Scientists at the Large Hadron Collider (LHC) announced the discovery of a Higgs-like boson on July 4 – but what does that mean? What’s a Higgs boson? And how can a particle be like a Higgs? Read on to learn more about the new particle and how it fits into our world.
The following questions were asked on Twitter on 4 July 2012, the day CERN announced the discovery of a new particle with a mass of approximately 126 GeV.
How many Higgs bosons are there?
In the Standard Model there is just one, but many theories predict more. For example, supersymmetry predicts at least five. Supersymmetry also predicts other supersymmetric scalar particles. Models in which the Higgs is composite with internal constituents suggest that it would be accompanied by an infinite number of other composite particles, in which the constituents are arranged in different ways.
What are the key features of this newly discovered boson that would identify it as the Standard Model Higgs?
The decay rates of the new boson could help to identify it as the Standard Model Higgs. The Standard Model predicts certain rates of decay, and, if this boson matches the expected rates, it would offer solid evidence that it is this Higgs. Also, the Standard Model Higgs should have a specific value of spin. If the spin of the new boson differs from predictions, it might be a sign of new physics.
Do you envision a time when we will be able to manipulate Higgs to do things, as we do electrons, perhaps to vary mass?
As a scientist, one should never say never, but it is not clear how it could be done. It would require achieving the same energy density as in collisions at the LHC, but over a large region of space.
What is the difference between the Higgs boson and the Higgs field? Is the field composed of Higgs bosons?
The Higgs field stretches out through the whole of the universe. A massless particle would just glide through, not interacting with the field. A heavier particle would collect more mass. It’s like a skier skimming over the top of a field of snow. The snow would barely be affected, but someone with just boots on would sink deeply into the snow. The Higgs field is the area of snow, while the Higgs bosons are the snowflakes that make up the snow covering the ground.
See video: What is the Higgs boson?
Where do the researchers go from here and how are theories relating to the theoretical dark matter affected?
We need to check whether the new particle has the essential features expected for a Higgs boson. Once we know more about the properties of this boson, we can move forwards. In many theories, including supersymmetry and some composite models, one of the particles associated with the Higgs may make up the astrophysical dark matter. Within these theories, measuring the mass and other properties of the Higgs boson can help to pin down the nature of dark matter.
Is the LHC adapted for the discovery of particles not predicted by theory? If yes how, and in which direction?
Yes. The LHC is a search-and-discovery machine. It uses composite particles (protons) as projectiles so the actual energy liberated (to be used for making new particles) in any given collision spans a wide range, covering the mass range of potential new particles. The ATLAS and CMS detectors are also multipurpose, able to detect all long-lived particles emanating from a collision, including those that arise from decays of heavier, perhaps new, particles. Papers published already by the collaborations include searches for new particles with masses of the order of 1-2 TeV. When the LHC increases in collision energy to 13-14 TeV in 2015 these searches can be extended to much higher energies.
How much data will be needed to isolate the nature of this new particle and possibly identify it as the Higgs boson?
It is very early days! The number of Higgs-boson candidates identified so far is of the order of tens. This is sufficient to be able to understand some basic properties, but not enough to determine details. For example, we know that its spin value must be an integer, but not 1, so does it have spin 0, as expected, or spin 2, say? It’s not yet possible to determine in which of many theories this particle fits. It certainly has properties consistent with the predicted Standard Model Higgs boson but these are very similar (with the current statistics) to the lightest neutral supersymmetric (SUSY) Higgs boson. And some SUSY models predict five Higgs-like bosons! By the end of 2012, the data samples of ATLAS and CMS should at least double, and this should point the way to which theory fits best. But it may be several more years before we understand the details – and indeed this new boson may not fit precisely into any current theory.
The discovery of the Higgs has been hailed as completing the Standard Model. What happened to the graviton?
The graviton has never been a component of the Standard Model. The gravitational force, for which the graviton is the postulated force-carrier, is far too weak to influence the quantum world. Some exotic theories, such as string theory, are attempting to unify all four known forces, but as yet there are no testable quantities.
Assuming the upcoming analysis of the boson turns out to show that it is the expected Higgs, what will be the LHC’s next task (What will the LHC look for now)?
The analysis of the newly discovered boson will certainly take many years. The amount of data so far accumulated is around 2% of that expected for the lifetime of the LHC (until around the year 2022). So this is just the beginning of the story.
Moreover, there are still many unanswered questions that are being tackled in parallel to the origin of mass that the Higgs boson addresses. For example, we know that 96% of the universe is not baryonic matter (the stuff we, the planets and the stars are made of); the nature of this dark matter and dark energy may be elucidated by ATLAS and CMS. And where has all the antimatter – assuming that it was created in equal amounts to normal matter at the time of the big bang – gone? This is something that LHCb in particular is tackling, as well as ATLAS and CMS. The ALICE collaboration plans to study quark-gluon plasma, believed to be present in the moments after the big bang, as it expends and cools, observing how it progressively gives rise to the particles that constitute the matter of our universe today.
But perhaps the most fascinating possibility is that the experiments at the LHC will discover things that we have not even contemplated, something new and unusual that pushes our knowledge forwards in ways we simply cannot predict.
Does today’s announcement mark the triumph of supersymmetry, or make it more likely?
Neither. It is far too early to determine whether the new boson belongs to supersymmetry, the Standard Model or something else.
How many particles were used and collided when this particle was found?
500 trillion – that’s a million million particles!
If the Higgs boson is discovered will that mean the end of CERN and its work?
Not at all. Once the Higgs boson is officially discovered, there are more questions. Scientists will continue to study the boson to figure out the way it works, as well as how it fits into current models as predicted, or if it has other aspects that may point to new physics.
CERN’s researchers conduct many more studies beyond the search for the Higgs. There are experiments looking for extra dimensions, dark matter and completely new physics. CERN also houses an antimatter facility. There, scientists are studying the properties of antimatter to figure out why, if antimatter and matter were produced in equal amounts during the big bang, there’s more matter in the universe now.
Do you think the public will maintain an interest in the Higgs boson as you continue to explore its properties?
We hope so. Once we know enough about the Higgs-like boson to confirm that it either is the Standard Model Higgs boson or it isn’t, there will be studies to examine exactly how the boson interacts with other particles – giving us more clues to the origin of mass and the beginning of the universe. And if this new boson is not the Standard Model Higgs boson, that’s a sign of new physics beyond the Standard Model. It’s an exciting time, and everyone should stay tuned.
Read more: press.web.cern.ch