Transcript Physics with Very Intense Muon Beams UCLA January 29 2007

Physics with Very Intense Muon Beams
W. Molzon
U.S. Neutrino Factory and Muon Collider Collaboration Meeting
UCLA
January 29 2007
Outline:
−General considerations
−Physics motivation for lepton flavor violation experiments
−Experimental status of LFV
−Prospects for improvement
−Concept of m-N→e-N experiment
• Physics of the conversion process
• Background sources
• Detector requirements
−MECO muon beam and detector concept
−Possible m-N→e-N experiment at Fermilab
−Possible m-N→e-N experiment at JPARC
General Considerations
• Physics goals
− Lepton flavor violation (m-N  e-N, m+  e+g, m+  e+e+e-)
− Precision electroweak (g-2, decay spectrum, lifetime, capture on p, edm)
− Very intense beams are useful for experiments in which the majority of the decays
do not cause rate in detectors and no accidental physics backgrounds
− Cooling is generally useful, usually a tradeoff with available intensity, cost, etc.
• Muon beam properties
− Charge – negative for conversion (use Coulomb bound muons) positive for others.
Positive muons produced using stopping pions (surface muon beams).
− Energy – many stopping experiments use low energy beams, some experiments
require specific energies
− Energy spread – generally, reduced energy spread is beneficial
− Time structure – depends on experiment, highly pulsed or DC generally preferred
− Intensity – in most cases limited by instrumental or background effects
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
2
Existing and Possible Muon Sources
• Available muon beams at TRIUMF(500MeV, 0.3MW) and PSI (590MeV, 1MW)
− DC beams with intensity of order 108 per second, higher for m+
− Limitations of low energy machines
•
•
•
•
Muons per watt of beam power low due to low pion production cross section at low energy
Fewer negative muons
Fewer options to make pulsed beam
More difficulty with beam power on target (wrt higher energy accelerators)
• Potential muon beam sources
− BNL proton synchrotron
•
•
•
•
few to 24 GeV proton beam
low frequency RF for acceleration – relatively easy pulsing
available slow extraction
beam power 20-50 kW at 8 GeV
•
•
•
•
Few to 40 (50) GeV proton beam
Relatively low frequency RF
Slow extraction being developed
Beam power 1 MW at 50 GeV
− JPARC
− Fermilab
• 8 to 120 GeV
• No existing slow spill
• Few 10s of kW at 8 GeV, few 100 kW at 120 GeV
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
3
Limitations: Detector Rates, Rate Induced Physics Backgrounds
For LFV experiments, stop muons and look at decay or conversion processes
− Detector rates from Michel decays (menn) decays
− Detector rates from other beam particles, muon capture processes, etc
− For most processes, physics backgrounds dominated by accidentals at useful rates
• Example: m+  e+g
sensitivity goal
10-14
running time
107 s
detection efficiency 0.1
macro duty cycle
1
stop rate
108
background dominated by accidental coincidences of Michel positron, photon from radiative
decay or positron annihilation in flight
− Without some care, detector rates are too high
• Example: muon conversion on a nucleus m-N  e-N
sensitivity goal
10-17
running time
107 s
detection efficiency 0.2
macro duty cycle 0.5
stop rate
1011
decay rate of 1011 Hz, instantaneous intensity higher with pulsed beam
even higher fluxes from neutrons, photons from muon capture
− Muon conversion experiment is unique in ability to use very high stopping rates
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
4
What Will Observation of m→eg or m-Ne-N Teach Us?
Discovery of m-N  e-N or a similar charged lepton flavor violating (LFV) process
will be unambiguous evidence for physics beyond the Standard Model. This
process is completely free of background from Standard Model processes.
• For non-degenerate neutrino masses, n oscillations can occur. Discovery of neutrino
oscillations required changing the Standard Model to include massive n.
