smaller than the eye of a needle, recreating the extremely hot conditions in those first few fractions of a second after the Big Bang. Detectors the size of a cathedral nave, made up of hundreds of millions of individual readout channels, will see tens of millions of collisions per second and look for the most fundamental constituents of matter. Rooms full of sophisticated electronics reject 99% of those events, and a data acquisition system built to handle ultra-fast data transfer rates can read out all the hundreds of millions of channels once every 25x10-9 seconds. In other words, 14,000 collisions happened in one of the main LHC detectors the last time you blinked, and less than one interesting event was recorded. I work on one of the LHC detectors, ATLAS, and specifically on one of the ATLAS subdetectors, the SCT. The SCT is the second-closest subdetector to the LHC beam pipe. A six million channel semi-conductor tracker made up of 4088 modules with 1536 strips of silicone per module, the SCT was built and tested in large part at Cambridge, and the Cambridge High Energy Physics (HEP) group still has a lot of effort invested in its smooth operation. The SCT measures the position of particles coming from LHC collisions to a precision on the order of 10-5 metres. Using this information, we can reconstruct the track of the particle from the beam pipe and through the other ATLAS detectors. From the curvature of the track, we know the particle’s momentum. Once we combine the information from all the subdetectors and know how much energy there is in all the final state particles from a collision, we can reconstruct the things that decayed early on, like the really exotic matter we are interested in finding: the infamous Higgs boson or, my favourite, semi-classical mini black holes. 

In the week leading up to the 2009 restart in late November, I was at CERN. Months before, I had bet a bottle of whisky that I would have LHC first collisions for my birthday on the 25th of November. When I arrived at CERN on the 16th to be on-call for more data-taking with cosmic rays, it looked like I would lose my bet, but on Tuesday morning everything changed. The word from the accelerator division was that the beam injection tests were moving faster than expected.

Suddenly, the ATLAS control room was flooded with people who had been waiting and working most or all of their careers for this day. After three days of rumours and wild excitement, by Friday night, the 20th, the control room was full. No-one could risk leaving and missing the first beam shooting past ATLAS for over a year. I sat with the other SCT experts in the satellite control room, running back and forth to the main ATLAS control room and waiting for the beam to make its way around to us. When we saw the first splashes and got to wash down our takeaway pizza with Champagne in plastic glasses, I knew it was going to be a good year, but it still seemed like I was going to lose that bottle of whisky; getting beams to collide in that tiny interaction point was going to take a while.

But two days later, something amazing happened. I stopped by the ATLAS control room on Sunday afternoon and the run controller told me that the accelerator division was ready to try collisions. I couldn’t believe it, but by Monday night it was true; for the second time in three days the Champagne was flowing, the control room was full, and we had the biggest particle collider in the world working beyond our wildest expectations. On my birthday I sat in the basement of our favourite Italian restaurant near CERN and called three cheers for the first LHC collisions. I couldn’t have asked for a better present.

At CERN, we are creating states of matter that haven’t been around in any substantial amount for 15 thousand billion years and measuring fundamental constituents of the Universe that haven’t been around to measure since the Universe began. J J Thomson needed 13 volts to free the electron from the atom.  It took 100 million volts to split the atom into protons and neutrons. The LHC will be smashing protons together with 10 thousand billion volts this year. Thousands of scientists in hundreds of countries will be working together to search for new physics in the highest energy collisions in the biggest experiment ever built, and the HEP group at Cambridge will be right on the cutting edge. I can’t wait to see what we’ll be toasting next November.