From “Physics Today” : “CERN’s Higgs boson discovery:: The pinnacle of international scientific collaboration?”

Physics Today bloc

From “Physics Today”

30 Jun 2022
Michael Riordan

Decades of effort to establish a global, scientist-managed high-energy-physics laboratory culminated in the discovery of the final missing piece of the discipline’s standard model.


Credit: Abigail Malate for Physics Today

Ten years ago, two of the largest scientific collaborations ever—spanning six continents and encompassing more than 60 nations—announced their discovery at CERN of the long-sought Higgs boson, the capstone of the standard model.

Physicists from all the countries involved could take well-earned credit for what will surely stand as one of the 21st century’s greatest scientific breakthroughs. It was a remarkable diplomatic achievement, too, at a moment of relative world peace, perhaps the pinnacle of international scientific cooperation. And it would not have been possible without a series of farsighted decisions and actions.

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Higgs


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Part of CERN’s success as a citadel of modern physics is due to the early-1950s decision to establish it in Geneva, Switzerland, a city and nation widely recognized for cosmopolitanism and political neutrality. Many thousands of scientists of diverse nationalities, not just Europeans, have eagerly pursued high-energy-physics research in this highly appealing environment, given its many cultural amenities—plus world-class hiking, mountain climbing, and skiing in the nearby Alps.

CERN grew steadily during more than five decades of increasingly important high-energy-physics research, reusing existing accelerators and colliders wherever possible in the construction of new facilities. It gradually developed a talented, cohesive staff that could effectively manage the difficult construction of the multibillion-euro Large Hadron Collider (LHC) and its four gigantic detectors: ALICE, ATLAS, CMS, and LHCb.

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LHC

LHC

THE FOUR MAJOR PROJECT COLLABORATIONS

ATLAS

ALICE

CMS

LHCb


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After the 1993 demise of the Superconducting Super Collider (SSC), CERN leaders decided to pursue construction of the LHC, but they realized they needed to attract significant funds for the project from beyond Europe. That transformation—effectively to make it a “world laboratory”—required extending its organizational framework and lab culture to embrace those contributions and the large contingents of non-European physicists that would accompany them.

Given that accomplishment, CERN will likely remain the focus of world high-energy physics as the discipline begins building the next generation of particle colliders.

Especially after the savage Russian invasion of Ukraine and the looming bifurcation of the world order, the lab now offers an island of stability in a global sea of uncertainty. National governments require strong assurances that the money and equipment they send abroad for scientific megaprojects are being well managed on behalf of their scientists and citizenry. In that regard, CERN has a remarkably robust, decades-long track record.

Funding international collaborations

Establishing a vigorous, productive laboratory culture does not happen overnight. It requires years, if not decades. In the late 1980s, SSC proponents failed to appreciate that essential process. Rather than electing to build their gargantuan new collider in Illinois adjacent to Fermilab and adapt the lab’s existing Tevatron to serve as a proton injector, they selected a new, “green field” site just south of Dallas, Texas.

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[Earlier than the LHC at CERN, The DOE’s Fermi National Accelerator Laboratory had sought the Higgs with the Tevatron Accelerator.

But the Tevatron could barely muster 2 TeV [Terraelecton volts], not enough energy to find the Higgs. CERN’s LHC is capable of 13 TeV.

Another possible attempt in the U.S. would have been the Super Conducting Supercollider.

Fermilab has gone on to become a world powerhouse in neutrino research with the LBNF/DUNE project which will send neutrinos 800 miles to SURF-The Sanford Underground Research Facility in in Lead, South Dakota.]
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Other factors were involved in the project’s collapse, too, among them the internecine politics of Washington, DC (see my article, Physics Today, October 2016, page 48). But mismanagement of the project (whether real or perceived) by a contentious, untested organization of accelerator physicists and military managers contributed heavily to the SSC’s October 1993 termination by the US Congress.

When the US quest to build the SSC finally ended, CERN was ready to push ahead with plans for its fledgling LHC project—and to make it a global endeavor. Whereas the SSC project had severe difficulty in securing foreign contributions for building the collider, CERN reached beyond its 19 European member states for contributions to the LHC. By the time the CERN Council gave conditional approval to proceed with the project in December 1994, the lab could anticipate sufficient funding from Europe for an initial construction phase based on a proposed “missing magnet” scheme: Just two-thirds of the proton collider’s superconducting dipole magnets would at first be installed in the existing 27 km tunnel of the Large Electron–Positron (LEP) Collider after its physics research ended. Some doubted whether the scheme was feasible, but it permitted the project to begin hardly a year after the SSC termination. And CERN then opened the door to additional contributions from nonmember states that would allow LHC construction to occur in a single phase.

In May 1995 Japan became the first non-European nation to offer a major contribution to LHC construction, committing a total of 5 billion yen (then worth about 65 million Swiss francs or $50 million). Russia made a similar commitment the following year, mainly for the construction of the LHC detectors. Canada, China, India, and Israel soon followed suit (although with smaller contributions). The US—still smarting from the SSC debacle—took longer. After lengthy negotiations with the Department of Energy and Congress, CERN director general Christopher Llewellyn Smith finally succeeded in securing a major US commitment worth $531 million in December 1997, including $200 million for collider construction. The US, Japan, and Russia were granted special “observer” status on the CERN Council, giving them a say in LHC management.

Russia provides an excellent case history of the negotiations and agreements involved in extending CERN participation to include nonmember states. Soviet and Russian physicists had been involved in research there since the mid 1970s, when they began working on fixed-target experiments on the Super Proton Synchrotron.

