Precision Physics at the Proton Facility
Precision Physics Experiments with Muon Beams
A muon to electron conversion experiment could be based on the detailed technical
design of the MECO experiment that was planned to be run at the BNL AGS operating
at 8 GeV. With low cost modifications to the current accelerator complex, this
experiment would detect LFV if xxx is as small as 2X10-17.
It would collect data for 2-3 years with little or no impact on the beam available
for the neutrino program, based on current plans to upgrade the 120 GeV beam to ~700 kW.
The Fermilab beam implementation would be superior to that planned for BNL due to
better duty factor (>90% vs. ~50%), superior micro time structure, and more running per year.
The MECO design has been reviewed for cost and technical feasibility in detail,
and a new experiment based on MECO could be developed into a reviewable project
at Fermilab with about one year of effort. Physics results at sensitivity below
10-16 would follow 4-5 years of construction and 2-3 years of running. Upgrades
to use a more intense beam following the SNuMI or Project-X construction would
be studied and then implemented following the first physics running period.
Precision Physics Experiments with Kaon Beams
The “KTeV-II” experiment described below is designed to make a precision measurement of
the K+ --> pi+ nu nu branching fraction that matches the small theoretical uncertainty.
In parallel with K+ --> pi+ nu nu running, the KTeV-II experiment can probe many other
decay channels including precision measurement of K --> enu and K --> pi mu e searches which
are both uniquely incisive probes of BSM physics. The “KOPIO” experiment described
below is designed to discover and measure the ultra-rare K0 --> pi0 nu nu decay process which
is very sensitive to CP-violating BSM amplitudes. Several BSM models can be discovered
or excluded on the road to the Standard Model expected K0 --> pi0 nu nu branching fraction of 3x10-11.
Upon acquiring the Standard Model sensitivity the experiment then becomes sensitive to very
high mass scale (>1000 TeV/c2) and extra-dimensional models through precision measurement
of the K0 --> pi0 nu nu branching fraction.
The KTeV-II experiment is based on the conceptual design of the CKM experiment
(Charged Kaons at the Main injector). Driving the experiment in the NuMI or
SNuMI era with the high duty-factor Tevatron stretcher simultaneously reduces
detector rates by x3 and the proton tax on the Main Injector neutrino program
from 30% to 5%. The lower detector rates reduce the technical risk of the
experiment and supports scaling of the CKM design to much higher sensitivity
in the Project-X era. The high energy separated kaon beam based on ILC crab
cavity technology drives this next step in ultra-rare K+ sensitivity with
samples of 100-200 K+ --> pi+ nu nu decays per year within reach. Project-X can further
increase the rare-decay sensitivities by x3 while maintaining a small 5% tax on
the Main Injector neutrino program. The CKM conceptual design has been technically
reviewed in detail, and could be developed into a reviewable project with one year
of effort. Several years (3-4) of funding and construction would then be necessary
to start detector operations 5 years following a decision to proceed with this opportunity.
Illustration of the K --> pi nu nu sensitivity space for BSM physics compiled by
F. Mescia for the CKM-2006 Workshop. The reach above the Standard Model
in units of current (2007) theoretical certainty of the Standard Model prediction
is indicated in orange, and is a space of about (50??x 600???for ( charged x neutral ) modes.
The current measurement of K+ --> pi+ nu nu based on 3 events by the BNL E787-949 experiment is x1.8
the Standard Model prediction. Several BSM models are indicated: Minimal SUSY (MSSM),
“Little Higgs Theories” (LHT), and “Minimal Flavor Violation” (MFV).
The experiment was originally designed and optimized for the BNL AGS 24 GeV proton source.
The KOPIO proponents have estimated the K0 flux at the Fermilab Booster energy of 8 GeV
and have found the flux to be comparable to the BNL AGS. The limited proton intensity of
the AGS drove the KOPIO design to an unusually large solid-angle kaon beam in order to
collect sufficient kaon decays to measure the K0 --> pi0 nu nu process. This large beam complicated
the detector design and contributed technical risk to the experiment. The very large proton
intensity of Project-X (x12 Booster intensity) motivates a re-optimization based on a much
smaller solid angle beam which could deliver sufficient kaon decays. This smaller beam could
significantly simplify the experiment and reduce technical risk. An experiment optimized for
Project-X intensities could still have sufficient sensitivity to discover the K0 --> pi0 nu nu process
in early running during the NuMI (no Nova proton tax) or SNuMI (10% Nova proton tax) era using
the Fermilab Booster as a proton driver. The lower intensities of the Booster driving a smaller
kaon beam would provide a natural timeline to develop and commission this challenging experiment.
The KOPIO conceptual design has been reviewed in detail, and could be developed into a reviewable
project with one year of effort. Several years (3-4) of funding and construction would then be
necessary to start detector operations 5 years following a decision to proceed with this opportunity.
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