PIP-II will provide the international particle physics community with a world-class scientific facility, that will enable discovery-focused research, transform our understanding of nature and strengthen the connection between advances in fundamental science and technology innovation.
PIP-II addresses two of the missions of the High Energy Physics program:
- “to illuminate and answer questions about the unification of the forces of nature, the nature and origin of dark energy and dark matter, and the origins of the universe,”
- “to deliver scientific breakthroughs and extend our knowledge of the natural world by capitalizing on the capabilities available at the national laboratories, and through partnerships with universities and industry.”
Fundamental questions in particle physics
- What is the origin of matter? Are neutrinos the reason matter exists?
- What unknown properties of the constituents of matter and forces that govern them drove the evolution of the universe from the big bang to its present state, with its complex structures that support life — including us?
- What is the nature of dark energy and how are the forces of nature unified?
These are some of the questions that particle physics seeks to answer.
Answering these questions requires powerful particle beams, which are possible only with the most advanced accelerator technology. The PIP-II accelerator complex, positioned at the forefront of accelerator technology R&D, will shed new light on these mysteries.
PIP-II will power the world’s most intense beam of high-energy neutrinos for DUNE, enabling the international collaboration to achieve its ambitious science goals.
The powerful PIP-II accelerator will also enable the exploration of new physics by delivering intense particle beams to multiple experiments, each of which provides new windows to the subatomic world.
The upgraded accelerator complex will provide unprecedented numbers of particles to help uncover theoretically predicted – but as yet unobserved — phenomena that are expected to be either incredibly rare or incredibly difficult to detect. The sheer numbers of particles will help draw out the subtle behaviors that would otherwise remain hidden.
Importantly, PIP-II’s leading-edge design will pave the way for future advances in accelerator technology.
Neutrinos are ubiquitous, yet possibly the least understood particles in our universe. With no electric charge and a mass so tiny (about a million times less massive than the electron) that it was for long thought to be zero, neutrinos go undetected even though about 100 trillion of them pass through our bodies every second.
Though elusive, these particles may hold the secret to our very existence. The universe as we know it consists almost entirely of matter, but we know that it began with equal amounts of matter and antimatter. Where did all the antimatter go? It turns out that the key to this deeply profound mystery may be related to the way neutrinos behave as they move in space and time.
There are three different types, or flavors, of neutrinos: electron, muon and tau. Evidence suggests that as neutrinos move from one point in time and space to another, their type changes, or oscillates — an electron neutrino, for example, may later be observed as a tau neutrino. What are the rules of this apparent flavor-changing behavior? These so-called neutrino oscillations may be able to explain the matter-antimatter asymmetry in the universe, and help answer other fundamental questions, such as the nature of dark energy and the unification of forces.
International neutrino program: PIP-II / LBNF / DUNE
Deciphering the role of neutrino oscillations in answering these questions requires powerful new accelerator facilities. In line with the recommendation of the 2014 U.S. Particle Physics Project Prioritization Panel, or P5, a three-pronged international neutrino program was launched. This includes: 1) PIP-II, the upgrade of the Fermilab accelerator complex to deliver a powerful, multi-megawatt, proton beam; 2) The long-baseline neutrino facility, or LBNF, to transform that proton beam into the most intense neutrino beam in the world and to prepare facilities at two sites, one in South Dakota and another at Fermilab, for the neutrino detectors; and 3) DUNE, the next-generation neutrino experiment with precision detectors located at both sites.
The neutrinos generated by the powerful PIP-II-enabled accelerator complex will first be detected near their source at the Fermilab DUNE detector, then travel 1,300 kilometers through Earth’s mantle to a second, much larger, detector located a mile underground at the Sanford Underground Research Facility in South Dakota. Scientists will compare the data from the two detectors to understand how neutrinos change as they travel over long distances.
The upgrade to the Fermilab accelerator complex comes in two phases. The initial phase, PIP-II, replaces the first section of the existing complex with a leading-edge, 800-million-electron-volt, superconducting radio-frequency linear accelerator. PIP-II also incorporates necessary upgrades to the existing Fermilab circular accelerators, Booster, Recycler Ring and Main Injector, to enable the complex to deliver at least 1.2 megawatts of proton beam power at an energy of 120-billion-electronvolt to LBNF and to provide a platform for multi-megawatts capability. The second phase comes later and replaces the Booster synchrotron to enable the ultimate beam power of 2.4 megawatts to be delivered to the LBNF target. These improvements should allow researchers to make definitive measurements to clarify the role of neutrinos in the early evolution of our universe.
The construction of LBNF and DUNE, powered by PIP-II, is the first international mega-science project based at a DOE national laboratory. PIP-II’s broad and powerful capabilities will enable a much broader research program in particle physics for many decades to come.
PIP-II will also enable research related to muons, for example, a second-generation muon-to-electron conversion experiment, or Mu2e, an upgrade to the Mu2e experiment presently under construction at Fermilab. Mu2e aims to observe forbidden decay processes that would point to incompleteness in the Standard Model of particle physics. The Mu2e program has a strong synergy with the muon g-2 experiment at Fermilab, currently delivering first results and hinting at deficiencies of the Standard Model. All muon-based experiments to search for forbidden processes rely on the very high beam power delivered by PIP-II.
The more than 1 megawatt proton beam power from PIP-II, coupled to a proton storage ring, could drive a megawatt-class proton beam dump facility to support a diverse physics program, such as searches for accelerator-produced dark sector particles, which could include evidence for sterile neutrinos.
Accelerator technology advances
The PIP-II linear accelerator, or linac, is the highest-energy and highest-power continuous-wave, or CW, proton accelerator ever built. PIP-II utilizes superconducting radio-frequency, or SRF, acceleration technology, the technology of choice for the vast majority of modern accelerators, due to its highly efficient acceleration of particle beams.
The continuous-wave operation regime imposes stringent requirements on the accelerating gradient and quality factor of the PIP-II SRF systems, which in several cases, exceed the state-of-the-art. The R&D to achieve the required SRF performance for PIP-II, advances the frontiers of SRF science and technology more generally and drives technological developments with broad applications to future accelerators.
The capability and flexibility of PIP-II’s design will allow for customized beams (for instance, in various patterns, such as pulsing) and for those beams to be delivered to different experiments simultaneously.
Advanced concepts under development for future accelerators, with promise for higher performance and lower cost, are being incorporated in PIP-II. For instance, PIP-II will use the transformative potential of artificial intelligence and machine learning to deliver flexible beam patterns to users quickly, reliably and with minimal operational effort.
In building PIP-II, scientists, engineers and technicians are providing a platform for cutting-edge accelerator developments that will support the advancement of next-generation accelerator technology.