Transcript A Muon to Electron Experiment at Fermilab Eric Prebys E Prebys

A Muon to Electron Experiment at Fermilab
Eric Prebys
For the Mu2e Collaboration
UCLA HEP Seminar, January 16, 2008
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Mu2e Collaboration
R.M. Carey, K.R. Lynch, J.P. Miller*, B.L. Roberts
Boston University
Y. Semertzidis, P. Yamin
Brookhaven National Laboratory
Yu.G. Kolomensky
University of California, Berkeley
C.M. Ankenbrandt , R.H. Bernstein, D. Bogert, S.J. Brice, D.R. Broemmelsiek,D.F. DeJongh, S. Geer,
M.A. Martens, D.V. Neuffer, M. Popovic, E.J. Prebys*, R.E. Ray, H.B. White, K. Yonehara, C.Y. Yoshikawa
Fermi National Accelerator Laboratory
D. Dale, K.J. Keeter, J.L. Popp, E. Tatar
Idaho State University
P.T. Debevec, D.W. Hertzog, P. Kammel
University of Illinois, Urbana-Champaign
V. Lobashev
Institute for Nuclear Research, Moscow, Russia
Currently:
50 Scientists
11 Institutions
D.M. Kawall, K.S. Kumar
University of Massachusetts, Amherst
R.J. Abrams, M.A.C. Cummings, R.P. Johnson, S.A. Kahn,
S.A. Korenev, T.J. Roberts, R.C. Sah
Muons, Inc.
R.S. Holmes, P.A. Souder
Syracuse University
M.A. Bychkov, E.C. Dukes, E. Frlez, R.J. Hirosky, A.J. Norman, K.D. Paschke, D. Pocanic
University of Virginia
*Co-contact persons
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Acknowledgement
• This effort has benefited greatly (and plagiarized
shamelessly) from over a decade of voluminous
work done by the MECO collaboration, not all of
whom have chosen to join the current
collaboration.
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Outline
•
•
•
•
Theoretical Motivation
Experimental Technique
A Brief History of MECO
Mu2e at Fermilab
 Now
 The future
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The Big Picture: Goals of Experiment
• Initial Phase:
 Exploit post-collider accelerator modifications at
Fermilab to mount a m->e conversion experiment
patterned after proposed MECO experiment at BNL
• 4x1020 protons in ~2 years
• Measure


 m  Al  e  Al
Rme 
 m  Al  capture


• Single event sensitivity of Rme=2x10-17
• 90% C.L. limit of Rme<6x10-17
• ANY signal = Beyond Standard Model physics
• Ultimate goal
 Take advantage of intense proton source being developed
for Fermilab (“Project X”) as well as muon collider R&D
• If no signal: set limit Rme<1x10-18
• If signal: measure target dependence, etc
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Search for Charged Lepton Flavor Violation (CLFV)
• There has always been an interest in the search for charge lepton
flavor violation (CLFV)
• CLFV is a powerful probe of multi-TeV scale dynamics:
complementary to direct collider searches
• Among various possible CLFV modes, rare muon processes offer the
best combination of new physics reach and experimental sensitivity
Muon-to-Electron Conversion: m+N  e+N
• Standard Model rate via Dirac neutrino mixing
is too small to be observed (~10-52)
• Very common feature of Beyond Standard
Model physics at much larger rates
• Similar to megwith important advantages:
m
105 MeV e-
 No combinatorial background
 Sensitive to other types of BSM physics
 Relative rate depends on details of physics
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me Conversion vs. meg
In general, two types of diagrams contribute to m+Ne+N:
Dipole (“penguin”)
transition:
Four-fermi contact
interaction:
?
?
?
• This type of diagram gives
rise to small CLFV through
virtual neutrino mixing
• Also contributes to. meg
if photon real
 Relative rate easy to calculate
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• Corresponds to exchange of
a new, massive flavorchanging neutral current
particle
• Does not produce meg
signal
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me Conversion Broadly Sensitive
Courtesy: A. de Gouvea
?
?
?
• At Rme~10-16 (first phase, this LOI),
the sensitivity is already very
compelling
• ~four orders of magnitude
improvement over existing limit
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MEGA
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Sindrum II
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Some Example Sensitivies*
*W. Molzon, Fermilab Wine and Cheese, 9/06
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Sensitivity (cont’d)
SU(5) GUT Supersymmetry: k << 1
Littlest Higgs: k  1
R(mTieTi)
Randall-Sundrum: k  1
R(mTieTi)
10-12
10-12
10-14
10-14
10-16
• Examples with k>>1
(no meg signal):
10-10
MEG
10-10
10-16
mu2e
10-15
10-13
10-11
Br(meg)
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10-13
10-11
10-9
Leptoquarks
Z-prime
Compositeness
Heavy neutrino
Br(meg)
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Decay in Orbit (DIO) Backgrounds
Ordinary:
m

