Information Density: CERN – Signal Evidence & AI Readability

[H3] European Laboratory for Particle Physics
At CERN, scientists from around the world use unique machines to explore how the Universe works, pushing the limits of technology for the benefit of society.
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[H2] Collide Stockholm recipient announced
Emilija Škarnulytė will complete an artistic residency at both CERN and the Nobel Prize MuseumRead more
[H2] Public consultation for the FCC project begins
CERN is committed to engaging with the local communities on the FCC projectRead more
[H2] Smarter decisions at the speed of collisions
Machine learning is reshaping how ATLAS and CMS filter collisions in real timeRead more
[H2] Collide Stockholm recipient announced
Emilija Škarnulytė will complete an artistic residency at both CERN and the Nobel Prize MuseumRead more
[H2] Public consultation for the FCC project begins
CERN is committed to engaging with the local communities on the FCC projectRead more
[H2] Latest News

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[H2] Explore CERN
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[H3] Visit CERN
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[H2] Accelerating science
IN PREPARATION
[H2] HiLumi LHC
The High-Luminosity Large Hadron Collider will increase by a factor of ten the number of particle collisions (called “luminosity”), vastly increasing the volume of physics data available for researchers.
This leap forward will allow physicists to explore the behaviour of the Higgs boson and other elementary particles with unprecedented precision, increasing the potential for discoveries after 2030.
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LOOKING TO THE FUTURE
[H2] Future Circular Collider
The Future Circular Collider could be Europe’s next-generation particle collider: a unique tool to explore the deepest mysteries of the Universe and to drive technology, innovation and skills for decades to come.
This new collider would help answer many questions about nature’s rulebook that lie beyond the reach of current colliders.
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[H2] Key achievements
[H2] The Higgs boson
Discovered in 2012 by the ATLAS and CMS experiments at the Large Hadron Collider (LHC), the Higgs boson confirms the Higgs mechanism, which explains how elementary particles acquire mass through interaction with the Higgs field.
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[H2] Neutral currents
Observed at CERN in 1973, via the Gargamelle bubble chamber, and provided the first evidence of the weak neutral force.
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[H2] W and Z bosons
Discovered at CERN in 1983, the W and Z boson mediate the weak nuclear force.
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[H2] The birth of the web
In 1989, CERN computer scientist Tim Berners-Lee invented the World Wide Web to enable efficient sharing of research data among scientists around the globe.
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[H2] Antimatter
CERN operates the world’s only dedicated antimatter facility, producing the first anti-atoms in 1995 and later trapping and transporting antimatter.
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[H1] 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.
[H3] What’s so special about the Higgs boson?
[H3] How did we discover the Higgs boson?
[H3] What have we learned since the discovery?
[H3] What’s next for Higgs boson research?
[H3] How does the Higgs boson impact our lives?
[H3] Higgs10 feature series
[H3] Higgs boson images
[H3] Higgs boson videos
[H3] What does “five sigma” mean?
[IMG: Artistic view of the Higgs field]
[H2] What is the Higgs boson?
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.
[IMG: Standard Model]
[H2] How do particles get mass?
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.
[IMG: CMS Higgs Search in 2011 and 2012 data: candidate photon-photon event (8 TeV): 3D, r-phi and r-z transverse views]
[H2] How did we discover the Higgs boson?
The Higgs boson can’t be “discovered” by finding it somewhere but has to be created in a particle collision. Once created, it transforms – or “decays” – into other particles that can be detected in particle detectors.
Physicists look for traces of these particles in data collected by the detectors. The challenge is that these particles are also produced in many other processes, plus the Higgs boson only appears in about one in a billion LHC collisions. But careful statistical analysis of enormous amounts of data uncovered the particle’s faint signal in 2012.
[H2] How did physicists know it was the Higgs?
On 4 July 2012, the ATLAS and CMS collaborations announced the discovery of a new particle to a packed auditorium at CERN.
This particle had no electrical charge, it was short-lived and it decayed in ways that the Higgs boson should, according to theory. To confirm if it really was the Higgs boson, physicists needed to check its “spin” – the Higgs boson is the only particle to have a spin of zero.
By examining two and a half times more data, they concluded in March 2013 that, indeed, some kind of Higgs boson had been discovered.
[IMG: Candidate event displays of a Higgs boson produced by vector-boson fusion and decaying into invisible particles.]
[H2] What have we learned since the Higgs boson discovery?
