Knocking on Heaven's Door - Lisa Randall [83]
Not too long afterward, a modest acceleration was applied to create 1.18 TeV proton beams, the highest-energy circulating beams ever. Only a week after the first LHC collisions, on November 30, these higher-energy protons collided. The net center of mass energy of 2.36 TeV exceeded the highest energies ever achieved before, breaking Fermilab’s eight-year-old record.
Three LHC experiments registered beam collisions and tens of thousands of such collisions occurred over the next few weeks. Those collisions won’t be used to discover new physical theories, but they were incredibly useful for determining that the experiments in fact worked and could be used to study Standard Model backgrounds—events that don’t indicate anything new, but could potentially interfere with real discoveries.
Experimenters everywhere shared the satisfaction of the LHC’s having reached record energies. Remarkably, the LHC did it just in the nick of time—the machine had been scheduled to shut down from the middle of December until March of the following year, so it was either December or several more months’ delay. Jeff Richman, a Santa Barbara experimenter who works on the LHC, joyfully shared this fact at the dark matter conference we were both attending, since he had made a bet with a Fermilab physicist as to whether the LHC would achieve higher energy collisions than Fermilab’s Tevatron before the close of 2009. His cheerful demeanor made it clear who had won.
On December 18, 2009, the wave of excitement was temporarily suspended when the LHC shut down after this commissioning run. Lyn Evans concluded his talk discussing the plans for 2010, when he promised a sizable increase in energy. The plan was to go up to 7 TeV before the end of the year—a substantial increase in energy over anything before. He was enthusiastic and confident—as turned out to be justified when indeed the machine came back on line at this higher energy. After so many ups and downs, the LHC was finally working according to plan. (See Figure 28 for an abbreviated timeline.) The LHC should continue to run through 2012 at 7 TeV, or possibly a bit higher energy, before shutting down for at least a year to prepare for raising the energy to as close as possible to the LHC’s 14 TeV target. During this and the following runs, the LHC will also try to raise the intensity of the beams to increase the number of collisions.
Given the smooth operation of the experiments and machines after turning back on in 2009, Lyn’s closing words for his talk resonated with the audience: “The adventure of LHC construction is finished. Now let the adventure of discovery begin.”
CHAPTER TEN
BLACK HOLES THAT WILL DEVOUR THE WORLD
For quite some time physicists had been looking forward to the LHC turning on. Data are essential to scientific progress, and particle physicists had been starved for high-energy data for years. Until the LHC provides answers, no one can know which of the many suggestions for what might underlie the Standard Model are on the right track. But before this book explores several of the more intriguing possibilities, we’ll take a detour in these next few chapters to consider some important questions about risk and uncertainty that are critical both to understanding how to interpret the LHC’s experimental studies and to many issues that are relevant in the modern world. We’ll begin this excursion with the topic of LHC black holes, and how they just might have received a bit more attention than they deserved.
THE QUESTION
Physicists are currently considering many suggestions for what the LHC might ultimately find. In the 1990s, theorists and experimenters first got excited