On July 4, 2012, the ATLAS/CMS collaborations at Large Hadron Collider, (LHC), announced the discovery by a new particle that had features similar to those predicted for the Higgs boson in the Standard Model particle physics. This discovery was a significant milestone in science history and caught the attention of the entire world. Francois Englert, Peter Higgs, and Robert Brout won the Nobel Prize in Physics a year later for their decades-old prediction of a new fundamental force, the Higgs Boson, which pervades all the universe and gives mass and energy to elementary particles.
“The Higgs boson discovery was a significant milestone in particle physics. It was the culmination of a decade-long journey of discovery and the start of a new era in particle physics research.” Fabiola Gianotti (CERN’s Director General and spokesperson for the ATLAS experiment) at the time of its discovery, says that it was a significant milestone in particle physics. “I still remember the day of the announcement with emotion. It was a day of great joy for the entire particle physics community as well as all those who have worked tirelessly for decades to make this discovery possible.
In just ten short years, physicists made huge advances in understanding the universe. They not only confirmed that the Higgs boson was indeed discovered in 2012 but also allowed researchers to begin building a picture showing how the ubiquitous presence of a Higgsfield throughout the universe was established one tenth of billionths of a second after Big Bang.
The beginning of a new journey
The Higgs boson was predicted by the Standard Model to be the new particle that was discovered in 2012 by international collaborations ATLAS and CMS. But is it really the long-sought particle? AtLAS and CMS began to examine in detail the characteristics of the new particle that they discovered. Data from the disintegration of the new particle into two photos, which are the carriers of electromagnetic force, was used to determine the underlying mechanism.
Experiments have shown that the new particle does not possess any intrinsic angular momentum or quantum spin, which is exactly like the Higgs boson predicted in the Standard Model. All other elementary particles known have spin, however, including the matter particles (the ‘up’ or ‘down’ quarks which form protons and neutrons) and the force-carrying particle, the W and Z bosons.
ATLAS and CMS confirmed the existence of Higgs bosons by observing them being formed from and then decaying into W or Z bosons. This is consistent with the Standard Model prediction. These interactions are strong enough to explain the small range of weak force. This is responsible for radioactivity and the nuclear fusion reaction which powers the Sun.
As predicted by the Standard Model, the experiments also showed that the top quarks, bottom quarks and tau leptons, which are the most heavy fermions, acquire their mass through interactions with the Higgs field. The experiment showed that the Higgs boson was produced in pairs with top quarks in the case where the top quark is the Higgs boson, while the tau and bottom quarks saw the boson decay into tau and bottom quarks. These observations confirmed that there is an interaction or force called the Yukawa interaction. It is part of Standard Model, but it is different from all other forces in Standard Model. The Higgs boson mediates it, and it’s strength is not quantified, that is it doesn’t come in multiples.
CMS and ATLAS measured the Higgs boson’s mass at 125 billion electronvolts (GeV), which is an astonishing precision of nearly one per mil. The mass of Higgs boson, a fundamental constant in nature, is something that cannot be predicted by the Standard Model. The Higgs boson’s weight, along with other parameters such as the mass of top quark, the heaviest elementary particle known, may be a factor in the stability of the universe’s vacuum.
These are only a few examples of the tangible results of ten-years of research into the Higgs boson at The World’s Largest and Most Powerful Collider, the only place where this unique particle is possible to be made and studied in detail.
Andreas Hoecker, spokesperson for ATLAS, says that “the large data samples provided to the LHC, performance of the ATLAS/CMS detectors and new analysis techniques have enabled both collaborations in extending the sensitivity of their Higgs boson measurements beyond what was possible when the experiments were constructed.”
The LHC collaborations discovered over 60 composite particles, many of which are exotic tetraquarks and pentaquarks, after the LHC began colliding protons at record energies. They have discovered a number of interesting hints that the Standard Model is not correct. In addition, they have explored the quark-gluon plasma which filled the universe’s early moments in unprecedented detail. They also have observed rare particle phenomena and made more accurate measurements of Standard Model phenomena. This has allowed them to search for new particles that are not predicted by the Standard.
Model, including particles that could make up dark matter that accounts most of the universe’s mass.
These searches have provided important insights into fundamental physics. Joachim Mnich, CERN’s Director of Research and Computing, says that discoveries in particle physics do not necessarily have to be new particles. “The LHC’s results over a decade have allowed us to expand our search area, set strong limits on extensions to the Standard Model, as well as to develop new data-analysis and search techniques.”
Surprisingly, the LHC results so far have been based only on 5% of all the data the collider will produce over its lifetime. Michelangelo Mangano, a CERN theorist, said that the LHC’s “small” sample has made big strides in understanding elementary particles and their interactions. “While all of the results so far have been consistent with the Standard Model theory, there are still many possibilities for new phenomena that go beyond what has been predicted.”
“The Higgs boson may itself point to new phenomena,” says Luca Malgeri, spokesperson for CMS. “ATLAS is conducting many searches to investigate all forms of unanticipated processes involving Higgs boson,” says CMS spokesperson Luca Malgeri.
The road ahead
Ten years later, what’s still to be learned about Higgs field & Higgs boson? There is a lot. Is the Higgs field giving mass to lighter fermions? Or is there another mechanism? Is the Higgs boson an elemental or composite particle? It can interact with dark matter to reveal the nature and origin of this mysterious type of matter. What is the Higgs boson? How does it generate mass and self-interaction Is it related to any twins?
These and other questions can be answered to improve our understanding of the universe on the smallest scales. They may also unlock the mysteries of the universe in its entirety, including how it got here and what its fate will be. Particularly, the Higgs boson’s own-interaction might be key to understanding the imbalance between matter, antimatter, and the stability in the vacuum.
Some of these questions may be answered by data from the LHC’s third run or the major upgrade to the collider, the high-luminosity LHC. However, other enigmas are beyond the reach and will require a future Higgs factory. CERN and its international collaborators are currently investigating the financial and technical feasibility of a larger and more powerful machine called the Future Circular Collider in response to a recommendation in the European Strategy for Particle Physics’ latest update.
Gian Giudice is the head of CERN’s Theory section. He stated that “high-energy colliders are still the most powerful microscope available to explore nature at the smallest levels and to discover fundamental laws that govern it.” These machines have tremendous social benefits.
The accelerator, detector, and computing technologies associated high-energy colliders had a significant positive impact on society. This includes inventions like the World Wide Web and detector developments that led the PET (Positron Emission Tomography). These detector developments also allowed for the creation of accelerators for the treatment of cancers using hadron therapy. The design, construction, and operation of particle Physics colliders and experiments has resulted in the training and collaboration of many scientists in other fields and a unique model for international cooperation.