m
e
Coherent:
e
m


m
e
e

N
• Very high rate
• Peak energy 52 MeV
• Must design detector to be
very insensitive to these.
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• Nucleus coherently
balances momentum
• Rate approaches conversion
(endpoint) energy as
(Es-E)5
• Drives resolution
requirement.
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Previous muon decay/conversion limits (90% C.L.)
m>e Conversion: Sindrum II
LFV m Decay:

 m   e  e m


m

 m   e g
 m   eee

 e  2g


 1.2 10  2

 1.2 10 11
 1.0 10 12
 7.2 10 11
High energy tail of coherent
Decay-in-orbit (DIO)


 m Ti  e Ti
12
Rme 

4
.
3

10
 m Ti  capture


• Rate limited by need to veto prompt
backgrounds!
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Mu2e (MECO) Philosophy
• Eliminate prompt beam backgrounds by using a
primary beam with short proton pulses with
separation on the order of a muon life time
~100 ns
~1.5 ms
Prompt
backgrounds
live window
• Design a transport channel to optimize the
transport of right-sign, low momentum muons from
the production target to the muon capture target.
• Design a detector to strongly suppress electrons
from ordinary muon decays
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Detector Layout
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Production Region
• Axially graded 5 T solenoid captures low energy backward and reflected
pions and muons, transporting them toward the stopping target
• Cu and W heat and radiation shield protects superconducting coils from
effects of 50kW primary proton beam
Superconducting coils
2.5 T
5T
Proton
Beam
Heat & Radiation Shield
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Production Target
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Transport Solenoid
Collimators
and pBar
Window
2.5 T
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• Curved solenoid eliminates
line-of-sight transport of
photons and neutrons
2.1 T
• Curvature drift and collimators
sign and momentum select beam
• dB/ds < 0 in the straight sections
to avoid trapping which would
result in long transit times
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Detector Region
• Axially-graded field near stopping target to sharpen acceptance
cutoff.
• Uniform field in spectrometer region to simplify momentum analysis
• Electron detectors downstream of target to reduce rates from g and
neutrons
Straw Tracking Detector
Stopping Target Foils
2T
1T
1T
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Electron
Calorimeter
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Magnetic Field Gradient
Production
Solenoid
Transport
Solenoid
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Detector
Solenoid
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Transported Particles
Vital that e- momentum
< signal momentum
E~3-15 MeV
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Tracking Detector/Calorimeter
• 3000 2.6 m straws
 s(r,f) ~ 0.2 mm
• 17000 Cathode strips
 sz) ~ 1.5 mm
• 1200 PBOW4 cyrstals in electron
calorimeter
 sE/E ~ 3.5%
• Resolution: .19 MeV/c
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Beam Related Rates
• Cut ~700 ns after pulse to eliminate most serious
prompt backgrounds.
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Sensitivity
Coherent Decay-in-orbit,
falls as (Ee-E)5
• Rme = 10-16 gives 5 events
for 4x1020 protons on
target
• 0.4 events background, half
from out of time beam,
assuming 10-9 extinction
 Half from tail of coherent
decay in orbit
 Half from prompt
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Expected Background (from MECO TDR)
For 4x1020 protons on target:
Source
m decay in orbit
Events
Comments
0.25 S/N = 20 for Rme = 10-16
Tracking errors
< 0.006
Radiative m decay
< 0.005
Beam e-
< 0.04
m decay in flight
< 0.03 Without scattering in stopping target
m decay in flight
pdecay in flight
Radiative pcapture
0.04 With scattering in stopping target
< 0.001
0.07 From out of time protons
Radiative pcapture
0.001 From late arriving pions
Anti-proton induced
0.007 Mostly from p
Cosmic ray induced
0.004 Assuming 10-4 CR veto inefficiency
Total Background
0.45 Assuming 10-9 inter-bunch extinction
Signal Events
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5 For Rme = 10-16
