The Long-Baseline Neutrino Experiment (LBNE) collaboration plans a comprehensive experiment that will fully characterize neutrino oscillation phenomenology using a high-intensity, 800 mile (1,300 km) baseline accelerator neutrino beam and an advanced liquid argon TPC far detector. The goals for this program are the determination of leptonic CP violation and the neutrino mass hierarchy, and underground physics, including the exploration of proton decay and supernova neutrinos. The U.S. Department of Energy has stated its intention to carry out this program in a phased manner. The scope of the initial phase focuses on accelerator neutrino physics and does not include deep underground placement of the far detector or the full near detector.
LBNE represents a substantial investment from the U.S. in a frontier facility for high energy physics. Thus, there is significant opportunity for new collaborators to leverage this major investment and add substantial scientific scope. Collaboration on the design and construction of the far detector, near detector or beamline could provide sufficient additional resources to allow us, together, to place the far detector underground in the first phase, and include a sophisticated near detector which would not only improve the accuracy of the long-baseline oscillation measurements, but have rich physics program in its own right.
In May 2008, the Particle Physics Project Prioritization Panel (P5) published its recommendations for a strategic plan for U.S. particle physics in the next 10 years. The report identified three frontiers of research: the Energy Frontier, the Intensity Frontier and the Cosmic Frontier.
The P5 report authors recognized the potential of Fermilab to contribute to the Intensity Frontier given the lab's unique capabilities and existing infrastructure. Combined with an underground laboratory a favorable distance away for neutrino oscillation studies, Fermilab is in a position to develop a world-leading program in neutrino science for the U.S.
In response, the Long-Baseline Neutrino Experiment (LBNE) developed a conceptual design to address the Intensity Frontier research priorities. It included a beamline at Fermilab designed to produce a high-intensity beam of neutrinos aimed at a far detector site; a near detector system on the Fermilab site to characterize aspects of the beam as it exits the beamline; and a massive deep-underground neutrino detector at the far site, the Sanford Underground Laboratory at Homestake, in Lead, S.D.
On March 19, 2012 William Brinkman, director of the DOE's Office of Science, notified Fermilab that the DOE "cannot support the LBNE project as it is currently configured." Brinkman indicated that the decision is due solely to the high cost of the project, not to its scientific merits. He asked Fermilab to "lead the development of an affordable and phased approach that will enable important science results at each phase."
A reconfiguration effort took place in mid-2012 and the resulting phase 1 configuration received CD-1 approval from the DOE in December 2012.
February, 2014: To pursue the transformative physics objectives of LBNE in an era of highly constrained funding for basic research in the U.S., the conceptual design has evolved so as to provide a flexible and cost-effective approach that maintains a world-leadership role for the U.S. over the long term. The full-scope LBNE detectors are a 50-kt (34-kt fiducial mass) LArTPC in a new experimental hall to be excavated at the 4,850-ft level of the Sanford Underground Research Facility, and a fine-grained near neutrino detector located on the Fermilab site. Simultaneous construction of a new neutrino beamline at Fermilab would permit operation with protons in the energy range of 60-120 GeV that are extracted from the Main Injector with an initial beam power 1.2 MW, enabled by upgrades to the front end of the accelerator complex to be carried out within the Proton Improvement Plan-II (PIP-II) program. In anticipation of potential enhancements beyond PIP-II, the beamline is designed to support upgrades to accommodate 2.3 MW.
The P5 had outlined the Intensity Frontier opportunities and recommendations in the executive summary of its 2008 report, from which some text follows:
Recent striking discoveries make the study of the properties of neutrinos a vitally important area of research. Measurements of the properties of neutrinos are fundamental to understanding physics beyond the Standard Model and have profound consequences for the evolution of the universe.
The latest developments in accelerator and detector technology make possible promising new scientific opportunities in neutrino science as well as in experiments to measure rare processes. The U.S. can build on the unique capabilities and infrastructure at Fermilab, together with DUSEL*, the Deep Underground Science and Engineering Laboratory proposed for the Homestake Mine in South Dakota, to develop a world-leading program of neutrino science. Such a program will require a multi-megawatt-powered neutrino source at Fermilab.
The panel recommends a world-class neutrino program as a core component of the U.S. program, with the long-term vision of a large detector in the proposed DUSEL and a high-intensity neutrino source at Fermilab.
The panel recommends an R&D program in the immediate future to design a multi-megawatt proton source at Fermilab and a neutrino beamline to DUSEL and recommends carrying out R&D on the technologies for a large multi-purpose neutrino and proton decay detector.
Construction of these facilities could start within the 10-year period considered by this report.
A neutrino program with a multi-megawatt proton source would be a stepping stone toward a future neutrino source, such as a neutrino factory based on a muon storage ring, if the science eventually requires a more powerful neutrino source. This in turn could position the US program to develop a muon collider as a long-term means to return to the energy frontier in the US.
The proposed DUSEL is key to the vision for the neutrino program. It is also central to nonaccelerator experiments searching for dark matter, proton decay and neutrinoless double beta decay. DOE and NSF should define clearly the stewardship responsibilities for such a program.
The panel endorses the importance of a deep underground laboratory to particle physics and urges NSF to make this facility a reality as rapidly as possible. Furthermore the panel recommends that DOE and NSF work together to realize the experimental particle physics program at DUSEL.
Scientific opportunities through the measurement of rare processes include experiments to search for muon-to-electron conversion and rare-kaon and B-meson decay. Such incisive experiments, complementary to experiments at the LHC, would probe the Terascale and possibly much higher energies.
The panel recommends funding for measurements of rare processes to an extent depending on the funding levels available.
* DUSEL is now obsolete; currently the Sanford Underground Research Facility occupies the site of the former Homestake Mine in Lead, SD, where DUSEL was sited.