• Charged LFV processes occur through intermediate states
with n mixing. Small n mass differences and mixing angles 
expected rate is well below what is experimentally accessible:
rate is proportional to [D(Mn)2/(MW )2]2
n
m
e
W
• Current limits on LFV in charged sector provides severe
constraints on models for physics beyond the Standard Model
Z,N
• Charged LFV processes occur in nearly all scenarios for physics beyond the SM, in many
scenarios at a level that current generation experiments could detect.
• Effective mass reach of sensitive
searches is enormous, well beyond
that accessible with direct searches.
-
 ML  3000 md ed TeV/c
William Molzon, UC Irvine
m-
Γ(μ N  e N)
16


10
Γ(μ-N  ν μN)
-
R me
m-N  e-N mediated
by leptoquarks
2
Particle Physics with Intense Muon Beams
d
md
L
ed
January 29 2007
d
e-
5
Sensitivity to Different Physics Processes
Supersymmetry
Compositeness
Predictions at 10-15
Λ C = 3000 TeV
Second Higgs
doublet
gHμe =10-4 ×gHμμ
Heavy Neutrinos
2
*
UμN
UeN = 8 ×10-13
Heavy Z’,
Anomalous Z
coupling
Leptoquarks
ML =
MZ = 3000 TeV/c 2
3000 λμd λ ed TeV/c 2
William Molzon, UC Irvine
After W. Marciano
Particle Physics with Intense Muon Beams
B(Z  μe) < 10-17
January 29 2007
6
Supersymmetry Predictions for LFV Processes
• From Hall and Barbieri
Large t quark Yukawa couplings
imply observable levels of LFV in
supersymmetric grand unified models
• Extent of lepton flavor violation in grand unified
supersymmetry related to quark mixing
• Original ideas extended by Hisano, et al.
Process
m -N  e-N
m +  eg
  mg
10 -10
10 -11
B(m  e g)
Rme
10-12
10-15
10-11
10-13
10-6
10-9
10 -12
10 -13
10 -15
10 -17
10 -14
10 -16
10 -18
mN→eN single event
sensitivity goal
PSI m→eg single
event sensitivity
10 -20
10 -21
100
William Molzon, UC Irvine
SUSY
level
Current MEGA bound
Current SINDRUM2 bound
10 -19
Current
Limit
200
300
me (GeV)
R
Particle Physics with Intense Muon Beams
100
200
me (GeV)
300
R
January 29 2007
7
History of Lepton Flavor Violation Searches
1
Branching Fraction Upper Limit
10-2
10-4
10-6
MEGA
10-8
10-10
m- N  e-N
m+  e+g
m+  e+ e+ e-
10-12
10-14
SINDRUM
2
MEG goal
K0  m+eK+  + m+e-
m-N→e-N goal
10-16
1940
William Molzon, UC Irvine
1950
1960
1970
1980
1990
Particle Physics with Intense Muon Beams
2000
2010
January 29 2007
8
PSI-MEG m+e+g Experiment
Search for me+ g with sensitivity of 1 event for B(me g) = 10-13
William Molzon, UC Irvine
• Italy
− INFN and University of Genoa
− INFN and University of Lecce
− INFN and University Pavia
− INFN Pisa
− INFN and University of Roma
• Japan
− ICEPP, University of Tokyo
− KEK
− Waseda University
• Russia
− JINR, Dubna
− BINP
− Novosibirsk
• Switzerland
− Paul Scherrer Institute
• United States
− University of California, Irvine
Particle Physics with Intense Muon Beams
January 29 2007
9
The MEG Experiment at PSI
0.95
–DEe : 0.8% (FWHM)
–Dqeg : 18 mrad (FWHM)
0.90
Eg / Emax
1.00
• Experiment limited by accidental backgrounds:
e+ from Michel decay, g from radiative decay or annihilation
in flight. S/N proportional to 1/Rate.
