Higgs Boson: Investigating the properties and implications of the Higgs boson.
Avi Aggarwal 14/10/2025
What is the Higgs boson?
You and everything around you are made of particles.
But when the universe began, no particles had mass; they all sped around at the speed of light. Stars, planets and life could only emerge because particles gained their mass from a fundamental field associated with the Higgs boson.
The existence of this mass-giving field was confirmed in 2012, when the Higgs boson particle was discovered at CERN.
In our current description of Nature, every particle is a wave in a field. The most familiar
example of this is light: light is simultaneously a wave in the electromagnetic field and a stream of particles called photons. In the Higgs boson's case, the field came first. The Higgs field was proposed in 1964 as a new kind of field that fills the entire Universe and gives mass to all elementary particles. The Higgs boson is a wave in that field. Its discovery confirms the
existence of the Higgs field.
Particles get their mass by interacting with the Higgs field; they do not have a mass of their own. The stronger a particle interacts with the Higgs field, the heavier the particle ends up being.
Photons, for example, do not interact with this field and therefore have no mass. Yet other elementary particles, including electrons, quarks and bosons, do interact and hence have a variety of masses. This mass-giving interaction with the Higgs field is known as the
Brout-Englert-Higgs mechanism, proposed by theorists Robert Brout, François Englert and Peter Higgs.
The Brout-Englert-Higgs mechanism
Quantum field theory had already formed the basis of quantum electromagnetism, a very successful description of the electromagnetic interaction. Applying a similar approach to the weak interaction was however not possible due to a fundamental issue: the theory didn’t allow for particles to have mass.
Specifically, the weak force carriers known as the W and Z bosons had to be massless, otherwise a fundamental symmetry of the theory would be broken and the theory would not work. This posed a major problem since the weak force carriers had to be massive to be consistent with the very short range of the weak interaction.
The solution to this problem was found with the Brout-Englert-Higgs mechanism. This mechanism has two main components: an entirely new quantum field and a special trick. The new field is what we now call the Higgs field, and the trick is spontaneous symmetry breaking.
A spontaneously broken symmetry is one that is present in the equations of a theory but broken in the physical system. Imagine a pencil standing on its tip at the centre of a table. A perfectly symmetrical situation, but only for a moment: the pencil would immediately fall, breaking the rotational symmetry by selecting a single direction in which the pencil would be pointing. The laws of Nature however would
remain unchanged, without a predefined direction written into them. So, the lack of symmetry was essentially “tricked” into the picture, without upsetting the symmetry of physics.
pencil standing on its tip both show spontaneously breaking symmetry – symmetry is present, but only for a moment.
The way this works for particle masses is as follows: when the universe was born, it was filled with the Higgs field in an unstable – but symmetrical – state. A fraction of a second after the Big Bang, the field found a stable configuration, but one that breaks the initial symmetry. In this configuration, the equations remain symmetrical, but the broken symmetry of the Higgs field gives rise to the masses of the W and Z bosons.
As it later turned out, other elementary particles also acquire masses by interacting with the Higgs field, giving rise to the particle properties we observe today.
What makes the Higgs Boson so special?
Needle in a haystack
Producing the new particle is only the first step, however. Given its lifetime, the Higgs boson almost immediately decays – or transforms – into other particles. So it is not possible to observe
it directly. The particles from the boson’s decay are the only traces that it leaves behind. These traces have to be detected and precisely measured by particle detectors.
Once the decay products have been detected, the next step is to determine whether we can say that the Higgs boson was produced. The problem is that the particles that the Higgs decays into are the same kinds of particles that are copiously produced in particle collisions. Simply seeing a pair of photons (one of the final states from the Higgs boson decay) is hardly any indication that the Higgs boson exists and is being produced in the experiment. Especially since the Higgs boson is only produced about once in a billion of these collisions.
Scientists thus need some way of determining when a pair of photons (or four muons or a different final state that the Higgs decays into) is coming from a Higgs boson decay and when it’s not.
This needle-in-a-haystack problem can be solved, but not directly. In other words, it’s not possible to find the needle but it is possible to verify that the needle is in the haystack somewhere.
A roll of the dice
Specifically, it’s not possible to know in which collision the Higgs boson was produced, but the fact that it is being produced can be confidently established after analysing enough collisions. Here's how:
When all of the decay products are detected and their properties measured, a quantity called invariant mass can be calculated from these measurements.
This invariant mass is equal to the mass of the Higgs, but only for particles coming from the Higgs decay (or almost equal, taking into account the precision of the measurement in the particle detector).
For particles coming from other sources, this mass is going to be different every time. In general, it will be a random number from a range of possible masses.
