A joint Fermilab/SLAC publication

European Strategy prioritizes Higgs factory


The 2020 European Strategy recommends pursuing a Higgs factory, investigating a next-generation hadron collider at CERN, and ramping up accelerator technology R&D.

The successor to the Large Hadron Collider in Europe should be a machine specifically designed for precision studies of the Higgs boson, according to the CERN Council and two representative bodies commissioned by the Council as part of the 2020 Update of the European Strategy for Particle Physics.

The updated strategy for particle physics in Europe [see PDF] recommends pursuing an electron-positron Higgs factory as the highest-priority facility after the LHC. The LHC is currently undergoing a major upgrade and is scheduled to continue running as the High-Luminosity LHC until late next decade.

The strategy emphasizes the importance of ramping up research and development for advanced accelerator, detector, and computing technologies to prepare for all future collider facilities, including the Future Circular Collider, or FCC-hh. The strategy calls for Europe, together with its international partners, to investigate the technical and financial feasibility of the proposed circular hadron collider with an electron-positron Higgs factory as a possible first stage.

LHC scientists discovered the Higgs boson in 2012 and, among other things, are currently studying its properties to search for signs of physics beyond the Standard Model.

“The Higgs is a very unique particle that raises profound questions about the fundamental laws of nature,” said Halina Abramowicz, the chairperson of the European Strategy update committee, during the open CERN Council session. “That led us to the electron-positron collider as a Higgs factory.”

Hadron colliders such as the LHC are especially prized for the high energies they achieve and their associated potential to discover new particles and forces. Electron-positron colliders, which collide point-like particles that annihilate one another on contact, provide cleaner and easier-to-parse results. An electron-positron collider would allow scientists to study the properties of the Higgs with even greater precision, opening the door to discovering discrepancies between theory and experiment that could reveal new physics. 

A possible first stage for the FCC-hh at CERN would be the FCC-ee, an electron-positron collider. The FCC-ee would collide electrons and positrons in a 100-kilometer (62-mile) circular tunnel passing under Lac Leman at the border of France and Switzerland. The FCC-ee tunnel would provide a ready-made home for the FCC-hh. 

The updated strategy encourages further investigation of the feasibility of each collider configuration, “such that we are in the position to decide on the project during the next strategy update,” in five to seven years, according to CERN Council President Ursula Bassler. 

The strategy highlights the long-term vision of a 100-TeV circular hadron collider similar to the LHC but up to seven times more powerful. This collider would enable scientists to look for extremely heavy particles that could help answer outstanding questions in physics, such as the identity of the mysterious dark matter or the origin of gravity.

“These are very exciting times, very dynamic times, but also very frustrating,” Abramowicz said in a Q&A after the announcement. “Many people are really scratching their heads.”

Both the electron-positron Higgs factory and the 100-TeV collider would be global endeavors that will incorporate knowledge and contributions from institutions around the world. “This is a strategy for Europe but within a global context,” CERN Director-General Fabiola Gianotti said. “I’m excited to be part of this adventure implementing the strategy and working with our colleagues from all over the world.”

Based on the strong endorsement of the need for a Higgs factory, the strategy also encourages the timely realization of the electron-positron International Linear Collider in Japan, which would be compatible with Europe’s own plans for a future facility at CERN. In such a case, the strategy expresses a willingness of the European particle physics community to collaborate in the ILC.

In addition to highlighting R&D on future colliders, the strategy reaffirms the importance of the ongoing work for the High-Luminosity LHC accelerator and detector upgrades and continued commitment to participate in long-baseline neutrino research in the United States and Japan. The strategy suggests, “In particular, [Europe and CERN] should continue to collaborate with the United States and other international partners towards the successful implementation of the Long-Baseline Neutrino Facility (LBNF) and the Deep Underground Neutrino Experiment (DUNE).”

LBNF/DUNE is hosted by the US Department of Energy’s Fermi National Accelerator Laboratory in Illinois, with CERN and several European nations as major partners.

DOE’s Office of Science has partnered with CERN on R&D efforts to develop next-generation accelerators for the past two decades. The updated European Strategy is consistent with DOE’s own program planning.

The strategy is also designed to be compatible with program planning for other fields, offering support for complementary projects in other related disciplines.

“In science, there is a tendency that if you want to make progress and reach higher precision, the equipment grows,” Bassler said. “As the equipment grows, we come together to support each other.”

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