0.90
0.95
Ee / Emax
William Molzon, UC Irvine
1.00
DEg : 4.5% (FWHM)
Dteg : 141ps (FWHM)
• MEG uses the PSI cyclotron (1.8 mA at ~600 MeV) to
produce 108 m per second (surface muon beam)
• Partial engineering runs autumn 2006, spring 2007
• First physics run 2007
• Sensitivity of 10-13 with 2 years running (c.f. MEGA 1.2x10-11)
• Possible improvements to reach 10-14 in later 2 year run
• Cooled beam would reduce backgrounds
Particle Physics with Intense Muon Beams
January 29 2007
10
Coherent Conversion of Muon to Electrons (m-Ne-N)
• Muons stop in matter and form a muonic atom.
• They cascade down to the 1S state in less than 10-16 s.
• They coherently interact with a nucleus (leaving the nucleus in its ground state) and
convert to an electron, without emitting neutrinos  Ee = Mm  ENR  EB.
Coherence gives extra factor of Z with respect to capture process, reduced for large Z
by nuclear form factor.
• Experimental signature is an electron with Ee=105.1 MeV emerging from stopping
target, with no incoming particle near in time: background/signal independent of rate.
• More often, they are captured on the nucleus: m-(N,Z)→nm(N,Z-1)
or decay in the Coulomb bound orbit: m-(N,Z)→nm(N,Z)ne
(m = 2.2 ms in vacuum, ~0.9 ms in Al)
• Rate is normalized to the kinematically similar weak capture process:
Rme 
(mNe-N)
(m-NnmN(Z-1))
Goal of new experiment is to detect m-Ne-N if Rme is at least 2 X 10-17
with one event providing compelling evidence of a discovery.
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
11
What Drives the Design of the Next-Generation Conversion Experiment?
Considerations of potential sources of fake backgrounds specify much of the
design of the beam and experimental apparatus.
Prompt
background
Expected
signal
Cosmic ray
background
SINDRUM2 currently has the
best limit on this process:
Muon
decay
Experimental signature is105 MeV eoriginating in a thin stopping target.
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
12
2. Radiative muon capture: m- N  nm N(Z-1) g
• For Al, Egmax = 102.5 MeV/c2,
P(Eg > 100.5 MeV/c2) = 4  10-9
• P(g  e+e-, Ee > 100.5 MeV/c2) = 2.5  10-5
• Restricts choice of stopping targets: Mz-1 > Mz
dN/dE
10-5
10-10
1. Muon decay in orbit –
• Emax = Econversion when
neutrinos have zero energy
• dN/dEe  (Emax – Ee)5
• Energy resolution of ~200 keV required
1
Potential Sources of Background
0
50
E [MeV]
100
3. Radiative pion capture: - N  N(Z-1) g
• Branching fraction ~ 1.2% for Eg > 105 MeV/c2
• P(g  e+e-, 103.5 < Ee< 100.5 MeV/c2) = 3.5  10-5
• Limits allowed pion contamination in beam during detection time
Other sources: beam electrons, muon decay, cosmic rays, anti-proton interactions
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
13
Features of a New m-N→e-N Experiment
• 1000 fold increase in muon intensity using an idea from MELC at MMF
− High Z target for improved pion production
− Graded solenoidal field to maximize pion capture
− Produce 10-2 m-/p at 8 GeV (SINDRUM2 10-8, MELC 10-4, Muon Collider 0.3)
− Muon transport in curved solenoid suppressing high momentum
negatives and all positives and neutrals
• Pulsed beam to eliminate prompt backgrounds following PSI method
(A. Badertscher, et al. 1981)
− Beam pulse duration << tm
− Pulse separation  tm
− Large duty cycle (50%)
− Extinction between pulses < 10-9
• Improved detector resolution and rate capability
− Detector in graded solenoid field for improved acceptance, rate handling, background
rejection following MELC concept
− Spectrometer with nearly axial components and very high resolution
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
14
Pulsed Proton Beam Requirement for m-N→e-N Experiment
• Subsequent discussion focuses on accelerator
operating 8 GeV with 41013 protons per second
and 50% duty cycle
– 50 kW instantaneous
beam power at 8 GeV
• Pulsed proton beam generated using RF structure
of appropriate accelerator or storage ring
• To eliminate prompt backgrounds, we require
< 10-9 protons between bunches for each proton
in bunch. We call this the beam extinction.
