Physics societies provide valuable input to the planning process.
Given the broad international collaborations involved in major scientific user facilities, timely formal and informal discussions among leaders of physics societies worldwide contribute to fortifying the scientific case that is needed to justify large, new enterprises. The past year, 2013, proved to be one of focused introspection and planning for major research facilities, conducted by learned societies and by government agencies in Asia, Europe and the US. All three regions developed visions for particle physics and in the US the government developed priorities and plans for a broad spectrum of scientific user facilities.
The Asia-Europe Physics Summit
In July, in Makuhari, Chiba, Japan, the third Asia-Europe Physics Summit (ASEPS3) – a collaboration between the Association of Asia Pacific Physical Societies and the European Physical Society – provided a forum for leaders in the respective physics communities to discuss strengthening the collaboration between Europe and the Asia-Pacific region (Barletta and Cifarelli 2013). These summits have three main goals: to discuss the scientific priorities and the common infrastructure that could be shared between European and Asian countries in various fields of physics research; to establish a framework to increase the level of Euro-Asia collaborations during the next 20 years; and to engage developing countries in a range of physics research. This year’s summit centred on international strategic planning for large research facilities. It also included a significant US perspective in three of the four round-table discussions.
High-energy physics programmes received particular focus
Round Table 1 offered perspectives on the technologies that enable major research facilities, while Round Table 2 looked to the issues of policy and co-operation inherent in the next generation of large facilities. High-energy physics programmes received particular focus in the discussion, where the three regions of Asia, Europe and the US have their own road maps and strategies. This round table clearly provided a special opportunity for a number of leaders and stakeholders to exchange their views. Participants in Round Table 4 discussed training, education and public outreach – in particular the lessons learnt and challenges from large research laboratories. Although the science motivations for major user facilities differ widely, many of the underlying accelerator and detector technologies – as well as issues of policy, international co-operation and training the next generation of technical physicists and engineers – are nonetheless in common.
Because both the update to the European Strategy for Particle Physics and the Technical Design Report for the International Linear Collider (ILC) had been issued by the time of the summit, and because the Snowmass process in the US was well under way, major facilities for particle physics set a primary, although far from exclusive, context for the discussions.
The European Strategy for Particle Physics
In January, a working group of the CERN Council met in Erice to draft an updated strategy for medium and long-term particle physics. That document was remitted to the Council, which formally adopted the recommendations in a special meeting hosted by the European Commission in Brussels in May. As expected, the updated strategy emphasizes the exploitation of the LHC to its full potential across many years through a series of planned upgrades. It also explicitly supports long-term research to “continue to develop novel techniques leading to ambitious future accelerator projects on a global scale” and to “maintain a healthy base in fundamental physics research, in universities and national laboratories”. In a period in which research funding is highly constrained worldwide, these latter points are a strong cautionary note that maintaining “free energy” in national research budgets is essential for innovation.
Beyond the focus on the LHC, the strategy recommends being open to engaging in particle-physics projects outside of the European region. In particular, it welcomes the initiative from the Japanese high-energy-physics community to host the ILC in Japan and “looks forward to a proposal from Japan to discuss a possible participation”. That sentiment resonated strongly with many participants in the 2013 Community Summer Study in the US, especially in the study groups on the energy-frontier study and accelerator capabilities. In September, the Asia-Pacific High Energy Physics Panel and the Asian Committee for Future Accelerators issued a statement that “the International Linear Collider (ILC) is the most promising electron positron collider to achieve the objectives of next-generation physics.”
The 2013 US Community Summer Study
In the spring of 2012, the Division of Particles and Fields of the American Physical Society (APS) commissioned an independent, bottom-up study that would give voice to the aspirations of the US particle-physics community for the future of high-energy physics. The idea of such a non-governmental study was welcomed by the relevant offices of both the US Department of Energy (DOE) and the National Science Foundation (NSF). The APS study explicitly avoided prioritizing proposed projects and experiments in favour of providing a broad perspective of opportunities in particle physics that would serve as a major input to an official DOE/NSF Particle Physics Project Prioritization Panel (P5). The study was broadly structured into nine working groups along the lines of the “physics frontiers” – energy, intensity and cosmic – introduced in the 2008 P5 report and augmented with studies of particle theory, accelerator capabilities, underground laboratories, instrumentation, computing and outreach. In turn, the two conveners of each working group divided their respective studies into several sub-studies, each with three conveners, generally.
Beginning with a three-day organizational meeting in October 2012 and culminating in a nine-day session at the end of July/beginning of August 2013 – “Snowmass on the Mississippi” – the 2013 Community Summer Study involved nearly 1000 physicists from the US plus many participants from Europe and Asia. Roughly 30 small workshops were held in 2013 to prepare for the “Snowmass” session at the University of Minnesota, which was attended by several hundred physicists.
Snowmass activities connected with the energy frontier were strongly influenced by the discovery of a Higgs boson at the LHC. Not surprisingly, the scientific opportunities offered by the LHC and its series of planned upgrades received considerable attention. The study welcomed the initiative for the ILC in Japan, noting that the ILC is technically ready to proceed to construction. One idea that gained considerable momentum during the Snowmass process was the renewed interest in a very large hadron collider with an energy reach well beyond the LHC.
The conclusions of each of the nine working groups are presented in a summary report, which defines the most important questions for particle physics and identifies the most promising opportunities to address them in several strategic physics themes:
• Probe the highest possible energies and distance scales with the existing and upgraded LHC and reach for even higher precision with a lepton collider. Study the properties of the Higgs boson in full detail.
• Develop technologies for the long-term future to build multi-tera-electron-volt lepton colliders and 100 TeV hadron colliders.
• Execute a programme with the US as host that provides precision tests of the neutrino sector with an underground detector. Search for new physics in quark and lepton decays in conjunction with precision measurements of electric dipole and anomalous magnetic moments.
• Identify the particles that make up dark matter through complementary experiments deep underground, on the Earth’s surface and in space, and determine the properties of the dark sector.
• Map the evolution of the universe to reveal the origin of cosmic inflation, unravel the mystery of dark energy and determine the ultimate fate of the cosmos.
The study further identifies and recommends opportunities for investment in new enabling technologies of accelerators, instrumentation and computation. It recognizes the need for theoretical work, both in support of experimental projects and to explore unifying frameworks. It calls for new investments in physics education and identifies the need for an expanded, co-ordinated communication and outreach effort.
Although the activities of 2013 on possible perspectives and scenarios for major science facilities were neither a worldwide physics summit nor a worldwide physics study, they served to open the door for extensive engagement by physicists to build a compelling science case for major research facilities in Asia, Europe and the US. They identified ways to increase the scientific return on society’s investment and to spread the benefits of forefront physics research to developing countries.
During the meetings in 2013, it became clear that a possible future picture could be construction of the ILC in Japan and a long baseline neutrino programme in the US, while Europe exploits the LHC and prepares for the next machine at the energy frontier, which can be defined only after LHC data obtained at 14 TeV in the centre of mass have been analysed. Therefore, despite highly constrained research budgets worldwide, future prospects look bright and promising. They represent today’s challenge for the next generation(s) of scientists in a knowledge-based society.