Thanks to Burton Richter for asking in this venue, “Should the US join CERN?” CERN is the preeminent institution in the world for the study of hadron collisions at very high energies and the exploration of physics on the electroweak scale. The extraordinary Large Hadron Collider (LHC) and its complement of superb detectors, which make possible a sweeping range of investigations, have already reaped their first immense reward—the discovery of the Higgs boson. Hundreds of other measurements and searches have been reported in the journals, and we have just begun to tap the LHC’s potential. We can only guess what new wonders await when the center-of-momentum energy increases from 8 TeV toward the 14-TeV design energy and the number of events recorded grows by an order of magnitude.
Thanks to CERN’s openness and enlightened support from our funding agencies, physicists from institutions in the US have teamed with their colleagues from CERN member states and beyond for the scientific adventure of a lifetime. American physicists and laboratories have made notable contributions to the collider itself, to the principal detectors, and to the intellectual life of the experiments. As Richter notes, we must plan now for the next phase of collaboration with CERN.
I believe that an appropriate step is to forge a lasting link between CERN and the US, not only to secure continued participation of American experimenters in the LHC program, but also as a show of solidarity and common purpose. Particle physics is strengthened, and its returns to society enhanced, if we plan and execute major initiatives together. The US could, for example, seek associate membership in CERN and commit to specific contributions to the development of the LHC complex and its suite of experiments. Negotiations need not, of course, be limited to the existing membership categories.
|
A deepening partnership between the US and CERN must have a strong element of reciprocity. Farsighted physicists of an earlier day made a commitment to openness and exchange a key component in the practice of particle physics worldwide. An understanding adopted by the International Committee for Future Accelerators (ICFA) anticipated that major experimental installations for high-energy physics would be few in number and located in different regions of the world, and recognized that experimental physicists from all regions would wish to pursue research at these few machines.
ICFA guidelines stipulate that scientific merit, technical feasibility, capability of the experimental group, and availability of the resources be the criteria for selecting experiments and determining their priority—not the nationality of the proponents. Expecting that international participation would be balanced among regions, laboratories did not require experimental groups to contribute to costs of running accelerators or operating experimental areas (though an exception was foreseen for large global projects).
ICFA’s mandate for open access encourages physicists to seek the best place to carry out their proposed experiments and stimulates the formation of international collaborations. Every laboratory’s scientific program is immeasurably stronger for the contributions of visitors from other parts of the globe.
Europe looks abroad
The European Strategy Group convened under the aegis of the CERN Council has issued an update of the European Strategy for Particle Physics. Two recommendations speak directly to reciprocity: “Europe should explore the possibility of major participation in leading neutrino projects in the US and Japan,” and “Europe looks forward to a proposal from Japan [for the International Linear Collider] to discuss a possible participation.” No commitment has been concluded, but the door is open for discussion.
The willingness of our European colleagues to consider investing collectively in a major particle physics project in the US is welcome news, but we must earn their confidence. Our national laboratory for particle physics must be a credible peer to CERN in research, innovation, education, and collaboration. We must put forward, and elaborate with potential partners, ambitious ideas worthy of the world’s attention that enhance the diversity and scale diversity of the experimental portfolio. To be seen as trustworthy associates, we must break the pernicious cycle of launching experiments and projects, only to see them cancelled.
Opportunities for world-leading science abound. Some experiments of exceptional importance cannot be carried out at the LHC because they require intense, well-regulated beams of different particle species, at a range of energies. One important class comprises neutrino experiments over long and short baselines. These will extend our understanding of neutrino mixing, and aid our search for evidence of CP violation in the neutrino sector (CP is the combined operators for charge conjugation and parity). Ultimately, there are possible implications for leptogenesis as the origin of the observed matter excess in the universe.
Another vital project searches for phenomena that are highly suppressed in the standard model of particle physics, such as the decay as K+ → π + νν‾ and other candidates for the observation of flavor-changing neutral currents, muon–electron conversion, and other lepton-flavor-violating transitions, neutron–antineutron oscillations, and intrinsic electric dipole moments of neutrons and electrons.
A third category includes measurements of unprecedented precision, including improved knowledge of the anomalous magnetic moment of the muon and incisive new studies of the structure of the nucleon and other hadrons.
