On April 5, the Breakthrough Prize Foundation announced the 2025 Breakthrough Prize in Fundamental Physics recipients. The award was given to four major international collaborations—ALICE, ATLAS, CMS, and LHCb—conducting experiments at CERN’s Large Hadron Collider (LHC).
The prize was awarded to the collaborations for their “detailed measurements of Higgs boson properties confirming the symmetry-breaking mechanism of mass generation, the discovery of new strongly interacting particles, the study of rare processes and matter-antimatter asymmetry, and the exploration of nature at the shortest distances and most extreme conditions at CERN’s Large Hadron Collider,” and the award acknowledges results published based on LHC Run-2 data through July 2024.
KEK has played a vital role in the ATLAS experiment over many years. Approximately 20 scientists from KEK’s Institute of Particle and Nuclear Studies (IPNS) and the World Premier International Research Center Initiative – International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles (WPI-QUP) contributed to multiple aspects of the project, including the development and construction of key detector components as well as the analysis of physics data. Makoto Tomoto, Deputy Director of KEK’s Institute of Particle and Nuclear Studies, leads the team and serves as Co-Spokesperson of ATLAS Japan (https://atlas.kek.jp/).
In addition, KEK contributed to the development of accelerator technology, particularly through its participation in the design and fabrication of superconducting quadrupole magnets that help focus the particle beams at the LHC’s collision points.
These efforts have been carried out closely with universities and industry partners across Japan.
ATLAS experiment and Japan’s contribution
The ATLAS experiment employs one of the world’s largest particle detectors, measuring 25 meters in diameter and 46 meters in length. Among the four major international collaborations at the LHC, ATLAS is the largest in scale, comprising approximately 6,000 researchers from around 40 countries and regions, including about 3,000 scientific authors. From Japan, around 160 researchers from 13 universities and institutions—including KEK, University of Tsukuba The University of Tokyo, Ochanomizu University, Waseda University, Institute of Tokyo Science, Tokyo Metropolitan University, Shinshu University, Nagoya University, Kyoto University, The University of Osaka , Kobe University, and Kyushu University—are engaged in the experiment. Together, they pursue the study of elementary particles that governed the universe in the moments immediately following the Big Bang.
In the construction of the ATLAS detector, Japan contributed significantly by developing key components. These included the silicon tracker, which measures the trajectories of thousands of charged particles derived from beam collision points, the muon detectors and associated electronics for detecting muons produced in the decay of particles such as the Higgs boson, and the superconducting solenoid magnet essential for the momentum measurement of charged particles. The development and construction of these components involved numerous Japanese companies, and the collaboration of academia, industry, and government was central to their success.
The ATLAS and CMS experiments independently discovered the Higgs boson in 2012. In recognition of their theoretical work, Dr. Peter Higgs and Dr. François Englert, who had proposed the theory, were awarded the Nobel Prize in Physics in 2013.
The Breakthrough Prize and KEK
The Breakthrough Prize is an award funded by the Breakthrough Prize Foundation, backed by Google co-founders and other Silicon Valley entrepreneurs. It recognizes the world’s top scientists working in the fundamental sciences.
This is not the first time a Breakthrough Prize in Fundamental Physics has been awarded to a project involving KEK. In 2015, the 2016 prize was awarded to five international collaborations for their achievements in neutrino oscillation research, including the K2K and T2K experiments, both led by Professor Emeritus Koichiro Nishikawa, former Director of the Institute of Particle and Nuclear Studies at KEK.
Comment from Makoto Tomoto, Deputy Director of KEK’s Institute of Particle and Nuclear Studies / Co-Spokesperson of ATLAS Japan
It is a great honor for all of us in the ATLAS Japan Group to witness the international collaborations—ALICE, ATLAS, CMS, and LHCb—receive such a prestigious award.
Japan has been involved in the ATLAS experiment since its inception when CERN decided to conduct experiments at the LHC. Through this international collaboration, we have made significant contributions in every aspect of the project, from the development and construction of the accelerator and detectors to the computing infrastructure. These achievements would not have been possible without the exceptional efforts of the Japanese industry. We take pride in our central role not only in the discovery of the Higgs boson but also in uncovering its properties.
