At first glance, particle physics appears to be a clearly defined sub-discipline of physics. On closer inspection, however, we see a differentiated research landscape with a broad spectrum of questions. The Swiss Institute for Particle Physics (CHIPP), the umbrella organisation for Swiss particle physics, has now drawn up a roadmap of the research priorities for the coming years and decades.
By their very nature, scientific results cannot be predicted. However, planning – of a long-term nature – requires accelerators and experiments, without which progress in high-energy physics is no longer imaginable today. Accelerators and experiments in fundamental physics research are highly complex and their development time is correspondingly long. Experiments are furthermore designed in such a way that they can be expanded step by step over years or even decades to incorporate new findings.
A vision as a model for politics
A scientific vision for the further development of the discipline is essential in particle physics. However, this long-term planning sometimes contrasts with the budgetary timescales of the political actors who subsidise this research. Or in the words of CHIPP President and ETH physics professor Rainer Wallny: "As physicists, we are concerned with the question of which experiments should be in operation in 2045. What we need in terms of resources for such long-term experiments can hardly be broken down to the next SERI budget." With the SERI budget, Wallny refers to the research budget that the State Secretariat for Education, Research and Innovation (SERI) prepares for the Federal Assembly for a period of four years (next time for the period 2025-28) and through which, among others, Swiss particle physics research is strongly supported.
When Swiss particle physics publishes a roadmap of its research priorities for the coming years and decades, it inevitably is a compromise between a scientific vision and - at least on the time scale of particle physics research - a rather short-term oriented resource plan for the attention of politicians. The roadmap presented by the CHIPP representatives in spring 2021 meets this dual requirement. It is not a premiere. Back in 2004, CHIPP published a roadmap on behalf of Swiss particle physics (and then updated it in a follow-up document in 2011). However, particle physics has evolved since then, as the discovery of the Higgs boson in 2012 or the latest exciting results from CERN or Fermilab demonstrate (cf. the articles 'When the coin shows 'heads' more often than 'tails'' and 'Various results shake up the Standard Model'). Particle physics has also become broader in recent years: New experiments in astroparticle physics are on the frontier of astrophysics. Swiss particle physics, organised in CHIPP, will therefore work more closely with CHAPS (College of Helvetic Astronomy Professors) in the future.
A successor for the LHC
The new CHIPP roadmap is a 100-page document that describes current developments in the field of particle physics and anticipates future developments. Four development directions can be highlighted as examples for the broad field of research: The discipline has a clear perspective with the 'Future Circular Collider' (FCC), a 100 km long ring accelerator that is envisaged to replace the current Large Hadron Collider (LHC) in 2045. "This is the flagship project the Swiss particle physics community is united behind," says Rainer Wallny. Initial feasibility studies have been launched for this major project - part of CERN's European Strategy for Particle Physics.
Swiss particle physicists geared their research years ago to be able to contribute an important building block to this large-scale project: namely magnets of unprecedented performance, which are needed to keep protons accelerated to almost the speed of light in a 100-km orbit. This is the purpose of the CHART research initiative, whose second funding period will end in two years. "We are determined to do everything we can to ensure that this Magnetic Manhattan Project is extended beyond 2023, because it sets the stage for the construction of the FCC, which will build the bridge for our discipline into the second half of this century," says Rainer Wallny.
Understanding neutrinos, finding dark matter
CERN is a flagship of high-energy physics. The research facility on Geneva ground plays an important role for Switzerland. CERN is also of great importance for neutrino physics - another field of particle physics - through the CERN Neutrino Platform. Neutrino physics is dedicated to the study of the electrically neutral, lightweight neutrinos, which occur in three types and can transform into each other in almost miraculous ways. Over the next few years, two large-scale neutrino research experiments will be built in Japan and the USA under the names 'Hyper-Kamiokande' and 'DUNE'. For historical reasons, Swiss researchers are involved in both experiments, and the CHIPP roadmap recommends the continued involvement in both projects for the future.
A third area in which the roadmap points to the future relates to the research of Dark Matter. In recent years various experiments have been set up, including a series of experiments under the name XENON at the Grand Sasso underground laboratory in the Italian Abruzzo to search for the elusive dark matter. The Swiss face of the search for dark matter is Laura Baudis. She had the XENON experiment in her luggage, so to speak, when she moved to the University of Zurich as a professor in 2007. Even though the experimental detection of dark matter particles appeared to be within reach in the recent past, no signal has been discovered so far. Yet the search for dark matter continues. For example, the DARWIN experiment is scheduled to start operation around 2028 as the successor to the XENON experiments. In parallel, accelerators are searching for new particles that could be candidates for dark matter. Promising is also the indirect search via astrophysical observations, from which one could learn where the Dark Matter is located in the universe.