• Gap between proton pulse and start of detection
time largely set by pion lifetime (~25 )
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
15
Secondary Extinction Device in Proton Beam
• Improved extinction performance close in time to
the filled buckets (particularly just before the filled
bucket is important)
• A means of continuously measuring secondary
extinction at the target is essential
• Conceptual idea for a secondary extinction device
− Time-modulated magnetic deflection synchronized with
filled buckets to deflect protons between buckets out of
-500
beamline
− Field integral required depends on beam optics – ~500
G-m
− Ideal time structure is rectangular wave – magnet
pulsed at 731 kHz with rise and fall time < 50 ns
− Less ideal solution is a time structure approximating a
rectangular wave using multiple harmonics
1.5
FOUR HARMONICS
"RECTANGULAR WAVE"
FIRST HARMONIC
TWO HARMONICS
1
0.5
0
0
500
1000
-0.5
-1
-1.5
• Conceptual design of technical implementation completed
− Stripline magnets with 7x7 cm2 bore, 5 m long, with peak field ~75
Gauss
• Provides ~1.5 mrad deflection
• Low-loss ferrite return yoke decrease power and radiated energy
− Resonantly driven magnets, with one or more harmonics
Magnet cross-section
William Molzon, UC Irvine
•
•
•
•
•
•
Q of 100 reduces the required delivered power by ~100
Shape (and complexity) can be adjusted for conditions
Modular design suggested: peak currents of order kA and peak voltages of order kV
Commercial high-voltage, high current capacitors found
Commercial ferrite with low losses at high frequency found
1st two harmonics are in AM radio band, where commercial power amplifiers in
needed power range (10 kW) are available
Particle Physics with Intense Muon Beams
January 29 2007
16
Monitoring Extinction
Measure time of originating in the muon production target
− Dual magnetic spectrometer to measure 1-2 GeV secondary protons
•
•
•
•
•
•
Target, production solenoid fringe field, first collimator gives passive momentum selection
Two collimators with magnet between them gives second passive momentum selection
TOF counters reject soft background giving accidental coincidences
Calorimeter gives energy measurement
Trigger between bunches to get out-of-time beam rate
Periodically trigger in time with bunches to get normalization
– also a good monitor of beam macrostructure
Production solenoid bore
calorimeter
William Molzon, UC Irvine
production target
magnet
collimators
incident
proton beam
TOF counters
secondary
proton
Beam dump
Particle Physics with Intense Muon Beams
January 29 2007
17
A Model Muon Beam and Conversion Experiment
Straw Tracker
Muon Stopping
Target
Muon Beam
Stop
Superconducting
Transport Solenoid
(2.5 T – 2.1 T)
Crystal
Calorimeter
Superconducting
Production Solenoid
(5.0 T – 2.5 T)
William Molzon, UC Irvine
Superconducting
Detector Solenoid
(2.0 T – 1.0 T)
Collimators
Particle Physics with Intense Muon Beams
January 29 2007
18
MIT PSFC – MECO Design of
Magnet System for m-N→e-N
Experiment
5T
2.5 T
•150 MJ stored energy
•5T maximum field
•Uses surplus SSC cable
•Can be built in industry
William Molzon, UC Irvine
•Very detailed CDR completed (300+ pages)
•Complete 3D drawing package prepared
•TS and SOW for commercial procurement
developed
•Industrial studies contracts let and completed
2T
Particle Physics with Intense Muon Beams
1T
1T
January 29 2007
19
Muons Production and Capture in Graded Magnetic Field
Pions produced in a target located in an axially graded magnetic field:
• 50 kW beam incident on gold target
150 W load on cold mass
• Charged particles are trapped in
15 mW/g in superconductor
5 – 2.5 T, axial magnetic field
20 Mrad integrated dose
• Pions and muons moving away
from the experiment are reflected
• Superconducting magnet is protected by
Cu and W heat and radiation shield
2.5T
5T
Production
target
William Molzon, UC Irvine
Heat
Shield
Particle Physics with Intense Muon Beams
mW/gm in coil
Azimuthal position
Superconducting
coil
Axial position
January 29 2007
20
Production Target for Large Muon Yield
Production target region designed for high
yield of low energy muons:
• High Z target material
• Little extraneous material in bore to absorb /m
• Diameter 0.6 - 0.8 mm, length 160 mm
• ~5 kW of deposited energy
Water cooling in 0.3 mm cylindrical shell
surrounding target
Measured vs. Theoretical
