Now that we've "found" the Higgs boson, what are we going to do with it?
Actually, physicists at the Large Hadron Collider (LHC) at the European Center for Nuclear Research (CERN) near Geneva, Switzerland, still have a lot of work to do before the Higgs is fully explored and its properties measured. After all, as the lead scientists of the CMS and ATLAS detectors of the LHC half-cautioned at the historic July 4 announcement , they've seen a preliminary signal in their data that suggests they've found a boson at around the predicted energy for a standard Higgs boson.
But what if another, unpredicted particle is parading as a Higgs boson ? What if there's a whole family of Higgs'? But most importantly, does this mean physics can pack up its textbooks and declare victory over space and time? The Standard Model of physics appears to be complete; no need to build any more expensive particle accelerators!
As it turns out, there are a myriad of answers to these questions, but in response to anyone who thinks a Higgs discovery is the end of physics, think again. We've barely even started.
But before we get stuck into the big question - what the heck does it all mean? - we have to take a little ride into a subatomic world where electronvolts meet superconducting magnets and briefly explore, with the help of science analogies, what a Higgs boson is and why it's so important that physicists track it down.
The Standard Model cake recipe
You may have heard the explanation that the "Higgs mechanism" is important because it "gives stuff mass". While this is true, it falls woefully short of explaining just how awesome the Higgs mechanism really is. But before we dive into its awesomeness, like any Higgs explainer we need to quickly skip through how the "Standard Model" works.
The Standard Model is a framework by which we understand how the Universe functions - think of it like a recipe for a cake that includes all the ingredients of matter and all forces in nature (except gravity, but more on that later). The Standard Model helps us understand what ingredients there are inside any given atom. Using the rules of the Standard Model, we know what would happen if we fused two atoms together, for example. Likewise, we can predict which particles will be created when we smash two protons head-on really hard. This is all because the Standard Model was born from decades of theory and robust experimental physics.
So far, the Standard Model has served us well, but for decades physicists have been blighted by the fact that even in its basic form, the cake recipe was missing an ingredient. The many experimental physicists who helped find the components of Standard Model have, over time, seen all the quarks (up, down, charm, strange, top and bottom), leptons (electron, muon, tau, electron-neutrino, muon-neutrino and tau-neutrino) and bosons (photon, gluon, Z and W) get discovered one by one. Each component seemed to "fit" in the Standard Model recipe. But one component has remained elusive: the fundamental mechanism that allows all these particles to have a weird, yet essential characteristic called mass. It's as if we had a cake, and the recipe says there must be flour in it, and yet no matter how hard we tried, we couldn't find a grain of flour in the mix.
A question of mass
OK, so the Higgs boson is the smallest component (or "quanta" if you want to get all physics-y) of the Higgs field and the Higgs field must permeate the entire universe, so how doesit give stuff mass?
In the Standard Model, the Higgs boson is theorised to be a particle that "does the work of the Higgs field". Where a photon (a boson) carries the electromagnetic force and the gluon (also a boson) carries the strong force inside atomic nuclei, the Higgs boson carries (or mediates) the Higgs field.
One of the biggest conundrums for physicists has been why different subatomic particles have different masses. For example, the rest-mass energy of a top quark is 350,000 times more massive than the electron. Why is this? There's no easy answer, but the Standard Model says that the Higgs mechanism is behind it all.
In 1993, in an effort to convince then UK science minister William Waldegrave to invest in the European LHC collaboration, David J Miller, physicist at University College London, created one of the finest analogies of the Higgs mechanism .
Miller described a situation where former Prime Minister Margaret Thatcher walks through a cocktail party in a room that is evenly distributed with people all wanting to speak with her. As she makes her way through the room, she collects more people clamouring to speak to her. This cloud of people adds to her collective mass as she moves, adding to her momentum. The cloud of people is therefore analogous to Higgs bosons imparting mass onto a particle (Thatcher) within the Higgs field - this is, basically, how the Higgs mechanism works. As a particle is created, Higgs bosons buzz around the particle like bees around a hive, endowing that particle with mass. This description is obviously a shorthand way of saying "the mathematics behind the Higgs is really, really hard," but analogies serve a very useful purpose in this case.
Since this famous analogy, other science communicators have used ping-pong balls in sand to bubbles on a swimmer's body in the hope of explaining what the Higgs mechanism is. But I have always thought of the Higgs field as a weird toll road where Higgs bosons enforce a "mass tax" on any particle travelling within it. Sometimes an overactive imagination comes in handy.
Create a Big Bang, catch a Higgs boson
So we kinda-sorta have an idea about how the Higgs mechanism works in a basic sense, but how do physicists go about detecting Higgs bosons?