Investigations of this character have been assembled under the rubric of the “intensity frontier”. (Perhaps the “sensitivity frontier” would be a more apt characterization of the physics goals.) Taken together, and in conversation with studies at the LHC, these experiments can speak to the existence of new forces of nature and new dimensions, including the quantum dimensions that supersymmetry entails, and can test and enrich our understanding of quantum chromodynamics and the electroweak theory. Quantum corrections to standard-model expectations are sensitive to new degrees of freedom at energy scales higher than those directly accessed by the LHC. When the LHC provides evidence for new degrees of freedom, highly sensitive experiments with diverse beams can supply critical insights.
Project X
In Fermilab’s plan for the future, Project X would enable these experiments and more. Project X is a versatile 8-GeV superconducting linac that dramatically increases beam power and makes beams with different characteristics available to many experiments at once. That machine would provide the foundation of future projects that might be indicated by scientific imperatives and technical feasibility, such as a muon-storage-ring neutrino factory to provide a millimole of neutrinos per year, a muon collider, or a very-high-energy successor to the LHC.
Some assert that particle physics can flourish in the US without a world-class accelerator. This attitude is misguided on every score. The state of our science motivates initiatives that complement the program of the LHC, and the US community has both the incentive and the capability to lead. Carrying out research at the highest level at home, while engaging with the world community both here and abroad, provides the greatest range of opportunities for our scientists, students, technicians, and engineers, as well as for the commercial enterprises that supply them. High-energy physics has special requirements—for high energies and high intensity or luminosity, along with the imperative for cost reduction in grand projects—that do not coincide with other accelerator-based research, including light sources. High-field accelerator dipoles made with superconductors of higher performance than niobium and stochastic- or electron-beam-cooling are leading examples of technological responses to the needs of particle physics.
While we contemplate our relationship with international organizations, we also must examine the state of our own institutions. In 2005, the Department of Energy’s Office of High Energy Physics (OHEP) altered the manner in which the experimental particle physics program in the US is planned. Traditionally, planning and executing the experimental program was the purview of the laboratory directors and their program advisory committees, with gentle oversight from DOE and the High Energy Physics Advisory Panel. HEPAP gave wise and decisive advice on new accelerators and other major projects. On the whole, that system worked admirably; the directors, though occasionally fallible, have been scientists of great substance who were able to make dynamic adjustments to their laboratory programs. They showed remarkable insight in looking over the horizon to fashion coherent futures for their laboratories and for the field. The PACs worked with remarkable energy and dedication to shape and improve proposals and monitor their execution.
In place of that system, OHEP has moved toward a NASA-style procurement system, in which scientific opportunities are identified at headquarters, experiments are selected by panels that report to the OHEP Director, and laboratory directors are charged to execute the program as defined. Modest expenditures are closely controlled, limiting a laboratory’s ability to explore alternative futures. It is unclear what role is left for Fermilab's PAC, and not obvious that ad hoc advisory panels can exhibit the same dedication to an integrated program that has marked the PACs at their best. The Particle Physics Project Prioritization Panel (P5) was born of noble sentiments, and its members have worked with dedication. But its record is decidedly mixed. Because of the way it is has focused on near-term funding requests, it failed to foresee challenges, such as uncertain prospects for the National Science Foundation’s Deep Underground Science and Engineering Laboratory (DUSEL). In the face of budget pressures, P5 has been an instrument to eliminate highly attractive initiatives.
There is no question that such a panel of experts can give essential advice about community aspirations, scientific merit, and urgency. But setting priorities that make long-term sense requires strong direction from those with an ongoing responsibility for implementing the research agenda and working with Congress and the executive branch to make superb science happen, starting with laboratory directors. HEPAP, the agencies, and the community can do better than once-and-done panels responding to budget scenarios that are crude approximations of a multivariate world.
The new protocol marks a radical change in the way we have organized research, and it has now been in place long enough to merit thoughtful public examination and refinement. I foresee the risk of much loss: A project-centered, directed economy might ensure that you deliver what you promise, but it virtually guarantees that you will never deliver more than you promise, because there is no place for the flexibility—which some might mistake for inefficiency—from which many of our innovations come. On the other hand, intrusive oversight in the name of accountability begets truly wasteful inefficiency.
Our research enterprise reflects the nation at large. The difficult environment for funding the physical sciences reflects, I believe, a deeper problem in our society. For more than a decade, the will to join together and undertake challenging and important causes for the general good has been too little in evidence. This is an aberration in American history, and we must change it.
Chris Quigg is a theoretical physicist at the Fermi National Accelerator Laboratory. The views expressed herein are the author’s.