250
Pressure Drop (psi)
• Simulated with 2D and 3D thermal and
turbulent fluid flow finite element analysis
• Target temperature well below 100 C
• Pressure drop is acceptable ( ~10 Atm)
• Prototype built, tested for pressure and flow
Fully developed turbulent flow in 300 mm water channel
Prototype 02 (measured)
Prototype 03 (measured)
Single Annular Channel (theory)
Two Right Angle Turns (theory)
200
150
100
50
0
0.0
(F05) Target 01 - High Permeability Alloy - 100% power
0.2
0.6
0.8
1.0
1.2
1.4
Flow (gpm)
Target - Inlet
25
0.4
Temperature (C)
20
15
10
5
Preliminary cooling tests
using induction heating completed
0
-5
0
100
200
William Molzon, UC Irvine
300
400
500
600
700
800
900
Time (sec)
Particle Physics with Intense Muon Beams
January 29 2007
21
Muon Beam Transport with Curved Solenoid
Features:
2.5T
• Curved sections
eliminate line of site
transport of photons
and neutrons.
2.4T
Goals:
− Transport low energy mto the detector solenoid
2.4T
− Minimize transport of
positive particles and
high energy particles
− Minimize transport of
neutral particles
2.1T
• dB/dS < 0 to avoid
reflections
− Absorb anti-protons
in a thin window
2.1T
− Minimize long transit
time trajectories
William Molzon, UC Irvine
• Toroidal sections
causes particles to
drift out of plane;
used to sign and
momentum select
beam.
Particle Physics with Intense Muon Beams
2.0T
January 29 2007
22
Sign and Momentum Selection in the Curved Transport Solenoid
Relative particle flux
3-15 MeV
William Molzon, UC Irvine
Relative particle rate in mbunch
Transport in a torus results in charge and
momentum selection: positive particles and low
momentum particles absorbed in collimators.
Particle Physics with Intense Muon Beams
2 + 1p2
p
s
D= 1 × s × p 2 t
0.3B R
s
Detection
Time
January 29 2007
23
Muon Beam Studies
• Muon flux estimated with Monte Carlo calculation including models of  production
and simulation of decays, interactions and magnetic transport.
• Estimates scaled to measured pion production on similar targets at similar energy
• Expected yield is about 0.0025 m- stops per proton
• Cooling would increase stopping fraction
Stopping Flux
Relative yield
Data
Model
0
0.5
1.0
Pion Kinetic Energy [GeV]
William Molzon, UC Irvine
Total flux at
stopping
target
0
50
Muon Momentum [MeV/c]
Particle Physics with Intense Muon Beams
January 29 2007
100
24
Stopping Target and Experiment in Detector Solenoid
• Graded field in front section to increase acceptance and reduce cosmic ray background
• Uniform field in spectrometer region to minimize corrections in momentum analysis
• Tracking detector downstream of target to reduce rates
• Polyethylene with lithium/boron to absorb neutrons
• Thin absorber to absorb protons
1T
Electron
Calorimete
r
1T
Tracking
Detector
2T
William Molzon, UC Irvine
Stopping Target: 17
layers of 0.2 mm Al
Particle Physics with Intense Muon Beams
January 29 2007
25
Magnetic Spectrometer to Measure Electron Momentum
Measures electron momentum with precision of about 0.3% (RMS) –
essential to eliminate muon decay in orbit background
Electron starts
upstream, reflects
in field gradient
• Must operate in vacuum and at high rates –
500 kHz rates in individual detector elements
• Energy resolution dominated by multiple scattering
• Implemented in straw tube detectors –
• Vanes and octants, each nearly axial, and each with 3 close-packed layers of straws
• 2800 detectors, 2.6-3.0 m long, 5 mm diameter, 0.025 mm wall thickness –
issues with straightness, wire supports, low mass end manifolds, mounting system
• r-f position resolution of 0.2 mm from drift time
• axial resolution of 1.5 mm from induced charge on cathode pads –
requires resistive straws, typically carbon loaded polyester film
• High resistivity to maximize induced signal
• Low resistivity to carry cathode current in high rates
• Alternate implementation in straw tubes perpendicular to magnet axis has comparable performance
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
26
William Molzon, UC Irvine
Spectrometer Performance Calculations

FWHM ~900 keV
• Performance calculated using Monte Carlo
simulation of all physical effects
• Resolution dominated by multiple scattering in
tracker and energy loss in target
• Resolution function of spectrometer convolved with
theoretical calculation of muon decay in orbit to get
expected background.