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Brief History of MECOMu2e
•
1997
•
1998-2005
•
2005
 MECO proposed for the AGS at Brookhaven
 Approved, along with KOPIO, as part of RSVP program
 Design refined
 Frequent favorable reviews
 June: final reviews, very positive
• Physics goals: HEPAP RSVP Subpanel
• Cost and schedule: “Wojcicki Panel”
 July: RSVP cancelled for financial reasons
•
2006
•
2007
• MECO and KOPIO “charged” for entire cost of continued AGS
operation.
 January: First informal meeting at BNL
 September: First meeting at Fermilab
 June: Mu2e expression of interest submitted to Fermilab Directorate
 August: First Mu2e collaboration meeting
 October: Letter of Intent submitted to Directorate
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Doing me Conversion at Fermilab
• Following the end of the collider program (~2010), the
immediate focus on the lab will be the neutrino program,
particularly the NOvA off-axis neutrino experiment.
• The proton intensity to the 120 GeV neutrino program is
ultimately limited by the capacity of the Main Injector.
• If the current suite of proton source upgrades is effective,
there should be at least enough excess 8 GeV protons to do
an experiment with similar sensitivity to MECO in a
reasonable amount of time
 The resonant operation of the 8 GeV Booster makes it
impossible to directly generate the desired time structure.
 There is a scheme to generate this time structure using the
antiproton Accumulator and Debuncher rings, which will become
available after the termination of the collider program.
 This scheme requires only modest modifications beyond those
planned for NOvA, with which it is fully compatible.
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The Fermilab Accelerator Complex
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microBooNE, August
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20th, 2007 - Prebys
Preac(cellerator) and Linac
“New linac” (HEL)Accelerate H- ions from
116 MeV to 400 MeV
“Preac” - Static
Cockroft-Walton
generator accelerates Hions from 0 to 750 KeV.
“Old linac”(LEL)- accelerate
H- ions from 750 keV to 116
MeV
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20th, 2007 - Prebys
Booster
•
Accelerates the 400 MeV beam
from the Linac to 8 GeV
• Operates in a 15 Hz offset resonant circuit
• Sets fundamental clock of accelerator
complex
•From the Booster, 8 GeV beam can
be directed to
•
The Main Injector
• The Booster Neutrino Beam (MiniBooNE)
• A dump.
•More or less original equipment
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20th, 2007 - Prebys
Main Injector/Recycler
• The Main Injector can accept 8 GeV
protons OR antiprotons from
• Booster
• The anti-proton accumulator
• The Recycler (which shares the
same tunnel and stores antiprotons)
• It can accelerate protons to 120 GeV (in
a minimum of 1.4 s) and deliver them to
• The antiproton production target.
• The fixed target area.
• The NUMI beamline.
• It can accelerate protons OR
antiprotons to 150 GeV and inject them
into the Tevatron.
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20th, 2007 - Prebys
Proton Timeline: Now and Post-Collider
Present Operation:
“wasted” loading time
15 Hz Booster
cycles
• In order to increase protons to the NOvA neutrino
experiment after the collider program ends,
protons will be “stacked” in the Recycler while the
Main Injector is ramping, thereby eliminating
loading time.
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Available Protons: NOvA Timeline
MI uses 12 of 20 available Booster Batches per 1.33 second cycle
Preloading for NOvA
Recycler
Available for 8
GeV program
Recycler  MI
transfer
MI NuMI cycle (20/15 s)
15 Hz Booster cycles
Roughly 6*(4x1012 batch)/(1.33 s)*(2x107 s/year)=3.6x1020 protons/year available
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Delivering Protons: “Boomerang” Scheme
MI-8 -> Recycler
done for NOvA
Recycler
(Main Injector
Tunnel)
New switch magnet
extraction to P150
(no need for kicker)
• Deliver beam to Accumulator/Debuncher enclosure with
minimal beam line modifications and no civil construction.
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Present Operation of Debuncher/Accumulator