This creates a unique mix of results: in the majority of cases the mass is a random number, but in some – very few – cases it is not random but instead a fixed, always the same, value. Imagine rolling the dice a large number of times, but with a small caveat: most rolls are normal, but every once in a while someone stealthily manipulates the
die such that it shows a predefined number chosen by that someone. Three for example. If we do this many times, the fact that someone is interfering can be observed just based on the results. Normally we would expect all the six possible
results of a dice roll to have the same probabilities, but in this situation one of them will have a probability slightly higher than the others.
The final element needed is statistical analysis of the results. Whether we think of invariant
masses or dice rolls, the signal that we're looking for can be visualised by plotting a histogram of
the results, on which the signal will appear as an excess, or “peak”, in one specific spot. To be able to tell that the peak is there, two conditions need to be satisfied: the peak needs to be big enough and the total number of results need to be big enough.
Five sigma
How much is enough? The answer is given by statistics: for a given excess in a given data sample it is possible to calculate the probability that an excess of this size would appear purely by chance.
The common agreement is that an excess is called a discovery when this probability is about 1 in three and a half million, which corresponds to an excess of five standard deviations above the expected value – the famous “five sigma”.
On 4 July 2012, the ATLAS and CMS collaborations reached this five sigma threshold - a new particle consistent with the long-sought Higgs boson had been discovered.
What have we learned since the Higgs boson discovery?
Is it really the Higgs boson?
The first step of that exploration was to check whether the newly discovered particle was indeed the elusive Higgs boson, or something entirely different. But how to establish the identity of a particle?
Every type of particle is characterized by a set of properties: mass, electrical charge, lifetime etc. For the Higgs boson, mass was the only unknown. For a known mass, all the other properties can be calculated from theory. Measuring them experimentally and comparing them with the result of these calculations allows scientists to verify that they have really found the Higgs boson.
One of the first things to check was “spin”. Spin is a quantum-mechanical property of particles, a form of intrinsic angular momentum. All particles that make up matter – quarks and leptons – have a spin of 1/2, and all the force-carrying bosons have a spin of 1. The Higgs boson is unique in that it has a spin of 0, making it the only known elementary particle with no spin.
The spin of a particle can be established by looking at its decay. The new boson was discovered by observing decays into photons and Z bosons, which already provides a strong constraint: only a particle with a spin of zero or two can decay into both photons and Z bosons. Through careful analysis of angular correlations – patterns in the directions in which the decay products fly off – physicists were able to disprove the spin-2 hypothesis with high confidence, confirming the spin-zero nature of the new boson.
So despite the discovery announcement on 4 July 2012, it took until March 2013 – and two and a half times more data – for physicists to be sure that some kind of Higgs boson had been discovered.
Measuring interaction strengths
The bulk of the studies performed over the past 10 years have been measurements of Higgs boson interaction strengths with other particles – called “couplings” by physicists – to see whether they match those predicted by theory.
Couplings to different particles correspond to the masses of these particles, since these masses result from interactions with the Higgs field. These couplings are seen experimentally by looking at Higgs boson production and decay: the heavier a particle – and the stronger the coupling – the more likely the Higgs boson is to decay into or be produced from it.
Strengths of the Higgs interaction with other bosons were determined at the moment of discovery by observing its production from gluons and its decay into photons and W and Z bosons.
The next step was to measure the strengths of interaction with matter particles.
The decay of the Higgs boson to pairs of tau leptons was discovered in 2016 through a combined ATLAS/CMS analysis. The coupling to the tau was measured and was found to be compatible with expectations. The next milestone was the measurement of the top quark coupling.
For top quarks, the only way to probe the coupling was through the production process, since the top quark is heavier than the Higgs boson, and, as a result, the Higgs boson cannot decay into a pair of top quarks. Higgs boson production from a fusion of two top quarks was measured in 2018 by observing the ttH process, a Higgs boson being produced together with two top quarks.
The Higgs boson decay into b quarks was also observed in 2018, six years after the discovery announcement, despite being the most likely: 58% of Higgs bosons decay to b quarks. But b quarks are produced in the LHC collisions in such numbers, that a search for a Higgs boson decay faced an overwhelming background, making the measurement extremely challenging.
With the above interaction confirmed, scientists now know that the Higgs field does indeed give mass to the tau lepton, and top and bottom quarks, particles from the heaviest of the three known families, or generations, of matter particles.
What’s next for Higgs boson research?
Higgs boson or Higgs sector
The simple version of the BEH mechanism, with just a single Higgs boson doing all the work, doesn’t necessarily have to be the one realised in Nature. In many extensions of the Standard Model there is a whole “Higgs sector” of particles stemming from some more fundamental principles.