• Geometrical acceptance ~50% (60-120)
• Cooling would reduce energy loss in target,
improving resolution ( ~factor of two on width, much
reduced tails) – offset by need for thicker proton
absorber
Particle Physics with Intense Muon Beams
January 29 2007
27
Expected Signal and Background with 4x1020 Protons
Background Source
m decay in orbit
(cooling)
Tracking errors
Events
0.25
Comments
S/N = 4 for Rme = 2  10-17
< 0.006
Beam e-
(cooling)
< 0.04
m decay in flight
(cooling)
< 0.03
m decay in flight
(cooling)
0.04
Scattering in target
Radiative  capture (?)
0.07
From out of time protons
Radiative  capture (?)
0.001
From late arriving pions
Anti-proton induced (?)
0.007
Mostly from 
Cosmic ray induced
Total Background
0.004
0.45
10-4 CR veto inefficiency
With 10-9 inter-bunch extinction
No scattering in target
Background calculated
for 107 s running time
at intensity giving
5 signal event for
Rme = 10-16.
Sources of background
will be determined
directly from data.
Factors affecting the Signal Rate
5 signal events with
0.5 background events
in 107 s running
if Rme = 10-16
William Molzon, UC Irvine
Factor
Running time (s)
Proton flux (Hz) (50% duty factor, 740 kHz mpulse)
107
4 1013
m entering transport solenoid / incident proton
0.0043
m stopping probability
0.58
m capture probability
0.60
Fraction of m capture in detection time window
0.49
Electron trigger efficiency
0.90
Geometrical acceptance, fitting and selection criteria efficiency
0.19
Detected events for Rme = 10-16
Particle Physics with Intense Muon Beams
5.0
January 29 2007
32
Implementing a MECO Experiment at Fermilab
• Complex of accelerators underused after Tevatron run finished
• Proton beam could be shared with neutrino program –
“15-20% loss of protons to neutrino experiments not a problem
for a second high quality physics program” (P. Odone)
• Encouraged by Fermilab director, especially in context of less than most
optimistic NLC rampup
• Implementation builds on mostly available accelerators, concepts of the MECO
experiment
− Momentum stack 3-4 booster
bunches in the accumulator
− Transfer to the debuncher
− Rebunch the beam with RF
(bunch spacing 1.6 ms)
− Slow extract to new area
− Very good macro duty cycle
− Proton beamline, target station,
muon beamline, experiment
following MECO
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
33
Required Fermilab Beam Modifications
•Increased booster throughput (approved)
•Transfer line from booster→accumulator
symbiotic with neutrino program
(unapproved)
•Transfer line accumulator→debuncher
•RF for rebunching
AP4 Line
A-D Line
AP5 Line
Conservative intensity projection
•Slow extraction
•Secondary beamline, experimental hall …
•Concerns
− Impact on protons for neutrino program
− Radiation impact (losses, shielding)
− Resource availability (NLC)
William Molzon, UC Irvine
Beam Energy
Bunch Trains / sec:
fTRAIN
Bunch Spacing: DTB
8 GeV
0.682
No. of bunches/train: NB
85×104
No. protons/bunch: nP
2.16107
Bunch Length (2.5s) : tB
150 ns (s=60ns)
Protons/train (4 batches)
1.841013
Protons/year (107 secs)
1.251020 (1.441020 MECO)
Particle Physics with Intense Muon Beams
1.6 ms
January 29 2007
34
LOI to Implement a MECO Like Experiment at JPARC
• Uses JPARC high energy synchrotron running at 8 GeV
− 4x1013 protons per second
− 2x107 seconds running time
− 7x10-4 muon stops per proton
− Pulsed, slow extracted proton beam with good extinction, 1.17 ms pulse spacing