• Protons are
accelerated to 120
GeV in Main Injector
and extracted to
pBar target
• pBars are collected
and phase rotated in
the “Debuncher”
• Transferred to the
“Accumulator”, where
they are cooled and
stacked
• Not used for NOvA
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Momentum Stacking
• Inject a newly
accelerated Booster
batch every 67 mS onto
the low momentum orbit
of the Accumulator
• The freshly injected
batch is accelerated
towards the core orbit
where it is merged and
debunched into the core
orbit
• Momentum stack 3-6
Booster batches
Energy
T=0
1st batch is injected onto the injection orbit
T<66ms
1st batch is accelerated to the core orbit
T=67ms
2nd Batch is injected
T<133ms
2nd Batch is accelerated
T=134ms
3rd Batch is injected
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Rebunching in Accumulator/Debuncher
Momentum stack 6
Booster batches directly
in Accumulator (i.e.
reverse direction)
Phase Rotate
with 40 kV h=1
RF in
Debuncher
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Capture in 4 kV h=1 RF System.
Transfer to Debuncher
Recapture
with 200 kV
h=4 RF system
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Resonant Extraction
• Exploit 29/3 resonance
• Extraction hardware similar to
Main Injector
 Septum: 80 kV/1cm x 3m
 Lambertson+C magnet ~.8T x 3m
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Beam Extinction
• Need 10-9
• Get at least ~10-3 from beam bunching
• Remainder from AC Dipole in beam line
• Working with Osaka (FNAL+US-Japan funds) to
develop AC dipole design, as well as explore
measurement options
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Proposed Location
• Requires new
building.
• Minimal
wetland issues.
• Can tie into
facilities at
MiniBooNE
target hall.
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Cost and Time Scale
• A detailed cost estimate of the MECO experiment had been
done just before it was cancelled*
 Solenoids and cryogenics: $58M
 Remainder of experimental apparatus: $27M
• Additional Fermilab costs have not been worked out in detail,
but are expected to be on the order of $10M.
• Hope to begin Accelerator work along with NOvA upgrades
 ~2010 (or 2011 if Run II extended)
• Based on the original MECO proposal, we believe the
experiment could be operational within five years from the
start of significant funding
 Driven by magnet construction.
 ~2014
• With the proposed beam delivery system, the experiment
could collect the nominal 4x1020 protons on target in about
one to two years, with no impact on NOvA
 NOvA rate limited by Main Injector
*Costs in 2005 dollars, including contingency
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Post-Collider: The High Intensity Frontier
• There has long been an interest in an intense 8 GeV proton
source to take the place of the aging Linac/Booster
 Increase power to long baseline neutrino program
 Provide excess capacity for diverse experimental program
• Many have favored an 8 GeV linac which could take
advantage of superconducting RF technology developed for
the ILC, however
 The number of protons needed for 2MW Main Injector
operation corresponds to ~3 times the integrated single pulse
intensity of the ILC
 This has significant implications for the design.
 Precludes “plug compatible” design for high energy linac and
ILC
• Also, if ion stripping is in the Main Injector, then the excess
8 GeV protons are in the form of “useless” 1 ms pulses of Hions.
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“Project X” Scheme
• Three 5 Hz pulses every 1.4 s Main Injector cycle = 2.3MW at 120
GeV
• This leaves four pulses (~200 kW) available for 8 GeV physics
• These will be automatically stripped and stored in the Recycler, and
can also be rebunched there.
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Project X Linac
“PULSED RIA”
0.5 MW Initial 8 GeV Linac
11 Klystrons (2 types)
449 Cavities
51 Cryomodules
Front End Linac
325 MHz
0-110 MeV
β<1 ILC LINAC
1300 MHz
0.1-1.2 GeV
2 Klystrons
96 Elliptical Cavities
12 Cryomodules
ILC LINAC
Modulator
Modulator
Single
3 MW
JPARC
Multi-Cavity Fanout at 10 - 50 kW/cavity
Klystron Phase and Amplitude Control w/ Ferrite Tuners
H- RFQ MEBT RTSR SSR DSR
