Picture yourself as part of a team that is given the task of learning the mechanics and assembly of a car, except that you are not allowed to directly observe it or take it apart by hand. What would you do? After a few minutes of thought, some common ideas might be to use sonar to learn the overall shape and density of the car, or infrared to determine the heat sources. Suddenly, a voice from the back of the room suggests that you bang it against something and see what flies off.
While this example might seem a little crude, it does exemplify the underlying process scientists use to examine the minute pieces of our universe. Around 13.7 billion years ago, a collision occurred that changed the very structure of the universe. While we cannot begin to know the state of anything before this time, science is beginning to unravel the mystery of the very particles that now make up our existence.
In less than 10-22 seconds after this “big bang,” quarks and electrons were created, which quickly grouped together to form protons and neutrons. It is impossible to conceive the amount of energy needed to produce this type of collision, or the heat expelled from it. However, physicists at the Large Hadron Collider (LHC) in Geneva, Switzerland are reaching energies equal to those just moments (10-15 seconds) after the big bang.
Let us go back to the car example for one moment. In the first experiment, you decide to speed the car up to 30 mph, and crash it into a wall. A few major parts here and there may come off, but nothing too exciting. So the next time you decide to crash the car at 100 mph. Now pieces are flying everywhere, allowing you to start reconstructing the overall makeup of the car. For your last experiment, however, you decide to speed the car up as fast as possible, and crash it at 500 mph. At this speed, the entire car will be demolished, leaving you with pieces that you never knew existed before, giving a detailed explanation of the overall makeup of the car.
The same holds true for collisions happening in the LHC. Physicists there were able to produce collisions that were never possible before, and this opened up a whole new range of opportunities for discovery. One of these particles that became feasible to discover due to the new capabilities of the LHC was the Higgs boson particle.
The Higgs particle has been a missing link in Standard theory, which models the relationship between three of the four forces that govern our universe – strong, weak, and electromagnetic – and the sub-atomic particles that we know of. One of the main flaws with this model is that it does not account for where particles acquire their mass. The Higgs boson is believed to be the connecting piece, as it gives all particles their mass.
Sau Lan Wu, professor of physics at UW–Madison, described the Higgs field in a lecture given at the Wisconsin Institutes for Discovery. She said to imagine the Higgs field as a room full of scientists standing around and talking to each other. At one point, a random person walks into the room and through the crowd of people, quietly weaving his way without making too much of a fuss. Suddenly, Albert Einstein walks into the room. As soon as he begins to try and walk through the crowd of people, all of the scientists converge around him, forcing him to slow down.
You build this big machine and you hope that all your theories are right and all your predictions are correct and say, ‘It should be here’Wesley Smith
Similarly, Higgs particles (scientists) are all around us, and while some of them, like that first random person, can move through the Higgs field without attracting much attention from the Higgs particles, others are extremely attractive, and become much more massive as the Higgs particles begin to attach onto them.
However, the major problem in detecting Higgs particles comes from its rapid decay rate, something to the order of 10-22 seconds. So the big question then becomes, how do you detect something that disappears almost instantaneously? The answer: you find the rare pattern of particles that it decays into. Enter the CMS and ATLAS experiments happing at the LHC.
The search for this missing boson particle was split into two different teams at the LHC. They each were independently tasked to find the Higgs particle using two different types of detectors. I spoke with Wesley Smith, professor of physics at UW-Madison, about his involvement on the CMS team, as well as UW-Madison’s overall role in the project.
Inside the CMS detector, beams of energy collide every 25 nanoseconds, resulting in around 20 proton-on-proton collisions. This adds to about one billion collisions per second. With such a large number of collisions to be examined, a trigger system was designed to sift through the billions of collisions that just record background radiation and pick out the important results. This is a two-stage process, where the first stage eliminates about half of the recorded collisions that were not important, and the second stage chooses around 400 of those events to be further examined. All in all, in only one in a trillion events is a Higgs particle observed.
Smith was directly involved in designing the trigger system for the CMS project, as well as the construction and commission of it. This large project included about 100 physicists and engineers from tens of different countries, as well as a conglomeration from the University of Wisconsin. Speaking about the role UW-Madison had played on the ATLAS and CMS teams, Smith said, “[The University of Wisconsin] was not just participators, but played a leading role in this project.”
All of these efforts culminated on July 4th, when CERN announced the discovery of a “Higgs-like particle.” Further experiments will be necessary to examine the characteristics of this new particle, but they reported that the probability that the particle they discovered was instead random background radiation to be one in three million, or confident out to five standard deviations.
When I asked Smith about this tremendous breakthrough, he said, “You build this big machine and you hope that all your theories are right and all your predictions are correct and say, ‘It should be here’, but now we start the work.” He described it as a new era for physics, saying that, “The actual discovery that it’s there is extremely exciting, [but] the reason to look for it was to do all the science with it.”
In the end, Smith and the rest of physicists are left with exactly what they wanted, more questions to be answered. While this was a monumental discovery, it opens the possibilities for decades more research to be done, research that is helping us to define the very nature of our universe. And while this may seem daunting to us, for Professor Smith it is just another day at work.