The Intensity Frontier
Experiments at the Intensity Frontier search for new physics phenomena at energies
many orders of magnitude higher than in experiments at particle colliders. At this
frontier, scientists address central questions in particle physics that may not be addressed
for many years at the Energy Frontier. Over the next twenty years, Fermilab's Intensity
Frontier program will use protons to produce intense beams of neutrinos, muons and kaons,
and high yields of heavy nuclei. Experiments using these beams and nuclei will study rare
processes more precisely and with more sensitivity than ever before.
Throughout history many new phenomena in physics were first discovered through the
study of rare processes, including the first observation of the weak interactions, the indirect
detection of the neutrino and the prediction of the charm quark mass. Major scientific goals
at today's Intensity Frontier include the search for CP violation in neutrinos, which may
provide the critical information needed to solve the puzzle of the excess of matter over antimatter
in the universe. Intensity Frontier experiments will investigate the mysterious new
physics of leptons to understand precisely how and why lepton flavor is not conserved.
Experiments to observe and measure ultra-rare kaon decays and search for electric dipole
moments of the muon and electron may reveal new forces and new physics.
The initial phase of Fermilab's new program at the Intensity Frontier program is already
well underway and builds upon the unique and extensive Fermilab infrastructure to provide
a powerful and dramatic suite of experiments with neutrinos and muons. The second phase
includes construction of the Long-Baseline Neutrino Experiment and Project X. LBNE's
critical scientific mission is to determine if leptons experience CP violation.
Project X will be the world's most intense and flexible particle accelerator, and is the
centerpiece of Fermilab's long-term strategy to develop the world's leading Intensity Frontier
physics program. Project X will enhance and permit extremely detailed studies of neutrinos
at LBNE, enable the study of the rarest processes involving muons and kaons and permit
the creation of heavy nuclei that provide unprecedented sensitivity to the detailed properties
of electrons, neutrons and nuclei themselves.
Theoretical Physics at the Intensity Frontier
The NOνA near detector
A scientist conducts tests on the NOνA near
detector, which also acts as a prototype for the
15,000-ton far detector in Ash River, Minnesota.
The Fermilab theory group plays a major role in shaping the Intensity Frontier physics
program. Fermilab theorists will continue to mentor the Fermilab neutrino program, from
helping to define the physics case for NOνA and LBNE to proposing novel physics searches
in short-baseline experiments. Theorists actively consult with experimentalists on all aspects
of Intensity Frontier physics at all stages of the Fermilab program: what aspects of physics
are investigated by the experiments, and how to place limits and define new physics
Flavor physics has been a cornerstone of Fermilab's lattice gauge theory effort. Fermilab
theorists have helped craft the case for measuring rare-kaon-decay rates in the LHC era,
and are focusing on the constraints these imply for TeV-scale physics. Fermilab's Lattice QCD
calculations are important for Intensity Frontier physics, for example by driving the evolution
of the precision of quark-flavor physics results, or by determining the hadronic contributions to
the magnetic moment of the muon as required by the Muon g-2 experiment.
Experiments in neutrino physics address three fundamental goals. The first goal comprises two
parts: measuring θ13, the mixing angle between first- and third-generation neutrinos without
which there can be no CP violation; and determining whether the neutrino mass hierarchy is
like that of quarks or if it is inverted. The second goal is to observe CP violation in neutrinos,
such as an asymmetry between the oscillation rates of νμ→νe and νμ→νe. The third goal is to
determine the nature of neutrino mass. Fermilab's long-baseline neutrino program is ideally
poised for precision measurements that address the first two goals.
Near-Term Neutrino Program
Sensitivity to sin22θ13
Colored bands show for what fraction of
CP-violating phases a given value of sin22θ13
can be distinguished from zero at the 3σ
confidence level, assuming a normal mass hierarchy.
