Particle physics: Together towards the next frontier

As emerging players shake up old ambitions, Nigel Lockyer calls for the next generation of particle physics projects to be coordinated on a global scale.

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This year was a turning point for particle physics. The decades-long quest to discover the Higgs boson is all but over. Still abuzz after a Nobel Prize for the prediction of the Higgs, the particle physics community is feeling satisfied. It’s time to pause, reflect and consider what comes next.

The Higgs boson is the final piece of the puzzle in the Standard Model of particle physics, but the model fails to explain some fundamental aspects of our Universe. From the very small neutrino mass to dark matter and dark energy, we know there is more going on. But where could the next clue be hidden?

We really don’t know. Each physicist has their own opinion, and countries and regions are preparing to explore different strategies to identify the territories most ripe for exploration. What we do know is that the next generation of particle accelerators will be expensive. And requests for government funding will face budget constraints around the world.

As the new director of the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, I have spent the past six months discussing the future of particle physics in the United States. But particle physics is an international activity, with projects and participants from many different countries. The United States is well positioned to take the lead in some areas, such as neutrino physics, but the global landscape is uncertain. Resources must be pooled and new players are emerging. The talents, infrastructure and ambitions of China and India must now be factored into the global equation.

We are at a critical moment for the field. Each country and each major project must take into account its impact on the company as a whole. The opportunity is enormous: a truly cohesive approach to accelerating progress and combining disparate forces. But the risks are just as great: failing to agree on major efforts, losing international partners, and sacrificing progress in a downward spiral of too many partially approved projects.

The high-energy frontier near the Higgs will soon be within reach of the Large Hadron Collider (LHC) at CERN, Europe’s particle physics laboratory near Geneva, Switzerland, currently the highest-energy accelerator in the world. When it comes back on in early 2015 after a two-year upgrade, the machine will be operating near its design energy of 14 teraelectronvolts (TeV), about double that at which the Higgs was discovered. Now that the Standard Model is complete, any new particle found will revolutionize our view of physics.

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Beyond that, there are plans to upgrade the LHC in the 2020s to deliver even brighter beams and detectors capable of handling the huge data rates that will be produced. Even modest upgrades will cost around $1 billion, requiring contributions from non-member states as well as member states.

Other borders are promising. We still don’t understand how neutrinos interact, the origin of their tiny masses, or their role in the early Universe. Fermilab is leading a US proposal to build a long neutrino beam experiment, traveling 1,300 kilometers from Fermilab to Homestake Mine in South Dakota. An ambitious 35 kiloton liquid argon detector located nearly 1,500 meters below the surface emerged as the project of choice when the American community gathered in Minnesota for a ten-day planning symposium in July. This would help us understand the masses of neutrinos and whether these particles contribute to the matter-antimatter asymmetry of the Universe.

With a total construction budget approaching $1 billion, the experiment will require international partners – a new approach for US domestic science. The US Department of Energy’s Office of Science said it would support such a large proposal if Europe and Asia were involved.

A long-baseline neutrino experiment is needed somewhere. Alternatives are on the table: one in Europe would see neutrinos travel from CERN to Finland; another has neutrinos traveling through Japan. But the world can only afford one.

Japan is perhaps the strongest contender, with leading programs in neutrino physics, a lower quark (“b-quark”) factory, and kaon and muon experiments. The country hopes to host the International Linear Collider (ILC) – a 30 kilometer long 500 gigaelectronvolt electron-positron collider to study the Higgs boson that would surpass the LHC in accuracy by the late 2020s. construction will begin later this decade.

Japan is about to launch a campaign to gain its support for this international project, which would require the participation of the United States and Europe. Most particle physicists support the ILC, but many would like to see what discoveries will come out of the upgraded LHC first. If no new particles emerge, the greater precision available to the ILC would make its construction even more appealing. If another discovery is made at the LHC, the community might need a different machine to explore the new energy regime.

Since we don’t know what the next fertile energy range is, many particle physicists believe we should aim as high as possible. Some argue for an even higher energy lepton collider, such as a muon collider or the Compact Linear Collider (a higher-energy European competitor to the ILC) that would reach 3–5 TeV. Europe is assembling a team to design a 100 TeV proton-proton collider, with a tunnel 100 kilometers in circumference, to probe all the particles likely to be discovered by the upgraded LHC and at higher energies. This machine could start in the 2030s.

And the United States still has ambitions to host a high-energy frontier machine, having shut down Fermilab’s Tevatron accelerator in 2011 and failed to achieve the superconducting supercollider in the 1990s. high energy relay could be sent back to the United States. Fermilab is still a world leader in high-field magnets for proton accelerators, which would be needed for any 100 TeV proton-proton collider.

“If China leaps forward, it will change the landscape of science. ”

To add to the suspense, there is the evolution of China’s role. Historically a small player in particle physics, it entered the world stage last year with impressive results in reactor neutrino physics, including showing that two of the three types of neutrinos mix much more than expected. This great mixing implies that fundamental symmetry differences between neutrinos and antineutrinos could be observable in a long-baseline experiment, telling us about the imbalances of matter and antimatter in the early Universe. Emboldened, could the Chinese overtake the world by hosting the 100 TeV machine? The machine would be cheaper to build in China, although the nation needs help from the rest of the world to design and build it.

If China leaps forward, it will change the landscape of science, leveling the playing field with emerging economies. Discussions on global advances in particle physics should explicitly include heads of state from China and India as well as North America, Europe and Japan.

Physicists don’t care where they do their research. But the vast scale of particle physics projects means that all new mega-accelerators require global planning, agreement and joint construction. Governments around the world will have to make unprecedented financial investments in other countries, challenging the traditional political calculus that taxpayers’ money is primarily spent domestically for short-term direct benefit.

Governments are trying to figure out which models best suit their national interests. We speak less of “brain gain and drain” and more of “brain circulation”. Countries and intellectual communities thrive by participating in the global conversation, not necessarily by owning most of the players.

Care must be taken to ensure the health of large regional laboratories, such as CERN, Fermilab and the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan: these are the only places where major particle physics are currently feasible. Demands from emerging economies such as China to host other projects will challenge the long-term plans of existing leaders. Scientists in the United States and Europe will need to find the best way to use international competition as a spur to advance projects on their own soil while being good international partners. It can get tricky.

Higgs bosons are not export controlled, nor are deep space images taken by advanced telescopes. But the technologies developed, often through international collaborations, can have dual uses – for defense applications or for economic gain, for example, as well as for basic science. Countries will need to decide how to responsibly monitor and exploit these opportunities.

Particle physics leaders need to be more vocal and aggressive in setting and advocating for the global agenda. After all, a suite of global particle physics facilities help us understand how the Universe works.

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Correspondence to Nigel Lockyer.

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Lockyer, N. Particle physics: Together towards the next frontier.
Nature 504, 367–368 (2013). https://doi.org/10.1038/504367a

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