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Moving forward together

Physics World April 2020

Physics World

 
Comment: Forum Physics World  April 2020

Moving forward together

In the run-up to a pivotal announcement on the future of particle physics in Europe, Tessa Charles urges backers of rival colliders to unite around whichever project gets the go-ahead

New look The successor to the Large Hadron Collider is likely to be just one of four competing designs. (CERN)

Every five years or so, members of the European Strategy Group (ESG) for particle physics face a monumental task: recommending medium- and long-term plans for the community’s future. In January this group – which comprises scientific delegates appointed by each CERN member state; directors and representatives from major European laboratories and organizations; and a few non-European invitees – met for the final time in Bad Honnef, Germany. We now await their recommendation, which is due in May when the CERN council announces the laboratory’s future direction.

I sincerely hope the announcement will fill the particle-physics community with renewed motivation and engagement. However, particle physicists, accelerator physicists and engineers must reckon with the fact that many of us have dedicated years of our lives to a single project. For some, it has been decades. As a result, we have become so strongly sorted by project allegiance that we resemble opposing sides of a political debate. And the reality is that, come May, some of us could learn that our project is being mothballed.

In the wake of the ESG’s recommendation, we will need to ask ourselves, “Where to from here?” The world only needs so many high-energy colliders. Once the eventual decision is made (even if it’s not immediately conclusive), and as effort is redirected from one project to another, we will need to learn how to work and live well together as a single, unified community.

Building on consensus

For some time, consensus has been brewing that the next high-energy machine should be a positron–electron (e+/e) or muon collider of sufficient energy to spawn copious Higgs bosons. This so-called “Higgs factory” would enable a detailed investigation of the once-elusive Higgs boson, and would add shading and nuance to our understanding of the Standard Model of particle physics, while not precluding the construction of a proton–proton collider at some later date. Yet the question remains: which collider should CERN pursue?

At this point, readers may well be asking where my own biases lie. The answer is that I have worked on both major CERN-based post-Large Hadron Collider projects – the Compact Linear Collider (CLIC) and the e+/e Future Circular Collider (FCC-ee) – and I see merits in each. In any discussion of this tumultuous subject, this is something that bears repeating: there are merits in both projects. Beyond Europe, Japan’s proposed International Linear Collider (ILC) and plans for a Chinese Electron Positron Collider (CEPC) must also be taken into consideration as we plan our next moves within a global context. The same goes for the recently funded electron–ion collider in Brookhaven, US, and the renewed interest in muon colliders.

The competition between CEPC and FCC-ee has spurred rapid advances in both designs. Similarly, the non-guaranteed future of all four major projects (CLIC, FCC, ILC and CEPC) has demanded rigour from the physicists working on them. Rivalry and disagreements have strengthened each proposal, lending support to the notion that ideas subjected to criticism evolve and grow stronger than ideas left unchallenged. The result is four strong proposals. If ambition were the selection criterion, all four would be overqualified.

Respectful academic disagreements of this type have advanced our field. Embedded in this respect is an acknowledgement that our favoured project might not go ahead. Disappointment for some is inevitable, and many in the community are bracing for it as we try to envision a path forward. For so many of us, what we do for work forms a strong pillar of our identity. We’re dedicated to our research because we love it. But because we love it, and because it forms part of who we are, the ESG’s recommendation could be shattering.

The particle accelerator community is known for its adaptability, problem solving and perseverance. Our next challenge will be to find the capacity and skill, as well as the generosity and courtesy, to hold colleagues from other projects in the same regard as we hold favourite colleagues from our own projects. We can be disappointed, and we can express disappointment, but only in a tone that assures respect.

It is also important to recognize the wider impact of our curiosity-driven search for the next collider. Regardless of the outcome from Bad Honnef, advances and innovations from the various projects have already made their mark on the accelerator community. As a large, low-emittance electron storage ring, FCC-ee has rekindled ties between the collider and light-source communities. Decades of work on CLIC have produced X-band technology that is now being used in medical accelerators. The CLIC accelerating structures have also been repurposed as an XFEL driver known as CompactLight. Meanwhile, the high-field magnets of an FCC hadron-colliding variant (FCC-hh), if demonstrated, would have a profound impact on MRI machines. A wise strategy would be to seek to capitalize still more on these pioneering developments, independent of the project from which they arose, and independent of the ESG’s decision.

Common goals

Once the decision is made (which may take a while, especially if the ESG’s recommendation is not conclusive), there will be an opportunity to welcome talented people from unsuccessful projects into the endorsed one. As we near the date of the report’s release, proponents from each side must find a way to live and work well together. After all, we share common goals: to advance human knowledge, to be inspired by the physics of nature, and to continue the scientific and technological advances in our fields.