I would like to extend my heartfelt congratulations to everyone who has contributed to the LHC experiments. I am also deeply grateful to those who continue to support our endeavors.
Comment from Tatsushi Nakamoto, Professor, Cryogenics Science Center, KEK Applied Research Laboratory
Like the international experiments at the LHC, the construction of the accelerator itself was a truly global endeavor involving research institutions around the world. KEK was responsible for developing and constructing the superconducting quadrupole magnets that focus the beams at the collision points—an essential component of the experiments—and we are proud to have successfully fulfilled this role. It is deeply satisfying to know that these magnets have continued to perform reliably over many years, contributing to the success of the beam collision experiments.
Developing superconducting magnets for a collider like the LHC, which demands exceptionally high performance, requires cutting-edge scientific and engineering capabilities. I would like to express my sincere appreciation to the many industrial partners who supported the development and production of these magnets.
Looking ahead to the High-Luminosity LHC, which is scheduled to begin operations around 2030, the superconducting magnet systems near the collision points will be upgraded for even higher performance. KEK is once again contributing to developing and constructing these next-generation magnets, and we are committed to doing our utmost to support the continued success of the experiments.
Comment from Shoji Asai, Director General of KEK
Many Japanese universities and institutions, including KEK, participate in the LHC experiments. This award not only recognizes the tremendous scientific achievements made possible through global cooperation but also highlights the broader significance of such international collaboration.
Research in the field of particle physics is inherently comprehensive, advancing the frontiers of hardware, computing, and physical analysis. It is only possible thanks to the support and partnership of many stakeholders, including those in the industry. I would like to take this opportunity to express my deepest gratitude to everyone involved.
The Higgs Boson and the Higgs Field
In 2012, the ATLAS and CMS experiments announced the discovery of the Higgs boson, showing that our universe is filled with an invisible field known as the Higgs field. This discovery confirmed the Higgs mechanism, which explains how the W and Z bosons—carriers of the weak force—acquire their mass through their interaction with the Higgs field. This finding further validated the electroweak unification.
Subsequent experiments have confirmed that the third-generation elementary particles, such as the top quark, bottom quark, and tau lepton, acquire their mass through interactions with the Higgs field. Recently, evidence has emerged suggesting that the mass of the second-generation elementary particle, muon may arise in a similar manner. The extensive and accurate measurements of the Higgs boson’s properties conducted in the decade following its discovery have contributed to this year’s Breakthrough Prize in Fundamental Physics.
To deepen our understanding of the Higgs field and uncover new physical principles behind it, large amount of experimental data—especially from the upcoming High-Luminosity LHC (HL-LHC) experiment starting in 2030—will be essential.
LHC Operations and ATLAS Data Acquisition
The Large Hadron Collider (LHC) started collecting collision data for physics analysis in 2010. Its experimental period has been divided into three: Run 1 (2010–2012), Run 2 (2015–2018), and Run 3 (2022–2026). The center-of-mass energy for proton-proton collisions increased across these runs: 7–8 TeV during Run 1, 13 TeV in Run 2, and 13.6 TeV in Run 3.
During Run 1, the ATLAS experiment recorded data from roughly three quadrillion (3×1015) proton-proton collisions, which led to the discovery of the Higgs boson. In Run 2, the number of recorded collisions in ATLAS were increased to around 150 quadrillion (1.5×1017) . Results based on the analysis with this dataset contributed to the Breakthrough Prize.
Currently, Run 3 is ongoing and has already accumulated data equivalent to roughly 180 quadrillion (1.8×1017) collisions. This run continues until 2026. Looking ahead, the High-Luminosity LHC is scheduled to start in 2030 and operate until 2041. It is expected to collect data equivalent to around 3,000 quadrillion (3×1018) proton-proton collisions, which will enable even more precise studies of the Higgs boson and the exploration of potential new physics.
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