The BEH mechanism can also have a bigger impact than “just” generating mass. At the heart of the mechanism is the spontaneous breaking of the Quantum Field Theory , an event that occurred right after the Big Bang, transforming the universe from a symmetrical state with massless particles to the state that we see today. But how did that happen? Was it a gradual change or was it more akin to a pot of boiling water, with “bubbles” of broken symmetry popping into existence in different places? In certain cases, this phase transition could have been the source of the matter–antimatter asymmetry, seen today in the universe.
To learn about this, researchers are going to be looking for Higgs boson interactions with second generation matter particles, the muon and the charm quark, and also looking for extra Higgs-like particles.
The Higgs boson mass matters
Even the mass of the Higgs boson, seemingly just an ordinary property of the particle, has far-reaching implications. The observed value of this mass is, from the theoretical point of view, unnaturally small, suggesting that either the Higgs boson is a more complicated object (for example a composite particle) or that the theory needs new symmetry or some other mechanism that would stabilise the Higgs boson mass.
The mass also relates to whether the present state of the universe is stable. All observations so far indicate a stable universe, but for certain values of the Higgs boson and top quark masses, theory predicts a
meta-stable universe, which can transition to a lower energy state. Precise measurement of the Higgs boson mass is going to tell us if this is the case. If yes, we need to find a whole new mechanism to stabilize the vacuum, otherwise the theory would not agree with reality.
Another unknown is where the Higgs mass originates from. If it results from the interaction with the Higgs field, it should be possible to observe the Higgs boson “self-interaction”, with the production of pairs of Higgs bosons being the signal to look for. Observing and measuring this process is the “holy grail” of the Higgs research programme, with the potential to shed light on the nature of the Quantum Field Theory breaking mechanism itself. Being extremely rare, it is most likely going to require the upgraded High Luminosity LHC to be observed, and an entirely new future accelerator to be studied fully.These depend on the current measured Higgs(~125 GeV) and top quark masses(~173 GeV)
Using the Higgs boson to search for new physics
Discovering a new particle means it has to be produced in a collision or have some other indirect effect on known phenomena. For this to happen, the new particle has to be able to interact with known particles.
But for new particles that don’t feel the electromagnetic, strong or weak force, such interaction would be almost nonexistent, making them invisible and inaccessible in practice. This could for example be the case for particles of dark matter.
These particles could however interact with the Higgs boson. .The interaction between the Higgs boson and the top quark is also very sensitive to the influence of new particles. This makes the experimental measurement of the Higgs coupling to the top quark one of the more promising ways of searching for new phenomena. More exotic possibilities are also being studied, for example new heavy particles decaying
into a Higgs boson and a different particle, or Higgs boson decays that would be forbidden in the Standard Model – for example into a top quark and a muon.
The Higgs boson is a fantastic laboratory for new physics searches. The journey is only just beginning.
How does the Higgs boson impact everyday life?
It can be said that the Higgs boson has indirectly affected everyday life, since many of the technologies developed to find it are now in use all over the globe, in areas well beyond particle physics.
The search for the Higgs boson using the Large Hadron Collider (LHC) pushed the limits of technology. Extremely high energies were needed to accelerate particles to almost the speed of light, unprecedented detail and precision was needed to accurately detect the collisions of these particle beams, and unrivalled computing technology was needed to map and record each of the millions of particle collisions produced per second.
For example, the invention of the World Wide Web at CERN was born out of particle physicists’ needs to share data across institutes. Now, society depends on the World Wide Web every day to communicate and work. Similarly, in the early 1970s, engineers from CERN contributed to the advancement of touchscreen technology by trying to create a simple interface to use with one of CERN’s particle accelerators. Since then, touchscreens have gone on to be a mainstay in everyday life.
Another field that has benefitted from particle physics research is healthcare. Accelerator technology is used to treat cancer, in hadron therapy and electron radiotherapy. Further, particle physics detectors are used in medical diagnostics, such as the 3D colour X-ray scanner, based on technology developed at CERN. Particle accelerators also led to the development of Positron Emission Tomography (PET), which is essential for imaging and diagnosing conditions in the brain and heart.
Detector technology has also helped advance the aerospace sector, improving research even beyond our planet. The extreme environments in space are very similar to those found in underground particle physics experiments. This means technologies such as radiation monitoring can be applied in space to protect equipment and the safety of astronauts.
And it’s not just in the fields of science and technology, either. Particle physics detectors have even been used to protect our cultural heritage, such as unveiling a long-lost artwork by the great Renaissance painter Raphael.
There are plenty more, too: new technologies are continuously being developed from particle accelerators such as the LHC, despite their primary goal of searching for particles like the Higgs boson. These all have benefits to many different areas of society and will only continue expanding as research advances.