Modulator
Modulator
Elliptical Option
48 Cavites / Klystron
DSR
10 MW
ILC
Multi-Beam
Klystrons
β=.47 β=.47 β=.61 β=.61 β=.61 β=.61 β=.81 β=.81 β=.81 β=.81 β=.81 β=.81
or… 325 MHz Spoke Resonators
1300 MHz β=1
Modulator
8 Cavites / Cryomodule
8 Klystrons
288 Cavities in 36 Cryomodules
Modulator
Modulator
10 MW
ILC
Klystrons 36 Cavites / Klystron
β=1 β=1 β=1 β=1 β=1 β=1 β=1 β=1 β=1 β=1 β=1 β=1 β=1 β=1 β=1 β=1 β=1 β=1
Modulator
Modulator
Modulator
Modulator
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2008
β=1UCLA
β=1 HEP
β=1Seminar,
β=1 β=1
β=1 16,
β=1
β=1 β=1 β=1 β=1
β=1 β=1 β=1 β=1 β=1 β=1 42
β=1
Future Upgrades to mu2e (Phase II)
• Our Phase I proposal is based on a data sample of 4x1020 protons,
obtained with modest modifications to the existing complex
 90% C.L. limit of Rme<6x10-17 (improvement over existing limit of more
than 4 orders of magnitude).
• The Project X linac would provide roughly a factor of ten increase
in excess 8 GeV flux.
• In addition to the increased flux, alternate solenoidal tranport
channels have been proposed, based on the “helical cooling channel”
which is being developed for the neutrino factory/muon collider
 Potentially a factor of five incrase in muon production efficiency
• Together, these could potentially produce enough stopped muons
for a sensitivity on the order of Rme~10-18
• However, there are many challenges
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Helical Cooling Channel
A helical cooling channel (similar to a “Siberian Snake”) provides
transverse cooling of muon beam:
This, together with an ionizing degrader could allow the forward
muons to be used, for a much higher efficiency.
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Experimental Challenges for Increased Flux
•
Achieve sufficient extinction of proton beam.
 Current extinction goal directly driven by total protons
•
Upgrade target and capture solenoid to handle higher proton rate
 Target heating
 Quenching or radiation damage to production solenoid
•
Improve momentum resolution for the ~100 MeV electrons to reject high
energy tails from ordinary DIO electrons.
 Limited by multiple scattering in target and detector planes
 Requirements at or beyond current state of the art.
•
Operate with higher background levels.
 High rate detector
•
•
•
Manage high trigger rates
All of these efforts will benefit immensely from the knowledge and
experience gained during the initial phase of the experiment.
If we see a signal a lower flux, can use increased flux to study in detail
 Precise measurement of Rme
 Target dependence
 Comparison with meg rate
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Status and Plans
• The Mu2e Collaboration submitted a Of Intent in
October, 2007, which was presented to the Fermilab
PAC in November
• The PAC encouraged the collaboration to work toward a
Phase I proposal in the Fall of 2008.
• We are working toward that goal with our primary
efforts focused on:
 Resurrecting the MECO simulation software to adapt and
upgrade it for our situation
 Continuing on the Accumulator/Debuncher beam delivery
scheme and beam line design
• We are actively involved in the Project X planning
process, with an eye toward designing and upgraded
experiment, and possibly designing parts of the
experiment fo the higher rates from the beginning.
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Not a good time for concrete planning!
(from Dep. Director Y-K Kim)
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Conclusions
• The mu2e experiment is an opportunity for Fermilab to make
an important measurement
 In the initial phase (without project X) we would either
• Reduce the limit for Rme by more than four orders of magnitude
(Rme<6x10-17 @ 90% C.L.)
OR
• Discover unambiguous proof of Beyond Standard Model physics
• This experiment benefits greatly from both the voluminous
work done for the MECO proposal and by fortuitous
configuration and availability of Fermilab accelerator
components.
• With a combination of Project X and/or improved muon
transport, we could either
 Extend the limit by up to two orders of magnitude
OR
 Study the details of new physics
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