Discovering the Higgs boson was just the beginning. In the ten years since, physicists have examined how strongly it interacts with other particles, to see if this matches theoretical predictions.
Interaction strength can be measured experimentally by looking at Higgs boson production and decay: the heavier a particle the more likely the Higgs boson is to decay into or be produced from it. Interaction with tau leptons was discovered in 2016 and interaction with top and bottom quarks in 2018.
But there is much more still to learn about this elusive particle.
[IMG: 3D dipole integration panoramic poster]
[H2] What are we going to look for next?
We still have much to learn about the Higgs boson.
Is it one-of-a-kind or is there a whole Higgs sector of particles? Does it help to explain how the universe was formed, with matter triumphing over antimatter? Does it get its mass by interacting with itself in some way? And why is its mass so small, suggesting the existence of a whole new mechanism.
Could dark matter and other new particles be found thanks to interactions with the Higgs boson?
Ten years after the discovery, the journey has only just begun.
[H2] How does the Higgs boson impact everyday life?
The Higgs boson has, and will continue to have, an impact on our lives, in ways you may not have imagined.
It is part of the answer to why we – and everything we interact with – have mass, feeding our natural human curiosity about our universe and how it evolved.
In the search for this particle, accelerator and detector technologies were pushed to the limits, leading to advances in healthcare, aerospace and more.

[H1] The birth of the Web
The World Wide Web was invented by British scientist Tim Berners-Lee in 1989 while working at CERN
Tim Berners-Lee, a British scientist, invented the World Wide Web (WWW) in 1989, while working at CERN. The web was originally conceived and developed to meet the demand for automated information-sharing between scientists in universities and institutes around the world.
[IMG: home.cern,Accelerators]
Screenshot of the recreated page of the first website (Image: CERN). Source: CERN (CDS)
The first website at CERN – and in the world – was dedicated to the World Wide Web project itself and was hosted on Berners-Lee’s NeXT computer. In 2013, CERN launched a project to restore this first ever website: info.cern.ch.
On 30 April 1993, CERN put the World Wide Web software in the public domain. Later, CERN made a release available with an open licence, a more sure way to maximise its dissemination. These actions allowed the web to flourish.
[H3] A short history of the Web
[H3] Licensing the Web
[H2] Browse the first website
Discover the World Wide Web’s humble beginnings with this earliest incarnation
[H2] The WorldWideWeb browser
Surf the Web using a recreation the first browser that was written in 1990
[H2] The line-mode browser
The line-mode browser, launched in 1992, was the first readily accessible browser for the Web

[H1] Antimatter
In 1928, British physicist Paul Dirac wrote down an equation that combined quantum theory and special relativity to describe the behaviour of an electron moving at a relativistic speed.
The equation – which won Dirac the Nobel Prize in 1933 – posed a problem: just as the equation x2 = 4 can have two possible solutions (x = 2 or x = −2), Dirac’s equation could have two solutions, one for an electron with positive energy, and one for a particle with negative energy. But classical physics (and common sense) dictated that the energy of a particle must always be a positive number.
Physicists interpreted this new particle as an “anti-electron”, a particle with a mass identical to the electron but with opposite electrical charge. The existence of this particle was demonstrated with Carl Anderson’s discovery of the positron in 1932.
Today we know that every type of matter particle has a corresponding antiparticle with matching properties, except for opposite electrical charge. This symmetry has two consequences: particles and antiparticles are always produced in pairs, and they annihilate upon contact, leaving only energy behind, predominantly in the form of photons and pions.
[H2] The matter-antimatter asymmetry problem
According to our understanding, during the first fractions of a second after the Big Bang, the hot, dense universe was filled with pairs of particles and antiparticles popping in and out of existence. But if matter and antimatter are always created and destroyed together, then today’s universe should be filled with equal amounts of both. Alternatively, it should contain nothing but leftover radiation from the annihilation of all the matter and all the antimatter produced in the Big Bang.
However, what we observe is neither of the above. The Universe is clearly not empty, yet the 50% of antimatter is nowhere to be found. In fact, the Universe appears to contain almost no antimatter whatsoever. The current best explanation for this is that after the Big Bang some unknown mechanism created a tiny excess of matter – approximately one extra particle per billion antiparticles. When all the matter and antimatter annihilated, this excess is all that remained. This forms everything that we see today, from the smallest life forms on Earth to the largest stellar objects.