According to the landmark publications of Peter Higgs and other international researchers in the 1960s, a single Higgs boson is massive. As announced by the CMS lead scientist Joe Incandela on July 4, the boson that his team has detected is the most massive boson ever observed, weighing in at over 130 times the mass of a proton - agreeing with Prof. Higgs and co's theory.
But to generate sufficient numbers of Higgs bosons in a particle accelerator, it has taken decades for our technology to become powerful (and focused) enough to generate the energies required to catch a glimpse of this massive particle. But with the (delayed) completion of the LHC in 2009, physicists finally acquired the tool to isolate a Higgs boson signal using a subterranean 27-kilometre ring of ultra-efficient superconducting electromagnets. Without a doubt, the $10bn LHC is the most complex and profound machine mankind has ever built.
In a nutshell, the LHC is a time machine; capable of recreating the conditions immediately after the Big Bang, some 13.75 billion years ago (this is why it has the "Big Bang Machine" moniker). Just after the Big Bang, the universe was nothing more than a soup of energy which cooled and condensed (eventually) into all the particles and forces we now see. During the proton-proton collision events inside the LHC, for the shortest of moments inside the tiniest of volumes, the relativistic particle collisions create mini-Big Bangs where the primordial soup of energy can exist and then quickly condense into the purest forms of matter: quarks, leptons and bosons. The collisions act like particle factories, churning out the whole spectrum of known (and, potentially, as yet unknown) particles. The bigger the collision energy, the more massive the particles generated.
And now, the missing piece of the Standard Model is beginning to show itself, like a crisp television signal gradually getting sharper and sharper through a sea of white noise. As the billions of particle collisions are measured by the complex, cathedral-sized CMS and ATLAS detectors, a fingerprint of the Higgs boson is slowly becoming obvious.
At an energy of around 126 GeV, just as the standard Higgs theory predicts, a "bump" is forming in the LHC collision data. This bump corresponds to an excess of particles - in this case photons - that are being created by some previously undiscovered mechanism. It just so happens that this excess relates to the Higgs mechanism.
The LHC appears to be generating highly unstable Higgs bosons that rapidly decay into pairs of photons. Rather than seeing the Higgs itself, the CMS and ATLAS detectors are seeing these decay photons; the Higgs' fingerprint. But physicists need to collect as much data as possible, increasing the definition of this "bump" so the properties of this Higgs candidate can be studied. The data collected by the LHC detectors is a bit like a photographic plate being exposed to a light source - the longer the plate is exposed, the sharper and more defined the image becomes.
The US Tevatron particle acceleratory at Fermilab in Illinois, also hot on the trail of the Higgs boson before it was retired last year, has also detected a small signal around a similar energy to the LHC results, boosting the level of confidence in the July 4 CERN announcement. The fact that two detectors in the LHC and experiments on the other side of the Atlantic are all in approximate agreement boosts physicists' confidence that they are onto something.
A doorway to the exotic
For now, this is exciting and very strong evidence for the existence of the Higgs boson, at least the existence of the Standard Model Higgs boson.
But as time goes on, we may find there are more Higgs bosons not in agreement with the Standard Model. This scenario wouldn't come as a surprise to physicists as the model doesn't include gravity - a fundamental force of nature characterised by Einstein's famous general theory of relativity. Also, as astronomers are now acutely aware, 84 per cent of all matter in the universe is locked in something known only as "dark matter". This exotic form of matter - assumed to be some kind of subatomic particle - is not part of the Standard Model recipe. To use the horribly simplistic cake analogy, the cosmic cake is four times heavier than all the ingredients we thought it was baked with.
So, in an attempt to confront these mysteries, physicists will continue pushing the boundaries of nature with tools such as the LHC to see how exotic particles and forces may be created. Perhaps they will stumble across super symmetric particles that may help explain why the universe has so much unseen mass; they may even unravel the extra-dimensions as hypothesised by string theory. Might the LHC provide evidence for the existence of other universes? Could the ever-increasing energies seen inside the LHC even create micro-black holes ?
This may all sound like science fiction, but modern physics cannot explain some of the observations of our universe using the Standard Model alone. Sure, it has formed a stable foundation, but now it's time to build the rest of the structure. Now that there's strong evidence for the Higgs, and it looks like the Standard Model foundation is sound, we can probe deeper into the exotic fabric of the universe to unravel some of the most vexing questions of our time.
Ian O'Neill is Space Science Producer for Discovery News . He is also the founder and editor of space blog Astroengine .
Follow him on Twitter: @astroengine