Cooperation with astronomy
In astroparticle physics, particle physics has always had contact to the neighbouring discipline of astronomy. Thus CHIPP is seeking closer contact with its partner organisation in astronomy, the 'College of Helvetic Astronomy Professors' (CHAPS). One possible collaboration is the planned 'Cherenkov Telescope Array' (CTA), an array of several dozen Cherenkov telescopes for exploring astronomical gamma-ray sources. Another possible joint project would be the future European Einstein telescope to observe gravitational waves. The latter were predicted by Albert Einstein in 1916 and first detected by the US LIGO detector in 2015.
In addition to these four exemplary areas, the roadmap covers a wide range of other research areas in which Swiss researchers are often at the forefront. The CHIPP roadmap is thus the voice of all the approximately 450 scientists working in Swiss particle physics. By highlighting the longer-term prospects of this basic research, the roadmap also has an important function in promoting young scientists. After all, the more attractive the research projects in a subject, the more scientists will be attracted to the subject.
The responsibility of the future generation
Behind the roadmap is also a kind of generational contract, as Rainer Wallny points out. After all, if the roadmap supports a research facility such as the FCC, which is scheduled to start operation in about 25 years, it means that today’s active scientists are planning the infrastructure for those researchers who are just being born today. However, the future researchers will probably have different life plans than those active today. Dr. Katharina Müller, particle physicist at the University of Zurich, who played a major role in the CHIPP roadmap, points to the current climate debate as an example: "With whatever experiments we want to conduct particle physics in the future, we will have to justify the effort not only financially, but also in terms of the environment and climate. This effort is necessary so that the future generation has a research infrastructure at its disposal that it can justify to its own conscience and to society."
Author: Benedikt Vogel
The ten recommendations of the CHIPP Roadmap
The quintessence of the CHIPP Roadmap are ten recommendations for the research priorities of Swiss particle physics in the coming years and decades. The recommendations are reproduced below in an abbreviated and simplified form:
Recommendation 1: Switzerland continues to strongly support CERN as the world's leading particle physics research institute. Switzerland participates in the CERN programme for the construction of a 'Future Circular Collider' (FCC), which aims to replace the LHC particle accelerator around 2045. The focus in preparation for the first FCC sub-project (FCC-ee) is on detector development, theoretical research, but also data analysis and simulation. Switzerland supports the continuation of the successful Swiss Accelerator Research and Technology (CHART) programme, which is developing powerful magnets for the second FCC subproject (FCC-hh).
Recommendation 2: Switzerland strongly supports the scientific programme at the optimised CERN particle accelerator under the name 'High Luminosity Large Hadron Collider' (HL-LHC for short, in operation from 2026). This includes the operation and upgrade of the HL-LHC experiments ATLAS, CMS and LHCb, in which Swiss researchers are significantly involved. In order to cope with the growing amounts of data from the HL-LHC, Switzerland is helping to expand the computer infrastructure, possibly in cooperation with other scientific disciplines that rely on high-performance computers.
Recommendation 3: Strong support is given to fundamental research at the Paul Scherrer Institute (PSI). The precision experiments performed there work with particle beams of high intensity and lower energy than at the LHC. These are experiments at the existing HIPA accelerator or also at the planned very high intensity muon beam (HIMB). CHIPP supports the construction of a fixed-target facility with high-power at CERN or elsewhere, but also further experiments aimed at "new physics" - i.e. findings beyond the Standard Model of particle physics.
Recommendation 4: Switzerland strongly supports the neutrino experiments Hyper-Kamiokande (Japan) and DUNE (USA), which investigate the properties of neutrinos when travelling long distances ('long-baseline'). In neutrino research, experiments are also being carried out to detect neutrinoless double beta decay.
Recommendation 5: The direct search for dark matter will continue to be supported, involving not only the 'weakly interacting massive particles' (WIMP) but also other potential building blocks of dark matter. In addition, indirect paths are being taken in the investigation of dark matter via astronomical observations through all available channels such as astroparticles, electromagnetic and cosmic radiation, but also neutrinos and gravitational waves ('multi-messenger astronomy').
Recommendation 6: The links between particle physics (CHIPP) and astronomy (CHAPS) are further developed scientifically and technically. In the interest of both disciplines, Switzerland participates in the CTA project (Cherenkov telescopes in the northern and southern hemispheres for the observation of astronomical gamma-ray sources).
Recommendation 7: Switzerland continues its strong presence in theoretical particle and astroparticle physics and in cosmology.
Recommendation 8: Swiss research institutions continue and expand their knowledge and technology transfer activities. This cooperation strengthens many Swiss and foreign companies, and it will continue to produce a sizeable number of start-ups with innovative business ideas, as in recent years.
Recommendation 9: CHIPP members maintain the exchange of scientists in particle physics with the public through proactive public relations work, including lectures, visitor programmes or events for high school students.
Recommendation 10: Particle physics institutes develop strategies to support young scientists, such as continuing education programmes or exchange platforms.