One of the greatest challenges in physics today is figuring out what happened to the antimatter and understanding the source of the observed asymmetry between matter and antimatter.
To answer this and other questions, physicists at CERN make antimatter for study in experiments. The starting point is the Antiproton Decelerator, which slows down antiprotons so that physicists can investigate their properties with very high precision.
[H2] Experiments studying antimatter
[IMG: View of the CERN Antiproton Decelerator (AD) and portrait of Prof. Tommy Eriksson, in charge of the AD machine.]
The Antiproton Decelerator
[IMG: AEGIS experiment - Laser Part]
AEgIS
[IMG: Chris Ørum and Steven Armstrong Jones from ALPHA experiment working on LASER]
ALPHA
[IMG: ASACUSA]
ASACUSA
[IMG: Stefan Ulmer, Spokesperson BASE Collaboration, in Base Experiment]
BASE
[IMG: Photowalk 2018 - Ciaran McGrath]
GBAR
[H2] Frequently asked questions
[H3] Which experiments are currently active within CERN’s antimatter programme?+
Six collaborations are active in the AD/ELENA Antimatter Program: AEGIS, ALPHA, ASACUSA, BASE, GBAR, and PUMA.
AEGIS, ALPHA, part of ASACUSA, and GBAR study fundamental properties of antihydrogen to test matter–antimatter symmetry and the weak equivalence principle, using plasma traps, atom traps, atomic beams, and high-resolution laser spectroscopy. ALPHA has measured antihydrogen properties to 12 significant digits. ASACUSA additionally studies antiprotonic atoms to determine the antiproton–electron mass ratio. BASE uses cryogenic Penning traps to compare proton and antiproton properties; its 11-digit charge-to-mass comparison is the most precise baryonic matter–antimatter test. PUMA will use antiprotons to probe neutron-rich nuclei.
[H3] How can we store antimatter?+
It is very difficult to contain antimatter. Any contact between a particle and its anti-particle leads to the immediate annihilation of both. To contain anti-particles, therefore, we must isolate them from all normal matter. This means keeping them in extremely high vacuum, in fact the best vacuum ever reported in an experiment on Earth – 5*10-19 mbar – was achieved in the BASE experiment at CERN, where antiprotons were stored for more than a year.
Electrically charged antiparticles
It is possible to contain electrically charged antimatter particles such as antiprotons by using electromagnetic traps that confine the particles within a magnetic field, preventing them from annihilating with other particles. However, particles of the same charge repel each other, so the more particles there are in a trap, the larger the trap has to be and the more energy is needed to power the electric and magnetic fields that contain the antiparticles. The biggest current traps, such as those in the GBAR and PUMA experiments, can contain up to approximately a billion anti-particles of the same charge, which in everyday terms is equivalent to about 10-18 kilograms (0.000000000000000001 kg).
Electrically neutral antiparticles
For electrically neutral antiparticles or anti-atoms like antihydrogen, the situation is even more complicated. It’s not impossible however: antihydrogen atoms are slightly magnetic and can be trapped in a very strong and specially shaped magnetic field, first demonstrated by the ALPHA experiment at the antimatter factory. They can be stored for many hours, allowing physicists to perform precise studies of their properties. In principle up to 100 000 particles could be stored this way with the current technology.
[H3] How much antimatter can we produce?+
Antimatter does not occur naturally, except for single particles produced in nuclear or cosmic ray interactions. Therefore, the only way to obtain it is to produce it. At CERN, we have a dedicated facility for this purpose: the Antimatter Factory. When operating, it delivers approximately 400 million antiprotons per hour to experiments studying antimatter, of which the experiments are able to capture about 10%. In the ALPHA experiment these antiprotons can be used to create antihydrogen atoms at a rate of up to 3000 per hour and they can be stored for up to 100 hours.
Even if we could somehow construct a trap that could hold large quantities of antihydrogen without losses and run the CERN Antimatter Factory non-stop for a year, we would only accumulate about 30 million atoms, equivalent to 3*10-20 kilograms (0.00000000000000000003 kg). The total number of antiprotons delivered would be 300 billion, which is still only 3*10-16 kilograms.