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
35
JPARC Muon Beamline and Detector Schematic
• Backward pion collection, production solenoid much smaller than MECO version
• Transport with constant direction bend, drift compensated with dipole field
• Converstion electrons transported to detectors in curved solenoid
− Suppresses transport of low energy
electrons
− Transverse drift compensated by
superimposed dipole field
− Non-monotonic field gradient in
transport region – allows for gradient
in electron transport to improve
acceptance
• Expected sensitivity of 1 event for
Rme 4x10-17 for 2x107 s running with
0.34 expected background events
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
36
William Molzon, UC Irvine
END
Particle Physics with Intense Muon Beams
January 29 2007
37
Summary
• A muon-to-electron conversion experiment at sensitivity below 10-16 has excellent
capabilities to search for evidence of new physics and to study the flavor structure of
new physics if it is discovered elsewhere first.
• A well studied, costed, and reviewed experimental design exists that could be the
starting point for a new effort at Fermilab.
• A group of physicists is interested in exploring the possibility of doing this experiment
at Fermilab and is eager to attract more interested physicists at the beginning of the
effort.
• This experiment would complement the neutrino program at Fermilab in the decade
following the end of the Tevatron program and the beginning of a major new program.
• An appropriate proton beam can probably be built and operated for such an
experiment at Fermilab with net positive impact on the planned neutrino program:
Dave McGinnis will discuss the beam and operational issues.
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
38
MECO Experiment Design as a Template for Fermilab Experiment
MECO collaborators at various stages in the experiment
Boston University
I. Logashenko, J. Miller, B. L. Roberts
Brookhaven National Laboratory
K. Brown, M. Brennan, W. Marciano, W.
Morse, P. Pile, Y. Semertzidis,
P. Yamin
University of California, Berkeley
Y. Kolomensky
University of California, Irvine
M. Bachman, C. Chen, M. Hebert,
T. J. Liu, W. Molzon, J. Popp,
V. Tumakov
University of Houston
Y. Cui, E. V. Hungerford, N. Elkhayari,
N. Klantarians, K. A. Lan
University of Massachusetts, Amherst
K. Kumar
William Molzon, UC Irvine
Institute for Nuclear Research, Moscow
V. M. Lobashev, V. Matushka
New York University
R. M. Djilkibaev, A. Mincer,
P. Nemethy, J. Sculli, A.N. Toropin
Osaka University
M. Aoki, Y. Kuno, A. Sato
Syracuse University
R. Holmes, P. Souder
University of Virginia
C. Dukes, K. Nelson, A. Norman
College of William and Mary
M. Eckhause, J. Kane, R. Welsh
Particle Physics with Intense Muon Beams
January 29 2007
39
Other Potential Sources of Backgrounds
4. Muon decay in flight + e- scattering in stopping target
5. Beam e- scattering in stopping target
• Limits allowed electron flux in beam
6. Antiproton induced e• Annihilation in stopping target or beamline
• Requires thin absorber to stop antiprotons in transport line
• Motivates proton energy not much above anti-proton production threshold
7. Cosmic ray induced e- – seen in earlier experiments
• Primarily muon decay and interactions
• Scales with running time, not beam luminosity
• Requires the addition of active and passive shielding
William Molzon, UC Irvine
Particle Physics with Intense Muon Beams
January 29 2007
40