Fermilab's near-term long-baseline neutrino-oscillation experiments—MINOS, which is
currently operating; MINOS+, its next phase; and NOνA, currently under construction—
provide a powerful evolutionary progression in neutrino measurement capability
and are also sensitive to relatively large new physics phenomena. The 735-kilometer-baseline
MINOS experiment has already provided the world's most precise measurement of
Δm232, as well as highly competitive constraints on many other phenomena in neutrino
physics. MINOS+ will search for sterile neutrinos and for non-standard neutrino interactions
that could point to new physics. NOνA, with an 810-kilometer baseline, will measure θ23,
|Δm232| and θ13 with greatly increased precision. NOνA will also measure the sign of
Δm232 (the neutrino mass hierarchy) provided θ13 is relatively large, as has been hinted by
recent results from the T2K, MINOS and Double CHOOZ experiments.
The short-baseline experiments MiniBooNE, MINERνA and MicroBooNE provide a
rich ensemble of complementary experiments in this decade. They measure the cross sections
and kinematics of neutrino processes to high accuracy, offer a unique discovery potential for
new phenomena, and can significantly advance our understanding of the underlying
dynamics of neutrino-nucleus interactions, vital to the future worldwide neutrino program.
Sensitivity to mass hierarchy
Colored bands show for which sin22θ13
values and for what fraction of possible
values of the CP-violating phase the
Fermilab neutrino program can distinguish
the normal and inverted mass hierarchies
at the 3σ confidence level, assuming the
actual hierarchy is normal.
The LBNE experiment will have an unprecedentedly long baseline of approximately 1300
kilometers. This will significantly enhance the experiment's sensitivity to θ23, Δm232 and
θ13. As its main goal, LBNE will search for a CP-violating asymmetry in the oscillation of
muon neutrinos and antineutrinos to electron neutrinos and antineutrinos. LBNE will
be the first experiment capable of discovering CP violation in the neutrino sector over a
large range of possible θ13 values. LBNE's capability to measure θ13 and determine the
mass hierarchy will greatly exceed that of NOνA even for small θ13.
An important aspect of LBNE will be its versatile and massive far detector. This will
be either a water Cerenkov detector with a mass of up to 200 kilotons or a liquid-argon
time-projection chamber of several tens of kilotons. Such massive detectors are crucial for
collecting sufficient event samples over such long distances. Liquid-argon detectors have
not yet been realized on such large scales, but Fermilab is playing an active role in the
development of this detector technology. The upcoming MicroBooNE experiment will
serve as a demonstration of the technology, which is also under active study for dark-matter
and neutrinoless-double-beta-decay detection.
Both detector technologies allow for a rich physics program beyond neutrino oscillation
studies. This includes a high-sensitivity search for proton decay, which probes the grand unification
scale of order 1016 GeV, and high-sensitivity studies of neutrinos coming from
supernovae within our galaxy.
Neutrino Program with Project X
Project X provides a significant upgrade path for the neutrino program. Project X supplies a
neutrino beam power that is more than three times larger than the Fermilab accelerator
complex will produce for NOνA. Its flexible beam energy and power enhance the sensitivity
of LBNE, particularly to leptonic CP violation, turning a 3σ measurement of CP violation
with NOνA's 700 kW beam into a 5σ measurement with Project X. The physics achievable
by LBNE in 10 years with Project X would take more than 30 years without it.
Project X will also drive new short-baseline programs to study the physics of neutrino
interactions with superior precision. Enhanced short-baseline detectors driven by a Project X
beam could become discovery machines for new physics.
(click image for larger version)
Project X will be the world's most intense
and flexible proton accelerator. The key
to Fermilab's long-term world leadership
at the Intensity Frontier, it will simultaneously
provide 2.3 MW of proton beam
power at 60—120 GeV; up to 200 kW at
8 GeV; and 2.9 MW at 3 GeV. Fermilab is
pursuing the design and construction of
this unique facility in collaboration with
national and international partners.
Experiments at Project X
Project X will produce intense beams of neutrinos, kaons and muons, and will produce
copious quantities of heavy nuclei. Starting in the 2020s, experiments using Project X
beams will be essential to break through to a deeper understanding of nature and the
origins of matter, either discovering new phenomena or providing the critical clues that
explain new physics discovered elsewhere.