[H3] How much energy is released in annihilation? Can it be used as an energy source?+
When antimatter comes into contact with matter the two annihilate, converting their mass into high-energy photons and pions. The efficiency of this process is nearly perfect, since almost all the mass of the annihilating particles is converted into the energy of the particles produced. In terms of efficiency, this is about 50 times better than nuclear fusion.If we were somehow capable of producing and trapping large quantities of antimatter, large-scale annihilation could theoretically be used to produce energy. But, using the antimatter as an energy source would be very difficult since it would be challenging to convert the high energy pions and gamma radiation produced in the annihilation into a usable form of energy.Be that as it may, we are currently incapable of producing any significant quantity of antimatter (see previous answer). The maximum amount of antihydrogen that we imagine making in one year, even if we could trap it all and make it annihilate all at once, would produce a few thousandths of a Joule of energy. This is equivalent to the amount of energy released by gently tapping a phone screen with a finger.All the antiprotons produced by the Antimatter Factory running non-stop throughout a whole year would equate to about 500 Joules of energy, enough to light a 100 W light bulb for five seconds.
[H3] Can we transport trapped antimatter? +
Yes, the first attempt to transport antimatter was made by the BASE experiment at CERN’s Antimatter Factory. In November 2025, BASE-STEP trapped antiprotons inside a special transportable ion trap and loaded them onto a lorry to transfer them to a facility where scientists could study them with greater precision. Transporting antimatter outside of CERN would allow other European laboratories to conduct additional independent research with antiprotons.
[H3] What equipment is needed to transport antimatter?+
An almost one tonne piece of equipment transported by crane or forklift. The apparatus used by the BASE-STEP experiment is actually quite small compared to other Penning-trap experiments. It is designed to fit on a lorry, the frame being narrow enough to fit through ordinary laboratory doors. Most of its weight comes from the superconducting magnets weighing 600 kg.
[H3] Is antimatter transportation dangerous?+
STEP traps between 100 and 1000 antiparticles. If the trap fails during transport and the antiparticles annihilate, the energy released will be about a millionth of a Joule. A single key press on a keyboard is about 10 000 times more than that. So antimatter transportation is no more dangerous than any other form of goods transportation.

[H1] Physics
CERN’s physics programme ranges from nuclear to high-energy physics and from studies of antimatter to the possible effects of cosmic rays on clouds.
[H1] Accelerators
Particle accelerators propel sub-atomic particles to extremely high velocities for a variety of uses from high-energy physics research to medical scans and treatments.
[H1] Experiments
Diverse experiments at CERN investigate physics from the early universe to supersymmetry.
[H1] Engineering
Engineers at CERN build and test the machines and systems that physicists rely on, and technicians keep these systems running smoothly, performing repairs and upgrades where necessary.
[H1] Computing
Experiments at CERN generate colossal amounts of data. The Data Centre stores these data sets and sends them around the world for analysis.

[H1] W boson: Sunshine and stardust
The W boson carries the weak force. It can change the character of particles of matter – allowing the Sun to burn and new elements to form
The W boson is a fundamental particle. Together with the Z boson, it is responsible for the weak force, one of four fundamental forces that govern the behaviour of matter in our universe. Particles of matter can interact by exchanging these bosons, but only over short distances.
With a charge of +1 or -1, the W boson can change the identity of particles. It is responsible for many nuclear processes, including those letting stars burn. This burning also creates heavier elements and, when a star dies, those elements are tossed into space as the building blocks for planets and people.
CERN announced the discovery of the W boson on 25 January 1983. Two collaborations, UA1, led by Carlo Rubbia, and UA2 led by Pierre Darriulat, presented their observation in seminars a few days earlier. The discovery was due to an idea that Rubbia and others had presented: converting the SPS into a proton anti-proton collider with the necessary energy to produce the W boson. This conversion was made possible by Simon van der Meer’s invention of stochastic cooling. As a result, Rubbia and van der Meer received the Nobel prize in physics in 1984.
The W boson is the fourth heaviest particle in the Standard Model and its mass is reliant on the Brout-Englert-Higgs mechanism. This mechanism called for the existence of a Higgs boson, which was discovered at CERN in 2012.
Since the 1983 discovery, experimental physicists have continued to compare measurements of W boson properties with theoretical predictions. Studies at the LHC now build on those at its predecessor, LEP, probing properties, particularly the mass, with increasingly higher precision. Any deviation from theory could hint towards yet unknown physics.
[IMG: W boson press conference on 25 January 1983]
On 25 January 1983, CERN announced the discovery of the W boson. Left to right: Carlo Rubbia, Simon van der Meer, Herwig Schopper, Erwin Gabathuler, Pierre Darriulat (Image: CERN)