Over the past few days, there’s been a lot of hype over something called the Higgs boson, popularly known as the “God particle”. Yesterday, physicists at CERN, the European Organization for Nuclear Research, presented results that strengthen the case for the existence of the Higgs boson, much to the excitement of the scientific community. Before we get into why this research is so groundbreaking, let’s back up and try to answer the question most of us are probably wondering – what exactly is the Higgs boson???
Simply put, the Higgs boson gives other particles mass. It is the missing puzzle piece to the Standard Model of particle physics, which explains the interactions between subatomic particles. There are seventeen particles in the Standard Model, as depicted below.
Since its development in the 1970s, discoveries of the bottom quark (1977), W and Z bosons (1983), the top quark (1995), and the tau neutrino (2000) have strengthened the case for the Standard Model. The theory describes three fundamental interactions:
- Electromagnetism between charged particles, via the exchange of photons.
- The strong nuclear force, which binds atomic nuclei together through gluon interactions.
- The weak nuclear force, which governs radioactivity and hydrogen fusion through interactions of W and Z bosons (and possibly the Higgs boson).
The Higgs boson remains the only predicted elementary particle within the Standard Model that continues to elude scientists to this day. If physicists prove its existence, it would not only make the Standard Model more plausible, but would explain why other particles have mass.
What exactly does it mean for the Higgs boson to give mass to other particles? The following analogy is commonly used to describe the phenomenon: Imagine a party with a room full of physicists. They are all quietly partaking in the usual conversation topics – you know, string theory and black hole thermodynamics – when someone starts the rumor that the Higgs boson has been discovered. This rumor causes people to cluster into groups and chat excitedly about the news. In this analogy, the room filled with physicists is like the Higgs field, a lattice framework that fills the universe, and the clusters of scientists are the Higgs particles.
Scientists believe that when a particle passes through the Higgs field, it obtains mass. To understand how this works, re-imagine the room full of physicists (i.e. the Higgs field). This time, in walks a reincarnated Albert Einstein. As he moves through the room, clusters of physicists gather around him. By attracting a crowd, Einstein acquires momentum – an indication of mass. Because he has gained momentum (i.e. a crowd of admirers), it is harder to slow Einstein down once he is moving, and harder to get him to start moving once he has stopped. This is how the Higgs mechanism works — just as Einstein acquires momentum while moving through the physicists’ party, a particle gains mass while moving the Higgs field. Similarly, Higgs bosons interact with particles moving through the Higgs field just as the scientists at the party interacted with Einstein when he entered the room.
In this scenario, high-profile scientists are likely to attract larger crowds. These are the Isaac Newtons and Stephen Hawkings of particles — massive giants, which acquire more momentum as they move through the the Higgs field. Less famous scientists will cause less of a disturbance — these amount to particles with less mass.
Another way to think of the Higgs field is to think of it as a muddy field, as described by Joel Achenbach in this National Geographic article. As different particles trek through the mud, they accumulate different amounts of mud. Massive particles, such as top quarks, have big boots that pick up a lot of mud. Electrons, which have extremely small masses, wear little shoes that hardly gather any mud. Massless photons don’t wear shoes at all – like phantoms, they just glide over the mud.
In addition to explaining how particles acquire mass, the discovery of the Higgs boson could also explain why W and Z bosons are some of the most massive particles known, while photons are massless. Photons, carriers of electromagnetic forces, are shown to have no mass. Meanwhile, related W and Z bosons, which govern the weak nuclear force, are shown to have enormous masses. This raises mathematical inconsistencies in the Standard Model. The existence of at least one other particle, such as the Higgs boson, could account for this discrepancy.
There’s a lot at stake in this search for the Higgs boson. Its discovery could confirm that we hold a basic understanding of how the universe works. In order to observe the Higgs boson, researchers slam particles together at mega-high speeds in CERN’s $6.5-billion Large Hadron Collider (LHC), housed in a tunnel hundreds of feet underground near Geneva, Switzerland.
In smashing particles together, the physicists hope to create a Higgs boson. The higher the energy of the collision, the more likely it is to make a Higgs particle. Once the Higgs is created, it lasts for a fraction of a second before decaying into other particles. Therefore, to determine whether a given collision produced a Higgs particle, researchers must look for evidence in the decay products.
Now, two independent research teams, ATLAS and CMS, report that they are one step closer to finding the evasive Higgs particle, or set of particles. Both teams involve collaborations between around 3,000 scientists and engineers from around the world. Their latest data suggest that, if the Higgs boson exists, its mass most likely falls within the ballpark of 115-130 billion electron volts (GeV), which is on the lower end of the mass spectrum for particles produced in the LHC. These results come from some 500 trillion proton-proton collisions performed in the LHC. The ATLAS team presented a range of 115-130 GeV, and the CMS team a range of 117-127 GeV, both to a high degree of confidence. Furthermore, there is evidence for the mass falling specifically between 124-126 Gev, which is within the range predicted by the Standard Model.
That both teams have produced such narrow parameters independently of one another bodes well for more promising results in the near future. Indeed, researchers say that, based on their current trajectory, they should be able to unequivocally confirm or refute the existence of the Higgs boson by the end of next year.
Moreover, this mass range holds implications for future research in particle physics, supporting theories that expand upon the Standard Model and predict the existence of more particles still. For example, a Higgs boson mass of 124-126 GeV works for the theory of “supersymmetry”, which posits that all Standard Model elementary particles have a corresponding “superpartner” that differs by half a unit of spin. These superparticles have not yet been observed, but scientists at CERN have been searching for the partner of the W boson, and experiments at Fermilab, in Illinois, seek to find the partners of quarks and gluons. One such superparticle might make up “dark matter”. Unraveling the mystery of supersymmetry could also help explain why gravity is much weaker than other natural forces.
Further study into the Higgs boson can provide insight into other questions, such as why known particles have specific masses. Future research might look into mechanisms of production and decay for the Higgs boson. For now, scientists continue to eagerly await results either proving or debunking the existence of the fabled Higgs boson – the tiny particle that could hold the answers to so many of our questions about the physical world.