Long- and short-baseline neutrino
experiments will search for leptonic
CP violation and study the physics of neutrino
interactions with unmatched precision
Experiments could discover
unexpected lepton-flavor violations or
subtle new physics at the quantumloop
Ultra-rare kaon-decay experiments
will either test the Standard Model with
uniquely high precision or discover new
physics at the 1000-TeV scale
Ultra-sensitive electric dipole
moment searches will approach limits of
10-31 e-cm or discover a new type of
CP violation in the strong interaction
The Neutrino Factory
Sensitivity to CP violation
Sensitivity of the Fermilab neutrino program for
detecting CP violation at a 3σ confidence
level. NOνA is unable to detect CP violation at
this level of significance over the plotted
range of θ13.
The ultimate stage of Fermilab's neutrino physics program is the construction of a Neutrino
Factory. Such a facility would use the high-intensity proton beam from Project X to
produce a high-quality muon beam that can be accelerated and circulated in a storage ring.
The muons would decay, yielding superb, background-free beams of electron and muon
neutrinos. Neutrino detectors would be located at distances of up to several thousand
kilometers, making the Neutrino Factory an ideal tool to study perturbations of the
oscillation pattern induced by the matter through which the neutrinos travel.
Small values of θ13 require a high-energy Neutrino Factory. For large θ13 a low-energy
Neutrino Factory is optimal, as the high-energy facility would suVer from larger backgrounds
due to CP-conserving electron-muon oscillations. Fermilab is studying both a
high-energy Neutrino Factory with a 25 GeV muon beam and a low-energy option with a
5 GeV muon beam. The Neutrino Factory would provide high-intensity beams of both
electron and muon neutrinos, which would enable superior measurements of the parameters
of the neutrino mass and mixing matrices. The Neutrino Factory would study up to 12 of
the 18 known three-flavor oscillation channels, thus exhaustively covering the landscape
of both standard and non-standard neutrino physics. The low-background environment of
a Neutrino Factory will also provide enhanced sensitivity to subtle new physics effects and
will cover a much larger range of possible phenomena than any other existing or currently
proposed neutrino facility.
μ-to-e conversion sensitivity
Comparison of the sensitivity to charged LFV
of the MEG (μ→eγ) experiment at the Paul
Scherrer Institute at a transition rate of 10-13 and
the Mu2e experiment using the Fermilab
Booster at the rate of 10-16 to 10-17.
High-intensity sources of muons enable ultra-precise measurements of their fundamental
physical parameters, as well as searches for new physics phenomena in rare processes involving
muons. Such measurements could yield significant discoveries, such as the unexpected violation
of lepton-flavor symmetries or subtle new physics entering at the quantum-loop level.
The anomalous magnetic moment of the muon, g-2, measured by the E821 experiment at
Brookhaven National Laboratory with a precision of 0.54 parts per million, remains discrepant
with the Standard Model and is a possible indication of new physics. A new Muon g-2
experiment at Fermilab, which will reuse the Brookhaven muon storage ring with the former
Fermilab antiproton source, will achieve a fourfold improvement in precision. Combined
with improved theoretical analysis, the new g-2 measurement will provide an important
constraint on new physics phenomena.
The observation of an electric dipole moment for any elementary particle would constitute
a major discovery of a new source of CP violation. The current 95% CL muon EDM limit
is 10-19. The Muon g-2 experiment will also search for a muon EDM with a sensitivity
100 times better than current experiments. A next-generation experiment with Project X
could further improve the sensitivity by another three orders of magnitude.
Rare decays of muons, if observed, could be harbingers of new physics phenomena. Starting
late this decade the Mu2e experiment will search for one such rare-decay process, the conversion
of a muon to an electron. This process, known as charged lepton flavor violation, is
predicted by many theories that include new physics to occur at rates that could be within
reach of Mu2e. Such studies provide sensitivity to mass scales of new physics phenomena that
may lie at thousands of TeV for certain scenarios, significantly beyond the reach of the LHC.