In the early 1990s, Russian physicists made major contributions to the design of the CMS detector for the LHC, for which the RDMS (Russia and Dubna member states) collaboration, led by the Joint Institute of Nuclear Research (JINR) in Dubna, Russia, played a formative role.

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Cutaway view of the original Compact Muon Solenoid, or CMS, detector. Credit: CERN.

The total cost of materials and equipment produced in Russia for the CMS has been estimated at $15 million, with part of the amount provided by CERN and its member states. Russian institutes contributed a similar value of equipment and materials to the ATLAS experiment—again funded partly by CERN and its member states. Hundreds of Russian physicists have since been involved in both experiments.

And those globe-spanning experimental collaborations benefited extensively from the creation and development of the World Wide Web at CERN by Tim Berners-Lee.

By the time CERN shut down the LEP in November 2000 and began full-fledged LHC construction, the lab had effectively been transformed from a European center for high-energy physics into a world laboratory for the discipline. The “globalization” of high-energy physics was off to a good start.

A crucial aspect of that global scientific laboratory is the Worldwide LHC Computing Grid, a multitier system of more than 150 computers linked by high-speed internet and private fiber-optic cables designed to cope with the torrent of information being generated by the LHC detectors—typically many terabytes of data daily. Initial event processing occurs on CERN mainframe computers, which send the results to 13 regional academic institutions (Fermilab and JINR, for example) for further processing and distribution. The grid enables experimenters to do much of the data analysis at their home institutions, supplemented by occasional in-person visits to CERN to interact directly with collaborators and detector hardware. In addition, thousands of these physicists make extensive use of the World Wide Web to share designs, R&D efforts, and initial results as well as to draft scientific articles for publication.

CERN has been able to establish a successful laboratory culture, conducive to the best possible work by thousands of high-energy physicists, because the lab has essentially complete control of its budget, which exceeded a billion Swiss francs annually as the new century began. Accommodations have been made for specific national needs (for example, the costs of German reunification), but the resulting budget remains under CERN auspices. Important decisions are made by physicists—not bureaucrats or politicians—who better appreciate the ramifications of those decisions for the quality of the scientific research to be done. Contrary to the case of the SSC, meddlesome military managers were not involved.

Discovering the Higgs boson

Scientists’ control of their own workplace, which begins with laboratory design and construction and continues into its management and operations, is an important factor in doing successful research. When a meltdown of dozens of superconducting dipole magnets occurred shortly after LHC commissioning began in September 2008, for example, it was a crack team of CERN accelerator physicists who dealt with and solved the utterly challenging problem, taking more than a year to bring the machine back to life. Protons finally began colliding in November 2009, albeit at a reduced collision energy of 7 TeV and at very low luminosity (collision rate).

Serious data taking began in 2011, as LHC operators nudged the luminosity steadily higher and proton collisions began to surge in. By year’s end, both the ATLAS and CMS experiments were experiencing small excesses of two-photon and four-lepton events—the decay channels expected to give the clearest indication of Higgs boson production—in the vicinity of 125 GeV. But both collaborations stopped short of claiming its discovery.

When similar excesses appeared in the experiments during the spring 2012 run, their confidence swelled—especially after combinations of the two-photon and four-lepton events exceeded the rigorous five-sigma statistical significance required in high-energy physics. I was fortunate to be present at CERN (if a little groggy from jet lag) when that crucial threshold was crossed in late June by a group of ATLAS experimenters, many hailing from China and the US, who began noisily celebrating in an adjacent office. (See the accompanying essay by Sau Lan Wu.)

The 4 July 2012 CERN press conference announcing the Higgs discovery—timed to coincide with the opening day of the 36th International Conference on High Energy Physics in Melbourne, Australia—was televised around the globe to rapt physicist audiences on at least six continents. Americans had to awaken in the early morning hours of their nation’s 236th birthday to watch the proceedings. In the packed auditorium, along with former CERN directors (including Llewellyn Smith) and current managers sitting prominently and proudly in the front row, sat theorists François Englert and Peter Higgs, who would soon share the Nobel Prize in physics for anticipating this epochal discovery (see Physics Today, December 2013, page 10). “I think we have it,” stated CERN director general Rolf-Dieter Heuer after the ATLAS and CMS presentations, perhaps a bit guardedly. “We have observed a new particle consistent with a Higgs boson.”

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At the Higgs discovery announcement, CERN Director General Rolf Heuer congratulates François Englert and Peter Higgs, who would later receive the 2013 Nobel Prize in Physics for their theoretical description of the origin of mass—which was confirmed by the Higgs boson detection.

It was certainly a European triumph, a vindication of the continent’s patient and enduring support of science—but also a triumph for the global physics community. Both the ATLAS and CMS collaborations then involved about 3000 physicists. ATLAS physicists hailed from 177 institutions in 38 nations; CMS included 182 institutions in 40 nations. Physicists from Brazil, Canada, China, India, Japan, Russia, Ukraine, and the US, among many other nations, could rejoice in the superb achievement, along with those from Belgium, France, Germany, Italy, the Netherlands, Poland, Spain, Sweden, the UK, and other CERN member states.

If the Higgs boson discovery does not represent the pinnacle of international scientific cooperation, it surely sets a high standard. It will be a difficult one to match in the coming decades, given the conflicts and cleavages that have been erupting since Russia’s brutal Ukraine invasion. Russian scientific institutes have been at least temporarily excluded from future CERN projects—and the ban may well become permanent. And the costs of European rearmament could easily impact the CERN budget in the coming years. The first two decades of the 21st century will certainly represent a special moment in history when so many nations could work together peacefully in a common scientific pursuit of the greatest significance.

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