Mu2e will use the 8 GeV proton beam from Fermilab's Booster and the beamline from the
former antiproton source to search for the muon-to-electron conversion process with sensitivity
at the 10-16 to 10-17 level, 1,000 to 10,000 times better than previous experiments. Project X
would increase the beam power to the experiment by more than a factor of 10, further
improving the sensitivity to the 10-19 level if the first phase of the Mu2e experiment does not
discover charged lepton flavor violation. If a discovery is made in the first phase, a Project X-era
experiment would offer the unique capability of distinguishing the underlying new physics by
measuring the muon-to-electron conversion rate using a variety of nuclear targets.
Project X experiments based on 1000 Standard
Model events can probe new physics
phenomena with greater than 5σ sensitivity.
A global suite of experiments seeks to measure ultra-rare decays of kaons, either to test the
Standard Model with uniquely high precision or to discover new physics phenomena at
the 103 TeV scale. The Project X era at Fermilab will offer unmatched sensitivity to ultrarare
decays of kaons.
The rare kaon decay processes, K+→π+νν and KL→πOνν, provide physicists with the
opportunity to test the Standard Model with high precision or discover new physics, since
both modes are extremely suppressed in the Standard Model. The KL→πOνν is a purely CP-violating process, with a hadronic matrix element that is known theoretically at the
one percent level of precision. The observation and precise measurement of this rare process
will constitute a major triumph in kaon physics.
Fully exploiting the opportunities of kaon physics requires experiments capable of detecting
about 1000 decays in each mode, thus achieving a statistical error that approaches the
theoretical uncertainty. The high-intensity proton beam of Project X would readily enable
experiments at the 1000-event level. The continuous-wave linac technology proposed for
Project X would provide ideal conditions for these experiments, which would yield simplifications
of the experimental apparatus and reduced technical risks. Both neutral and charged
kaon-decay measurements would reach precisions of a few percent, comparable to the
uncertainty on the Standard Model prediction, thus offering greatly increased sensitivity
for new physics phenomena in these processes. Kaon experiments at Project X would also
be sensitive to a variety of other rare decays involving possible exotic final states.
Search for New Physics with Heavy Nuclei
Project X can be used to produce large quantities of heavy short-lived nuclei, such as radon,
radium, americium and francium, which offer significantly amplified sensitivity to the
electron EDM. The current 90% CL limit on the electron EDM of 10-27 e-cm already rules
out generic models of supersymmetry. Project X-era experiments using heavy nuclei and a
combination of nuclear shape and relativistic effects could approach limits of 10-31 e-cm,
or discover a new type of CP violation in the strong interaction.
The target station of a facility to produce heavy nuclei with Project X could also include
an ultra-cold neutron capability, the development of isotope-production techniques
for beta-beams, biological studies with radiotherapeutic (alpha-emitting) isotopes, and
materials-science studies with implanted radioisotopes.
Clean Nuclear Energy Applications of Project X
In addition to its broad program in fundamental science, Project X could support
R&D towards the destruction of spent fuel from conventional nuclear reactors, and the
development of accelerator-driven subcritical systems for safe and abundant nuclear
The issue of high radio-toxicity and the long lifetime of conventional spent nuclear
fuel is a global challenge. Accelerator-driven systems can be used to transmute spent
nuclear fuel, significantly reducing the lifetime and toxicity of nuclear waste. Accelerators
can also drive fission reactors that incorporate advanced fuels, such as those based on
thorium. This has advantages over conventional reactor fuels, including a fuel supply that
can meet global demand for 100 to 1000 times longer; less long-lived nuclear waste;
reduced possibility of nuclear weapons production; and relatively safer operation. Fermilab
will not establish a full-scale accelerator-driven nuclear reactor development program, but
key elements for the future of accelerator-driven nuclear energy can be studied and developed
with Project X.